texts: What tolerance do typical components have to wrong-polarity voltages/currents?

texts:
I've always been a bit hesitant to do continuity tests on populated PCBs, on the basis that if there is no trace connecting the two probes, I will be applying some finite voltage to arbitrary IC pins (quite possibly in the wrong polarity) while leaving others unpowered. Is there a 'safe' voltage/current limit for doing this sort of testing?

Another reason for asking this now is that I've noticed that when the output is supposedly switched off on my cheapo bench power supply, it's actually supplying -50mV with an impedance of ~1Kohm. I would guess that this is some way outside the 'safe' limit...


texts:
We have a field device that is connected to the secondary winding of a transformer. The device  is replaceable, but when it is disconnected, the open circuit can cause problems elsewhere on our circuit.

Here's a rough diagram of our device, connected to the transformer (Connected):

We need to be able to disconnect the device from the transformer, but leave a short circuit instead of an open (Disconnected):

We're hoping for a solution that doesn't involve microchips or other digital technology, but that's a preference that we can work around if we can't have it.
Ideally, we'd like a packaged solution, but it's been difficult enough for us just to find something that fits our description, so even a schematic or basic theorycrafting would be helpful.


texts: What combinations of motor and control strategy are compatible with high static holding torques?

texts:
I am aware of permanent magnet motors, synchronous motors, induction motors, and stepping motors, as well as frequency control, vector control and stepping control. Servomotors and controllers are a separate category again.
My assumption is that stepping and servomotors are designed to hold static position torques, and other solutions are either not good at the task or the controllers would not be designed to allow it.
What considerations are there on motor and controller selection that ensure static torque holding functionality on a new build? What parameters in a controller ensure it has the feature(s) required?


texts: Electronics can fail due to overheating, overvoltage, and mechanical stress. Are there other causes?

texts:
My experience with power electronics failures have generally fallen into three categories: overvoltage, overheating, or mechanical failures.

Each might have manifold sub-causes, of course. Overvoltage might be inductive kick, common mode noise, line transients, or static shock. Overheating might be caused by high frequency oscilliation of a switching device, or by high RMS currents, or by unexpected ambient conditions. Mechanical failure can be caused by vibration, or incorrect assembly, or just dropping the thing on the floor. But all failures I've seen seem to fit one of these three categories.

I can imagine a few others like radiation or aging, but I haven't personally seen them. Are there others? Is there a definitive list of ways to kill electronic components?


texts:
I am new in proteus and I have done a pcb design.I have the following doubts in pcb design using proteus.

I need to connect a 100W bulb through the relays. Now the trace style is
T30 .Is it sufficient for AC transmission to power a 100W bulb?
I don't know how to get the dimension of the pcb I have done. I would like to
know how to get the length and width of the pcb...? what is the dimension of
a single tile in the grid...?


texts: How to create an ATX -5 volt rail for vintage Macintosh

texts: I am trying to build a simple adapter for a mini ATX power supply for a vintage mac, I need a 5 volt rail that has it’s own separate ground (+5 volts to -5 volts) how would I go about doing this?


texts: Resolving interrupt-on-change mismatch conditions in a PIC16F877

texts:
I am using pic16f887 to quickly simulate encoder to later use it in a bigger project. reading signals from A and B encoder using interrupt on change for portb and the program was :

if(RBIF)
{
  value++;
  UART_Write('b');
  __delay_ms(100);
  RBIF = 0;
}

and when I changed it to:

if(RBIF)
{
  asm(" MOVF _PORTB" );
  value++;
  UART_Write('b');
  __delay_ms(100);
  RBIF = 0;
}

and this This ends mismatch conditions!!
my question is what is the mismatch conditions and why loading w with portb ends that?

Thanks in advance


texts: Confused about this simple Comparator Circuit Output Waveform

texts:
Below is my Circuit and Voltage Waveforms for the Comparator Circuit. My question is -- In the Highlighted area in the waveform - why is the V(CMP_OUT) not high since inp_u2 (blue) is higher than inp_u1(green) for this interval?

My goal is that CMP_OUT should be high whenever inp_u2 is higher voltage than inp_u1.


texts: Does curling lithium ion battery plates change its performance or reliability?

texts:
If you dig into the technical details of how lithium ion batteries work, it discusses "intercalation" of the anode and cathode plates, which basically means that they have a nanoscale comb-like structure that allows ions to slide in and out of the plate surface, without causing the plates to be chemically eaten away and damaged with each charge and discharge cycle.
For an example of this comb-like structure, see figure 4 of this research paper:

Computer Simulation of Cathode Materials for Lithium Ion and Lithium Batteries: A Review, https://onlinelibrary.wiley.com/doi/full/10.1002/eem2.12017
Energy and Environmental Materials, Volume 1, Issue 3, September 2018, Pages 148-173
First published: 29 October 2018, https://doi.org/10.1002/eem2.12017
Wiley Online Library, free access
Citations: 15

,
Does curling the plates to fit them inside a cylindrical cell have any negative impact on the performance characteristics of this comb-like structure?
Imagine taking a flat plastic hair comb, heating it to soften the plastic, and then curling the spine. The comb tines are either spread far apart in a useless manner, or the tines are bunched up and overlap in an equally useless manner.
It seems possible to me that physically bending or curling the nanoscale structures of an intercalated plate could have similar negative effects on its performance.
Is there is any measurable loss of performance between the tight inner layers and the more gently curled outer layers of a cylindrical lithium ion battery?
I notice that the inner core of many cylindrical lithium ion cells is hollow. Is this because the loss of performance is so severe that it is not worth the effort to attempt to completely pack the center with extreme curled plates?


texts:
I've been reading various app notes as well as Ott trying to figure out how to lay out multiple converters on a board. Most explain how to route the data lines but not much about routing the power supply or reference. Ott mentions layout A for multiple converters. This makes sense for the data lines but this would seem to mix up the reference and data lines. Layout B doesn't partition the ground plane and just passes the reference around in the analog half of the board. This seems to make more sense to me but Ott mentions that some partitioning might be helpful when using converters with bit depths beyond 16-bits. He also mentions stripline, which appeals to the microwave designer in me, but this will be the first run of a board and it would be helpful to be able to cut and bodge traces. Any suggestions? 20-bits takes some serious discipline I reckon so any help is appreciated.
The pink trace corresponds to a bus of kelvin connections back to the DAC. It is not a single wire. The orange wire corresponds to the entire SPI bus. It, too, is not a single wire. The DAC symbol is not just the DAC IC, it is a symbol inclusive of the DAC, and supporting hardware including but not limited to its reference buffers necessary to make the Kelvin connection.


texts: Would it be ok if I try to measure an audio signal using a 15m BNC Cable?

texts:
I would need to use a 15 meters BNC Cable (RG58) in order to measure an audio signal that goes directly to a pair of earbuds. This means, the test point would be exactly before the balanced armature speaker located in the earpiece. The idea is that I would leave a BNC jack in the DUT a connect this directly to an oscilloscope.
I need this setup in order to check signal integrity during EMC Testing and we would prefer to place the oscilloscope outside the chamber.


texts: Finding current through thevenin theorem

texts:
Find the current through 20 ohms using thevenin theorem.

!

I am unable to apply thevenin  theorem on this circuit. Can somebody give me hint on how to simplify this..

I first short circuit the 20 ohms and then used kvl to find the current through the three branches.

Equation: 45-120-5(I2+I3) -10(I1+I3) =0

I1 is current in left branch, I2 in right and I3 in bottom.

10(I1+I3) +5(I2+I3) +5(I3) =20

I can't seem to find the third equation.. Can someone help


texts: Measuring pendulum dynamics with magnetic field sensor

texts:
I've been working on this project which measures pendulum position and motion. Currently I use a 9-DOF inertial measure unit (IMU), like that used in this project/question. The method works very well, but I'm finding that this approach leads to other complications in my application. That being said, I've been brainstorming alternative methods.

The method/idea that I'm considering would make use of an electro-magnetic field. I'm not an electrical engineer, so maybe what I'm looking for exists, I just don't know what to call it. At the same time, I don't know the technical language/terms so I'm just going to give an elementary description of what I'm envisioning.

What I envision basically extends the concept of this simple circular potentiometer with the ability to infer azimuth and tilt position of the pendulum. OK, bear with me...imagine a doughnut or (bagel if you will) that represents the base of an electro-magnetic field. The pendulum rod would be secured in the middle of the doughnut, yet free to swing. Located on the pendulum rod would be an object which disturbs the electro-magnetic field (a magnet or coil??). When the pendulum is static, the electro-magnetic field is balanced, as the object is located at the concentric center. As the pendulum swings, the object causes the electro-magnetic field to change. Ideally the strength of the electro-magnetic field would be proportional to how close the object was to the doughnut (i.e. give the tilt angle) and the azimuth angle (0-360) could also be inferred.

Based on previous research, I think this would be similar to a Hall sensor? If so, do they make "circular" Hall sensors that would match what I'm envisioning above?

I'm completely open to ideas, comments, and/or suggestions. The main thing I like about the idea above is that I don't have to run a cable carrying data and power to the IMU on the pendulum. Instead, all the electronics are "in the ceiling" and I passively observe the object on the rod.


texts: How to calculate current through a resistor and LED?

texts: Question C asks how's to calculate the current over the led and 3k resistor? Can someone please help me understand how to do it?


texts: How does this Boolean simplification work?

texts:
I've just started learning about Boolean identities and simplification, and I'm already puzzled by one rule. I'm following this tutorial, which presents the following rule:
A + AB = A

The proof is as follows:
A + AB
  ↓         Factoring A out of both terms
A(1 + B)
  ↓         Applying identity A + 1 = 1
A(1)
  ↓         Applying identity 1A = A
  A

I understand the second and third steps. B + 1 must be equivalent to 1 because if one input to an OR gate is 1, the output will always be 1. And the third step makes sense too, because whether 1 x A evaluates to 1 or 0 depends on the value of A.
What I don't understand is the first step. It's been many years since I've studied algebra at school, and the intuitive leap that "factoring A out of both terms" leads from A + AB to A(1 + B) is beyond my rusty skills.
I would greatly appreciate an explanation to help my understanding of how you "factor out" a Boolean variable for an equation, and how I would know to do this for any given equation.


texts: Why am I getting signs of high RF radiation, while the desktop computer turns off?

texts:
The desktop computer doesn't have any Wi-Fi accessories. The keyboard and the mouse are wired. But even when the computer and the LCD monitor are turned off
(while the power plugs are still connected), I get a high frequency signal from several accessories.

When I am moving a RF detector (which suppose to detect RF signals at frequencies between 100Mhz-2500Mhz), I get high frequency signals from the wired keyboard, the wired mouse, in front and behind the wired monitor (even when it turns off) and around the desktop case (whenever it turns on or off).

