texts: To share or not, grounds of two power supplies

texts:
I'm using Arduino to control 2 stepper motors via two l293D drivers.
I'm using a separate power supply for the steppers (6V).
I'm looking forward to expand the system to 3 up to 10 motors.

Now i have read that i should share the grounds so i have connected the ground of the Arduino (powered from the USB cable) with the ground of the secondary power supply.
It works all right. I haven't tested disconnecting the grounds. Now i read in an answer here in this site which is selected as the correct one (albeit for a different question) "Never share grounds."

Powering a Servo: Do I need a separate power source?

Can someone explain a bit what is the case?

Thanks for the answers. Now please a bit more so to get it, I'm a newbie.

Now in the l293D (2 of these) i have connected the grounds all together (4,5,13,12).

In one of the answers the author talks about opto-isolation of the 2 power supplies (control and load). This means that if i raise the voltage and the current of my load i.e. use more motors, the circuit in it's current stage may misbehave and i should opto-isolate the grounds for precaution?


texts: Why does increasing sampling density in the frequency domain separate overlapping artifacts in the spatial domain?

texts:
I have employed the fourier(projection) slice theorem in matlab. I have a 3D image, P(x,y,z) defines their pixel intensities at a given location int he image volume, it is discrete and uniform. I take the FFT of this image and get a 3D volume in the frequency domain. I then take a 2d slice from this 3D volume at an arbitrary angle making sure that the centre of the slice and the centre of the 3D FFT image volume pass through the same point. I then inverse FFT this 2d extracted plane to get a projection of my 3d volume.

I have noticed that I get an overlapping of artifacts but they are shifted by bit, also their intensity is reduced. If I sample at a higher rate the shift becomes greater to a point where it doesn't overlap anymore. Why does sampling at a higher rate increase the shift of the overlapped image? What can I do to stop the artifacts from being produced?


texts:
I was given a homework assignment shown below and I have a few quick questions that I appear to be stuck on. Any help would be appreciated.

I can get Part i) and the answer is 168.64 degrees.

Part ii) I can't seem to get correct. My professor gave us the equation:

$$\displaystyle V_{L_{rms}} = \frac{1}{\pi} \int_{Q_{1}}^{Q_{2}} (V_p\sin(\theta)-1.4)^2 d\theta$$

with Q1&2 being the two points at the which diode conducts (5.68 and 174.32 degrees respectively). When I integrate this is, I get huge numbers like 249Vrms which doesn't seem be correct. Does anyone have any guidance on what I could possibly be doing wrong?

Thanks


texts: Trying to understand vhdl led blinking code

texts:
I have a led blinking code for MachXO2 breakout board written in VHDL. Actually I am new to VHDL.

I am not able to understand the meaning of these lines:

--internal oscillator
   COMPONENT OSCH
      GENERIC(
            NOM_FREQ: string := "53.20");
      PORT(
            STDBY    : IN  STD_LOGIC;
            OSC      : OUT STD_LOGIC;
            SEDSTDBY : OUT STD_LOGIC);
   END COMPONENT;
BEGIN
   --internal oscillator
   OSCInst0: OSCH
      GENERIC MAP (NOM_FREQ  => "53.20")
      PORT MAP (STDBY => '0', OSC => clk, SEDSTDBY => OPEN);

Can you please tell me What these lines are doing?


texts: Why does turning on my desk lamp crash my board?

texts:
Whenever I turn on my desk lamp, my board crashes. Sometimes I get garbage out of the serial port, sometimes it resets.

I tried adding some extra bypass capacitors on my breadboard, but that made no difference.

(My desk lamp uses a 20W, 12V halogen bulb. It has a transformer in the base)

Can anyone offer suggestions as to why this might happen and how I can stop it?

Here are two of the boards - they were USB dongles, but are both now powered from a single wall-wart via a 3.3V voltage regulator.

Watching on a scope, when I flick the light switch I see a spike on both 3V3 and wall wart lines.

Edit:

Here are traces of the input and output of the 3V3 regulator when turning the light on and off respectively.

5V is on the top, 3V3 on the bottom

The regulator is a ZSR330.

Edit:

Some careful reading of the datasheet threw this up:

  The RESET_N pin is sensitive to noise
  and can cause unintended reset of the
  chip. For a long reset line add an
  external RC filter with values 1 nF
  and 2.7 kΩ close to the RESET_N pin.

My programming cable connects a long wire via a breadboard to the reset pin. I suspect that this was the problem.


texts: Easiest way to get minterms from a SOP Boolean expression?

texts:
So far, I've come across problems were I need to get the list of the minterms in a truthtable from a SOP Boolean expression. For example;

They way I've tackled these problems was to convert the expression into a K-map, and get the minterms from there. I wonder though if there's an easier or simpler way to get the minterms? I've searched for this but nothing really came up.


texts: ULTRA X3 D0409 1000W PSU and high 3.3v rail voltage

texts:
I just got ULTRA X3 D0409 1000W PSU for a rig which I'm building and before putting it in, as always, I have it checked with PSU tester and came up that 3.3V rail voltage is going high (up to 4.1) but it will fluctuate after that between 3.7 and 4.0

I think going above 3.8V it should to trigger over-voltage protection in the PSU but it didn't.

Any thoughts on that? Is this can be adjusted by a resistor or something else?


texts: High-side switch with BJT for 24V controlled by logic level

texts:
Earlier I have asked another question and I got very good answers but I couldn't get a solid success as per my size considerations and an unexpected solenoid type change. And I am now giving another try this time using small signal transistors instead of FET's.

simulate this circuit – Schematic created using CircuitLab

With this design I can have a good ON and OFF using 5V, 12V supplies but not with 24V. If the input is HIGH I can get a full ON (24V) but, if I put the input in LOW state, I have sort of half ON (12.4V). I have tried different resistor values considering saturation and cut-off currents but I couldn't make any difference by that.

I appreciate your valuable inputs from now and I am open to any other suggestions in terms of design.

Note that: I have just picked the transistors randomly from common examples. 2N3906 is rated for a maximum 200mA, not sure it is even good enough for my load.


texts: How do I create a USB cable with a capacitor in-line?

texts:
I have a USB powered device powered from a car lighter socket to USB adapter. When starting the car the power turns off briefly, I need to maintain power to a USB powered device over this time.

I want to make a USB cable (or circuit board) with a built in bypass / power holdup capacitor in order to maintain power.

How can I do this?


texts: The book we are reading states that the maximum slope of this graph occurs at B, but I cannot understand from this graphic how that is possible. It appears to me the maximum magnitude of slope occurs at Q because it is closer to being vertical, which is infinite slope. How is this the case?


texts: I read about different parts of micro-processor like ALU, registers etc. all different digital parts. Are there any analog parts inside the processor?


texts:
I need to count how many miliseconds does it take my interrupt to finish its service. Before I started using FreeRTOS, I just did something like this:

void HAL_GPIO_EXTI_Callback(void)
{
    uint32_t diff;
    start = HAL_GetTick();
    // do anything
    diff = HAL_GetTick() - start;
}

But when I started using FreeRTOS, HAL_GetTick value stopped changing, moreover Systick Interrupt do not work, so there is no chance to increase tick value. Any ideas what should I do to bring back Systick Handler working in interrupt or other solution so I will be able to measure time in interrupt?


texts: Connecting two DC converter's inputs in series

texts:
I know it won't work, but I want to make sure I have the right explanation why it won't work.
Given are two devices which have a build in converter (I have this digital voltmeter in mind). They need 12 - 24 V AC or DC supply. And apparently the supply is galvanically isolated from the measurement inputs. Also given is a let's say 40 VDC power supply.
One could falsely come up with the idea of just connecting the two voltmeters power inputs in series with the 40 VDC supply in order to save two (e.g.) 24V Converters.
My explanation why this won't work is as follows: Since those digital voltmeters while have internally some sort of buck converter with a feedback-loop (due to the variable input voltage), the voltage will not divide 50:50. The ratio will either tilt to one or the other side, depending on which device has a slightly higher load when turning everything on. I would say the measurement input connectors have no influence on this and could theoretically be connected since there is a galvanically isolation anyway. The only problem is that these two feedback loops behave unstable and in the end tend to apply almost all the voltage to one of the two devices. This will most likely kill one of them (or at least the fuse).
Does this explanation sound valid, or is there a more reasonable explanation that I have overlooked?


texts: Raspberry Pi Pull Down GPIO Pin using Arduino

texts:
Setup:
An Arduino
A Raspberry Pi with pin 20 setup as INPUT_PULLUP.
The Arduino and the Raspberry Pi are on different power supplies.

Question:
Is it possible to pull down pin 20 on the Raspberry Pi using the Arduino?

Many thanks!


texts: How to ensure data integrity when using I2C with a PIC

texts:
When master device transfers a piece of data, slave will acknowledge back once the data has been received by slave. So it's not possible to ensure the data integrity by only polling ACK.

I implemented a C function:

unsigned char i2c_write_byte(unsigned char s);

Here I'm returning the ACKSTAT bit.
So if there is not an ACK sent by the slave, I will try to send the data again by using:

while(!i2c_write_byte(data));

I know the ninth clock is for ACK, but what if there is no ACK sent back by slave device.
Then it should be detected as NACK meaning the slave didn't drive SDA low which is slave never received data transferred.

So on this occasion, should I send data again or send data after a restart?

I can only think of re-send data to work around NACK problem and still can't solve the error happened in the data while in a transfer.

So how to ensure data integrity in I2C?


texts: Can LiFePO4 BMSes be connected in parallel without causing charge/discharge issues?

texts:
I have two LiFePO4 battery packs in 4S configuration: one with 2x4 cells (4S2P) and one with 3x4 (4S3P) cells. Each pack has a 4S BMS.
Are there any potential issues with connecting those two in parallel at the BMS charge/discharge side?
As the batteries drop in voltage when discharging, will there be a lot of losses in 'cross feed' between the two packs, where one will charge the other?


texts: How does DC braking stop an AC motor without considering current direction?

texts:
When a motor is coasting to standstill, if I apply a DC voltage across the windings I will brake that motor... We'll at least that's what I've read.

Now here's the thing.  With reverse current braking I literally reverse the direction of the motor until it's at 0rpm,and then I disconnect the supply. Which is understandable. But when it comes to DC braking,  I just apply the voltage across a winding,  without taking current direction into consideration, and the rotor will stop.
How does this happen? In fact, why does it stop to begin with?


texts: What is the technology used for buttons in the US Post Office readers?

texts: If you have used a US Post Office card reader, you may have noticed how crisp and somewhat unusual the feel is of their buttons. They have a very short throw, yet a very distinctive click. I have encountered this type of button nowhere else. What is the technology behind it? What is this type of button called?


texts: Reliability of battery retainers for coin cells

texts:
I'm thinking of using a coin cell battery retainer on an upcoming project.  The target application will be in a medium-to-high vibration environment with around 1-2 years between battery changes.  Unit will be in a dust-tight enclosure.

