texts: Why did my LED resistor burn while lighting four LEDs in series?

texts:
I have tried to create a circuit to switch a large 7-segment LED display (LDS-CD16RI) using a pair of MOSFETs, as follows:

simulate this circuit – Schematic created using CircuitLab

Here I am trying to use a 3.3V logic signal (illustrated as the circled 1) to switch the 24V to drive the LEDs. This circuit is repeated for each of the segments of the display.

The typical forward voltage of each of the LEDs (which are in series inside each segment of the display) is 6.8V, and their max steady forward current is 20mA, so I aimed for 10mA current through the LEDs. Since my supply voltage is only 24V I planned to actually drop about 5.75V across the LEDs to give me some headroom for the voltage dropped across M2 and R2.

I arrived at the value for current-limiting resistor R2 at 100Ω using: $$ R = \frac{V_s - V_f}{I} = \frac{24 - (5.75*4)}{0.01} = 100Ω $$

Before building this circuit I calculated the power dissipated by R2 as follows: $$ P = \frac{V^2}{R} = \frac{1^2}{100} = 0.01\mathrm{W} $$

0.01W seemed safely below the 0.25W limit of the through-hole resistors I used, so I proceeded with constructing and testing this circuit.

To cut a long story short: R2 burned up shortly after a segment was illuminated. This occurred for each of the separate instances of this circuit driving the various display segments, suggesting that it was a design error rather than a single component failure.

From my calculations and further analysis, I cannot yet understand why this occurred. To check my work, I re-constructed the circuit in a simulator which suggested that power from R2 would in fact be 6.84mW, which is a result I cannot explain but in any case one smaller than what I had calculated above.

I expect I have made an error somewhere in my calculations or my assumptions, but I have been unable to locate it. Assuming the problem is that the resistor is indeed dissipating too much power, can my circuit be adjusted to address this? Is R2 a red herring here and the problem exists elsewhere in my circuit? Is my approach itself flawed?


texts: Will the constant voltage appear across the capacitor?

texts:
Could you please help me with this question? (Because I'm new here, it seems that I couldn't post an image.)

The circuit diagram is the first picture from this lecture

Voltage Vg is the node voltage between Rg1 and Rg2.

My question is, if the DC voltage Vg is much higher than the amplitude of the small variable signal Vsig, then the charge caused by Vg on either plate of the capacitor should be very large (I think), can Vsig still pass through the capacitor and have a component on Vg? If the left plate of the capacitor is full of negative electrons because of voltage \$V_{dd} \dfrac{R_{G2}}{R_{G1}+R_{G2}}\$, how can small signal Vsig still have influence on the voltage Vg? Thank you!


texts: How do I calculate the base and collector current in this circuit?

texts:
I have the following circuit, using a BJT NPN transistor:

How can we calculate the current going into the base and collector?

I was thinking of using Kirchoff's current law:

\$I_1 = I_b + I_c\$ where \$ I_1 \$ is the current coming out from the positive terminal.

Which gives us \$ I_b = I_1 - I_c \$ and \$ I_c = I_1 - I_b  \$

I then however need to find \$I_1\$ and either \$I_b\$ or \$I_c\$ to calculate the last constant.

If this was an easier circuit, what I would do is add the resistors together with the formula

\$ \frac{1}{R_t} = \frac{1}{R_1} + \frac{1}{R_2}\$

and then treat them like one resistor. I could then use Ohm's law to find \$ I_1 \$. However, the LED and the transistor confuse me. Does this method still work in this case? And if it does, would it just leave me with 1 resistor? Would I then ignore the other components?


texts: Altium: Repeated Sheet in Hierarchical Design has Duplicate Sheet Number

texts:
I am working on a schematic design in Altium Designer 17.1 that makes use of the Repeat() command for a child sheet. I have a certain sheet repeated 8 times for 8 channels of the device.

However, when printed out, the schematic shows all 8 sheets with the slightly different designators for each component (this is as it should be), but the sheet number (a parameter defined in the Document Options dialog) is duplicated for all channels.

Schematic:

Document Options "Sheet Number" parameter:

Having 8 "Sheet 2"s in the schematic printout is obnoxious and terrible practice. Is there a way to modify the parameter so that it increments for each channel? For example, instead of having Sheet 0 (hierarchy overview), Sheet 1, and 8 Sheet 2s, I would like Sheet 0, Sheet 1, Sheet 2, Sheet 3... Sheet 8, and Sheet 9.

EDIT: I have found out how to display the individual duplicate sheet numbers as Sheet 2.1-2.8, but I would like it to display whole-number sheets instead of decimals. Additionally, when I use the 2.X option it changes the total sheet number to 10 for just the repeated sheets, and having 2.8 sheets of 10 is not what I'm looking for.

EDIT2: I solved part of the problem. There is a tool buried in Altium called "Annotate Compiled Sheets", found in Tools -> Annotation -> Annotate Compiled Sheets. In this dialog the user is allowed to manually enter Sheet Numbers for each of the sheets, including the repeated ones that do not show up in the "Projects" panel.

However, the Sheet Total still shows "10", even though I changed it to "9".

Also, when I run the OutJob the individual sheet numbers do not carry through to the final schematic. They show up correctly in Altium, but when printed it only shows "Sheet 2" every time.


texts: flexible and cheap solar cells? howto transform the energy?

texts:
I would like to charge my iphone through solar energy, but i need to know a couple of things:

. What should I do to convert the solar energy into energy delivered through the usb?