Why do I get those high frequency results?


texts: Is Icbo amplified in reality in Common Base configuration?

texts:
Regarding the active mode of operation: Icbo is leakage of the reverse biased C-B junction. It flows whether or not the emitter is floating, as long as there is a complete C-B circuit. The emitter just has to be floating in order to measure it. But It always flows whether or not the emitter is floating. So the conclusion Icbo always flows. The question is does it always(CB and CE) flow through the emitter base junction. It seems to me that it doesn't flow through emitter base junction in CB but it does in CE (?). Now to express my confusion I start from the basic equations and develop the question as follows:

Now the following equations are valid for a BJT in any configuration CB or CE ect.:

Ic = α×Ie + Icbo

Ie = Ic + Ib

So from those above the following can be derived:

Ic = (α/(1-α))×Ib + (1/(1-α))×Icbo

Since α/(1-α) = β

Ic = β×Ib + (β+1)×Icbo

Now above the second part of the equation is (β+1)×Icbo and it is called Iceo.

This means Icbo is amplified and became Iceo.

But here my question is: The above equation are valid both for CB and CE configurations. But in common base configuration Icbo is not flowing through emitter base junction yet it appears in the formula as if it is amplified as being (β+1)×Icbo.

This is confusing, is my knowledge is wrong or how should we interpret this amplification of Icbo appearing in the formula of CB configuration.

Edit:

Here is an excerpt from a text:

I saw many paragraphs like above which states "However, when the transistor is in the common-emitter connection...". Obviously these are telling that this Icbo is more a problem in CE because Icbo flows through emitter base junction and gets amplified.

But again in CB we still have the same equitation with (β+1)×Icbo which indicates Icbo multiplied by factor of β. This is very confusing why they relate the issue only with CE but not CB. I hope I made the question more clear now.

Another example:

It says "The leakage current in CE is larger than that in CB" and the reason is given by Iceo = (β+1)×Icbo.

But this same equation appears in CB as well

Ic = β×Ib + (β+1)×Icbo

Where am I wrong? Why is the leakage current in CE is larger than that in CB? Can we show it explicitly by an equation.


texts: Production testing, design-for-test, test points, and other techniques

texts:
I have been working with some board layouts that include a test point for every net on the circuit (or close to it). This lead me to a search for other topics about test points and general design-for-test procedures and guidelines around here, but I found nothing. So, my question is a bit broad and ill-defined, but here goes:

What manner of production testing do you commonly employ on your product designs?
Is there a point at which some methods become worthwhile, and where are these points? E.g. manual testing of populated board, to flying probes, to bed-of-nails, etc.
I read about the design and building of the BeagleBoard, which is considerably more complex than our board, but it does not appear to include any of this sort of testing at all (e.g. no bed of nails or test points, they have a software test).
All of our boards are microcontroller based. Are the basic functions of power, ground, and clock reliable enough in manufacturing to use the micro for a built-in self test?


texts:
I have atmega8a-pu and not problem with 5v.

but when i connect 3v3 to atmega my PORTC.0,PORTC.1,PORTC.2,PORTC.3 and PORTC.6 have not very good output!!!

See this image, in image each two circuits is connected to 3v3 supply...

But   portc.5  has a good voltage and portc.3 doesn't have good voltage

I set this variable to my code:

PORTC=0x00;
DDRC=0x7F;
PORTC=0b1111111;

What is the problem? Thank you


texts:
Here is the assignment:

The assignment is to calculate various values across the circuit.

Here are the important values:

\$R=3.3k\Omega\$

\$ U_1 = U_2 = 4 V\$

The diodes are ideal with the following current voltage relation:

Here is my thought process what I tried and where I failed:
I am assuming all diodes are on because there is nothing directly blocking them, like an air valve.

Lets say I want to calculate \$I_5\$. I know \$I_5\$ is half of \$I_2\$ and is equal to \$I_6\$ and \$I_7\$.

The resistance should be \$2R\$ and the Voltage should be because the diodes are in parallel \$4V- 1.4V = 2.6 V \$

But then it all stops making sense after I try to calculate it, something must be wrong with my approach.

Here are my questions:

How do I go about this circuit,how do I split up this circuit in to the correct Kirchhoff meshes ?

Can you give me a hint or a direction how I would go about solving this ?

Update: here is the marked solution:


texts: Highest frequency that can be generated with SPWM?

texts: If you use the Arduino low pass filter "trick" called SPWM (sinusoidal PWM). What determines the highest frequency that can be generated like this ?


texts: Is it ok if I use all pins on non AC connector for AC

texts:
I intend to use non AC connector Hirose DH40 and DH37 for single AC line (230VAC).

Connector single pin is rated 30V 0.3A. They did also did a test for 100VAC for 1 min.

Plan is to use two connectors and all 10 pins on both connectors just for single AC line (so 20 pins on a single AC line).

I did a test the connectors with load for several hours and it works.
My main concern now is safety and certificates.

Does anyone have experience with this?


texts: Does anyone know how to access the iPhone's serial port, from a program on the iPod to allow that application to send signals. The idea is that the iPod could be used as the brain for some kind of robot by using the serial port to tell an arduino what to do.


texts: How to Calculate Basic Cycles in MSP430?

texts:
Hey all I am fairly new with the MSP430 and I have begun using it to do very simple projects and I am trying to keep track of how many cycles I use within my program, and I have a two simple questions that I cannot find the answer for.

How many cycles does it take to run the 'ret' or 'reti' from my program? How many cycles does it take to assign a variable in MSP430 or to call the variable as seen in my "mov.w #COUNT,r13" as seen below?  Here is the part of the code that I am using:

COUNT       .equ    <number>                ; <-- Does this take any cycles?

callLoop:   call    #myDelay                ; 2 cycles
            sub.w   #1,r12                  ; 1 cycles
              jne   callLoop                ; 2 cycles
            jmp     RESET                   ; 2 cycles

myDelay:    mov.w   #COUNT,r13              ; 1  <-- Is it only one cycle to run the mov.w?

delayloop:  sub.w   #1,r13                  ; 1 cycles
              jne   delayloop               ; 2 cycles
            ret                             ; ???  No idea what this would be.

r12 has already been assigned a value earlier. Let me know if you need anything else from me.


texts: Atmel SAMC21 MCU internal oscillator based counter inaccurate

texts:
I am programming a SAMC21 for a control system and I need a milliseconds counter similar to the millis function in arduino to keep track of samples, etc. To do this I first set up a clock channel for the internal oscillator (48MHz) whose output I divide by 48. I then set up an 8 bit Timer/Counter with a period of 100. Everytime the TC reaches 100 it overflows and I use a callback to call a function which simply increments my millis counter variable (volatile uint32_t). This works fine but the counter is quite slower than it should be and delays by between 5 and 15s every minute. Why is that so and how could I make it more accurate?

Note: I use the UART driver over the Debug USB to read the counter value.

Here is the code which is called appropriately in main:

 void configure_gclock_generator(void) // Configuration of internal oscillator and channel
 {
     struct system_gclk_gen_config gclock_gen_conf;
     system_gclk_gen_get_config_defaults(&gclock_gen_conf);
     gclock_gen_conf.source_clock    = SYSTEM_CLOCK_SOURCE_OSC48M;
     gclock_gen_conf.division_factor = 48;
     system_gclk_gen_set_config(GCLK_GENERATOR_1, &gclock_gen_conf);
     system_gclk_gen_enable(GCLK_GENERATOR_1);
 }
 void configure_gclock_channel(void)
 {
     struct system_gclk_chan_config gclk_chan_conf;
     system_gclk_chan_get_config_defaults(&gclk_chan_conf);
     gclk_chan_conf.source_generator = GCLK_GENERATOR_1;
     system_gclk_chan_set_config(TC3_GCLK_ID, &gclk_chan_conf);
     system_gclk_chan_enable(TC3_GCLK_ID);
 }

void configure_tc(void) // COnfiguration of TC on internal oscillator
{
    struct tc_config config_tc;
    tc_get_config_defaults(&config_tc);
    config_tc.counter_size = TC_COUNTER_SIZE_8BIT;
    config_tc.clock_source = GCLK_GENERATOR_1;
    //config_tc.clock_prescaler = TC_CLOCK_PRESCALER_DIV1;
    config_tc.counter_8_bit.period = 100;
    //config_tc.counter_16_bit.compare_capture_channel[0] = 48;
    tc_init(&tc_instance, CONF_TC_MODULE, &config_tc);
    tc_enable(&tc_instance);
}

void millis_count(struct tc_module *const module_inst) { //millis increment function
    millis++;
    if (millis>=1000000000) {
        millis=millis-start;
        start=0;
    }
}

void configure_tc_callbacks(void) //Set up of Callback for millis function.
{
    tc_register_callback(&tc_instance, millis_count,TC_CALLBACK_OVERFLOW);
    //tc_register_callback(&tc_instance, millis_count,TC_CALLBACK_CC_CHANNEL0);
    tc_enable_callback(&tc_instance, TC_CALLBACK_OVERFLOW);
    //tc_enable_callback(&tc_instance, TC_CALLBACK_CC_CHANNEL0);
}


texts:
datasheet: L6203 DMOS FULL BRIDGE DRIVER
I was testing this H bridge on wire wound high power resistors. I have noticed a high drop in the output voltage. The measurements taken are as follow:
Vin=13V;
Vout=9V;
Iout=2.7A
=>Rds=1.48 Ohms
Vin=12.8V;
Vout=8.7V;
Iout=2.46
=>Rds=1.6 Ohms
Vin=15.2V;
Vout=10.8V;
Iout=3A
=>Rds=1.46 Ohms
Vin=17V;
Vout=11V;
Iout=3.3A
=>Rds=1.8 Ohms
Vin=20V;
Vout-19V;
Iout=0.56A
=>Rds=1.78 Ohms
Ofcource some of the test where done where the Driver was really Hot (near 140 C as measured by an infrared Thermometer) so here is the temperature Derating:

Also There is another curve that describes the variation of the supply voltage
:

The curves implies that Rds on should never reach higher 0.8 Ohms (suppose derating due to temperature = 2 @ 150C)
Tests I also tried:

Use of a demo board that uses the same chip but SMD footprint. Almost identical results
Use of 99% duty cycle signal instead of a constant DC signal at the PWM inputs of the driver (maybe charge pump needs that). Same results
Use of 5V logic instead of 3.3V logic for PWM and enable signal... Same results.
Trying to drive a motor instead of series wound resistors. Same results.
Removed snubber/schottcky diodes at output. Same results
Buy drivers from a different supplier to make sure that the driver isn't a counterfeit component(I didn't trust the supplier).Same results.