The retainer in question is MPD BK-5033.  I'm concerned with maintaining good battery contact, as it powers a uC storing values in RAM.  The application is very, very low power, and there are some capacitors to prevent millisecond length glitches.  What bothers me is the idea of creating a pad on the PCB that has to maintain contact with the battery terminal.

If anyone has experience with this type of battery holder, I would love to hear any pointers.


texts: Why was the term electromotive "force" used instead of voltage or potential difference in original Faraday's law?

texts:
Faraday's law is always given as:

'

I always wondered why a phenomenon which is totally "electrical" and electromagnetic has anything to do with a terminology from mechanics like "force".
If there were anything like an electrical machine like an AC motor the term torque makes very sense.

But what could be the reason historically Faraday himself gave this name "force" on the left side of the equation  instead of using the term "voltage"? In this law there is no force like in the Biot-Savart law, etc.


texts: Why/How do higher amp hour batteries for tools provide more power?

texts:
I have seen power tool brands have battery packs ranging from 1.5Ah to 9Ah. Their advertising indicates that the larger amp hour battery packs can run the tool longer and with more power (such as a circular saw cutting through thicker material). These are all 18v battery packs, so I can only assume that there is circuitry within the packs that are limiting the amount of current per cell. That way, the packs with more cells can provide more current. Is that correct?

If it is a circuit to limit current (for short/heat protection purposes?), how are they going about doing this? Just an off the shelf solution they stick in there?


texts: Propagation delay in asynchronous circuit

texts:
Consider the circuit shown below where delay of each flip flop is 10ns and delay of each AND gate is 5ns each. What is the total propagation delay ?

My Attempt:-

1) Consider that initial state i.e Q0Q1Q2 = 000 . So, after 10ns (5 + 5), we get inputs for all flip flops.

2)Now when we apply the clock to 1st flip flop (T0), it produces output after 10ns which acts as an input for T1.

3)After 10ns, T1 produces output in 20ns and activates T2. But by 15ns, output of 1st AND gate reaches simultaneously to T1 flip flop and 2nd AND gate and 2nd AND gate produces output in 20ns (15 + 5).

4)Now T2 takes another 10ns to produce output Q2 at 30ns (20+10).

So total propagation delay should be 30ns according to me.

But the answer is 30+5+5 = 40ns.

Please can someone tell me where am I going wrong ?


texts:
I'm having trouble with this question. Can somebody help?

I know the equation for part a) is:

$$P_{\text{max}} = \frac{1}{4} \cdot \frac{\mid{}V\cdot{}t\cdot{}h\mid{}^2}{R_\text{L}}$$

And I'm sure that I have to cut out the \$R_\text{L}\$ resistor from the circut and just focus on getting the thevenin equiv. for the transformer circuit.

Any ideas?


texts: Connecting a 75 ohm device to a 50 ohm antenna

texts:
I have a device operating at low-frequencies (470 - 790 MHz, Television White Space), which works with a 75 ohm antenna. I want to connect this to a 50 ohm antenna instead. The 75 ohm end has an F-type female connection and the 50 ohm end has an SMA-type female connection. I've been looking for the appropriate 'adapter' for this situation but most items are difficult to come by, expensive, and have numerous names. For example, there are items like:

Impedance matching pads
Impedance converters
Impedance matching transformers
And just plain F type to SMA type adapters

I am sure the plain F type to SMA type adapter is out of the question, but which of the other types is suitable for my application? Or is there a different type of device suitable for this.


texts: Why do we rectify then invert current in induction heaters?

texts:
I was trying to build a simple zone refining prototype, so I thought of How to simplifying induction heater for zone refining?

I throughly read What does a beginner need to know to build an inductive heater? And decide to drop this idea.

But all resources on internet and two very nice instructables:

http://instructables.com/id/Powerful-yet-simple-induction-heater/
http://instructables.com/id/30-kVA-Induction-Heater/

have one thing in common, and that is my question:

  Why do all of them first rectify AC to DC & then convert it back to AC?

Is there a simpler way of doing this? I do understand 110V-220V is way too much for induction coil but I've heard of regulator IC, can they simplify this task?


texts: How to choose a PIC for a BLDC Motor Controller?

texts:
I just made a BLDC motor controller, but I'd like it to be able to go to higher frequencies (have less dead time, faster firmware, etc).  In particular, I'm aiming for 20kHz-to-50kHz range, but am having trouble getting beyond 10kHz without seeing my top speed drop off significantly.

I realize this depends on both circuit design as well as the firmware, and to some extent the layout, but am interested in a better microcontroller choice right now, maybe one that is more optimized for BLDC motor control.  I like developing with PICs right now and was wondering if anyone had any suggestions on how to pick a better PIC or if there was a family you've used before that you think would be good to sample.

I've recently discovered that some offer programmable dead time, although I'm fine with offsetting that manually.  Are there any other features I should consider?

Thank you,


texts: What is the power voltage pin outs for a Playstation 5 PS5 power drive connector on the motherboard?

texts: I ripped off the drive power connector from the motherboard on a PS5 and looking to get this repaired, but I need to find the power pin outs in order to fix it. Where can I find the voltage pinouts diagrams?


texts:
I am trying to make a serial servo controller using pic18f4550 microcontroller.

following if the complete code that i've tried..

please note that i'm currently sending 8bit hex to control only one servo.
i'm sending this data from one pic to another..

#define FREQ 20000000
#define baud 9600
#define spbrg_value (((FREQ/64)/baud)-1)

unsigned char rx_data(void);
void tx_data(unsigned char);

void main()
{
int i;
double state;
int ip1=0;
SPBRG=spbrg_value;      // Fill the SPBRG register to set the Baud Rate
RCSTA.SPEN=1;           // To activate Serial port (TX and RX pins)
TXSTA.TXEN=1;           // To enable transmission
RCSTA.CREN=1;           // To enable continuous reception

TRISB.RB0=0;

while(1)
{
    ip1=rx_data();    // Receive data from PC

    //this part doesn't gets executed!!
    state=max((ip1/4)+1,12);
    LATB.LATB0=1;

    for (i=0;i<state;i++)
       delay_us(10);

    LATB.LATB0=0;

    for (i=0;i<200-state;i++)
       delay_us(1);
}
}

void tx_data(unsigned char data1)
{
TXREG=data1;                                     // Store data in Transmit register
while(PIR1.TXIF==0);                             // Wait until TXIF gets low
}

unsigned char rx_data(void)
{
while(PIR1.RCIF==0);                           // Wait until RCIF gets low
return RCREG;                                 // Retrieve data from reception register
}

i've made sure that proper data is being sent by the master pic by hooking up to the PC's serial port and observe output..

as stated in code the part after ip1=rx_data(); doesn't gets executed.

i've also confirmed by commenting out the ip1=rx_data(); part and then replacing ip1 variable with an int value... then the servo moves to the proper position according to the value instead of ip1(which ranges from 0 to 255).

any help?

UPDATE:

with the suggestions given in the answers i've cross checked the following.

1.Both PICs running on 20mhz so frequency is correct.

2.serial data format is correct. i am receiving the proper data to the PC.

3.Wiring checked.

4.decoupling( plz explain how to do proper decoupling).

5.power supply. ( both running of a 5v 1 amp wall chargers).

so the most probable problem (other than the software) may be the improper decoupling. can anyone explain this to me?


texts: Two parallel CR123A batteries DC voltage converter

texts:
I selected two non rechargable CR123A lithium-manganese battery to power my project due to their ability to operate under extreme temperature. A single battery is 3V with a rated capacity of 1550mAh. Since I need more capacity I decided to wire them in parallel so that the total capacity is 3100 but the voltage is the same.

Bonus question: Is it bad to wire them in parallel for a consumer product? :)

I read somewhere in this site that non-rechargable batteries might explode if someone inserts a fully charged one with a semi charged. I have not a safety circuit in there.

Now I need this to regulate them into 3.3V for my project.

Since I want efficiency two options exists:

Boost converter
Buck/Boost converter

Theoretically we want to go from the battery pack's 1.2-3V into 3.3Volts so we go up. A boost converter is the best choice since it can accept cut-off voltages down to 1.2Volts squeezing every little drop of energy from the batteries.

Practically I measured a battery bought from a local supplier and its voltage is 3.25Volts. What if a weird CR123A manufacturer makes a battery more than 3.3 Volts? Should I use a buck/boost converter and sucrifice the efficiency? Buck/Boost converter start from a Vin min=1.8 Volts and I would rather not use them if I could avoid them...

How should I solve this?

I could use a boost converter to regulate 3.3 from 3Volts but what if a user inserts a 3.5Volt CR123A bought from a weird chinese manufacturer from eBay?

Do I need a buck-boost converter to regulate 3.3V from rated 3V battery?
I am afraid that the actual voltage in the batteries might be more than 3V in the beginning.


texts:
I'm measuring pulses from a device with a constant frequency. The oscilloscope's usual frequency indicator shows 600 Hz. But when I use "Measure" button and then Type is set to Frequency, then that indicator shows around 300 Hz.

Then I measure it with a DAQ board and analyze it with MATLAB and I find again 300 Hz.

Whats going on here? Does oscilloscope's generic frequency indicator (at the right bottom corner in mine) interpret edge rise and fall as one signal? Why would it read double?


texts:
In an attempt to create a single transistor flipflop I made this :

The Idea : When the base is triggered by a pulse ,current starts flowing from collector to emitter . From the emitter it divides and goes to the base and ground keeping the circuit open .

The Reality : Current stop flowing when trigger is removed .

Adding a resistor to the base made no difference .Adding a capacitor from the base to the emitter got me the expected results but when the capacitor was fully charged the current stopped flowing from collector to emitter .

I have two question ,
1) Why will this not work ?
2) What did the capacitor do to make it work  ?


texts:
Is it possible to connect the XBee to the Arduino without a shield? Currently most of the sources that I have looked at have some sort of shield connected.

I use this shield currently: http://www.adafruit.com/products/126.

From the looks of it, the shield only ensures that the power levels are regulated to 3.3v from the 5v output that the Arduino gives. Can I then just build a small regulator circuit rather than purchase the entire shield for $10 + shipping?


texts: Self-resonance frequency of MLCC in Buck converter circuit

texts:
Let´s assume I use a synchronous buck converter switching at 1MHz and a 47µF MLCC at its output whose self-resonance frequency is right at 1MHz.

For my understanding, using an DC/DC converter output capacitor near or at its self-resonance frequency is not a bad idea. But I am not sure. I think, there should not be instability issues as long as the resonance frequency of the inductor/capacitor combination is well above or below the 1MHz. So, for 47uF and 2.2µH, I have resonance near f = 15kHz, which should be fine.