. Where can I fine cheap and flexible solar cells?

Sorry, I don't know where to start.


texts: MATHCAD for electronics circuit analysis usable for production testing

texts:
Do anyone have any Idea how to use MATHCAD for electronics circuit analysis.

For example, can I find the Worst Case Analysis ( maximum and minimum values at testpoints) of a complex DC circuit for Battey Management including EMC filter circuits.

I guess this will give an more accurare voltage levels at every testpoints which in turn support PCB testing during series production.

Or any other suggestion to analyze the circuit for PCB testing during production line?

edit: I also want to check the values of all components at production line testing.

Thanks


texts: What is the difference between L293D and L293NE?

texts: I tried to find a L293D motor driver but I was able to find only the L293NE. What is the difference (even google could not tell me)?


texts: Microcontroller with lots of PWM outputs

texts:
I'm looking at some microcontrollers for power converters control (dsPIC33F and some ARM Cortex M3/M4 like the STM32F372CBT6 for instance) and I'm a bit worried by the limited number of PWM outputs (they top at around 8-11).

Since in the future my needs may change, I'd like to avoid finding myself in a situation where I need more PWM outputs.
Therefore I'd like to know if it would be better to (in order to increase the number of available PWMs):

Use multiple microcontrollers and communicate between them (via CANbus for instance), each microcontroller controlling its own PWMs
Use external PWM generator modules via SPI/I2C (do they exist?)
Any other microcontroller/DSP family supporting more PWM outputs?
Creating as many PWM as needed using an FPGA? Not sure about this (IMHO probably over-complicated)

Why this many PWM? I don't think they are so many in fact ...
With 10 PWM signals you could only control 2 H-bridges and a synchronous Buck converter.

Feel free to ask more questions if not clear enough.


texts: About measurement of pulse using oscilloscope

texts:
When I measured the optical pulse using photo-detector and oscilloscope, some negative voltage was measured after strong peak.
What did I get negative voltage?
How is it possible?


texts: USB-C breakout board, using V and G with a NiMH charger am I doing this wrong?

texts:
I’m pretty new to electronics so trying to find my way around.
I’ve purchased this breakout USB-C:
https://www.amazon.co.uk/Chenyang-24pin-Female-Socket-Connector/dp/B00VJ944V2
And this NiMH battery charger:
https://www.amazon.co.uk/Battery-Dedicated-Charging-2S-Without-Terminal/dp/B087NVJBCX
I’m connecting using 30-gauge wire. My understanding is that I need to solder the V and G on the breakout to the GND and VIN on the NiMH charger. It doesn’t really work or do anything after soldering (besides flash red once very dim) but only if I plug the charger in. If I grab my cell battery pack and connect the + and - to the NiMH board it also just flashes red once. All signs are pointing to me not understanding this correctly so any pointers would really help.
Essentially I am wanting to supply some kind of power to the board to then connect the other end of the NiMH board to a battery to charge a small device. Thanks in advance for any pointers.


texts: Switching between +9V and -9V (using 5V logic)

texts:
I got some linear actuators today and found out that when I give them +9V they extend and -9V makes them contract. This is easy enough to test by hand, simply by wiring the actuator up to the battery backwards for the negative voltage, but when I hook it all up I'm going to be driving all of them from my Atmega1284, which uses 5V logic.

In anticipation of this, I got a bunch of relays that run on 5V logic as well so I can control whether or not there's +9V running through with my 5V microcontroller. However, I have no way to programmatically provide -9V.

My question here is how can I switch between giving +9V and -9V when all I can do from my microcontroller is either push out 5V or 0V? Will I need more than just my relays? Is there some spiffy EE trick to make this work? Thanks!


texts: How to connect Aref (Avcc and Agnd) and where to place the bypass capacitor?

texts:
This is my schematic:

Should I connect a capacitor between the PIN 32 and GND Pin or AGND Pin?

From the AVR Hardware Design Application Note:

  2.2.
  Analog Supply

  The AVR devices that have a built-in ADC which have a separate analog supply voltage pin, A V CC . This
  separate voltage supply ensures that the analog circuits are less prone to the digital noise originating
  from the switching of the digital circuits.

  To improve the accuracy of the ADC, the analog supply voltage must be decoupled separately, similar to
  the digital supply voltage. AREF must also be decoupled. The typical value for the capacitor is 100nF. If a
  separate analog ground (AGND) is present, the analog ground should be separated from the digital
  ground so that the analog and digital grounds are only connected at a single point (at the power supply
  GND).

Grounds are all same. Right? So does it make a difference if it is decoupled with analog one or the digital one?

NOTE : It doesn't need an critical ADC application but I would want to use ADC later. Application doesn't need precise or accurate ADC since it is more sort of learning project but it would be helpful if solutions or suggestions provided are for making it perfect.


texts:
I am attempting to write some data to my stm32 discovery board (STM32F4VET11).
Following the data sheet:
(Sector 11, address 0x080E0000).

The code compiles, however, the write never takes place. When I enter debug mode and check rdBuf, the addresses hold 0x00.

Any tips?