All measurements are taken using a true RMS multimeter. Vin is the voltage between GND and VS. Vout is between OUT1 and OUT2. I am measuring exactly at the pins so no drops are present because of the PCB/wiring.
circuit:

Question is obvious: WHAT THE HELL IS GOING ON? The efficiency is crap and the driver is overheating quickly. I'm using a very large heatsink, still, the driver is unable to drive more than 2A continuous!! What am I doing wrong??


texts: Is it okay to use a screw and a nut to connect minus wires from parallel circuits?

texts: I want to connect several 12 Volt sockets in parallel. On the positive side the wires are connected to a fuse box which is connected to the positive pole of a 12 Volt lead battery. How do I connect the negative wires? Is it okay to use ring terminals and put them on a single screw/nut?


texts: I can't go into great detail but in our EMC room we have vertical polarity antennas as well as horizontal polarity antennas. If the device being tested is failing at roughly 65MHz in the vertical antenna position but passed in the horizontal antenna position does that mean it could be the orientation of the device's wiring that is is being run? Most of the wiring is run horizontal at a length up to 5 feet at the most.


texts:
I have an Artec QDD2 overdrive circuit and I recently powered it up with reverse voltage by accident and it doesn't give any sound on the stages of distortion, however it is allowing the bypass on selection. I believe the problem may be the ic that is on the board, its the only component that looks like it would get damaged by reverse voltage. I retrieved the smd code from the chip to be 33x1..... however when decoded seems to lead to nowhwere. I have attached a picture of the component and and hopefully someone turns up with the datasheet. ID like to know if it is damaged or if i must now go and attempt to find a seller of the exact ic or similar. I have attached voltage measurements as well. B+ being 9VDC.
edit: I have drawn the circuit for a better look at what my problem could be.... I really just want this to be solved.


texts: Why does adding an analog input change the voltage in this circuit?

texts:
I have an Arduino and am trying to measure the voltage across R1. To do this I am connecting SW1 to an analog input. Using a multimeter I measure the voltage across both R1 and R2 to be 1.56V which is what I expect.

However, when I close SW1 the voltage across R1 jumps to 1.83V - why is this?

simulate this circuit – Schematic created using CircuitLab


texts: Orientation of magnetic flux in a induction motor?

texts:
1) The rate of change of stator flux creates rotor emf and current which in turn produces rotor flux. What is the relationship between stator flux and rotor flux? In what direction is the rotor flux oriented with respect to stator flux?

I assume that spatially both flux would be orthogonal if rotor pf is close to 1 and 180 degree if rotor pf is close to 0.  Am i right?

2) How are poles of the rotor in induction motor decided?


texts: LiIon tp4056 with protection, avoid drop out voltage at output

texts:
I have checked some behaviour in TP4056 boards (with protection circuit) that i don't like at all. (see schemas at the end)

When you use the TP4056 module with the protección board, you will get a dropout voltaje of 0.4 - 0.7V in the output.

That is because the forward voltage of the reverse diodes of the mosfet of the FS8205A.

DW01A pin 3 is for overcharge control and is connected to pin 5 in FS8205A
DW01A pin 1 is for discharge control and is connected to pin 4 in FS8205A
Also, overcurrent protection use the DW01A pin 1

The TP4056 already control to protect for overcharge the battery, so what about a bypass between FS8205A's pin 6 or 7 and FS8205A's pin 1 or 8 (see datassheet)

We will loose overcharge protection of DW01A, but we have already the TP4056's one.
We will change over current protection as the Ron of the mosfets of FS8205A that DW01A will see, will be the half, so we will change over current protection from 2.5A to 5A (I think both of them are useless, 2.5A is usually a lot for our projects). You can "repair" it by putting a resistence of 30mOhm or bigger instead of the direct bypass.

With this modification we will get the real battery voltaje in our output only loosing the overcurrent protection (more or less), won't we ?

I hope you understand me, what do you think ?

Regards,


texts: SD card: cmd 17 (read single block) response always 0x01

texts:
I'm trying to connect a micro-SD card to a PIC32 controller. At the moment I'm bitbanging the SPI protocol to communicate with the card. (In the near future I will use the proper pins to use real SPI, but for now I have to use this solution). Long story short: I am able to initialise the card and get correct responses for all commands, but when I try to issue the cmd 17 command, it responds with 0x01 (idle) instead of 0x00 (ready) and any subsequent reads all return 0xFF. The token 0xFE never comes. I've tried a lot of different sectors as argument for cmd 17, but that doesn't make a difference.

These are the commannds and responses:

>> (0) 40 00 00 00 00 95
<< (0) 01

>> (8) 48 00 00 01 AA 87
<< (8) 01 00 00 01 AA

>> (55) 77 00 00 00 00 65
<< (55) 01

>> (41) 69 40 00 00 00 77
<< (41) 01

>> (58) 7A 00 00 00 00 FD
<< (58) 01 40 FF 80 00

>> (16) 50 00 00 02 00 15
<< (16) 01

>> (17) 51 00 00 00 00 55
<< (17) 01

They all look good to me, except the last one.
(BTW, I'm always using the correct CRC even though I'm aware that it's not neccesary)

The card is powered with 3.3V. The voltage doesn't drop when accessing the card. All lines excepct clk have a 100k pullup resistor.

What could be the reason for cmd 17 not giving the correct response?

Edit: clock frequency is about 145 kHz. Remember it is bitbanged. Could this have any influence on the read command?


texts:
Ok so I have finished laying out a board. I have an ATMega328P running with a 8MHz crystal. The board has two layers and I have chosen the top layer as the ground plane (GND) and the bottom layer as the power plane (VCC). Following design guidelines, I have kept the trace length between the crystal and the AVR minimal.
Take a look at the layout and suggest any improvements if you can and also be sure to point out the faults.

EDIT: Added schematic.

EDIT2: I updated the board. The new one is here.


texts:
If we considered the Diodes states to be:
D1 : OFF
D2: ON
D3:OFF
Now if we apply KVL on the closed loop, will it look like this?

-Vout +Vout -4 v+ Vin =0
Knowing that the volatge across R3 is +Vout

My confusion is that I2 has to pass through the positive terminal of R2 (since a resistor absorbs energy and if current passes through negative terminal of an element this means the element is producing energy which is not possible for the resistor to do since it is a passive component and not an active one)
Thus, if I2 is passing in the direction indicated in the image, it has passed through the negative terminal of the V of R3 which is Vout which cancels out Vout from the KVL. Is there anything wrong with my thinking/approach?

Thank you


texts: Is Non-Passive Cooling bad for Lithium Ion Cells?

texts:
I'm in the process of designing a device capable of charging, discharging and testing internal resistance of 18650 cells. My device will be capable of testing 100x 18650 at the same time, each will have their dedicated module which allows them to run independent from one another.

The pre-designed modules are capable of charging and discharging at 1A however they also have a feature which throttles and reduces the wattage when the battery becomes too hot. This feature is important as this will help answer my question at the end.

In the charging phase of the test they are only charged at around 250ma as this helps to find cells with internal problems and cause the cell to run hot, so no throttling will occur.

During the discharge phase however I need to test the cells at 1A discharge but often the modules will throttle because the battery is getting warm/hot.

I've read comments, forums and even articles saying you should not cool lithium batteries since they cook inside or they change the chemistry within the battery, but I'm unable to find any reputable information that could be considered fact, I know that many electric cars have air ducts to help cool the battery but this doesn't mean its good for the batteries? I'm really unsure and confused.

Is there any scientific reason why you should NOT blow air across batteries while in use or during a charge cycle?


texts:
I have a bridge rectifier that is converting 240v AC into approx 358V DC

The rectifier is smoothed by 2 X 10,000uf capacitors

Under full load, I am drawing 3000 watts on the DC side but for some reason the voltage drops down to 280V DC yet the AC side stays at 240

My question is why is my voltage dropping so much?  The DC cables are 300 feet long #10 awg wire but the voltage measures the same at both ends +/- 1% so its not lost in the cable. I also checked that all the connectors are tight and making proper contact.  Nothing is getting hot either..

The meter I am using the measure with is a "Circuit test DCL-320"

Here are the components I am using:
https://www.digikey.ca/product-detail/en/crydom-co/M5060SB400/CC1656-ND/752672

2 X https://www.digikey.ca/product-detail/en/rubycon/400LSU10000MNB90X151/1189-1911-ND/3927506

Thanks for any assistance

John


texts: Picking transistor and base resistor to dim LED using PWM

texts: I'm working on a project where I need to dim a 30 cm LED strip. I'm using a STM32 pin to drive the base of a NPN BJT-transistor. The pin is can source a maximum of 25mA. The LED strip consists of 12 parallel ordinary LEDs, each one in series with 1.4 kOhms resistance. The collector is connected to the LEDs, which in turn are connected to 8V Vcc. I have read that I should use a base resistor on the transistor, is it really necessary? And how do i proceed to select the right transistor?


texts:
Unlike other broadcast standards such as DVB-T where
the transmitter sends a reference TimeStamp counter
(CTS,PTS) as a global reference clock information to receiver,
in digital radio standards such as DAB there are
no reference timestamp from transmitter. Only by using
the local clock the receiver estimates a worst case delay.

How does the radio receiver does the audio synchronization
with transmitter clock, to avoid audio buffer overflow and
under runs ?
Is the audio and RF clock are derived from same source
like mpeg2 systems ?


texts: Amp measures board twist (unfortunately!)

texts:
Well, this is a toughie -- though fairly simple.  Does anyone have experience with board twist affecting your circuit?

We have a board design that is supposed to measure a loadcell.  We have finally tracked a system accuracy fault down to the amp IC.  When we twist the board, the amp IC changes its output.

_

Added RM:

Circuit:

Datasheet here

Gain is 100,000 / R7 =~ 454.5 according to datasheet p15.

I get +80mV when I twist the board from its 4 corners.  I'm using the amount of twist that I use to unlock my car with my car key.  I get -80mV when I twist the other way.  The amount of twist is proportional to the variance in output voltage.

Alternatively, if I put, say, typical pencil pressure on the top of the IC, I get +20mV.  This is the most sensitive corner of the IC near pin 1.

To isolate the amp circuit, I have shorted its input and disconnected other circuits from it so that what you see in the diagram is what we're testing with.

I'm stuck.  What physics principle would cause this?  How can I prevent it?

Notes:

This is a system fault, not a single-board fault.  It happens on all our boards.
I have tried re-soldering the pins.  That's not the problem.
It isn't the gain resistor R7.  I've put that on long leads to test its twist separately.  Twisting it doesn't make any difference.
The resistor R7 is 220 ohms which equals an amp gain of 456
The power supply rail, AVdd, measures steady at 3.29V
The IC is the industry-standard AD623ARM (uSOIC package)
For those who really must see it, here is the board -- though I'm afraid that it will raise more red herrings than answers:


texts: Why is Ib proporional to Ic in a bipolar transistor?

texts:
I am really puzzled why the collector current is considered proportional to the base current in a bipolar NPN transitor, ie

$$ I_c = \beta I_b $$

Where I_c is the collector current, I_b the base current and below I_e the emitter current. I can't find any explanation in the books, it seems to be just stated as an empirical result. Is that how I should treat it, just an empirical result?