Is the "loss" or even "turnover" of the phaseshift of the capacitor a problem in that situation? I should note, that the converter uses constant frequency PWM and (as far as I can deduce from the block diagram below) peak-current mode control.


texts: MSP430 Timer A interrupt flags are wacko

texts:
Trying to setup a timer on my MSP430F5529 that should interrupt after approx. 2 seconds.

My initial setup looks like this:

TA1CTL      = (TASSEL_SMCLK | ID_DIV8 | MC_UP |TACLR | TAIE | TAIFG);
TA1EX0      = (TAIDEX_DIV4);
TA1CCR0     = 0xFFFF;
TA1CCTL1    = (CM_NONE | CCIS_A | CAP_0 | CCIE_1 | OUT_1 | COV_0 | CCIFG_0);

As far as I know, this should setup Timer A to interrupt approx. every 2 seconds.

SMCLK frequency = 1 MHz

TA1CTL is divided by 8 with ID_DIV8, and again by 4 with TAIDEX_DIV4 so in total is divided by 32. This means TA1R gets a tick every 32us.  It counts until it reaches TA1CCR0, which is at 65,536. 65,536 * 32us = 2.09715 seconds.

The interrupt is successful, however it incorrectly sets several flags.

It sets CCIFG in TA1CCTL0, TA1CCTL1, and TA1CCTL2.  Not just TA1CCTL1, as I expected.

Another question I have is this: Why am I forced to use TA1CCR0 to specify what value gets counted to, when I am using TA1CCTL1? I tried specifying a value in TA1CCR1 initially, but the counter never incremented.  This makes no sense at all to me.

So if anyone out there is pretty familiar with the MSP430 and could help, it'd be greatly appreciated.


texts: Is the charge accumulation linear in time for image sensors?

texts:
Reformulating the question:
Does the rate of charge of the pixels photodiodes in an image sensor depends of the previous accumulated charge?

The pixel sensor integrates light during a specific amount of time called exposure time. Suppose that the image sensor scanning time is in perfect synchronization with a light source that generates square pulses. That is, when the pixel start scanning the light is starting to arrive to its surface (ideal conditions). Now, If the pulse has the same duration as the exposure time of the pixel I will get an integration quantity, q1. Now, if the pulse is on just half of this time, is it my new quantity half of the previous (q2=q1/2). Does the pixel behaves linearly with charge? How can I measure this effect, taking into account that I'm not able to reproduce the ideal conditions of perfect synchronization?
Thank you!


texts: Is there such a thing as a fully differential line driver?

texts:
I'm looking to find something similar to the TI drv134 (http://www.ti.com/lit/ds/symlink/drv134.pdf), but then with differential inputs instead of single ended.

Is there even such a thing? I can't seem to find it.
I can of course easily place an opamp before the drv134's input but i'd rather have one less component.


texts: What I know is Variable has no hardware representation. So does it comes under the category of Non-synthesizable codes in VHDL?


texts: Why can't solder stick onto the tip of my iron?

texts:
I can't tin the iron properly, because feeding solder onto the tip has it flow downwards and collect into a blob before splitting off and creating a mess.

My iron may not be calibrated. And I don't know how to measure its temperature without a device to do so (I only have a multimeter). It is supposed to go from 250 Celsius to 450 Celsius (840 °F), but I can only solder onto the pad quickly at 450 °C. The solder melts at around 300 °C, but it doesn't flow quickly.

The iron I use is the T12 type.


texts: Improvements on a circuit that charges a battery from a solar cell

texts:
I am working on the circuit in the picture below. This circuit represents how to power a battery from a solar cell.

I understand the logic behind the diagram but I was thinking what improvements to make to the circuit. I am new at electronics therefore I didn't have much ideas on what would be a good improvement.

Some ideas that I had was to use a mechanical arm for the solar cell so that it will follow the sun direction. But I am not sure if this improvement is related to the circuit.

Can you please help me with this?


texts:
I have a simple resistor circuit that i would like to know the equivalent resistance of(as seen from the multimeter terminals):

The image is from Multisim and the resistance is here measured using simulation. I am not sure about the calculation by hand, but my bet is(from right side of the circuit):

(R10+R9+R8)+(R5||R7)+((R6+R2+R1)||(R4+R3))

Which equals:

This is close to the simulated result, but I am not sure if my equivalent calculation is correct.Do I need to apply a Star/Delta ?                         Can anyone state a correct method of solving this          or come up with the correct answer  with working ?


texts:
I am having a lot of difficulty answering this problem as I need every answer right to complete the assignment but it doesn't tell you if each answer is right or wrong, only if you get them all right or had at least 1 mistake.

1-3 clearly invalid,
4 looks invalid but not 100% sure.
I think 5 & 6 are short-circuited,
7 looks valid,
8 & 9 look invalid because in both a larger current goes in and a smaller one goes out,
and 10 looks valid.

Any help would be appreciated because I keep getting the problem wrong but I have no idea where I'm going wrong.

Image source

Indicate if the circuit connections of the ideal sources and resistors are VALID or INVALID (invalid = have inconsistency)


texts:
I can't understand, how,

The DC resistance seen by the inverting terminal of the 1st op amp is R1 || R2.
The DC resistance seen by the inverting terminal of the 2nd op amp (which in fact turns into the 3rd op amp at low frequency and dc) is R2.

What does it mean by resistance seen by a terminal?


texts: I am trying to build this circuit  but I don't know how to test it. When I am measuring the voltage on the gate of high side mos is almost 12 volt like VCC. So to speak .. the boostrap circuit isn't working. Dou you have any ideas ?


texts: What is the difference between source-synchronous and source clocked signals in DDR4?

texts: Main signals comes under the source-synchronous group are data, ECC and strobe lines. My understanding about source-synchronous signal is that all of these signals would be latched on both edges of the clock signals and the direction of clock and source-synchronous signals are be same. What is source clocked signals? How is it different from source-synchronous signals? ( Source clocked signals - Address, Bank address, bank group, clock enable etc)


texts:
So, I'm kinda new to the field and the time has come to design my first PCB heater. The main concept is to drive it using a Raspberry Pi and a temperature sensor as feedback.

Here is the whole procedure I followed in steps.

Since my AC/DC adapter outputs 12V/3A I need a heater around 4 ohms in order to be efficient.
By using this trace width calculator and applying the following values I managed to get a result of 3.73 ohms and a voltage drop of 11.2V.

current: 3Amps
thickness: 35um
temp rise: 65 (I want to be able to reach 90C)
ambient temp: 25
trace length: 7m

Given that I want a heater of 13mm width I calculated the number of traces that will be created. Which is: \$trace\_length/heater\_width = 7m/13mm = 7000/13 = 538\ traces\$
Then by multiplying \$number\_of\_traces\ *\ trace\_separation = 538\ *\ 0.12mm(120um) = 64.56mm \ heater's\ length.\$
Finally, I have a heater with the following characteristics:

length: 64.5mm
width: 13mm
trace width: 1.14mm
trace separation: 0.12mm

I would like to mention here that in calculator's page there are results for internal and external layers. For my calculations, I used the values of the internal layers and I'm not sure if I did well. So what do you think? Is this procedure and calculations reasonable? Would you suggest a different approach?


texts:
I am kind of new to Labview.

I am trying to control a Keysight N5173B RF signal generator to do an amplitude and frequency sweep.

I made some block diagrams, but I could not get a proper result. I could only do frequency sweep, but could not do amplitude and frequency sweep together.

Is there a generic way for amplitude and frequency sweeping? If so, could you please tell me?


texts: I know the values of resistors if they are gold-colored at the end. When both ends are the same, such as brown-o-p-brown and red-x-y-z-red, I am in problems. How to know which side has the last colour and which side is the starting end?


texts: What's the benefit of not soldering NC pins compared to soldering them to a disconnected pad?

texts:
I've been looking at my scope's power supply board and I noticed that R7731A  "Burst Triple Mode PWM Flyback Controller" in DIP has two NC pins which are not connected to absolutely anything. They've been inserted into holes, but there are no matching pads on the solder side.

On the other hand, in various other devices I've seen components with NC pins which are soldered to a pad, but the pad is not connected to anything else.

So my question is: What's the benefit of not using solder pads for NC pins?


texts: When do the holes in semiconductor appear?

texts: I'm trying to understand the concept of semiconductors, as far as I know whenever an electron moves it leaves a hole, so how can we say (for example) that n-type semiconductor has a majority of \$e^-\$, won't every electron let a hole?


texts:
I would like to measure the resistance of a resistor in the most basic way by running a current through it and measuring current and voltage. I understand that I have basically two options to place voltmeter and ammeter:

If I measure the voltage over the ammeter+resistor, I get an error due to the non-zero resistance/voltage drop over the ammeter. So basically the voltage I measure is not the voltage over the resistor but somewhat larger. The measured current is correct though. This method should work well if the measured resistor has a much larger resistance than the ammeter.
If I measure the voltage over the resistor, the measured voltage will be correct, however now the measured current will be larger than the current through the resistor. I understand that if the resistor has a much smaller resistance than the voltmeter this error should be negligible. This method should work well for measuring small resistances.

I have two questions:

If the resistor to be measured has a resistance value that lies in-between those of voltmeter and ammeter, how do I decide which method to use?
If a series resistor (of known resistance) is used, how would I set up volt/ammeter?

Please keep the answer simple as I am not an electrical engineer.


texts: Is a current source a single component or the same as a voltage source?

texts:
Is a current source a component on its own or is it the same as a cell?

If the two are different why does the current source supply only current and a cell supply both current and voltage?


texts: 74HC688 magnitude comparator and enable pin

texts: I'm using a 74HC688 8-bit magnitude comparator (datasheet) with Arduino. My question is how to generate active LOW E (enable) signal with Arduino? Is there another possibility (I want to enable the 688 chip)? Currently, I have the enable pin connected to ground. Is that the correct solution or do I need a resistor between enable and ground?


texts: Is there an FPGA based vector graphics card project?

texts:
I have been messing around with VGA projects as my latest interest. I have a Xilinx Spartan 3E 250K FPGA, which has just barely too little RAM for a full 640x480 frame buffer. So, I'm looking at making things more "interesting". Namely, by instead going for a vector approach rather than bitmap. However, it's a bit mind boggling as far as how to do it. Are there any known and open source vector based VGA graphics cards?

I'm not going to be using this in any kind of "production" scenario, so I don't really care if it can only effectively render at 1fps or something. I'm just looking at an interesting project idea.


texts: How does a half adder made of crossbar latches operate?

texts:
I am researching memristors, and one application that's frequently cited is a crossbar latch that sandwiches memristors between two layers of wires to form a grid. In most examples, this is configured as a half adder. I've included an image from Wikipedia below and here is a link to a relevant HP patent with more illustrations.