//setup memory
HAL_FLASH_Unlock();
FLASH_Erase_Sector(11, FLASH_VOLTAGE_RANGE_3);
HAL_FLASH_Lock();

//write to memory
HAL_FLASH_Unlock();
uint8_t rdBuf[5];
uint8_t wrBuf[5] = {0x11, 0x22, 0x33, 0x44, 0x55};

uint32_t flashAddress = 0x080E0000;
for(uint32_t i=0; i<5; i++)
{
    HAL_FLASH_Program(FLASH_TYPEPROGRAM_BYTE, flashAddress, ((uint8_t *)wrBuf)[i]);
    flashAddress++;
}
HAL_FLASH_Lock();

//read
flashAddress = 0x080E0000;
for(uint32_t i=0; i<5; i++)
{
    *((uint8_t *)rdBuf + i) = *(uint8_t *)flashAddress;
    flashAddress++;
}


texts: Do Thermal Cutoff switches exist for temperatures below 50 C?

texts:
I have been trying to find some passive thermal cutoff switches for a project, but it seems that all of them are for 65 degrees C and up.  Is there another name for lower temperature TCOs?

Any help in finding these would be very much appreciated.


texts: Individual Phase plot looks different than the Bode plot

texts:
My transfer function is

with Omega_n = 1000.8 and Lambda = .5004 and k = 3

But when I try to individually plot the phase I get something like this

I believe my equation for finding the Phase using ArcTan function is right. Does anyone know why my individual phase plot does not look like phase plot in BodePlot?


texts: Does using "High Leg Delta" 3-phase electricity require a different equation for calculating Amperage/Power?

texts:
The basic equation I've been using to calculate the amount of Amperage required to achieve a particular power output using 3-phase electricity is:

  Amp. = Watts / (√3 × PF × Voltage)

where PF = Power Factor, which in my case is assumed to be 1.0 (heating elements). For example, to run 18000 on 230 volt 3-phase electricity would require 45.2~ amps.

  Amp. = 18000 / (1.732 x 1.0 x 230) = 45.2 amps

However, if the voltage is High Leg Delta, even though the 3 phases are each measuring approx. 230 volts, but 2 of the legs are much lower than the third, should the same equation be used to anticipate required amperage?

BONUS QUESTION: In real-world applications, multimeters are obviously reading different amperages for each live wire, but on paper, the total amperage may in fact be found using the aforementioned equation. This poses a particularly difficult challenge when using Thermal Overload Relays that are used to set the overload threshold. We are seeing that for people using High Leg Delta, the setting isn't actually factoring in individual legs, but the overall amperage as the relay isn't being tripped when the legs excede the setting. The side effect of permitting this strange high amperage, but not really, to pass is that other equipment sensitive to amperage is being damaged. My inclination is to overcompensate, but figured this must something that has been addressed.

Any guidance is appreciated.


texts:
Here I know how we apply nodal analysis, but can somebody explain how can we calculate the current 'i' if there is no resistor in that particular wire?
I have shown my approach and working so far. I would really appreciate any guidance to steer me through the next steps to the solution.


texts: How would you calculate the input impedances of these circuits?

texts:
How would you calculate input impedance of this circuit?
I have tried and obtained these calculations for 1.3, but apparently my teacher told me that I am supposed to ignore the 2 10k resistors. This was my exam question that I was absolutely clueless about, so I am reviewing them here.


texts: What would happen if I connect two different DC voltage sources in parallel?

texts:
I have a computer power supply that I'm hacking together as a bench supply. For this particular model to power on, I need a minimum load across both +5V and +12V.

"Easy," I thought, "I'll just connect both +5 and +12 to my power resistor!" And it worked, but then I started thinking, what does it mean to have these two different voltages connected in parallel? If the voltages were the same, then I would be increasing current. But what about different voltages?

Also, what if I connected +5 and +12 in series, and then put a load on that? The equivalent voltage would be +17V; what would be the difference between that and parallel?

Or am I going about this the wrong way; should I put a separate resistor on each rail? It seems like I can do better than that.


texts:
I have tried many ways but to no avail. It keeps having this warning: inferring latch for variable 'count_reg'.

    begin
process (control)
   variable count : std_logic_vector (3 downto 0) := "0000";
    begin
        if control = "001" or control = "010" then
            address <= count;
            count :=  count + "0001";
        elsif control = "000" or control = "011" then
            address <= count;
            --count :=  count;
        else
            count := (others => '0');
            address<= count;
        end if;
end process;


texts: What's the difference in a digital optocoupler and a non digital

texts:
I'm looking at 2 different optocouplers.The Avaago ACPL-K44T and the ACPL-227.

The ACPL-K43T states that it's a digital opto-coupler while Avago ACPL-227 doesn't.

Schematically, they're a bit different. The K43T needs a Vcc and has parameters like Vol,Voh,Ioh,Iol, etc.

I'm wondering what exactly are the applications you'd need the K44T for compared to the 227.

http://www.avagotech.com/products/optocouplers/industrial-plastic/other/phototransistor/acpl-227-500e#documentation

http://www.avagotech.com/products/optocouplers/automotive/ipm-interfaces/acpl-k43t-000e


texts:
I know that Ohm's Law is V = IR but I am getting some very confusing current readings from multiple multimeters.  Here is my very basic breadboard configuration:

V = 6v

R = 200 Ohms

I = Should equal 30 mA but it does not (see multimeter pic)

The multimeter shows 18.8 mA but I do not know why.  I have also tried with 3.3v and it registers 6.6 - 7 mA.

I would like to know why this is happening.  I have tried different resistors, LEDs, multimeters, breadboards, power supplies but it continues to happen and I am very confused with the readings.


texts:
after routing a PCB I've added a GND polygon like :

My question is why some GND Pin aren't connected to the  Polygon ? should I connect them manually ?


texts: Possible Issues with battery Powered sensor and collector star network

texts:
I am designing a wireless Sub-Ghz network consist of many battery powered sensor nodes with a single collector node.