I know that it can be derived by assuming that the proportion of (conventional) current that enters the emitter from the base is a constant fraction of the collector current, ie

$$ I_c = \alpha I_e $$ and that $$I_b + I_e = I_c $$

but that begs the question why is the fraction of base current entering the emitter stream always assumed to be a fixed proportion?


texts: Multiplex based autoscale, question on simple circuit

texts:
I was looking for a clever way to automatically scale voltages from, say, 0-50V with a mux to an ADC (0-5V) without worry of damaging my inputs.

My thought a simple amplifier with selectable gains would work: Select the lowest gain ratio first (i.e. 0.1x), and then raising that to eventually have the voltage fall nicely within my desired range, and of course I know which ratio is selected on the mux.

I stumbled across this clever circuit when looking for a solution, but it is confusing to me:

I gather that this is more or less what I am sort of looking for: I assume the DC offset of 2.5 is to allow negative voltages to be scaled (with protections diodes in place before that point) and read as a multimeter would do maybe, of which is my intended project.

The formulas given do not lay up very well however:

i.e. 0.1x gain, Rf/Rin (100k:10k), with Vin of 10 = 1V (or 3.5V I suppose with the offset?) - this is nice, however in the formula provided:

\$2.5V - (10 - 2.5V) * \frac{10k}{100k} = 1.75\$

And to me of course that does not make sense!

Will ignoring the formula and simply assuming it divides evenly and I know by how much work? (if it is just some strange "on paper" formula, and not something meant to be done on the processor, since \$V_{out}-2.5gain\$ or whatnot is a looot easier..) What is that given formula and how does it work if it does? Will the mux add any downsides (leakage current?) and should I choose lower resistors in that case to swamp that? Can you suggest any alternative circuits that simplify what I am trying to do if this is just a bad idea in general?


texts: Why do two different ICs have wildly different high level output voltages?

texts:
I have two ICs on a breadboard (74ls374 D type flipflop and 74ls04 hex inverter) and I have an arduino measuring the voltage on the respective output pins of those ICs. The outputs are both at a logic high, but the flip flop output voltage sits around 3.3V, while the inverter is at 4.5V. There is no load resistor or anything like that.

Why might this be happening?

EDIT: The reason I am using the arduino ADC is because I am a skint college student who cannot afford a multimeter at the moment. Arduino is the best I have


texts: What does it mean if input impedance given as a current regulator?

texts:
This SSR relay has an input impedance given in its datasheet as:

It says "Nominal Input Impedance is a current regulator". At 5V 16mA.

But how can I model this type of input impedance? I will use 12V input but there is no info that I can estimate the current or input impedance.

Does that mean whatever voltage applied it will regulate the current to around 16mA?


texts:
I am trying to design frequency dependant negative resistor circuit that is not based on the generalised impedance converter. I have found the GIC based FDNR to be unstable and difficult to understand.

The circuit I have designed is based on an active capacitor circuit. I replaced the resistor with a capacitor, in order to turn the op amp B into a differentiator. The idea is to make the reactance at node a to be a second order differential, instead of the first order differential of the original circuit.

It seems to be working. I have used it to implement the equivalent of an un-damped L C low pass filter. Using the FDNR in place of the capacitor and a resistor in place of the inductor. It seems to be more stable than the GIC based FDNR.

The only problem I have is that as I vary the resistor that is equivalent to the inductor, the resonance changes. The resonance decreases as the resistance increases. This does not happen with the classic GIC circuit.  So my question is why is the the resonance changing as I vary the 'inductance' resistor, is this because I don't have a true FDNR?


texts: Effect of increasing Detector Range in Power Usage

texts:
I have two separate systems. System 1 can measure well biochemical events in the frequency [1,180] Hz.
System 2 is designed to measure low frequency electromechanical processes in the frequency [0.001,1] Hz.
However, separate systems are not enough.
Electromechanical processes also come to the biochemical events' frequency bands sometimes such that measuring unsteadily there and there is not possible.
I need to measure both systems at the same time.

However, I have no idea about how the accuracy of the measurements can change if you decide to measure 10^3 bigger segment.
I think it should not change, but the power should instead change.

Proposal for the measurement system

Sampling rate: 360 Hz
Resolution up to 180 Hz and down to 0.001 Hz.

Problem. I cannot understand how it is possible keep sampling rate fixed when increasing resolution from (down to 1 Hz) to (down to 0.001 Hz).
How does the sampling rate changes when increasing resolution from 1 Hz to 0.001 HZ?

Comments

I am not sure how the situation would differ if we would change the range from 180 Hz to 180 x 10e3 Hz. I think nothing. When going down or up, the situation is the same for the power. Is this a right assumption?

Power and Safety

I am not sure how accuracy changes when measuring so big scale.
I think uncertainties mostly come from the system but nothing else.

I think the wider range should be possible in theory by just increasing power, as described in the thread increasing metal detector range.
However, the problem in my application is that I cannot increase the power too much.
A cheap transformer is used 220 V in the chip ADuM4400 which withstands 5000 V for 60 seconds.
There is no risk when 380 V peak (<< 5000) which is well within safety margins, currently with separate systems.
Power usage is as a function of CPU usage.
Power measurement error is normally distributed.

Unknown is the relation between Detector Range and Power

\begin{equation}
l \propto_{?} P
\end{equation}
where l is the size of the range in the detector, and P is the system power.

How can you estimate the effect of 10e3 x range in the power usage of the system?


texts:
I'm in the process of building a lamp. It is about a
Pendant lamp in which a coaxial cable with an outer braid is used for the power supply in order to swing the light objects (5 pendulums). In the light objects there are LED modules that require CC with 700mA. This connects the GND of all 5 constant current sources in the canopy of the lamp is the idea. I am therefore looking for an LED driver (or an LED driver IC) that can handle common cathodes. The luminous objects should each have their own KSQ. Do you know something suitable? Maybe even a circuit diagram?
If you want to understand more this is the concrete setup:
It is a pendant lamp, the pendulums are on one
Suspended steel cable. In addition, a coaxial cable with a copper braid on the outside and an insulated conductor on the inside leads to each pendulum. The pendulums each have built-in LED modules which require a constant current of 700mA / approx. 14.8V. Each pendulum should have its own KSQ. But since there is a connection to the canopy due to the suspension of the pendulum by the coaxial cable and its screen (which should act as a negative pole), I need a KSQ which works with a common cathode. Because ultimately all Vout- the individual KSQ's have a connection to each other via the metal canopy.


texts: Can a slave i2c IC prevent the master from pulling the the signal low?

texts:
I have an MSP430F6659 connected to a ISO1541 via I2C with 1.5K pull-ups.  The I2C bus is through wire instead of PCB trace so I'm able to swap out identical PCBs with the ISO1541 ICs.

One of these boards with the ISO1541 works just fine.  I can see the clock and data signals in the scope.  However, when I connect the other one and try to send a byte with the same MSP430, the signal remains flat at 3.3V.

Doesn't the master have a say as to whether or not the signal goes low?
Can any of the slaves prevent the master from bringing the line low?


texts:
I am using I2C and I have earlier posted doubts about I2C here. I am using PIC controllers and using their compiler C18. I used their libraries to build a function to write data in EEPROM via I2C, and when I crosschecked the SCL lines they were fluctuating.

I have made up a function to write to EEPROM but I have missed out on delays as the datasheet says "minimum 5ms delay for each write operation in to I2C is required".

I trust it is causing the troubles. The problem is SCL does not stay at 100kHz and fluctuates between 54kHz and 100kHz but never beyond that. Is that because Control byte,address and data is sent along the function?

float ee_write_float(unsigned char ee_addr, float f)
{
     void i2c_init(); //initialize I2c
     unsigned char *p = (unsigned char *)&f;
     unsigned char  i;

   for (i = sizeof f; i != 0; --i)
   {
      EEByteWrite(EE_I2C_ADDR, ee_addr++, *p++);
   }

}

How important is the dela for I2C write operations?

Could that be the cause of problem?

Should I put a delay after the EEByteWrite function to compensate?

Noted: the SCL becomes somewhat stable after the baud rate is reduced to 20kHz
then it fluctuates between 17kHz and 19kHz. I would be extremely happy if you found out any reasonable cause to fix this trouble..or any valuable suggestions will be welcomed whole heartily.


texts: DIY Rotary Phase Converter with starter motor, cutout relay in parallel with load?

texts:
I am working on a DIY Rotary Phase converter with pony motor. This will use single phase 240v and run capacitors to feed 2 legs of a 3 phase motor, which will generate the 3rd leg.

It uses a 1/2 HP 120v motor (pony motor, starter motor) to start a 5 HP 3 phase motor. I would like auto-start and cutout, so the idler and starter are never energized separately and the starter cuts out after the idler spins up.

The approximate design is below. A 120v switch turns on the starter motor and a 2 pole relay to power L1 and L2 of the idler. The idler has run capacitors between L1-L3 and L2-L3. When the idler starts, L3 will energize the cutout relay (240v NC), which turns off the starter motor. L1, L2, and L3 would be used to drive a 3 phase load.

I used ground symbol for neutral in the schematic.

My primary concern is with the cutout relay wired in parallel with the load on L3. Will this cause problems? If so is there an easy modification I can make to the circuit? Will the cut out relay energize prematurely due to the run capacitors?

simulate this circuit – Schematic created using CircuitLab

Information regarding rotary phase converters:
http://www.metalwebnews.com/howto/ph-conv/ph-conv.html
http://www.paragoncode.com/shop/rotary_converter/

Final simplified design:

simulate this circuit

The circuit diagram tool doesn't have an option for aux contactors or 3 pole relays, so RLY AUX indicates a 3rd pole or an AUX connection on the contactor


texts: Is it safe to measure 220Vrms@50Hz on DSO directly?

texts: I borrowed my friend's DSO to complete my project(Hantek DSO5072), but on scope it says CAT II/400V. So is it safe to measure 220Vrms@50Hz with it?


texts: Is there anything inherently wrong with routing a power trace, which is used to pull up logic pins on an IC, through a pin of that same IC? Please see the example below -- the trace in question is "3.3v"


texts:
I have a power supply of 5 volts @ 1A. I want to reduce the current from 1A to 250mA. Which resistor should be use?

I tried this equation(Ohm's Law):

R = V / I
 = 5/(0.75)
 = 6.66 Ohms.

I tried the 6.66 Ohm resistor but it only reduce few mili Amps.


texts: How close do I really have to place a 25MHz crystal?

texts:
I'm laying out a very space constrained PCB. Normally I would place a 25MHz crystal absolutely as close as possible to the chip using it. However, on this PCB, something else really needs the space that the crystal would be.

How bad is it really to move the crystal about 5-7mm from the chip?