From the patent, I get that there is some sequence of voltages applied to the wires that lock in values, then pass them on. However, I can't understand what exactly is happening. I'm familiar with half adders made of simple logic gates: 1 XOR with 1 AND gives Sum and Carry outputs. Could someone please explain the crossbar latch half adder in a similar context?


texts:
I am having trouble selecting a microcontroller/processor for a robotics project in C++. I have a program working on my computer that is 1.5+ KLOC and relies on data in twenty other files to function, so please do not suggest I use another language. I tried translating it to C, but could not get it to work, perhaps because of the program's heavy reliance on fstream and strings. The program is about 1 MB on my computer right now and takes up 3 MB while running, so I suppose the microcontroller/processor would need either to be capable of supporting 4 MB of ram if it is von-Neumann/MHA and 1 MB of flash and 3 MB of ram for Harvard. I need PWM, SPI and UART/USART on the processor to communicate with other sensors, and I plan to use a hard drive for the other files and external ram for the program and its data. I will need at least 90 IO pins (40 IDE + 40 servos + sensors).

Summary:

>90 IO pins
PWM
SPI
UART/USART
if von-Neumann/MHA, capable of supporting >4 MB of ram
if Harvard, >1 MB program flash and >3 MB of ram
supports C++

What do you suggest? Please also provide information on how to program the processor, if possible.

So far, I have found Freescale’s i.mx25, but I am not sure how to connect this processor to my computer for programming, if it uses C++, or the details of how to turn my current Windows .exe program into a .hex compatible with this processor.

@m.Alin I am using a hard drive because I started out with AVR and found a tutorial describing how to communicate with an hdd from an AVR. I could not find a similar SD card tutorial.

@MikeJ-UK The program currently runs on my laptop, an x86-64 Windows 7.

@darron

"1MB binary implies more than 1500 LOC" The program is 643 KB now, not 1 MB. I apologize for the confusion. I said 1 MB because I am still working on and expanding the program, so the prospective processor will need to be able to handle its future larger size.

"add a peripheral board for the servos" "io offloading onto an FPGA..." I do not know how to do this. After a quick search, I was unable to find any affordable FPGA's. Do you know of any >$50?

@Rocketmagnet 1500 lines.

@vicatcu I do not think 8 io pins will be enough.

@AndrejaKo For the most part, the servos will not need to be controlled at the same time. I like your multiple microcontroller/demultiplexer option, but I do not understand what is wrong with using an i.MX25 with Linux? It has 128 io pins.


texts: Does the lm7805 have a minimum current requirement?

texts:
I'm running into an issue when I tried to build this: http://www.instructables.com/id/20-minutes-USB-solar-charger/. I'm using a 9v solar panel. As soon as I connect the ground from the lm7805 to the ground of the circuit, my multimeter reads 0 volts on the output pin on the lm7805. Before I connect the ground, it reads about 9 volts. I even replaced the lm7805 thinking something was wrong with it. I think I'm not understanding something simple, but I don't know what it is. I'd appreciate some insight into this issue I'm having.

One possibility I'm wondering about is if the lm7805 requires a minimum current, and the solar panel isn't meeting some minimum current requirement. Is that even a possibility?


texts:
I have doubt how to length matching (if necessary, idk if it is really necessary). Iam checking a layout board in my company and looking on it I realized theres a mismatch for RS-485 communication using chip MAX485E.

I have a connector which I will read MODBUS using RS-485 protocol and looking on MAX485E datasheet it states that differential driver output R= 27ohm (RS-485).

I think it means I need to do length matching for this impedance, but how to calculate it using Saturn calculator, for instance or any other calculator like Kicad calculator?

I would like to know how to calculate trace width and gap to route differential pair in this situation. I have a 2 layers board, using FR-4 (Er=4.6) ; TanD = 0.02 ; Height of substrate (thickness): 1.6mm ; Rhou = 1.72e-08. Im using Kicad with diff pair width = 0.2mm and width gap = 0.25mm set as default in Software. If someone have any document to help me about theory too gonna be good.


texts: What is the difference between a casez and a casex statement in Verilog?

texts: I know that a case statement in Verilog can start with case, casex, or casez. However, with casex and casez, when would I use one over the other?


texts: How long should 8, 1.5V batteries last for?

texts:
I purchased a GPS tracker from Amazon and instead of wiring it to the car battery I would like to simply attach my own power battery pack.

I am a complete noob when it comes to electronics and I attempted using a 9V battery. It worked but the GPS tracker stayed on for about two hours. It consumes at 300 mAh, I've been told.

I then attached 8, 1.5V rechargeable batteries with 2300 mAh. How long should it last? Is it simply (8 * 2300) / 300? 61 hours?

What other batteries would you recommend to get the GPS tracker to last as long as possible. No car battery or acid batteries please!


texts: Protection for Solid State Relay.. Advice please

texts:
Please excuse me if this question is not appropriate for this site..
I wish to switch a Pool Pump using a Solid State Relay.. The pump is rated at 10Amps, 240 Volts AC.
Allowing for a safety margin, I intend to use a SSR rated at 20Amps...
My question is....Do I need to include additional components to protect the SSR from spurious inductive feedback from the motor.. Given the cost of high current SSRs, I consider it important to seek advice before proceeding!
Thank you...


texts: Solar cell power output comparison without MPPT

texts:
I am interested in measuring the relative power output of a solar cell when it is placed behind glass and other materials. For example, one might guess that the cell's power output is reduced by 70% when placed behind frosted glass.

One thought I had to measure this was to use a very small resistor. Going by this diagram for the cell (Maxeon C60), we can see that we don't want voltage going over ~0.5 V, or the current drops. A small resistor ensures we stay in the constant-current region of the cell:

Assuming an absolute maximum current of 10 A, that means we need a 0.5 / 10 = 0.05 Ohm resistor.

Since $$P = \frac{V^2}{R}$$ we can see that e.g. if we measure half the original voltage, our power output is 25% of the original.

Does that make sense? I am wondering how accurate this will be. Are there any cases, like very low light, where this can break down? Thanks.


texts: Async SRAM Chip. Write Cycle. Data inputs timings

texts:
I'm working on my home project of building the 8-bit computer and now I'm on the RAM building stage.
I'm going to use this chip for as my RAM UTRON UT62256C (datasheet). This chip is to be connected to the common bus, to which 8-bit registers are connected through 3-state buffers.
My question is about write cycle timings (see the diagram below)

The doc says that after !WE goes down there is a period of time twhz when signals on I/O pins must be not applied: "4.During this period, I/O pins are in the output state, and input signals must not be applied. "

Question #1: Does that mean that I CAN NOT set-up the data upfront and then just put the !WE low for some period of time? If I do so, will it damage the chip?

Having said that !CE is to be always LOW, I assumed that my write cycle could look like this:

Set up the address using
Set up the data on the bus
Make !WE low for certain period of time.

As it's an educational project I wanted write cycle to be like this because it simplifies design for manual mode of putting data to the SRAM. I was going to use dip switchers to set up the data and the address and one button to move !WE from High to Low maybe with 555 timer to set-up the pulse length.

Question #2: If I must not put the data on I/O pins before twhz, I was thinking about could you please advice some circuit that will allow to do manual programming with dip switchers

I was thinking about adding 3-state buffer between I/O pins and the dip switchers and some circuit that generates two pulses with the right timings triggered by pushing the button:

First !WE goes down for certain period of time for example 555 timer could be used.
!WE pulse triggers the second 555 timer that generates !OE pulse on the 3 state buffer.

See the picture below. Looks like overcomplicated thing :)

Thanks for you replies in advance.


texts: Need some assistance with making a battery box

texts:
I recently bought a 12v deep cycle battery 75 AH and I made a battery box following these tutorials:
https://www.youtube.com/watch?v=cAErwLnsSIY and https://www.youtube.com/watch?v=torSEtjPZ2I (no need to watch it ofc, just to understand the basic idea).

A small description how it wires as well:
The battery is wired to the first fuse in the fuse block, which is wired to the "master switch", this switch gives power to the rest of the fuses which are wired to other components, and also gives power to the voltmeter for measurement of course.

The problem is that whenever I'm using other components such as leds etc the voltage in the voltmeter is dropping(not the actual battery voltage, but the voltage the voltmeter is reading) and I'm not sure how to change that.

for example, when turning the master switch, the voltmeter is reading 12.5v, then I'm turning on the leds and the voltage is dropping to 12.4v in the voltmeter and so on.

I can wire the voltmeter directly to the battery, but I don't want it to be powered all the time. I'm not 100% sure how it works, but I tried wiring the switch to the voltmeter, and from the voltmeter to the fuse block, but it still doesn't work. Any ideas?

Here are some pictures of the battery box, not great quality, and the wires are currently very messy until I'll fix everything:
https://imgur.com/a/uJLqyKF

Thanks, hope I made myself clear enough.


texts: How to send notification via bluetooth device

texts: I am running a Grocerry shop, I want to send offer notification via bluetooth to all my customer who enters my shop. If a customer comes within a range of 10 meter near cash counter auto offer notification should trigger. I don't have any idea about how it works. Can any one help me.


texts: Calculating input impedance of ICIS opamp circuit

texts:
My textbook just gives the formulas w/o derivations and I've been trying to prove them when possible. But I feel stuck while calculating the input impedance of below ICIS amplifier.

My work :

Since almost all the input current goes through \$R_2\$ , voltage at the meeting point of the 3 resistors is given by \$-i_{in}R_2\$ .

Then the output current is given by $$ - i_{out} = i_{in} + \dfrac{i_{in} R_2}{R_1}
$$

So the output voltage equals
$$V_{out} = i_{out}R_L - i_{in}R_2$$

Also we have \$V_{out} = -A_{VOL}V_{-}\$

With some algebra to above 3 equation we get
$$\dfrac{V_-}{i_{in}} = \dfrac{\left(1+\dfrac{R_2}{R_1}\right)R_L + R_2}{A_{VOL}} = \dfrac{\dfrac{\color{red}{R_L}}{B} + R_2}{A_{VOL}} $$

This is no where close to the given formula and I don't seem to simplify any further.  Also I feel my work is wrong because \$\color{red}{R_L}\$ should not be there... Any help ?


texts: How 18650 cells capacity is measured (what are the amperage and cut off voltage params)?

texts:
I have lots of used Li-Ion 18650s. I want to test their capacity.

There are however 2 important parameters that I cannot find anywhere which is amperage and cut off voltage. Some people use 500mA some people use 1000mA. Some discharge to 3.0V some do that up to 2.8V.

Depending on which parameters you choose you will get different capacity. Since capacity is defined for cells it's calculation must adhere to some standards for these parameters.

To wrap it up - what is the amperage and ending voltage for capacity measuring for single 18650 cell?


texts: Low battery level circuit - Changing "trigger" level

texts:
I am re-creating a simple low-battery level circuit that turns on a low-power LED to indicate that the battery needs to be changed. The circuit is shown below.

There are two things I would like to change on this circuit.