For lowest power possible, the sensor stays most of the time in sleep mode waking up periodically to send out data.

Possible problems I can think of are as follows

1) Since the network must agree on which band to use, is there any protocol to prevent collision when two or more nodes transmit at the same time including not just within the network, but also including interference from outside of the network?


texts: Why does this Arduino compatible not have all the recommended capacitors?

texts:
One of the sources I'm using as reference material in designing a new Arduino-compatible board is the Sparkfun SAMD21 dev breakout board (https://cdn.sparkfun.com/datasheets/Dev/Arduino/Boards/sparkfun-samd21-pro-breakout-v10.pdf). I've also been using the datasheet for the SAMD21 as my (main) reference, and it seems that the Sparkfun board is violating the recommended values and even leaving some caps off.

For example, the VDDCORE capacitor is rated only 0.1uF instead of the 1uF in the datasheet, and both of the 10uF capacitors are missing. Is this a mistake or possibly a cost cutting measure? How will the performance be affected?


texts: Solar cell trickle charging lead-acid without charge controller

texts:
Can somebody comment on sizing a solar cell for trickle charging a lead-acid battery bank without a charge controller for several months?

I found a non-authoritative source that claimed that cells with a power of 4% of the C20 capacity of the bank do not need a charge controller. - This corresponds to a charge current of about 0.23% of C20.

As far as I know, the float charge of lead-acid (if done with constant current) is typically done at 1% of C20 but requires the termination condition of dV/dt = 2.5mV/cell/hr.

So where does this 0.23% of C20 come from? Is the assumption that this balances the self-discharge of the cells perfectly?

Since the self-discharge varies from model to model, how does one size this properly? Size too small and the battery dies from deep discharge, size too large and it dies from slow overcharge?

Also: the balancing of self-discharge with a current of 0.23% of C20 does not sound quite right either. Assuming 5% discharge per month would imply a self-discharge current of the order of 0.007% of C20 - much smaller than the recommended 0.23% of C20 for "solar cell trickle charging".

Can anybody "shed light" on this for me?


texts: Can we operate a 6VDC Relay using Parallel Port signal, without a Darlington Transistor, with only these components?

texts:
Before anyone downvotes the question for my recklessness:

Disclaimer: I acknowledge that it is not advisable to make the connections mentioned in the question. This is just a hobby experiment where I can afford to dispose or damage parts in the name of learning.

I have the following:

Parallel Port in PC
LED
9V battery
6VDC 100-ohm relay

I can control Parallel Port signals through my software code.

I tried connecting the parallel port to LED and it worked
I tried connecting the 9V battery to relay and it worked.
When I tried connecting parallel port to relay, it didnt work - leads me to believe voltage (or current) was not enough.

(yes yes.. I know.. some of you are itching to punch me in the face)

With just the parts I mentioned above, without using Darlington Transistor or other such devices, is there any way in which I can connect them all, so that I can control the relay from the PC - at least for a short period of time?


texts:
I have the circuit pictured below.  I need to change the potentiometer from a 20K to a 5K and still get the 0-5 VDC output.  VCC = 5V

Is this possible?
What needs to change to make this possible?
What is this circuit called, a buffer?

Also, can a LM258 Op Amp do the same as the ICL7612?  (I have a lot of the LM258's on hand, but would have to order the 7612.)  I breadboarded a similar circuit using the LM258, but the output saturates at about 2.5V and will not go higher.


texts: Using a solar panel for laser light detection

texts:
I've been planning on putting together a laser tag system and one of the big concerns I have is that photoresistors/phototransistors have relatively small surface areas w/r/t a human body. On the other hand, solar panels have lots of surface area and the scrap ones are cheap enough to slap on a vest.

I've been doing some digging and I found this video where some students at a university manage to detect a modulated laser with a solar panel. They don't mention much in the way of parameters however. I don't know if it was a consumer grade laser pointer or if it was a commercial grade laser, for example. Neither do I know if the panel was extremely sensitive or if it was just any cheap panel they had around.

So I've come with questions. What are the basics of working with solar panels in terms of output characteristics? What equations do I need to know?

Second, does anyone have experience with either lasers or panels (preferably both) who might be able to point out any obvious pitfalls I've overlooked.


texts:
So I'm new to electronics and was looking at some Eagle schematics when I came across the following voltage regulator schematic:

My question is: would it be possible to change the regulator to another one (with the same caps), for example this one


texts: Can flyback transformer used for push pull converter?

texts: I am electrical engineering student and I am working on capstone project now. We decided to make paralleing input and series output push pull converters. (So combining two converters) However, we chose to do push-pull topology since it is best-suited for our project and we found good ic chip and then done with design. However, we are stuck now because we need to buy transformers, but all we can find is flyback transformers at coilcraft. We did found some puch-pull transformer, but we found that we have problem with either turns ratio or voltage rating or similar. I am wondering if it a good idea to use flyback transformer to make push-pull converter. If that so then is there any design consideration? If not then can you please recommend me any good websites that I can find good push-pull transformers? I tried to research about it, but still not sure. If any expert can help me then I would be very appreciate it!


texts: PIC 16F877A basic led blinking does not work

texts:
It has been quite a while since I haven't done PIC programming.
While trying to run a simple example I have ran into a problem.
#include <pic.h>

int main()
{
    TRISB = 0; // PORTB is output

    PORTB = 0xFF; // All leds are on

    while (1) {} // Loop forever

}

I use PICKit2 command line interface to load to program into the microcontroller.

pk2cmd -PPIC16F877A  -Fhelloworld.hex -M
PICkit 2 Program Report
1-10-2020, 21:19:44 Device Type: PIC16F877A
Program Succeeded.