The PCB is mostly digital electronics, but there will be some analog stuff about 20mm from the crystal.


texts:
I saw this ballast regulator on internet. On this scheme NPN based, I easily understood the
Vout = Vref - Vbe.

simulate this circuit – Schematic created using CircuitLab

But I don't understand this kind of ballast used in the MC9S12ZVLRM (page 677)

simulate this circuit

How do I pick the right transistor ?


texts: How can I create a rectangle drill in Orcad Layout Plus 10.3?

texts: I use Orcad Layout Plus 10.3 for PCB design and I have a problem at this topic.  For example, I have to use power jack footprint, I have created but the drill can't be rectangle.  I added a screenshot below.  I know I click rectangle but it is disabled.  What can I do?


texts:
In the loudspeaker crossover circuit below, I believe the purpose of the resistor is to attenuate the signal to the second speaker (the tweeter).

However, in circuits I've seen that are supposed to perform attenuation only (l-pads), there are two resistors, one parallel as well as series (see second image).

Is the parallel resistor not required in the crossover, because the 0.4mH inductor is serving this purpose?


texts: AOZ1014AI Vout problem 0.8V instead of 6.5V

texts:
My input voltage is 7.4 and I need to step it down to 6.5 with a 3A current. I've used an xls file from the supplier to calculate the followin scheme:

I might made some mistake in my PCB here:

But it doesn't work. It gives just 0,8V on Vout.

Here are the calculation results:

EDITED:
I've read the circuit notes in the datasheet and done some changes. Do you think this circuit can work?


texts:
I'm visually inspecting a bike light that does not work properly anymore after some years.
Do you have any idea of what's the "dirt" in the photos?
Is that cause of concern? Is it just rework during assembly or a component failure...?
The rest of the lamp looks fine, the light is waterproof and no sign of water leaks found.
What are those BSSAA components?


texts:
I have a problem designing a current source.
Basicalyy I need to drive this I->P converter which needs a 4-20mA input. If I understand well the datasheet the resistance inside the component is 500ohms max. Then I wanted to use this schema replacing the LED by my I->P converter:

Except that the input of the 741 would be a DAC output from my microcontroller.

In this schema the output current is I=Vin/R1 (I would choose R1 with the good value) and then I could drive the current as I want from the DAC.
But I think the problem is that at 20mA the voltage around my I->P converter would be V=500*0.02=10V and so Vout would have to be 15Volt which is not possible I think.

Am i right? If yes is there another simpler way to drive my component?


texts: Input impedance of a transistor amplifier from an example

texts:
Going on reading "The Art of Electronics", I am still stuck on another input impedance calculation for a transistor amplifier. This is really something I should overcome, maybe your explications will make me understand based on the following example:

The author writes "The input signal sees R1's resistance effectively reduced by the voltage gain of the stage [300Ohm to the ground in this case]". Why? How do we get this result, analitically and/or visually?


texts: Why isn't there any EEPROM in STM32F4 MCUs?

texts:
Why isn't there any EEPROM in the STM32F4 series MCUs?

Mostly I have Microchip MCUs and they have EEPROM available in them, but I just found out that it is not available in the STM32F4 MCUs... And it looks like not in other families as 'F0, F1, F2 and F3 either.

Is there a way around to save parameter values in the absence of an EEPROM?


texts: Full-bridge or half-bridge for a DC motor

texts:
So I have a DC motor which draws around 16A at 12V. I want to have some room to play with in the top values. I need to control the spinnig direction as well as speed.

I understand how half-bridges and full-bridges work. From that it seems to me that half-bridge is not an option for a DC motor as it can be used only for creating AC and not DC. On the other hand full-bridge can be used for both AC and DC. Am I right?

I am asking because many sites mention the differences between the two, but I have not found a site that would mention the difference when using it to control a DC motor.

Thank you for your replies


texts: Can I use a 3 volt DC 1 amp power source to light about 20 5mm 2 pin diodes?

texts: I'm very young (72) but like to tinker. I have an old Christmas window decoration that doesn't work (light-up). I have a 110 voltAC     to 3 volt DC adapter rated at  1 amp.  Can I use this to power about 20, or so, 5mm white  LEDs    on this rewired  window decoration, or is the amperage too high ? I'm guessing I would need a resistor or some other       form of current limiting ? Would 30mA be a sensible current for each white LED ?          Is there a source where I can find these answers?  or do I have to take up your time ?  Thanks for your help. BBs


texts: USB to ethernet chips like LAN7850 require GPIO to RESET pin?

texts:
I am designing a PCB which uses LAN7850 chip

This is the first time I'm using such a chip and I'm very newbie to PCB designing.

Please advise if this Chip requires a GPIO pin from the microcontroller to control the RESET_N as I have done in this image.

Design Rule Checks:


texts: I want to feed the load by 1.2V source. I want to control it by a voltage changes between 0 to 2 V. I want the switch be closed and feed the load if control voltage is lower than 0.2V and switch be open if the control voltage is above 0.2V. I have used a bc557. connect the 1.2V source to emitter and 0-2V to base. However, the switch operate when base voltage become 0.5V. Is there anyway to change this 0.5V to 0.2?


texts: Why does stepper motor not turn properly at different frequencies?

texts:
I have an 8 wire stepper motor and an unipolar motor driver. I wired the motor as unipolar connection. On motor 3.15V and 4.2A is written.

My connection is above. When I connect V to 24V 14A source to V, at 1 ms step, the motor (has 200 steps) rotates at 3 Hz, but I expect 5 Hz. When I set step to 10ms or 100ms, the motor rotates very absurdly, like rotating 20' to left and waits then rotating right to 40' and lots of unexpected rotations.

When I connect V to 5V, it rotates at 1 ms step (5Hz expected) at 2Hz but vibrates too much. When I set 10 ms (0.5 Hz rotation is expected), the motor rotates at 0.45Hz; and vibration is very low. At 100ms step it works as expected.

My conclusions are

High voltage is necessary for fast switching
High voltage does not work at lower frequencies (long step sizes like 10ms or 100ms).
Low voltage does not work at high frequencies (short step sizes like 1ms)
Low voltage works pretty well at low frequencies.

My questions are

Is my wiring schematic correct for unipolar scheme?
Why did high voltage experiment not work for low frequencies?
Why did low voltage experiment not work for high frequencies?
Which voltage should I give to V at the schematic to rotate the motor at both high and low frequencies?


texts:
I'm using a L7805C voltage regulator , to power an SMPS circuit. But its getting heated after 10 min or so , even if I've put a heat sync.

SMPS IC is used to convert +5V to -9V.


texts: Is the voltage across a turned off transistor a problem?

texts:
I was studying some stuff here and I came across a question that I couldn't find on the internet. I created this circuit for demonstrating my problem:

The transistor Q6 is a normal NPN transistor, the only difference is that it's maximum Vce is 30V. Now here is the situation: If I oscillate it, when it's ON the voltage drop will be on the resistors and there will be very low voltage between Colletor and Emitter. But when it's turned OFF the Collector wil be at 48V and the Emitter at 0V.

As long as the breakdown voltage is not reached we are good, but does the turning on of the transistor (that inicial drop between the 48V-30V) damages the transistor? I assume that the 48V drop on the turning on takes some time and in that time amount the transistor will be operating at a voltage higher than it should, is that true? Does it damage the transistor?


texts:
I have done a good amount of research, but cannot come to a conclusion. I am designing a circuit which involves a battery powered device and a USB connection to charge it. The circuit has several current paths.

In order to remain compliant to the USB 2.0 spec, I can only draw 100mA from the host when I am not enumerated, but once I am enumerated, I can draw 500mA. This actually presents a fairly large issue for the design, because 100mA means I have to put in way more effort into current limiting when not enumerated. Space is a massive issue and eliminating as many tiny chips as I can vastly reduces the complexity. We are talking a 1.5 sq inch board here or less.

I do not have plans to use a USB 2.0 connector, but want to go with a type C connector, because type C is very... cool because of its extra pins and reversible nature. However, I plan to use USB 2.0 high speed data and not 3.0+ speeds.

With this in mind, the type C connector has the CC pins. Now if I want to connect to a type A host (legacy host port), I need an adapter which will internally pull up the CC pins with a 56k pull up.

Here is my understanding of the resistor values on the CC pin. There are 3 pull up resistor values that advertise Default USB power (56k), 1.5A current, and 3.0A current. With regards to the 1.5A or 3.0A current advertisements, it is my understanding that I can just start drawing that much power right out of the gate without any enumeration. Is that assumption correct?

Default USB power for a type C connector is very fuzzy. All of the documents I read say 500mA for USB 2.0 or 900mA for USB 3.0. Is this "out of the gate", meaning I can draw that current without enumeration, or is this 'after' enumeration? If this is 'after' enumeration, it means I am back to square one in that I can only draw 100mA before enumeration and 500mA after enumeration. My hesitant guess is that this is 'after' enumeration, because as far as the legacy host port is concerned, it has no knowledge of the type C connector and is still connected to 4 pins on the cable on one end. However, you do have the converse that the type C spec and documents state that the port must allow up to 500mA of current.


texts: Calculate measurement accuracy of voltage divider with suppressor diode?

texts:
I have a voltage divider to measure the voltage in a DC Bus. I parallel to R1 I have a suppressor diode (D1) to protect the input of the microcontroller from transient overvoltages. This diode has a reverse leakage current that can be around 1% of the current through the resistors.

I know how to calculate the accuracy of the sensor without the diode, but... how does the diode alter the measurement? How can I do an extreme value analysis of this circuit?

simulate this circuit – Schematic created using CircuitLab


texts:
LM311 datasheet, page 18:

Is it a hysteresis so that when transistor opens, the reference voltage goes up? Or is it related to input signal filtering (then what is the corner frequency?). Can you explain the physics and the related process?

Can delta circuit of 50k, 1k and 1k be replaced with Y circuit, and simplified to two resistors? No it can not be simplified to two resistors.

Update: let me explain how I see it: negative input has voltage divider of 5k/1k, with RC action using 0.01uF capactior. 50k resistor is needed to have positive input pulled low (not floating) when opto-transistor is closed.

When transistor stars to open, the reference point (5k/1k divider's voltage) will move up. When transistor is closed reference point is at 5k/((50k+1k)|1k). When transistor is completely open reference point is at (1k|5k)/(1k|50k),

The question is why 1k between positive and negative inputs is taking place here, and what is its function. What is the point of moving reference so drastically when transistor opens?

Update 1: here's the simulation - there's a clear difference in the behavior.

and

Update: here's more accurate simulation. The result is very dependent on the timing, thus the circuit is made with specific maximal frequency in mind.


texts:
I have a problem in connecting Raspberry PI to an MCP3202. I am using MCP3202 at 5V and knowing that raspberry pi works on 3.3v.  I have found a solution to convert from 3.3V to 5V using 74HCT244.
And now i am searching how can i convert from 5V logic to 3.3V ? Could someone help me.
Thank you


texts: Can I make a double board at smart prototyping pcb service?

texts:
They have a 5x5cm minimum board size. My board is approx. 35x20mm so I can easily put two side-by-side and thus double the board count within this limit.
What is the best way to do this? I know how to duplicate it in Eagle, but would I set them apart, say 2mm, and design a connecting bridge with drill holes to make breaking apart easier?


texts:
I have a problem that I would like to have help with.