The cutoff voltage is approximately 6.9V. Based on my initial analysis, all I need to do to change this is to swap out the zener diode. The cutoff voltage is the sume of Vz (the zener knee voltage) and the 0.7V drop across the diode, Vd. So, if I want to have the cutoff be sooner during the discharge cycle (ie: 7.5V), my assumption is that I just need to swap out the 6.2V Zener diode with a 6.8V Zener diode. Is this assumption correct? Do any of the resistor values need to change?
I want to remove the green LED from the circuit, and the left-most Bc547 NPN BJT, and just have a "low battery" indicator. How do I reduce the existing circuit to just this?


texts: Slightly weird astable oscillator in a 555, where does this capacitor discharge to?

texts:
In the 555 datasheet, the cap is usually connected to pin 7 (discharge), but in this circuit, it's not:

When the capacitor voltage is >2/3Vcc, output will turn off and current will have no where to go. Does it go through Vbe?

Also, I've constructed this circuit with the 'normal' astable configuration and it seems to draw >1A current total on 9V, and after a while will kill the 555. I was under the assumption that most of the current will go through the transistor since we are controlling current via the 1k resistor.

The normal configuration works but the output voltage gradually decreases overtime, doesn't seem stable.

Never tried this configuration in the complete circuit, so unsure if same thing will happen.


texts: Max size smoothing capacitor without melting the rectifier

texts:
I am currently making a tube amplifier for a school project. I started out with a finished design, but have changed a lot and need some guidance as a result.

I am currently using a full wave rectifier bridge I made with 1N5404 diodes, and I will be rectifying 50Hz 230V AC into 325V DC. I have a 470uF capacitor I intend to use to smooth out the voltage, and I am wondering if it's even safe to put it directly after the bridge without resistors in series to limit the surge. The diodes should withstand a 200A surge, but I’m not sure how big the surge will get. Is the isolating transformer going to get saturated and limit the surge enough? I haven't bought one yet, but it will be a 30-50VA transformer. Also, would it be safe to test the circuit without an isolating transformer? I would like to test it out before I get it!


texts:
I need help with the above circuit.

I first need to calculate the voltage and current distortion. I calculate this as 8.75%(voltage) and 5.7% (current).

I then need to find the displacement power factor. I calculate the current through the circuit using Ohm's law  for the fundamental voltage and treat the harmonic as a short circuit and I get 0.97A<-13.68°.

For the fundamental:

Z(inductor) = 186m * 2pi * 50 j = 58.43j

By Ohm's Law:
240 = I(240 + 58.43j); I = 0.97A<-13.68°

For the 5th harmonic:

Z(inductor) = 186m * 2pi * 50 j *5 = 292.168jΩ

21 = I(240 + 292.168j); I = 0.056A<-50.6°

Therefore I assume the displacement power factor is cos(-13.68) as the voltage has no phase. This gives me a power factor of 0.97.

I then need to calculate the true power factor. I use the real power/apparent power equation. I find the total voltage in the circuit (RMS) to be 170.34V and the total current (RMS) to be 0.678A.

Total voltage = sqrt(harmonic voltage^2 + fundamental voltage^2) (all rms)

Total voltage = sqrt(169.7^2+ 14.85^2) = 170.34V

Total current = sqrt(harmonic current^2 + fundamental current^2) (all rms)

Total current = sqrt(0.686^2+ 0.039^2) = 0.678A

I multiply these two together for an apparent power of 115.49 VA. I then use I^2*R to find the real power on the basis that the impedance of the resistor will not vary with frequency. I obtain a true power factor of 0.95.

Have I approached this question in the right way and is my answer correct? Would appreciate some feedback/criticism.


texts: HX711 Load cell providing constant large and negative reading

texts:
I'm currently working on a project that uses the HX711 load cell amplifier while connected to a series of strain gauges in a full bridge circuit. I'm using an Arduino Nano and have the CLK of the HX711 connected to pin D5 and the DAT connected to pin D6. Hx711 manufacturer suggest pins D2 and D3 instead however I was under the impression that any digital I/O pins would work as long as the code was changed to signal this.
When the calibration code provided by the HX711 manufacturer is uploaded the serial monitor reads constant value of -78kg and will still read this value when the strain gauge circuit is connected. I have re-soldered the connections from arduino to hx711 so suspect that isn't the problem.
The connections from Hx711 to strain gauge bridge circuit are female to female jumper wires.
If anybody has experienced a similar problem and could help
I'd be very grateful!

Link for Hx711 setup with calibration code and Hx711 library:
https://learn.sparkfun.com/tutorials/load-cell-amplifier-hx711-breakout-hookup-guide/all

Link to Hx711 schematic:
https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/SparkFun_HX711_Load_Cell_v11.pdf

(https://i.stack.imgur.com/mic2J.jpg) = Serial monitor

(https://i.stack.imgur.com/2Xkb4.jpg) = Calibration code used

(https://i.stack.imgur.com/btzID.png) = Full circuit diagram

(https://i.stack.imgur.com/mio7e.png) = Load cell wiring, colours correspond to those coming out HX711 in full circuit diagram


texts: Polarized capacitors in common emitter amplifier

texts:
This is the basic common emitter amplifier.I have read that polarized capacitors should have proper polarity connected to terminals of DC voltage source and they may blow off if they are connected in a wrong way and the polarized capacitors cannot be used with AC voltage source.

But I have been asking myself how does a polarized capacitor can be used in this below circuit because we have an AC signal as input which is to be amplified and this AC signal passes through C1 capacitor.During the positive cycle the polarities are matched but when the AC signal is negative cycle the polarities doesnt match and capacitor should blow off but that doesnt happen. I was trying to figure it out the reason.Could anyone help me with this Thanks.I know this must be a basic question to understand.

I have been said that Capacitors are used to block DC and allows only AC.We block DC so that the operating point does not shift but Iam unable to understand where the DC signal comes from. Does an AC signal has dc components in it? or may be some other reason? if so can anyone provide me some good link.Thanks


texts: I need an SMT pushbutton on my PCB. I'm drowning in options on Mouser and just want to select something that is future-proof. Is there a standard size and footprint for pushbuttons that I can use to avoid shooting myself in the foot?


texts:
So we've been renovating (virtually new everything) a 1930s semi that hasn't been modernised since it was built and hadnt been lived in since the 70s.
Naturally a full rewire was high on the agenda which is 90% complete now, but my suspicion began when the 3000W fan heater I bought seemed not to be chucking out much heat.
At first I thought nothing of it putting it down to a poor quality appliance. But when a new kettle I tried took around 7minutes to boil, I started pondering if there was a fault somewhere causing a limit to max power these appliances were generating/drawing.
I had the plugs tested and they are producing 230v but before researching ohms law, I suspected a resistance issue.
To double check, I took the heater home and plugged it in and hey presto, belting hot heat.
I am awaiting an updated fuse board from Northern Power, which I'm sure will fix the issue but, I wanted to rule out any problem with my installation before I sign off with the sparky ideally.
The only other info I have is the original power was a shared supply to ours and next door and I wondered if some sort of phase drop was present grid side of our board. Is my next logical step testing resistance between board and consumer unit? Can you do that with a normal multimeter? My electrician who looks to have done a fantastic installation seems to be brushing it off like there's no problem but the house will be electrically heated and rented out so I can't have 2k worth of underperforming rads getting overworked.
All ideas, practical and theoretical appreciated. Sorry for essay.


texts: Superimpose a High Frequency AC Small Signal on a DC Power Signal

texts:
I am facing a challenging problem with a circuit that I am currently working on, I would like others input and thoughts.

I have a DC power signal that I am injecting a AC small signal this mixed signal is transferred over two conductors to a receiver circuit which then uses the DC power signal to power a load and also extracts the AC small signal for use.

Description of signals:

DC Signal: 30V generated by a boost converter that has noticeable amounts of noise under the working load of 500mA to 1A

AC Signal: ~2vpp @ 1MHz to 30MHz

simulate this circuit – Schematic created using CircuitLab

This is not an overly complex challenge given ideal components, however the real challenge I am seeing is the inductors sized to carry the currents required have a self resonant frequency typically <2MHz. From my understanding this means that they would not act as good filter component for the higher frequency AC small signal causing excess loading of the AC signal and a diminished signal at the receiver.

Very much looking forward to other's thoughts and opinions on the problem.

Thanks!


texts: What type of amplifier do I need for this project?

texts:
I'm trying to make a custom PA system for my car, but I am confused about what type of amplifier I might need, or do I need one at all?

I'm wanting to take the main sound unit out of a "personal soundtrack shirt" like this
http://www.thinkgeek.com/tshirts-apparel/interactive/a5bf/
but remove the speaker from the shirt and replace it with a PA horn.

I already have a pa horn that came with a "coga pa system" http://www.cogapa.com/.

I actually have already hooked up the sound unit from the shirt, to the pa horn, just by simply cutting the audio output wires, and hooking them to the wires of the PA speaker, and it does work, and is louder than I would have expected, but I don't think its nearly as loud as its potential.  The reason I think this is simply because the PA speaker is so much bigger than the cheap little speaker that came with the shirt, and the little sound unit amp in the shirt is run off 4 AAA batteries, whereas the Coga PA system the horn is coming from would run off 12 volt.

Couldn't find any specs on the shirt, but supposedly the Coga system would output 40 watts RMS 50watts Max to its speaker, so I'm guessing the speaker can handle 50 watts, and I just need to find a way to bump up whatever output is coming from the shirts sound unit, up to 50 watts.  But then, I really don't know anything when it comes to audio and amplification.

Can anyone help?


texts:
I have a circuit set up as in the following diagram. There are 4 vertical power rails, the left-most 3 are supplied with 15v, and the right most 1 is supplied with 5v. The purpose of the circuit is to drive a multiplexed array of electro-permanent magnets. It does this by using the shift registers running down the right side to operate the sinks and sources on the left side. I've only sketched up 4 of the electro-permanent magnets but the array size is 30x8. The bottom two drivers on the left provide the sink/source for the 8 rows, the remaining drivers provide the sink/sources for the 30 columns.

The programme being uploaded to the AVR will initially cycle through all of the electro-permanent outputs and polarise them one way, before making another pass and polarising them the opposite way.

When I supply power to the circuit and connect an AVRISP mkII to programme the AVR it all runs fine. If I subsequently remove the programmer and supply power to the circuit again it doesn't seem to run.

Occasionally when I plug it in I can hear a faint buzzing from the electro-permanent magnets as though it's trying to supply power. In this scenario I'm assuming that it's either not able to draw enough current to fully active the electro-permanent magnet, or the AVR is running too fast and not activating the coil for long enough to take effect.

I've read this similar question ATTiny Circuit only works when connected to AVR ISP and added a capacitor between the Vcc and Gnd connectors of the AVR but it makes no observable difference.

Firstly, is there anything obvious in my breadboard diagram that could be causing this?
Secondly, given that I have no scope, what else can I try to debug this?