You can see the schematics of the circuit here.

I meausured the voltage at the output of RB5 with a multimeter. It was about 300 mV.
Are there any ideas on how to fix this problem. Thanks.


texts: Problem with finding capacitors' purpose in PIR circuit

texts:
Hey guys, I am currently working on an Arduino project where I need to use a PIR(pyroelectric infrared sensor). I am building my own circuit for it from scratch. I am using the circuit example from the datasheet of the sensor I am using (IRA-E700, datasheet: http://www.farnell.com/datasheets/2199772.pdf). I have changed some values, however, to filter out 50Hz signals since i was getting a lot of noise with that frequency. I have almost understood the circuit completely, but there are a couple of things I still haven't understood:

What is the purpose of the capacitor C3? I am guessing it's used for some sort of filtering of the noise you get with a PIR. I'm just not sure how such a filter would work?
What is the purpose of capacitor C6? I know it has to do with getting the voltage up to 2.5V since the op-amp has 2.5V on its non-inverting input. I'm guessing the capacitor interacts with the op-amp somehow, but I just don't know exactly how.

Thank you in advance for the help guys! I apologize if I left any information out.


texts: In a Boost Converter, where is most of the heat dissipated?

texts:
In a circuit like this:

I am for now assuming that a lot of the head will be dissipated by the Diode, and hence I am preparing the PCB to include a heat sink for it just in case. But what about the inductor and the switching IC U2? And the MOSFET?

Any tips on PCB design to dissipate a lot of the heat that will come out of this circuit at max load?


texts:
It is known that there are limited read and write cycles for EEPROM. Suppose I keep writing some important information in EEPROM and read it after power off to ON. Suppose at some point of time the EEPROM fails, how to know this condition? What are the checks I can put? Another question is checking one byte of
EEPROM memory like writing known value and reading the same value is equivalent to checking the complete EEPROM memory say 4K.


texts: Maximum load current that is still indistinguishable from battery self-discharge

texts: I am designing an electronic device that will be powered by a battery, and I am trying to keep my device's current draw in standby to a minimum. Specifically, I would like to keep the current just low enough that it is insignificant compared to the battery's own self-discharge. In other words, I would like to determine the maximum current which, if constantly drawn from a particular battery, still would have no noticeable effect on the charge life of the battery. My device will be powered from 4 AA NiMh cells, although I would like to be able to figure this out for any cell size and chemistry I may encounter.


texts: Existence (or reason of lack) of simple cmos LIFO registers IC

texts:
There's a project I'm working on that needs a simple LIFO register.

What I mean by simple is to support the PUSH & POP operations, and I guess EMPTY and FULL indicators.

I must be searching with the wrong keywords on  Google, because searches such as "CMOS LIFO register" come with educational papers, and not ICs.

The 7400 series IC list I'm sticking to doesn't list an IC that does those.

While I can simply accept that there's no such IC, that would be surprising, as the demand, should be sufficient (I'm not a market nor electronics expert, I'm simply guessing). So, if there's no CMOS stack register out there , why exactly ?

So I guess my questions are :

Is there any basic CMOS LIFO register or equivalent ?
If there doesn't exist such IC, why ?

Sorry if my question is just a result of my poor Googling skills, by the way.


texts: What is the difference or relation between Rd and Rf in a diode?

texts:
For the small signal impedance of a forward diode we usually write:
$$r_d = \frac{n\cdot V_T}{I_D}$$
However, in datasheets one usually finds a specified forward resistance: \$r_f\$

Can anyone explain the difference and or relation between the two?


texts: ATND gets Response when Xbee Router AT is connected to Computer, no response when on breadboard

texts:
I have a Xbee Series 2 in Coordinator AT which is connected to a computer, a Xbee Series 2 in Router AT which is connected to a breadboard and powered by Arduino's +3.3V and GND rails.

Coordinator AT

atid
2001
atsl
40A74613
atdl
40B19213

Router AT

atid
2001
atsl
40B19213
atdl
40A74613

When I use Coolterm to send the command ATND from the Coordinator XBee, theres no response from the Router XBee. Connecting pin 13 of the Router Xbee to an LED causes the LED to light up, so I guess the Router Xbee is powered properly.

ATND sent from the Coordinator AT

atnd
0000
0013A200
40A74613

FFFE
00
00
C105
101E
00030000

However when I also connect the Router Xbee to the computer (so both Xbees are connected to the computer), ATND does get a response from the Router XBee.

ATND sent from the Coordinator AT

atnd
0000
0013A200
40A74613

FFFE
00
00
C105
101E
00030000

3626
0013A200
40B19213

FFFE
01
00
C105
101E
00030000

How can I troubleshoot this problem?


texts: freechragecontroller.org. Current is flowing even though M3's gate is not powered?

texts:
I'm using a visualization software in which I created an animated schematic for a part of the free charge controller:
http://everycircuit.com/circuit/4838391810097152

The entire schematic is here: http://1drv.ms/1AiMICL (or here)

Hopefully I have this set up right. I am questioning the purpose of C6 and C9. Why are they there? There doesn't seem to be current flowing between the terminals of C6 or C9. What is the main purpose of the induction coil?