In the image above I need to calculate the capacitance. The values I was given in the beginning was:

So I calculated U3, which was 17.3 V and I have tried using Uc = (1/w*C) * Ic, but with no luck...I've been stuck on this problem way to long. I've been trying to find information on the internet and on youtube, however I didn't quite find anything that could help me. I've tried, but I'm stuck.

Any kind of help would make me glad!:)


texts: What serial communication interface would work best for data logging when the nearest sensor and main MCU are (at least) 1 meter apart?

texts:
I would like to setup a "sensor array" which has 4 sensors attached to it. Each sensor is expected to send data at rates of up to 8 Hz. The data would be shipped off to an MCU that is around 1-2 meters away.This MCU will store the data into an SD card.

To illustrate this a little better:

I was thinking about using I2C to communicate between the MCU and the sensors on the sensor array, but I'm not sure how well I2C would work at this distance and if it would even be fast enough.

SPI seems to be big a no no in terms of distance.

Other interfaces that could potentially work is CAN and RS485, though I've never used either of them before. I've dug deeper into using CAN and while it looks like it could work well, it also seems that it might be a bit "overkill" for what I need.

So what serial communication interface could work best in this sort of scenario?

Any help is appreciated.


texts:
How large is an IR diode radiation spot area?
I put some IR diodes (receiver and transmitter) in front of each other.  I want each transmitter IR diode to only radiate on its reciever and not effect other receivers. I need to know how much space should be exist between receiver diodes.


texts: What is the characteristic of this common emitter diode feedback circuit?

texts:
Given the following circuit and that β=150, I'm asked to find the characteristic of  Vo with respect to Vi:

Vcc is not given but the reverse saturation current of the diode is considered negligible and the diode voltage drop is 0.4 volts when the diode is on.

I tried solving the problem but I have some gaps.

Region 1

We know at first that Vo=Vcc. Therefore as Vi increases we are entering the forward active region. At this point, since Vo is greater than Vin, the diode will be off.

As long as the diode is off, the output voltage is given by :

$$V_o=\frac{V_{cc}-I_c}{2000}=\frac{V_{cc}-150I_b}{2000}$$
Having this, how can I relate Vo to the input voltage? All I can think of is:

$$I_b=\frac{V_i-V_b}{100000}$$

However, what is the base voltage?

Region 2

The transistor will remain on until the base voltage is greater than Vo by 0.4 volts. Let's say that Vd is the voltage at the anode of the diode. So, the diode turns on when:

$$U_i-100000\times I_b=V_0+0.4=>U_i-100000\times I_b=\frac{V_{cc}-150I_b}{2000}+0.4$$

This is as far as I could get. I could solve for Ui but even if we consider Vcc a constant value, the base current is unknown.

So, I had a look at the solution manual I have and it seems I've done it almost completely wrong. I don't have the complete solution but this is what I can deduce from the result I saw in the manual:

The transistor is off until Vin=0.7V.
The transistor is now in forward active region and the following equation holds:
$$I_b=\frac{V_i-0.7}{100000}$$
The transistor turns on and remains on until we reach an input voltage given by the following calculations:

$$150I_b=I_c=>150\frac{V_i-0.7}{100000}=\frac{V_{cc}-V_o}{2000}$$

According to the above, I have two questions. First, why is the transistor off until 0.7V? And secondly, why is the voltage after the 100000 resistor 0.7V in the f.a. region?


texts: Why is there no reponse from ModbusRTU slave using converter?

texts:
There are two devices:

Eaton EM20/M (~like Northern Design Cube 400)
Volison ADM-5850G

Connected them like:

Trying to get data from EM20/M which supports ModbusRTU(RS-485) protocol using ADM-5850G converter ModbusTCP<>ModbusRTU.

Converter(ADM-5850G) and Slave(EM20/M) are set for 9600 baud rate.
Also, the converter's settings:

Some EM20/M's programming pages:

Created a packet containing 00 01 00 00 00 06 01 03 9e 42 00 01 which should read 1 register at address 40515 from EM20/M which Slave ID is 1. Register's address got from references below(links).

Sent same packet using two tools(wireshark shows same result for both tools):

modpoll(https://www.modbusdriver.com/modpoll.html)
Command: modpoll -a 1 -r 40515 -c 1 -1 192.168.1.104 -l 1000 -o 0.5
netcat
Command: echo -en "\x00\x01\x00\x00\x00\x06\x01\x03\x9e\x42\x00\x01" | nc -w 1 192.168.1.104 502

Result:

A "Cmd" on EM20/M led blinks one time after command having being sent and there's no response:
1 modpoll program outputs: Reply time-out!:

2 netcat just outputs nothing

The question:

Why is there no response?
Do we send a valid packet(also, note that "Cmd" led blinks shortly on EM20/M after command sent)?

References:

ModbusTCP: http://www.simplymodbus.ca/TCP.htm
EM20/M manual we didn't find, but found Cube 400's: https://www.ndmeter.co.uk/brochures/Manuals/Cube%20400%20Manuals.zip


texts: Can I use JTAG Boundary Scan if SRST is not available

texts:
I am attempting to integrate JTAG Boundary Scan onto an existing ARM9 board using SAM-ICE as the JTAG Emulator.

One unfortunate oversight is that CPU/System Reset (nRST or aka nSRST ) was not brought out onto the header on this board. However, JTAG nTRST is exposed.

Would I still be able to execute JTAG Boundary Scan without access to system reset pin? The documentation on this is not clear, as both reset pins are technically "optional".


texts: What is "Standard Test and Programming Language" (STAPL) and is it worth learning it?

texts:
I can see that the Standard Test and Programming Language is related to JTAG in some way, but is it something universal? I have not found any book on this language so far which is quite strange.
What can one do with STAPL?


texts: Can I add buttons to the Arduino ide that automates selection of serial port, board then compiles and uploads

texts: I am developing four different Arduino projects. I want to have a button on the tool bar for each project that automatically compiles uploads using a fixed board and port.


texts: Battery required for a portable immersion boiler

texts:
Immersion heaters like the one pictured are typically plugged in. I'm interested in potentially developing one that is battery operated so it can be used on backcountry camping trips. A water heating calculator (https://www.easycalculation.com/physics/thermodynamics/water-boiling-time-calculator.php) informed me that 500W will bring half a liter of 20°C water to 70°C in 4 minutes assuming 80% efficiency.

My question is: what size battery would be required to deliver 500W for 4 minutes say 20 times before requiring recharge? Would it be small/light enough to be practical to carry on an extended hike?


texts:
I recently bought a really cheap aux-in FM-transmitter. I didn't expect much from it, but surprisingly, it worked flawlessly the first time I tried it. After a week or so, it started stuttering (turning on and off at a very fast rate, sometimes not turning on at all), and then it failed completely.

I decided to open it up to have a look inside. I found that the battery leads and the whole area around it was covered in some sort of white powder. I have no idea what this is. Could anybody tell me what it is and whether it could have something to do with the failing of the device. It's also under the plastic cover to the side of the battery leads (which you can't see in the picture).

Just to be clear: the device did not get wet.


texts: Unexpected reversed voltage over shunt resistor

texts:
I'm trying to measure the current consumption of an accelerometer using a 1kOhm shunt at Vdd. I've read that there's a ~30kOhm resistor at SA0, so grounding it causes a much higher current draw.

When I indeed ground SA0, I see 100mV over the shunt. However, when it's connected to Vdd, I see -36mV over the shunt (measured using a UNI-T UT39A multimeter). The device works correctly, but this negative voltage doesn't seem right.

Does anyone know why pulling SA0 high causes a reversed current draw?

Thanks

EDIT

I've also tried 100R and 10R.

Here's the schematic. Note that I've picked a random part to represent the sensor. The idea is to indicate that the shunt is on the Vdd line.


texts:
I need to find a replacement for the defective temperature probe of some device (laboratory incubator), which is basically a NTC thermistor.  The only information about the defective unit is the following:

Nominal resistance 2252 Ohm @ 25 deg. C
operating range -50 deg. C to +150 deg. C.
Tolerance 0 to 50 deg. C +/- 0.2%.

This is the only information I was able to get from the manufacturer (the part is obsolete). So, I don't know the beta or Steihart-Hart coefficients for this part.  However, I have the new thermistor of another manufacturer with exactly the same parameters and with the known beta.  How can I determine whether the new thermistor could be used as a replacement?  The device has the possibility of automatic temp. calibration.


texts: What is the proper way to set the offset and sensitivity parameters for Allegro A1362 so MSP430 properly digitizes them?

texts:
What is the proper way to set the offset and sensitivity parameters for Allegro A1362 Programmable Linear Hall Effect Sensor so that TI MSP430 5528 properly digitizes them?

Using observed values of MSP430's digitization, how do I select a sensitivity for the A1362?   I am expecting the sensitivity to be around 5-6 mV/G and according to the data sheet the guaranteed range is 4.5-16mV/G

How do I set the steady state value of the A1362 to be around 1.25Volts? The MSP430 digitizes values from 0-2.5Volts, but the A1362 Hall-Effect sensor is bipolar, meaning the voltage increases and decreases.  I would need the A1362's steady state value (with no magnet) to be 1.25V to allow for both north and south pole variations.

I know both questions above will require some experimentation with the A1362 Hall-Effect Sensor and magnet in order to determine the exact offset and slope, but I was hoping someone in the community could either point me to a some kind of a tutorial (youtube or guidelines) or give me a general idea of the procedure to do what is described above.

Will the required procedure look anything like steps outlined on pg. 54 here?

My understanding is I will be applying voltage pulses using a standard power supply.

I would greatly appreciate all / any advise as this is my first time doing something like this.  Video tutorials would be much appreciated.


texts:
I am reverse-engineering a board which provides a VGA output signal for connecting an oscilloscope to an external monitor. I have quite a bit of experience with PCB design but there is a feature on this particular board which I have never seen before. It looks like a few SMD resistor footprints which are not populated with components, though the space between the pads appears to be a dark gray color, almost like carbon. What confuses me is the fact that there is soldermask over the pads themselves:

These footprints are on the R, G, and B video signal pins, as well as Hsync and Vsync. I am reverse-engineering from scans of the PCB. I have the ability to take the actual device apart and probe the card, but it is a bit of a pain in the neck and I would prefer that to be a last-resort. I am hoping I can get an answer without having to crack the thing open.

Any idea what these features might be? My suspicion is that they are some sort of carbon printed resistor, but I don't believe I've seen anything quite like this before.