The breadboard

Power supply schematic


texts: Why on earth are o-scopes earth referenced?

texts:
Thinking about it: You would never find a "Grounded" multimeter as robust and useful if a path to ground through the multimeter were introduced, modifying the circuit's behaviour and possibly damaging the multimeter with currents.

Why are so many oscilloscopes earth referenced? Upon reading some educational material, a majority of the "common mistakes made by students" are placing the grounding clip incorrectly and causing poor results - when the o-scope is just being used as a fancy voltmeter!

I've heard of a Tek scope having an isolation transformer within.. however ignoring that, and taking in to account that newer DSOs may have plastic cases (isolated from you most importantly I would assume) could I just remove the earthing pin, and install a 1:1 AC transformer inbetween the o-scope and outlet and be on my merry way probing various hot/neutral/earthed sources with no worries about a path to ground any longer through it?


texts: Can transformers be used to adjust capacitors?

texts:
It seems capacitors are subject to a "quality triangle", where we can only pick two out of three desirable traits:

High voltage rating
High capacitance
Cheap

For example, a high-voltage high-capacitance capacitor is not likely to be cheap.

But, can we get around that by adding a step-up transformer with a cheap high-voltage low-capacitance capacitor on the secondary? Since

$$Z_{reflected} = \left(\frac{N_P}{N_S}\right)^2 Z_{secondary}$$

then that low-capacitance capacitor will reflect a much greater
$$ \frac{1}{j\omega C_{reflected}} = \left(\frac{N_P}{N_S}\right)^2\frac{1}{j\omega C} \Rightarrow C_{reflected} = \left(\frac{N_S}{N_P}\right)^2 C $$

Not sure if this is a common practice or not (or, if the cost of getting a properly-rated transformer would exceed that of just getting the more expensive, high-voltage, high-capacitance capacitor in the first place!)


texts: Difference between optoisolator(optocoupler) and solid state relay?

texts:
I have been looking into relays and optoisolators. I am aware that there are different optoisolators, with some having a transistor on the detector side which allows current to flow in one direction whilst there are others with triacs on the detector side to allow current to flow in both directions:

Upon reading up on relays, I found that they work in a similar manner but using mechanical switching using electromagnets to isolate the two sides of the circuit.

I would have then expected solid state relays to be a sub category of relays, but when I looked them, by defintion they perform the same function as an optoisolator.

What is the difference between an optoisolator and a solid state relay, if any? Which is a sub category of which and what are the differences in terms of speed and applications?


texts:
I have a problem with the filtering stage of an spwm H bridge inverter,i have spwm signal 25khz and fundamental of 50hz.i make a low pass filter with a 1,5mh inductor in series an capacitor 2 μf parallel.All its perfect the signal is ok the voltage 220 volt ok..when i connect a load in the output the voltage drops dramaticaly,and the efficiency for 1000w inverter is  very bad..! (i thing current can`t pass from the inductor) what is the wrong?

Thank you for your answer's.it's an 12v-220v inverter .i have build a 340v dc-dc pwm stage with feedback for dc-dc bus,this stage has 4 of 250w hf feritte transformers.I connect the positive from the dc bus to the bridge for the ac stage.All wires are copper,4 wires of 1,5mm all striped together from the bus to the bridge,all negative conections are together.I connect the load normaly in Vout of bridge after the cap,as above.Earlier i run this iverter with square wave signal 50hz in the bridge(for no need filter)with a very bad and old battery(only 50Ah!)and works fine in 500 watts(i dont try bigger load,and the reason is the small battery size).Voltage was stable,the load was lamp's,and two 250 watt home motor's and all  work's fine.After that i decide to make the signal spwm in the bridge for sinewave.Now after the filter choke and capacitor i have problem even at very small load such a lamp of 25w!  my filter is exacly like the first picture above and my load connected to the V out.My filterS choke is a inductor when i find in an other machine,not too big but not too small,just like a ring with your finger,i measure it with lc meter and is 1,5mh, with yellow color feritte ring,with 2 of 1,5mm copper together,and a non polarize cap of 2 μf.My expected efficiency is at least 70% in full load,for that type of inverter.It has very small no load current and almost zero losses in first small loads.(i meter that with ampmeters in output an input,with small loads and with square wave signal earlier. Now even a small 25w lamp can't bright fast and full the problem is to the filter,but what is the most possible senario for this fenomeno,thank you.

NOTE,the size of core in the choke is like a ring of my finger.


texts: How to measure -170 dB GPS signal with spectrum analyzer

texts:
I'm looking for a way to measure noise signals (probably MCU harmonics) that affect the performance of my GPS receiver (Ubox sam-m8q-0-10). Can anyone point me to the right direction?

I own a spectrum analyzer up to 3 GHz, a set of magnetic field + electric field probes. Can anyone suggest to me documentation on how to use my HW in order to detect find the noise?


texts: What are the purpose of voltage doublers in flash memories?

texts: I'm wondering what is the need for charge pumps in flash memories.


texts:
bit of an amateur looking for some advice. I looked at the other question concerning my problem but i didn't find what i was looking for.

I need to switch ON and OFF a solenoid valve using my RPI. I found quite a lot of design.

But i can't decide on using a transistor like this design :

solenoid valve using transistor

or using a relay :

Can you tell me if the design are correct and what's the advantage/default of each one ?

Thanks.

PS : i will use this valve


texts: How to light the air-water flow inside a transparent pipe from outside of the pipe?

texts: I have 17 meter acrylic pipe with 80 mm diameter. There is an upward air-water flow inside the pipe. I need to somehow be able to light inside the pipe so I can show the flow regime inside the pipe better. I can only think about putting a line of led strips on the wall of the pipe to improve the view of flow regime. Can anybody help me with this if they have a better idea or know of a proper LED strings or any other type of light that can work?


texts: Power a circuit with power supply and USB port, my solution

texts:
I want to power a circuit I have from a dedicated power supply. But at the same time, I have a USB port that can also supply power but only when I decide to upload new firmware to a atmega32u2. Here is my circuit.

J2 is where my main voltage comes in and can be anywhere from +3.3V to +5V. Q1 acts as an ideal diode. Q2 is my load switch. R22 will pull the gate to ground. J4 is the USB port my circuit uses to connect to a PC. D1 isolates the USB voltage from the circuit's operating voltage. C3 is the bypass cap for my circuit. R21 and C1 mimic a tantulum cap. R15 and R16 are my current limiting series resistors for the USB data lines.
The idea here is to disable the use of J2's voltage whenever J4 receives voltage from the USB port. In other words, when +VUSB is present, it will go through D1 and supply about +4.7V which is good enough for communicating back to the PC and enough for my circuit to operate to receive code. +VUSB will have Q2's gate to +5V causing Vgs to be positive or zero volts, turning it off, and thus having +V only sourced from J4, despite J2 still supplying voltage.
Or at least I think so! I am basically asking for a design check to see if my understanding is correct. I am aware of power mux ICs but they are too expensive and I want to use "common parts" for this. In case this is needed, Q1,Q2 = DMP3056LDM-7 and D1 = SD1206S100S1R0. Current draw of the circuit is no more than 10mA.
EDIT 11/1/20:
User Ste Kulov informed me of a cheaper kind of power mux. I like the solution. Here is the new circuit. It uses the TPS2104DBVT. Q1 is still DMP3056LDM. Note that when one of the voltage inputs are disconnected, the potential is floating. I first had a pulldown resistor but the datasheet informs to not ground the INx pin if not used. I took that as no pulldown resistor as well.


texts: Please help identify capacitor - turntable motor drive PCB

texts:
My Rega Planar 3 turntable is belt driven. It has been a year in storage, and now the platter spins backwards. A Google search suggests that one of the motor capacitors is to blame.

I reckon I'll replace both, as the turntable is over 20 years old. But since this is a 220 V circuit, I don't feel comfortable basing my actions on assumptions, hence this question.

Here is a picture of the PCB that drives the motor.

The PCB is driving a "PREMOTEC 9904 111 31813" 50Hz 110V synchronous motor, even though the turntable is rated for a 50Hz 220V line. (Am I looking at a capacitive dropper?)

These two caps are the only components on the PCB (Update: I also found a 1MΩ bleeder resistor hiding under the Rifa). In addition, there's the motor, and a mains switch, and that's the whole circuit.

Here is a picture of the traces:

And here is the whole compartment. The white wires go to the mains switch.

An attempt at a schematic:

simulate this circuit – Schematic created using CircuitLab

First, to get the yellow capacitor (C1) out of the way:

It is a Rifa that hasn't gone boom yet.

The top is marked 220n X2
One side (visible in the picture) is marked 275 V ~ SH
The other side is marked  RIFA / PME 271 M / 40/100/56/B / 250VAC / K5

I suppose I can replace this one with any 220nF X2 class 275V rated mains filter cap, am I right?

The white one (C2) is harder.

The top is marked 220n K J0 (OR JO?)
One side (visible in the picture) is marked EVOX / MMK / 400-
The other side is blank.

So my main question is: What type of capacitor is this? Or rather; What type of capacitor is it safe to replace this one with?


texts: Why the current equation is different in BJT application?

texts:
This is the link I am refereeing for the my study. I am trying to learn how the diode current equation is applied in BJT for differential and common mode analysis. This is the current equation from the document:

And following is the diode equation:

By comparing both equations, a subtraction factor of saturation current is missing in the BJT application.
What could be reason for that?


texts: Bidirectional termination from one end only

texts:
Problem

I have been trying to figure out if it is possible to terminate a bidirectional bus from one end only. I have found techniques for terminating a bidirectional bus using both sides of the line, but haven't found one that just uses one side.

This is a circuit I came up with that attempts to terminate the bidirectional bus:

simulate this circuit – Schematic created using CircuitLab

The design is pretty simple, Rseries1 is a series termination for when XCVR2 is driving, and Rparallel1,2 are a parallel termination for when XCVR1 is driving.

Will this work? Is there is a better way that I'm missing? It doesn't need to perfectly eliminate reflections, it just needs to be better than an unterminated line.

Background

This is a debug bus for a SiLabs microcontroller. The board on the left is the programmer, and the board on the right is my board. The cable is ~6" ribbon with a characteristic impedance of ~80 ohms.

The vendor recommends just populating Rparallel1, but some people have had issues with that configuration. Running at a lower frequency is possible, but I'm more interested in this problem now :)

Edit: more information

Cable length: 6"
Prop delay: 1.25 ns/ft
Maximum bus freq: 12 MHz (~16 ns rise time max)
Maximum part freq: 50 MHz (~4 ns rise time max)


texts: Which output terminals to use in parallel connection

texts:
I have four batteries connected in parallel, I have seen diagrams showing where the output terminals are both coming off of the last battery and the parallel connection. I've also seen ones where the output terminals are on each ends of the entire battery. Which would be the correct terminals to use as output? Are there any benefits to either one?
Using opposite terminals

Using the same terminals


texts:
I am a novice but know enough to get by.  I was given an older Hunter Fan that is only operated via Remote.  I have cut the receiver out because I do not have the remote and from what I have read they are problematic and discontinued.