I've worked on this now for a spot and I added the MOSFETs I am curious because in Every Circuit simulation there seems to be current flowing through M3 even though M3's gate is not powered at all in my simulation.

I thought that http://everycircuit.com/circuit/6539292895608832 is a good buck converter. It seems that a synchronous buck adds the use of another MOSFET which is used in an opposing configuration where one is on the other is always off and vice versa. That I understand. The power I see flowing in every circuit is just a small trickle at 16.7 mA however its making it through with nothing connected to M3's gate. I'm not sure how that's happening yet.

It seems to be the use of the ground that is causing the flow of current through MOSFET M3 even though the gate is off. Why is this happening?

Another question I have about this design is the MOSFET:
http://www.jameco.com/Jameco/Products/ProdDS/669943IR.pdf

Every Circuit software wants to know how many nm's or mm's is the mosfet. I don't know what Every Circuit is talking about yet.

Thank you


texts: how to do a shift/add multiplier in verilog?

texts:
I tried this

module sum(X,Y,Q);
  input [31:0] X,Y;
  output [31:0] Q;
  assign Q=X+Y;
endmodule

module register(loadD, clk, rst, Q);
  input [31:0] loadD;
  input clk, rst;
  output reg [31:0] Q;
  always@(posedge clk, posedge rst) begin
    if(rst) begin
      Q<=0;
    end
    else if(clk) begin
      Q<=loadD;
    end
    else begin
      Q<=Q<<1;
    end
  end

endmodule

module multiplier(A,B,andS,regS,clk,rst);
  input [31:0] A,B;
  input clk,rst;
  output [31:0] andS, regS;
  sum BL1(A,B,andS);
  register BL2(andS,clk,rst,regS);
  assign A=regS&{32{B[0]}};

endmodule

But don't work


texts: Assign existing footprint to existing component in Circuit Maker?

texts:
I found the following two components in Circuit Studio that I am using in my design:

AOD407:

And IRLR8726:

The manufacturer recommended footprint is exactly the same for both, and they use the same 3D model in Altium. The trouble is, whoever did the footprint for the 407 on Octopart departed from the recommended footprint, making their own instead. This is undesirable for me, as my design needs symmetry.

Left: 407 Footprint (non-standard, custom), Right: 8726 Standard Footprint

In the parts page, I can add new footprints to the part, and I added one, but it starts with a blank template. I do NOT want to copy and paste the standard footprint into the template. This is too much effort for a professional tool. How can I import existing footprints in the footprint editor? This will allow me to standardize my footprints for these and other parts.

I am using Circuit Maker, which is essentially the community version of Altium.


texts:
How to lock ATMEGA328p-au to disable sketch read from Arduino IDE?
Is there a hardware way too?
What are the chances it can go wrong?
What will happen if it goes wrong?

Notice: I am a computer science guy and new to electronics. So please explain your answer in detail :-)

----More Info----

The chip in consideration is a new commercial product.

It is being given to people, who have highly technical staff at the back, for a few days, for some purposes of business opportunity evaluation.


texts: 18650 LiFePO4 Cell UVP/OVP Under/Over Voltage Protection

texts:
The vast majority of existing ancillary protection IC's available (such as Seiko) are not compatible with LiFePO4 chemistry due to the lower operating voltage. And the few vendors selling iron-phosphates often have a datasheet which is unclear about any built-in OVP/UVP circuitry. After contacting mine, the 18650's do not have internal protection, so must have it externally added. The vendor also does not have any solutions to recommend.

There are a metric ton of "BMS" and related cell and pack protectors on eBay, some claiming to work with LiFePO4. Which made me ask what these components were, and what I could use for my LiFePO4's...

Surprisingly, google knows very little about protection IC's for these batteries. After much searching and finding only lithium-ion protectors, I decided to look more closely at these "BMS" boards to try and determine which chips they were using. Most have some FETs on them, and a SOT-6 package labeled "3P20" or similar. I couldn't find any match to this part code, but I was able to get the manufacturer of the MOSFET from it's symbol, Alpha & Omega. So researching this company's products, they do have something like the AOC2806 which has a really low gate-drive voltage. Neat... so perhaps these are being used directly to "switch off" a cell when it's voltage goes below the gate threshold voltage of the FET? So I decided to simulate it. (Right-click and view in new page for higher resolution.)

The red trace is an imaginary "cell" voltage, starting at -1v for half a second, then ramping up to 3.2v, staying there for 2s, then ramping down again. Orange trace is the voltage response into load of the left-most circuit, yellow the 2nd circuit, green the 3rd, and blue the 4th.

The ideal response would be a sharp cut-off at 2.00v to zero, but as can be seen, achieving this is easier said than done. I am also very dubious about the real-world accuracy of the green and blue traces. Even if it did perform like that in reality, it still would not work well, as high-impedance loads would still drain the battery beyond 2.00v (due to the curve at the bottom) down to about 1.6v.

So my question is... does anyone know of a LiFePO4 UVP device? Or can suggest refinements to my simulation, or any other solution whatsoever? The only requirement I have (and it's a doozie), is that the solution must use as little quiescent current as possible. (Another reason for exploring the MOSFET-only route: gate leakage below VgsON should be very very low.)


texts:
What is the difference between debounce filter and glitch filter on a mcu?

I'm trying to implement a hardware debounce filtering on a ATSAM4S4C

(ATMEL SAM CORTEX-M4 - PAGE 575. http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-11100-32-bit%20Cortex-M4-Microcontroller-SAM4S_Datasheet.pdf).