UPDATE: I bit the bullet and I ripped the thing apart (as much as I didn't want to). The "devices" on the R, G, and B lines measure about 75 ohms, the ones on the Hsync and Vsync lines measure about 72k ohms. 75 ohm values are consistent with the characteristic impedance of the R, G, and B lines, so my guess is they're some sort of termination resistors. Not sure about the Vsync and Hsync though. Pull-ups/pull-downs?


texts: Need some advice for a voltage clamp for motor controllers

texts:
I'm working on a project that is powered by a 12V 100A PC power supply in line with 5 x 2.7V 350F supercapacitors. There are three 2x30A motor controllers driving wormgear DC motors. The supercapacitors are there for transient overcurrent beyond what the power supply can handle. I've been through a different of iterations with this board addressing different issues as they come up.

After a stalled motor sent a motor controller up in smoke I realized I need some better protection in place so I'm putting a 500A relay/contactor in place so that I can directly cut power to the motor controllers if needed.

I'm looking for help with two related pieces. First I need a voltage clamp (there's one on the motor controller but I want it separate) that will compare 12V from the power supply to the voltage coming from the motor controllers which can shootup in the case of regen.

The second would be a similar op-amp or comparator that would be used if voltage continues to rise above what the voltage clamp can handle that could be sent to a MOSFET to shutoff the 500A relay and directly cut power to the motor controllers.

I have an Arduino included for monitoring the supercaps. Maybe it could be used to control the MOSFETs instead of a comparator? I would need something like an optoisolator (possible?) to read the 12V signal and the voltage of the motor controllers.


texts:
Looking for a simple design to convert from 4-20mA signals to 0-3V3, I'm thinkin about configuration shown at picture attached.

And I would like to discuss its suitability.

It is based on:
- A follower configuration for a Rail-to-Rail OpAmp, powered  at 3V3.
- A 165Ohm resistor to get, 3V3 at 20mA, and 0V66 at 4mA.

What do you think about?
It is any improvement I can do?
Or it would be better to work with another more precise configuration?

It is thought for a low power applications (<5V), but it would like to know if it could work with 4-20mA transmitters powered at 24V too.


texts:
I have a fairly large (several pounds) old wire-wound transformer, which steps down 220V to 110V (or, I suppose any other suitable voltages, but that's the intended use).

I don't know the rating of this transformer. It is not indicated anywhere on the unit. Based purely on size and weight comparison to "modern" transformers1, I would estimate the rating at around 1000 VA, but I can't be sure.

I'd like to run an ~800 VA load on this transformer, but monitor for failure.

What would be the typical failure mode of a transformer me if I've exceeded the load? Overheating? Voltage drop on the load side?

1 "modern" is in scare quotes here because I don't think this tech has changed much in decades.


texts: Can I measure 220 V AC signal by spectrum analyzer ?

texts: I want to observe noise in mains voltage. Can I measure 220 V AC signal by spectrum analyzer to observe noise? My spectrum analyzer GSP-830. Thanks!


texts:
Hi,

I'm having a problem with the USART_RX_vect interrupt of the ATMega 328p. The receiving works fine and I'm able to evaluate the sent bits (so it's not due to the baudrate) but everytime I send a bit, the ISR gets executed 4 times.

So a ISR like this:

ISR(USART_RX_vect) {
    uart_transmit('t');
    uart_flush();
}

Will transmit {'t', 't', 't', 't'}

I have no clue why this is happening, and I hope you can help me.

My main is a empty loop (of course I execute uart_setup). My ISR is like above. I'm using avr-gcc on linux.

This is my UART Setup:

void uart_setup() {
      UBRR0H = (BAUDRATE >> 8);
      UBRR0L = BAUDRATE;

      // Set 8-Bit mode
      setBit(UCSR0C, UCSZ01);
       setBit(UCSR0C, UCSZ00);

      setBit(UCSR0B, RXEN0); // Receiver enable
      setBit(UCSR0B, TXEN0); // Transmitter enable

      setBit(UCSR0B, RXCIE0); // Enable RX Interrupt
      sei(); // Enable global interrupts
  }

void uart_transmit(unsigned char data)
{
    while (!( UCSR0A & (1<<UDRE0))); // wait while register is free
    UDR0 = data; // load data in the register
}

void uart_flush( void ) {
          unsigned char dummy;
          while ( UCSR0A & (1<<RXC0) ) dummy = UDR0;
  }


texts: MOSFET full H bridge, voltage spike protection

texts:
Preface, I'm a hobbyist not a electrical engineer, so please be gentle.

I was looking for a better than l298N motor control solution for higher currents and one that is similar price and size, but couldn't find one.

I searched the web for h bridge schematics to copy and make a PCB for my projects. So far this is the part of circuit that does the heavy lifting:
The design is from Lewis Loflin http://www.bristolwatch.com/k150/port5.htm

5v control signals (ATMega 328p, 500Hz PWM frequency), motor is 24V/5A (windshield wiper motor), MOSFETs are IRF3205 (N) and AO4407A (P, only have SMD p-channel MOSFETs on hand and all of them are -30Vds), BC547 NPN. The problem is that the circuit does not have a voltage spike protection (to my limited knowledge, unless the body diodes count as one) and AO4407A is rated to -30V Vds which is probably lower than the voltage spike that might occur.

What should I change in the circuit to protect the MOSFETs from releasing the magic smoke?

Would using PWM to slowly ramp up and down the motor help? The solutions that I've read about consist of either: diodes, MOVs, low pass filters, capacitors, coils, gate resistors, but which solution is considered not overkill and "good enough"? I don't have a oscilloscope to measure the voltage spike, so I'm not sure of values that the protective components should have.

Also I've read that for PWM control, you should only use PWM on 1 of the MOSFET (N, P) pair, is that right?


texts: Capacitor bank for smoothing full-wave rectification output

texts:
I need some insight on the best way to set up the inductor-capacitor portion of our circuit. My goal is to smooth the output from our diode bridge which rectifies the AC current input into DC current.

Here are some specifics for the output of the full-wave rectifier:

The current going will be about 180Amps. The current coming out should preferably be maintained around 180Amps.
The voltage going into the capacitor and inductor section will be around 16.5v to 20v at its peak voltage.
The frequency from both the positive and negative outputs of the diode bridge will be 120Hz (since it is doubled with the rectifier).

What specific setup would you recommend to smooth this voltage and current? I know it’d be best to split the capacitors into parallel to divide the current, but I am not sure what specific capacitance they should have or the best set up to arrange them in. It is at a different scale with the high amperage and low voltage compared to other typical circuits that use capacitors to smooth the rectified DC current. If you could propose a way to do this effectively without adding too much load on the circuit, I would appreciate it.

Additional information:

This power supply is for my fusion reactor which uses strong external magnetic fields to trap a well of a electrons under a vacuum, known as a Polywell. It needs a smoothed output because if it oscillates to 0v on it's 120Hz positive DC output the inductors creating the magnetic fields in my reactor will be weaker and not trap the electrons as well.

Update:

Since it seems very difficult to smooth the 180A output at a steady voltage, would a possibility be to split the 180A current into several parallel circuits and then use capacitors to smooth each output with less current? What is the maximum current at 20v that a single, cost-effective capacitor could smooth? Maybe I could split the circuit into 90 parallel wire sections each with one capacitor (preferably small sized and low cost) that could smooth 2A and 20v, and then bring the smoothed outputs back to 180A at a relatively steady 20v. Is this a realistic idea?

Jeremy


texts: Inductor kickback snubbing with capacitor

texts:
I cant seem to gasp why an inductive circuit with RC as a snubber element still produces voltage spikes even when msot online materials suggests that it should be able to solve the issues.  The below circuit is used to simulate the spike in LTspice, the inductor is assumed to be perfect with 0 series resistance, C1 is also perfect.

and this is the waveform it produces at v2:

One of the possible conclusions I came up with is that when switch S1 opens the current cannot instantly change and therefore although R3 is small there must still be some voltage across it when there is current passing it.
However when i add some resistance in series with the inductor suddenly these spikes disappear:

the voltage change is expected as the circuit isn't compensated.
The biggest change in the circuit is pretty much where V2 is measured. when measured after R4 (ie in series with inductor) the spikes suddenly disspear. But why is this? Why cant I increase R3 instead of R4 to reduce the inductive kickback.
A side question is, are there any designs where i can completely smooth the voltage kickback without putting in R4? Thanks


texts:
I was recently in a discussion with my professor in which he told me that 'absolutely in no way would this design work'.  I am hoping I could bounce it off you guys.

The question asked to design (in any way) an IC that, given a sequence of bits which would come as input on a clock cycle, would detect a given sequence (arbitrary, but 4 bit in length) inside that stream of input.

I implemented it with a 4 bit serial in, parallel out shift register whose parallel out fed into a comparator which compared against the desired sequence.

Am I crazy here or missing something? Would love some feedback and or advice!


texts: Designing PCB with Multiple power supplies

texts:
This is my first REAL project and i need some help.

I'm working on a project where I am trying to design a PCB for controlling the environment inside an enclosed cabinet to grow a tomato plant using hydroponics (cannot use the arduino dev board).  I plan to use the atmega2561 as the MCU, with multiple sensors to read information, and relays to trigger on fans and lights.
Here is where I run into problems, I need 12volts, 5volts and 3.3 volts coming from the same board to power these components.  I will be using an AC-DC converter to provide 12volts to the board, but how do I distribute these required voltages to the other components?? here is a list of what i plan to use

12Volts : 3 peristaltic pumps and 3 relays(will be using ULN2803 to connect these relays to the MCU.
5Volts : MCU, EC sensor, water level sensor, pH sensor
3.3 volts : temperature sensor, xbee module

I used TIwebench and exported the designs into eagle but still confused on how to implement them to my design.

Thank you!


texts:
I am using the buck-converter circuit from Low side N-Mosfet buck converter as the base of my design. And I want to replace the diode with a P-channel MOSFET. I also want to drive both MOSFETs with an op-amp like the following circuit:

Considering the direction of the p-channel MOSFET and the way it going to be drived I am wondering if this circuit works?
Update
For the sake of simplicity let’s consider the second circuit where MOSFETs are getting driven separately (for example by a micro-controller). Does this buck convertor work?


texts: DC current through diodes in AB amplifier

texts:
I can't figure out how the DC current through the diodes is calculated in eq. 8.22 on this PDF from University of North Carolina.

$$
I_D = \frac{V_{CC}/2-V_{BE}}{R_f+R_2}
$$

\$I_D\$ should be equal to the current through the resistor \$R_2\$ minus the current going through the base of the transistor \$Q_1\$. I am able to obtain this equation only supposing \$I_B = 0\$, which is not true, specially because they are matching the diode to the transistor to avoid thermal problems.


texts:
Given the following circuit:

Why is the current through the circuit 34.7mA instead of 35 mA? My thinking was that:

The LED draws two volts, so it effectively makes the battery 7V instead of 9V.
Voltage in = Voltage out, so 7V = 200 Ohms * 35mA

What accounts for the slight difference here (which becomes more pronounced as a calculation difference the more LEDs I add to the circuit) ? The circuit is shown here: http://everycircuit.com/circuit/5468024738676736

Also, with the circuit done in the CircuitBuilder on StackExchange (for LED I did not change any default params):

simulate this circuit – Schematic created using CircuitLab


texts:
Ok, I have modified my question again about the same circuit seen below:

I have to simplify the circuit using source transformation and then find the current ix.