The fan has 2 windings (70 Ohm and 47 Ohm).  I can wire (110V AC) the two windings in parallel and the fan will run but at a slow to mid speed.  I would like to get the fan to full speed. I feel I need to add a run capacitor in series with one of the windings, but do not know which one and how much capacitance should be used?  Any help would be greatly appreciated.


texts: What do these dashed/dotted lines mean in this power cord schematic, and how should I ground this device?

texts:
--Edited at Sparky256's suggestion for better clarity--

Background Information

I'm making a power cable for a piece of obscure, surplus military equipment (an AN/UGC-74B teletype, to be precise). I have the manuals that describe the power cable, but the wording doesn't account for part of the schematic, and I can't find a definitive answer that seems to make sense searching online. I'm somewhat familiar with electrical terminology and symbols though not an engineer by any means-- just a hobbyist who still doesn't know much compared to most of the people who will read this. I haven't seen anything like this before. If it's something simple, I apologize.

On the right side of the schematic we see the standard three-pronged 120-volt male adapter. BLK and WHT wires connect to pins K and M on the 12-pin Amphenol adapter (not all pins are used) on the other end of the cord, but BRN (or ground) stops at the dashed line that appears to make a circle around the other wires. Then, on the other end of the cord, we see another dashed circle, this time with another wire, also labeled WHT, seemingly coming off it to pin E.

Another schematic of the power input on the device itself shows that pin E appears to have no input from the cable but connects to chassis ground via something called E2-- see here:

Also note that there is not only this power input connector (labeled J2 in the schematics) to which my cable will connect, but there is also a ground terminal, and I'm not sure if I should bring the ground wire out of my cable and connect ground there or not, either. If the device isn't grounded via pin E through the power cord's ground wire, I'd assume that I'd need to ground via the GND terminal for safe operation instead.

This is an image of the power input and ground terminal to show you what I mean (additional photos of various parts of the teletype available here-- not my photos but the same model of TTY: http://imgur.com/gallery/FK5nB):

At this point, I just am not sure what to do about this.  I want to make sure I create the cable properly so I don't break anything; I understand everything else about how to make the cord, but not what to do with ground and pin E.

The manual can be accessed here. It's pretty hefty, so maybe I've just missed something it instructed somewhere-- but I don't think I did: http://www.nj7p.org/Manuals/PDFs/Military/TM%2011-5815-602-24-1%2015-Sep-87%20USAPA.pdf

The full schematics I referenced are on pages 143 (labeled 3-93 in the manual) and 396 (labeled FO-3), as well as additional information describing the power input wiring on page 96 (labeled 3-46).

The Specific Questions I Have

What do the dashed/dotted lines referenced earlier mean?
If the dashed/dotted lines indicate some kind of shielding, does the BRN AKA ground wire connect to the shielding and then the second WHT wire connect from the shielding to pin E, effectively grounding pin E?
If the ground wire does not connect to pin E through the shielding, would it be wise to instead connect my cord's ground wire to the GND terminal instead?


texts: What do HSDZ and HYDZ mean for piezo buzzers?

texts: I have some buzzers, which have a label on them, which states "HSDZ REMOVE SEAL AFTER WASHING". I know that washing is the process of removing residues of flux or something else with solvent. However, I can't find anything about HSDZ. What does it mean? Some buzzers on the internet have HYDZ instead. What do those letters mean?


texts:
A circuit has a resistance of 1 Ohm, a DC power supply rated at 9W is delivering power to the circuit. Using a DC boost-converter that takes in an input of 9W can it output different voltages? Even if the resistance is 1 ohm?

If the resistance is 1 Ohm and the power is 9W, from ohms law voltage is 3V and current is 3A, but can I use a DC boost converter to increase voltage to higher voltages?

EDIT: The location of the resistor is between power supply and the load, if a converter or constant current was added, the resistor will be after the converter/constant current source and before the load.


texts: Why is the voltage across a PN junction 0 v when it is in open circuit conditions?

texts: Why is the voltage across a PN junction 0 v when it is in open circuit conditions ?


texts: STM32 firmware upgrade (In-System Programming) over USB?

texts:
There are many ways to program an STM32 chip (in my case STM32L4R5):

USB DFU mode (using DFuSe utility from ST)
UART Serial Port (through something like FTDI chip)
JTAG or SWO debug ports
SD Card bootloader: https://github.com/akospasztor/stm32-bootloader

But often omitted in discussions is something similar to NXP's In-System Programming (ISP), see note AN10986 (PDF)

It is the easiest (avoids using a proprietary ST DFuSE utility), cheapest (avoids SD card receptacle BOM cost, or USB-to-Serial chip) of all but I couldn't find a solution anywhere on the internet. For example, the Teenage Engineering OP-Z firmware upgrade process is similar to NXP's ISP - i.e., connect the device to a computer over USB, it shows up as a Mass Storage Device and drag and drop the .bin/.hex file, eject and voila! the firmware upgrade process automatically starts. How can one implement such a way to upgrade firmware on STM32 devices?

I want the user to upload firmware on my device in the simplest, easiest way. It is OK for prototyping phase to use aforementioned methods (1-4), but it is unacceptable in a real production device.

Any insight into this matter would be greatly appreciated!


texts:
I have wired an RV with 12avg romex. Incoming shore power is 110v, to a distribution panel/box.

The lights that I want to use are recessed 12v lights, and the only ones I can find seem to have a transformer built into the line before the actual light, (I can't find any 110v lights that are small enough). I have wired the lights in series.

In total there are 9 lights on 3 switches.

Is it possible instead of using a transformer on each light, to have a larger 110v to 12v transformer on the main source wiring coming from the circuit panel, and this make the whole circuit 12v?

This might be a basic question, so apologies if it is, but also open to other ways of doing it. I just don't want to have to take the walls down and re-wire.

Thanks in advance.


texts: High side mosfet- Extra pulse on turn off

texts:
I am making a 3 phase motor drive H-bridge using N channel mosfets (IRFB3607) and BJT based custom mosfet driver such that my turn on and turn off time is about 200ns. Right now I am testing the system with a light load of 0.5A at 24V.

So during turn off, I see something interesting that I can't explain.

Yellow- Output

Blue - Gate

Red - (math) = Blue - Yellow

The differential signal says that the gate is turning off properly so this is caused by circuit inductance or capacitance of the low side mosfet.

Obviously there is a lot of stray inductance all over the place. This is supposed to drive an inductive load. But I have a feeling this is something else.


texts: Finding the resistance to charge/discharge for a LIFeMP battery

texts: I am trying to run an automotive systems simulator (ADVISOR) in Matlab, and I am having some trouble regarding my Energy Storage Unit. I am currently trying to simulate my system with a Valence U24-12XP battery pack. However in order to simulate the battery properly in the simulation I need to provide it with 1.) module's resistance to being discharged and 2.) module's resistance to being charged. I am at a complete loss over what these two terms mean or how I would obtain them from the datasheet I have for my batteries which can be found, here.


texts: Use of capacitor for data lines near sata port

texts:
Near the sata port of an embedded system, I noticed 10nF 16V X7R 10% 0402s in line with the data pins. What is their function?

Related drawing:


texts: Max potential difference that can be created in an analog signal using a microphone

texts:
I am a total newbie.

The main idea behind all this is that microphone produces analog signals which are fluctuation in Voltage.. So can I use an amplifier to amplify these Voltage? And after it can control the current flowing through circuit on the basis the input given to the microphone?


texts: Dependence of Inductance of a Coil on the gap between turns?

texts:
I was wondering how does inductance of a coil say wrapped around a core change by increasing the gap between turns ?

Usually it shouldn't depend on it from the Formula of L being equal to (uN^2A)/L
but is it affected ?

Also Part 2: Say if it was an iron core for a transformer and we were to introduce a small air gap in the transformer, then does it in anyway affect the inductance of the coil ?


texts:
I have a transformer that has the following specifications:

Primary: 220V
Secondary: 12+12V
Rating: 5A

Does this mean the transformer has two 2.5A windings? Or is each winding capable of delivering 5A as long as the total rating is not exceeded?

If I use it as a 24V transformer, is the total current 2.5A?

What happens (besides heating) if the transformer's current rating is exceeded?


texts: Why DisplayPort cables must isolate the power pin?

texts:
I've been investigating why my 2560×1440 DisplayPort monitor and my mini-DisplayPort MacBook Air don't play along, and, it turns out, this is likely due to a wire in the cable that connects the two together, which is supposed to be absent.

http://support.apple.com/kb/TS3533

  Certain cables advertised as being VESA 1.1a compliant may contain a construction issue that may result in the DisplayPort power pins at either end of the cable shorting together. VESA 1.1a compliant cables must isolate the DisplayPort power pins at either end of the cable.

This makes no sense to me!  Why is it that both the monitor and the graphics card have this pin connected, but a standard-compliant cable is supposed to provide isolation of the pin?

A "construction issue" causing the "pins at either end of the cable shorting together"?  Isn't that how wired cables are supposed to work?


texts: Isolating DC/DC converters to suppress undesired current return paths

texts:
I am working on a grounding concept for a vehicle (car, aircraft, you name it) where the vehicle's metallic structure is used as DC current return path for the various loads.

More specifically, I am having trouble with the situation depicted in the above figure . The load device on the right side has its DC power return and chassis ground connected together. The intended return path for the DC current (shown in red) runs via a cable (> 5 mOhms) to a well-defined bonding point. This bonding point is connected to the ground reference point (negative terminal of the battery) via the vehicle's structure (< 1mOhm).
In addition, there is a second undesirable DC current return path (shown in green) via the device's mounting points at the vehicle's structure, which has a resistance of less than 1 mOhm. Obviously, this second DC current return path carries the major part of the device's return current.
(EDIT: The undesirable DC current return path is not guaranteed to exhibit a low resistance, thus it is undesirable in terms of reliability; in addition, the affected structural components are not designed to permanently carry currents.)
What is a technically sound approach to deal with this issue? Both the input configuration of the device as well as the requirement to use the well-defined bonding point are beyond my control and thus cannot be changed.
One solution I've come up with is to use an isolating DC/DC converter as is indicated in the image below. From my understanding the current loops need to be closed as is illustrated in the figure and thus, the entire DC current has to travel via the intended return path.

My questions are:

Is this a valid approach for suppressing the undesired DC return current indicated in the first figure in green?

What is the name of this concept? I've done some googling on this subject but seem to lack the appropriate keywords.

(EDIT: I am aware of power isolation and ground loops. From my viewpoint, this application of the DC/DC converter is all about directing the DC current to the intended return path...)