But even though I selected slow clock and a cut-off frequency at 10 Hz I see false interrupts to be triggered at frequency higher than 10 Hz.

Also I notice that glitch filtering does not help me at all because it is clocked with the peripheral clock which is higher than slow clock.

Am I doing something wrong?


texts: Reliability of electronic components in space

texts:
The Tesla car being recently shot into space made me wonder about the reliability of common electronic components in hard vacuum. I'm asking about the kind of components you would find in Musks's car-turned-stellar object, not specific components designed for space applications. This is an "out of curiosity" question, I don't intend to build a spaceworthy roadster in my garage.

Would electrolytic capacitors lose their electrolyte and dry up?

Would LiIon batteries' pressure release safety valves pop?

Would chips popcorn due to moisture evaporating in vacuum?

Would the LCD's liquid crystals evaporate?

Obviously, air-cooling of electronics would no longer work.

Radiation would zap CPUs and RAM...

The evaporation of axle grease and coolant shouldn't matter that much due to lack of roads...

"Amateurs" have been shooting GoPros and other electronics into space for a while now, and it seems to work, at least for a few minutes. Still, the camera on the Tesla didn't last very long (just a few hours).

What could have failed first in that camera?...


texts: Are internal pull-up resistors in microcontrollers connected to Vcc internally?

texts:
I'm partly on my way into my first project with the ATMega32U4 and Im trying to understand the internal pull-up resistor. After lots of research, Im struggling to find an outright answer to my question but from my reading its been implied that the internal resistors are connected to an internal power rail. Is this correct? And therefore if I just connect a switch to ground and the pin will I be able to detect the button push?

To make it clearer:

Option 1

Option 2


texts: Closed loop shapes with zero mutual inductance?

texts:
I have done numerous searches trying to find any mention of theory or experimentation done on determining closed current loop shapes that have zero mutual inductance and...no dice!

Of course you can do things like put two loops infinitely far apart or surround both in thick mu-metal, closed shells, but things like that are not what I'm talking about.

What I am talking about is taking two or more finite length conductors, each with a head and a tale, and shaping them such that:

They don't intersect themselves before head and tail meet
They don't intersect other conductors
There is not any point where a conductor passes infinitesimally close to itself or another conductor without actually intersecting
And any other rules that allow each conducting loop to have its own self inductance without interacting with the other loops.

This is the equivalent of zeroing the Neumann mutual inductance equation:
$$ M_{m,n} = \frac{\mu_0}{4\pi} \oint_{C_m}\oint_{C_n} \frac{\mathbf{dx}_m\cdot\mathbf{dx}_n}{|\mathbf{x}_m - \mathbf{x}_n|} = 0 $$
But still allowing self inductance to be greater than zero:

$$ L_{m,m} = \frac{\mu_0}{4\pi} \oint_{C_m}\oint_{C_m} \frac{\mathbf{dx}_m\cdot\mathbf{dx}_m}{|\mathbf{x}_m - \mathbf{x}_m|} > 0 $$

If any of you have insight that could help with this curiosity, I'd love to hear it.


texts: How does async data transmission actually work?

texts:
I think I understand synchronised data transmission between A and B. They share a synchronised clock signal that indicates when the transmitter is sending a bit and the receiver should read the value.

What I don't understand is asynchronised data transmission. I realise that there are start and stop bits and possibly a parity bit too but how does the receiver know when to "take readings" from the signal between the start and stop bits?


texts: Current sensor: averaging and feeding +/- signal into ADC

texts:
I'm looking for a way to measure the +/-10A current in/out of a battery using this current sensor (10A variant). It needs a +/-15V supply and outputs +/-4V at it's rated current. I'll assume however that the output ranges from the full -15 to +15V and I'll just use an ADC with enough resolution to get the desired precision at +/-4V.
I think the MCP3425 16-bit ADC (datasheet) should be suitable but I'm not sure how to connect the two. On its differential inputs, it expects +/-2.048v to get the full 16-bit resolution, but the voltage on either pins can't be lower than -0.3V relative to GND.
This means that I can't just scale the +/-15V down to +/-2.048V using a voltage divider and feed it into the pins. I'd have to shift it up first. Maybe another option could be to set the PGA to 8x and scale the voltage to +/-256mV so it won't exceed -0.3V.
I'd also like to 'average' the output of the current sensor before feeding it into the ADC. The plan is to take 10 readings/s so I'd like each reading to approximately represent the average current over the last 100ms. I read about true RMS to voltage ICs but these are quite expensive and probably overkill. Can I just use an RC filter for this? If so, where exactly should I put it and which R and C values should I use? The switching frequency of the battery's current will probably be around 100kHz.


texts: Instrumentation amplifier, discrete or integrated?

texts: Since integrated instrumentation amplifiers are so readily available, does it still make sense to incorporate an instrumentation amp discretely built from multiple opamps and resistors? Would one see discrete instrumentation amplifiers in professional designs?


texts: What properties should I look for in a microcontroller if I just want to work with incoming 16 bit data?

texts:
I am very new to picking microcontrollers for projects.  I have a project in which I have 16-bit data coming in from an amplifier/ADC.  Simply put, I would like the microcontroller (very low power and in dimensions in range of ~7mmSQ,STM32 based also preferable) to manage the 16-bit data coming in.  Is there a specific property in microcontrollers that governs what resolution data it can manage? What is the name of that property?  Also, is there a good website for understanding how to choose microcontrollers for projects? Any help appreciated!