I have attached my attempted solutions but I do not get the correct answer of ix = 0.9A ( I am getting 4.3 amps now).

What I suppose I would like to know is:

Is my circuit simplification correct or have I made a mistake somewhere?

Or could I have solved the current ix easily from any of the earlier steps I made in my circuit simplification? i.e. when would you guys stop performing source transformation and circuit simplification and start with circuit analysis to solve the current ix?

Thanks.


texts: Electron flow in Lead Acid Cells in series to make a 12V

texts:
I am happy with how electrons flow from the lead negative anode to the lead oxide
positive cathode.
after chemical reaction at the lead anode where lead sulfate is formed and the electrons are released the electrons compelled to move towards the lead oxide
plate so they can be stable after the reaction at the cathode which forms lead sulfate and water at the cathode.

However when connect the positve cathode of first cell to negative anode of second cell why are the already stable electrons which are already part of the newly formed lead sulfate and water compelled to move from their stable position at the lead oxide cathode to the negative lead anode of the next cell. V confused.

thanks for any replies...


texts: Multiple power supplies/sources for LEDs, how/where to ground with data line

texts:
I have hit a point in my LED project where I am about to introduce a second power supply (5V 60A Source - Amazon Link Here) and I would like to ensure a common ground. Think of the project as one continuous LED strip with power introduced at intervals to ensure the lights are supplies with ample power.

So far, one supply has 4 terminals which can supply power to the Microcontroller and 3 different points along the LED strip. Adding a second supply brings up the question of how to share the ground.

My thought process is this:

The ground must be shared throughout the project/full LED strip like what we see in the image above.
With 2 power supply sources which are pulling from 2 seperate plugs introduces 2 different grounds, going against #1
Either:

A) The two power supplies should pull from the same source, like through a Distribution box (lunchbox or distro box for all us film industry folks Example of a Distro box here). So even though the 2 supplies are pulling  from different 2 plugs, the source of those 2 plugs is the same line.

-OR-

B) The grounds are connected after the fact and since they are connected, it just becomes one connected ground source.

The question:

Are either of these approaches correct?


texts: The Barkhausen criteria for sustaining oscillations states that the total phase around the loop must be 0 and the gain must be unity. I was thinking about this and got stuck :) The aforementioned criteria is most commonly explained as "at least the signal must not get smaller while travelling around the loop" so if these two conditions are met then it enhances itself. But doesn't it mean that the signal will continue growing until it hits one of the supply rails?


texts:
I understand why some transistors have a built-in (normal) diode from drain to source, so that when the transistor turns off, back-emf can flow back up, specially important in inductive charges, but why do some MOSFET like IRF540 have a zener? From what I understand, a zener diode conducts backwards with a specified drop voltage. I can only suspect that this zener has something to do with the absolute maximum voltage sustained between source and drain, specified in the datasheet, is that correct?

Also, I am trying to build this circuit:

But the transistor I am using as Q1 is currently IRF540 that has a zener diode instead of a normal one. As expected, it doesn't work very well. As proof of concept, with a normal diode (no Q1), Q2 I can successfully charge the gate and it lets current pass through.

I tried to put a normal diode in parallel with the intrinsic zener and it still doesn't work...


texts: Transfer function of frequency shifted signal

texts:
I have a system controlled by the function \$i(t)\$ and described by
this time-domain equation:

$$l(t)=A+\frac{Pi(t)}{CK}-\frac{Pi(t)-CK(O-A)}{CK}e^{-Kt}$$

Taking the Laplace transform I get this:

$$L(s)=\frac{A}{s}+\frac{P}{CK}\left[I(s)-I(s+K)\right]+\frac{O-A}{s+K}$$

How can I express this like \$L(s)=H(s)I(s)\$, with  \$H(s)\$ being the transfer function? I mean, what is the transfer funtion here? I got stuck because I had never seen a system in which something like \$I(s+K)\$ appeared. Can I rewrite it in terms of \$I(s)\$?

Interestingly $$\frac{I(s)-I(s+K)}{K}$$ looks like it could be \$-\frac{d}{ds}I(s)\$ in some kind of approximation but I'm still confused.


texts:
I am trying to design a non-inverting integrator to get a triangular wave from a square wave. (the square wave will be generated using a 555 timer)

I am using this design i found online: FIG1

I calculated its transfer function and i got: H(s)= 1/(RCs)

When I try to simulate the circuit (FIG2) using PSpice I get this output: FIG3

With the vaalues I used shouldn't I have to be getting a higer amplitude signal??
Is there something wrong with the desing/calculations??
Thanks a lot in advanced and sorry for my bad english :-/

** Since i cannot post more than one link there are all the pictures in a big one:


texts:
I am looking at implementing a PoE circuit based on the TI chip TPS23730 and on the evaluation board it has the RJ45 jack with PoE and is connected to the ethernet shield on its own ground plane (which for ESD reasons I understand should be connected to chassis ground), the power supply on a separate ground plane and the final load on another separate ground plane. The non-PoE data is then routed to a separate ethernet port to be connected to another device.
If I want to place a microcontroller on the same board, I would reference this to the final supply ground plane and have a couple of questions relating to what changes need to be made.
What I am unable to determine is how to route the data lines after the transformers. Do I route the data lines direct to the mcu after the transformer, do I need additional isolation and what plane to reference the surge protection to? Do I need to provide a particular plane below the data traces? I have put together a block diagram to show the isolation points.

I am fairly new to laying out ethernet and so far understand that the traces need to be short and have matching lengths. The evaluation board recommends having Smith resistor and capacitor off the centre tap, is this correct if the data lines will now run locally or do I need to move them?


texts: Is it possible to make a Raspberry Pi transmit FM on several frequencies at the same time?

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I have read a few questions here on transmitting on multiple frequencies at the same time. But all of them was about transmitting the same signal to all frequencies.

The PiFM and PiTX projects are examples of how to transmit audio over FM with no additional parts, including RDS data. This got me thinking. If I can receive multiple audio streams with my PI (say 5 different netradio stations), is it possible to somehow multiplex these on 5 different frequencies (say 100-105MHz) just modulating one pin on the PI, the same way PiFM works?

The end goal of this project would be to create a DAB-interface for a car stereo only supporting FM. I don't want any of the current solutions (external interface with single frequency FM transmitter, bluetooth, usb, etc). I would feed the antenna somehow directly into the cars antenna interface, hopefully stopping any transmission beyond my own car, while keeping nice strength for the FM radio.


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I was wondering, how to calculate the values needed for LC/RC filter when using it for digital to analog conversion?

Also, how does the square waves frequency affect DAC ?

For example: lets say I have 10 kHz 5V square wave output to the LPF. From it, I would like to get an analog value, with cut off frequency at 20kHz.

How would I calculate component values needed?


texts: Switch on a 10 A circuit with only a 20 mA signal

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I'm attempting to wire in a 12 V fan to my car that draws 7 A at full speed.  The fan is a fused link directly to the battery.  I have a 12 V 20 mA signal wire, but that doesn't appear to be strong enough to trigger a standard automotive relay RL44.

Are there any options to support such a high switching current from such a low signal current?

@Winny and @Spephro Pefhany suggested a pilot/bootstrap.  Is this the idea of how that would work?

simulate this circuit – Schematic created using CircuitLab


texts: Can two devices share a decoupling capacitor?

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I am working on a circuit that has two devices that are each supposed to have decoupling capacitors.  In this case however, the devices are right next to each other, and their power supply pins are right next to each other (let's say, 1mm apart).  Can a single decoupling capacitor be used for both devices?

Similarly, I have a LDO regulator for the power supply which requires a 1uF capacitor on its output for stability, can that be the same capacitor as the decoupling capacitor for both devices as well?  I can move the LDO right next to the power pins of both devices.


texts: nMOSFET not turning off properly using RPi GPIO pins

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I have an N-Channel MOSFET (model: FQP30N06L) which I tried hooking up the Gate connector to a RaspberryPi GPIO pin (3.3v, also tried a always-on 5v).

The Source connector connects to a wall-mounted powersupply that delivers 12v and 850 mA.

The Drain connects to a 10W LED Buck-Driver

simulate this circuit – Schematic created using CircuitLab

I've also tried turning the negative and positive around all together, and I get light from the LED. However it's not that bright. I assumed it might be the voltage from the RPi being to low, so i tried a static 5v output but it didn't do much to the naked eye.

So I hooked up another 12v power supply and just fed it straight on the Gate of the MOSFET, low and behold it lit up perfectly (just as it did with the 12v power supply straight on the buck-driver).

So that's worked out, I need more power on the gate or I need a different MOSFET. But how do you turn off the MOSFET? I assumed putting 0v across the Gate would cause it to shut off?

So I guess I have two questions that would help me go on learning these things.
1: How do you turn off this MOSFET
2: Is this wiring even OK?


texts: How to make sure this oscillator will be stable?

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In my textbook, the Wien-Bridge oscillator and the Twin-T oscillator needs a tungsten lamp as the self-adjusting resistance:

The lead-lag circuit connected to noninverting input has a gain of 1/3 on its center frequency. Since the lamp started with low heat (less resistance,) the starting close loop gain is big. As the output oscillation builds-up, the lamp heats up and thus close loop gain decreases until it reaches the point where gain is 3 so that \$A_{V(CL)}*\frac{1}{3}=1\$. This ensures stable oscillation.  (Well, that's how I understood it.)
How can I make sure that the tungsten lamp resistance will remain constant?
Won't the oscillation decay immediately if the resistance of the lamp increases even just a little bit since \$A_{V(CL)}*\frac{1}{3}\$ will now be less than one?


texts: Is it feasible to make a musical tesla coil

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Ive built a couple tesla coils so far, both a slayer and a spark gap (nothing overly complex).  I'm still a student so I dont know a ton about electronics but I have a decent foundation.  Has anyone here made a musical tesla coil before?  I'm considering making one, however, I'm not sure if I will be able to.  Theres not much information online about these; I've only really found one tutorial and it's much larger and more expensive than anything I have the ability to make.

Does anyone have any suggestions?  How should I approach this?


texts: Does priority inheritance cure priority inversion?

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In the Mutex description page of the FreeRTOS website the following sentence can be find:

  Priority inheritance does not cure priority inversion

From what I know I thought that priority inheritance was a cure for priority inversion. If the high priority task A is blocked by the low priority task B, with priority inheritance, task B inherits the priority level of task A (high). This means that no medium priority task can delay the execution of task A. As a consequence, priority inversion does not occur.
What is wrong in my reasoning?