Can anybody point me to some literature where such issues are discussed? I've done some reading in Lock / Joffe's Grounds for Grounding, however, I cannot find the topology corresponding to my problem in their text and a discussion in terms in currents as carried out in the first figure seems not to be available.

I am aware of the fact that cable shields etc. may provide additional current paths; I've omitted additional interconnect for the sake of brevity.
I am also aware of the additional problems caused by the use of DC/DC converters in terms of EMC.


texts:
I'm trying to debug some issues in an old (early-90's is old now, isn't it?) circuit, and noticed something in at least two different chip's truth-tables, and thought I'd ask here..

In the 74LS74 (Positive Edge-Triggered Flip-Flop) and the 74LS374 (Edge-Triggered Latch) datasheets, there are truth tables, showing in summary how data inputs are latched to output when the CLK input rises.

The truth-table then shows the status of the outputs when the CLK is driven low.

However, looking at this old design, it looks like the original designers are holding the CLK high; not low. There's nothing in the truth-table and no mention (that I've found) in the datasheets about what to expect when the CLK is held high. (Is it safe to assume, since it's NOT a rising edge, the outputs are already latched and will hold, just like if the CLK was low?

Edit to add, per comment: I was looking at copies of the TI sheets for both the chips above. ONE of the chips I got another vendor's sheet - and realized it was just a word-for-word copy of the Ti sheet I had, formatted differently.


texts:
Almost every LED light I've tested (hold an AM or shortwave radio antenna nearby) emits RFI or EMI across a vast frequency range.  The EM noise comes either from the base of the bulb, or from some box or wall-wart supplying a DC voltage to the LED fixture.

Is there any common solution to fixing or reducing this EMI?  Other than throwing all these LEDs away and going back to hot incandescents? (which may or may not be legal in some settings.). Putting a opaque Faraday case around a light bulb makes them useless for lighting.

Maybe some sort of filter boxes on the AC wiring, or the DC wiring if accessible?  A box of ferrite cores?

Does there exist any certified power efficient low EMI lighting?  (e.g. more than just generic required regulatory labels on the boxes which may or may not indicate anything about what's actually in the box).


texts: Given a diode circuit and some of its values, how do I find the temperature?

texts:
Let's say I am given the following circuit: along with $$dV_p/dT=0.139mV/K$$:

Defining V1 the voltage above Diode D1 and V2 the voltage above diode D2
, we use the expression for the current of a diode for both diodes :

$$I_{D1}=I_{S1}e^{\frac{V1}{V_T}}$$
$$I_{D2}=I_{S2}e^{\frac{V2}{V_T}}$$

If we solve with respect to the voltages, we get :

$$V_1=V_T\ln{\frac{I_{D1}}{I_{S1}}}$$
$$V_2=V_T\ln{\frac{I_{D2}}{I_{S2}}}$$

Subtracting, we finally get Vp :

$$Vp=V_T\ln{\frac{I_{D1}I_{S2}}{I_{D2}I_{S1}}}$$

What I know for sure, is that the thermal voltage VT depends on temperature and it is given by :

$$V_T=\frac{kT}{q}$$

I think that the saturation currents depend on the temperature as well. However, will these currents be different? Or can I just cancel them out in the logarithm above?

Cancelling them out, the result doesn't make sense:

$$\frac{dV_p}{dT}=\frac{k}{q}\ln{\frac{I_{D1}}{I_{D2}}}$$

The result is different form the given value of 0.139 mV/K and does not depend on T so I get no information from here.

So, it seems I can't cancel out the saturation currents .

After looking it up, saturation currents seem to depend on :

$$n_i^2=(5.2\times10^{15}T^{\frac{3}{2}}e^{\frac{-E_g}{2kT}})^2$$

However, even if I use the long expression for the saturation currents, ni1 and ni2 will still cancel out in the logarithm. Therefore the dependence of Vp on T vanishes even if the saturation currents depend on it.

Long story short, this was my attempt at a solution. How do I find the temperature?


texts: Verify schematic and board to get it ready for commercial release

texts:
Is there a paid service or platform to hire an electronic engineer to verify a schematic and pcb board I created to get it ready for commercial release?
It's the first schematic I ever created. I taught myself how to create schematics just recently and I'm sure I'm lacking some important knowledge.
I know that there are automatic tools to verify schematics. I however rather want real input and suggestions for improvements.
I don't want to post the schematics on some forum on here.


texts: Can I use IRFZ44N to ground the ground of 7805?

texts:
I have been trying to use IRFZ44 as low side switch to ground the ground terminal of an optional 7805 that I wish to use whenever I want. For this I have connected the drain terminal to to circuit ground and the source to 7805 ground. The 7805 Vin is already connected to 12V.
The MOSFET was turning on and off when the voltage regulator 7805 wasnt in the circuit. But after inserting it what I observed that when the MOSFET is turning On, the source voltage remains 0V, while the drain voltage attains a stable 9V! At the same time the 7805 isnt getting the circuit ground.

Cannot understand why is this happening. Any help is appreciated. Thanks in advance!


texts: Light bulb burns out -- why there is an arc in the switch?

texts:
I use light bulbs (common incandescent) in the room and they
burn out periodically, ca. one bulb in 4 months burns out.
Very often, exactly at the moment when it happens, I see an arc (blueish light flash) in the switch, so the bulb always burns when being switched on.  I don't see an arc anytime the bulb is normally switched, but only when the bulb burns out.

Question: does the bulb burn after the arc appears, or is it vice versa - when the filament burns it causes the arc in the switch?
My thought is that the bulb burns simply because of worn out filament, but
why is there almost always an arc in the switch at this moment?


texts: Is this negative regulator really meant to be an inverted positive regulator?

texts:
Project: make a power supply that can replace the 240V AC supply shown, so that I don't die when messing with the board that this connects to.

I'm only interested in the part inside the yellow box; the +40V output goes to the power amp section which I'm not working with.

So I went out and bought a 7812 and 7815, but then I got confused because of the general consensus that you shouldn't use a 7815 with inverted output pins as a negative voltage regulator, but it seems like that's what they're doing here.

I've ordered a 7915, but my question:

(a) Is this circuit doing something smart by connecting the 7815's positive output to ground and using its output as -15V?
(b) Is this circuit doing something weird, and I should use the 7915 to source -15V as the gods intended
(c) it's impossible to tell, needs more info

Note that I'm sourcing ±30V DC from a preamp circuit in this project, which is higher than what would be at the input in this schematic but well within tolerance for the 7812/7815/7915.

My schematic, using a 7915:

simulate this circuit – Schematic created using CircuitLab

Version with 'reversed' 7815:

simulate this circuit


texts: bjt transistor circuit - finding the resistances

texts:
I have been given the followign circuit diagram:

and have been asked to compute \$R_2\$ and \$R_C\$ such that, at the Q-point, the circuit will behave as follows:

\$V_{CE}=5\:\mathrm{V}\$
\$V_{BE}=0.7\:\mathrm{V}\$
\$I_C=2\:\mathrm{mA}\$
\$\beta=100\$

(where \$\beta =i_c/i_b\$)

I'm really not familiar with this type of circuit display, can someone help explain how I can find the two needed resistances?


texts: Finding necessary voltage for diode conduction

texts:
simulate this circuit – Schematic created using CircuitLab

In the following, I need to find \$V_a(v_{in})\$ such that \$D_3\$ is on. Assume a forward voltage drop of \$0.7V\$. From past computations, it turned out to be around \$10.75V\$ (as you can check from the sim, whilst putting \$10V\$ would turn it off); however, I can't find the issue in my computation.

Since $$i_1=i_2+i_3,\quad \frac{v_i-0.7-v_a}{R_1}=\frac{v_a}{R_2}+\frac{v_a-0.7+6}{R_3}$$
In order for the diode to turn on, I then set \$v_a=6.7\$ and solve for \$v_{in}\$; however, I find a bigger value (\$14.75V\$) than it should be. Where's that flaw?


texts: How do I pick a suitable SMD mosfet to control a 24V pneumatic valve with PIC32?

texts: I need to control a valve (https://datasheet.octopart.com/VXZ242FGA-SMC-datasheet-110849414.pdf) of which I do not know its power consumption and drawn current. I don't have the part yet and usually it is controlled by a PLC, but for my application, I need to control it myself using a PIC32 microcontroller. It operates on 24 Volts and the entire PCB is made with SMD components, so I prefer to use one of those.


texts: Calculating absolute roll/pitch/yaw angle of falling objects

texts:
I am wanting to build a device with gyro, accellero, gauss (compass) sensors and barometric sensor.

This device will record all data from the sensors over a period of about 15 minutes where a person is in freefall (jumped from an airplane).

Fall velocity is easy, using the barometer, but I am not sure about the angle.

I want to know the absolute angle along all axises of the person. Due to the acceleration after the jump, decceleration after opening of parachute and (de/a)cceleration due to change in position in freefall and therefore air resistance all the accelerometer forces will constantly change among all axises.

How would I be able to calculate the absolute angle/rotation of the person in 3 dimensions (roll/pitch/yaw).

Right before the jump, the person is in an airplane and full of adrenaline. Because of this combined with tight space and high noise from the engines, I want to prevent having to use calibration on forehand where possible.


texts: Are there stencils for thermal paste/grease?

texts: I recently came across a reference to the use of stencils to consistently apply thermal paste/grease between device and heatsink. I'm having trouble finding much better explanation of that concept. Are such stencils commonly used? If so, how does one use, construct, and/or obtain them?


texts: How can a system reach its steady-state if the I-action of a PID controller, u(t), doesn't go to zero as the system approaches its desired value?

texts:
The I-action of a PID controller, which integrates the error over time, results in the control signal:

$$u(t) = \int_0^{t}e(T)\text{d}T$$

This means that, when the system reaches its desired value and the error reaches zero, the control signal is a constant. So it is still there and larger than 0, while the P-action and D-action both are zero and have no effect anymore. So what is happening here exactly? Why can the system reach its final value if there is always a control signal active? Or is this the reason why overshoot happens? Is it that the error gets smaller once \$e(T)=r(T)-y(T)<0\$ and the integral gets smaller?


texts:
I deactivated all the independent sources and removed the load resistance across terminals a and b, then applied test voltage Vt=1V across 1V. I have to find It.
My calculations: It=i2-i1

Mesh 1: -1 + 11k i1 =0 => i1 =0.09 mA

Mesh 2: -1 + 5.6k(i2-i3)=0

i2-i3= 0.178 mA

Mesh 3: 2k i3 + 5.6k(i3-i2)=0

7.6k i3 -5.6k i2 =0

7.6k(i2-0.178mA) -5.6 k i2=0

2k i2 = 1.35

i2=0.6 mA

It=0.51mA

R thevinin = 1/0.51mA= 1960.7 Ohms whereas the answer should be around 570-600(as
etermined experimentally)