I realize the question is very vague but I am just starting out and would love to learn more about how to pick the right hardware any way I can.


texts:
I have stuck on implementing magnitude comparator for 2-bit numbers (three functions - greater, equal, less).

It is pretty easy to implement it with AND and OR gates, but the point is the task is to implement it with AND and XOR gates only. A little bit of help will be appreciated.

Thanks in advance.


texts: Can small wire gauge restrict current? powering a brushless motor

texts:
The question is related to quadcopters and else.
So my quadcopter (brushless dc motors and electronic speed controllers powere by 3cell lithium battery 2700mah 25C) has thin wires on the main power port, Im trying to figure out if it could affect current flow, I know that when gauge is too small it can overheat, burn or melt, but can it just restrict current flow without fires?

I having hard time to figure it out because once I tried to jump start a truck with cables that were too thin and the starter motor just weren't crancking the engine, wires weren't getting hot or anything... connecting another pair of wires in parallel resulted in successful start of the engine, and it was matter of seconds, not like the battery had time to recharge.

Can some one please explain this to me.


texts: Parallel high speed and high current mosfets

texts:
In order to speed up switching times and reduce power (I2R) losses, is it worthwhile to put a fast switching (but high RDSon) FET in parallel with a low RDSon (but slow witching and high Qgs) FET? That way the fast FET handles the switching transition (but only for a few tens of nS) so the high current FET can be soft switched on and off at low loss for the remainder of the switching cycle. The two FETs would have their own gate drive circuits. Does anyone think this is a practical way to switch tens of amps at MHz speeds or should I just bite the bullet and go with the more expensive GaN FETs?

I managed to get a PSpice model of one of the FETs I was thinking of using, if I can push ~6A of gate drive into it, I can switch it in <3nS, I don't need the 1/2nS switching times of GaN FETs nor the headache of dealing with the EMI problems that would cause. The switching losses at 3nS should be manageable provided I can keep \$R_{\theta JA}\$ to less than 10 \$^{\circ}\$C/W.


texts: 3 output MOSFET? does such thing exists?

texts: I need to control 30 high Current LED's, the issue is I don't want to have 30 MOSFETs, is there any way around this dilemma? any help will be appreciated, I am aware of the CSD17313Q2, but not sure if it has separated outputs, it appears to have 2 gate pins?


texts: For an inverting amplifier, Vin= 1V, R1= 5 ohms, Rf=10 ohms, frequency=100Hz. Why is output distorted

texts:
Can anyone explain how the low values of resistor are causing distortion in output.

Thanks


texts: change level of positive square wave signal to negative

texts:
A general question:

Lets say I have a square wave signal from 0 to 5 volts.
What I would like to do is create a circuit that will convert this 0 to 5-volt signal to a -2.5V to +2.5V for example. ( remove the dc )

I do NOT want to have a negative voltage reference for the -2.5V in my circuit.
What options do you think can create this kind of circuit? (for example, high pass filter maybe with Schmitt trigger? Other options? )
My square wave is at 200kHz and 50% duty cycle.

More info:

The square wave signal drives a transformer and after the transformer, a diode and a capacitor rectify the signal in order to create a DC output.

What I want to build, is a floating voltage that can be controlled by the frequency of my square wave. I need to connect this voltage in another circuit so that is why I use the transformer, for isolation and not having a ground reference on the secondary side.

The above question that I have is more general, in order to understand about level shifting.

In my case:
My AC waveform that I power on the primary side, can be a square wave or sine wave (I am not sure what is the best). The current that I need on the secondary side is about 1A. My transformer is a 1:0.8 (primary:secondary) and the voltage on the secondary side that I need, is about 10-12 volts and this voltage should be adjustable by the frequency or amplitude of the primary side's AC waveform.

Thanks a lot.


texts:
[Marcel Pelgrom, Analog-to-Digital Conversion]

Hi,

I'm a bit confused on how the author here derives the quantization power from the sawtooth wave. How exactly is he integrating using values from the y-axis? I attempted it by splitting a single sawtooth period into two triangles and calculating area, however my answer is different:


texts:
I have a RLC circuit to discover the characteristics of controlled system.
The block diagram has shown below

where

If I add a PI compensator to the closed loop system, Q(s)=1/s,and the transfer function of the system becomes. I’m wondering for which K the system will produce a response that has smallest overshoot. Is there there any correlation between the damping  and the value of K?


texts: Can (CPU) logic and (flash) memory be located on the same die?

texts:
Is it possible to manufacture semiconductors in a way that places logic (for example, a CPU core) on the same die with non-volatile flash (or other EEPROM memory) circuits? What about DRAM?

It certainly seems to be possible to have on-CPU-die SRAM (in the form of various caches); is there a technical reason that DRAM and non-volatile memory can't be included? Is this because SRAM consists of the same or very similar transistors as the CPU logic?

Or is that simply a matter of economics (being able to combine various CPU and memory types without expensive chip redesigns)?

Are there some specialized applications where those different semiconductor types are still combined on the same die because of space requirements (I'm thinking about things like smart cards which contain at least a CPU, ROM and some NVRAM)?


texts: 8051 programmer not working when laptop lid removed despite suggestions in comments

texts:
UPDATE

I took a suggestion of disconnecting my external monitor from my laptop and the results were the same. What I did notice however is that the AT89S52 chip always reports the correct signature when I use the new circuit (with the filters) but when I use the older version (without filters), the chip couldn't be recognized half the time.

Now I'm curious. would my problem be solved if I wrapped plastic wrap around the circuit and aluminum foil as the outer layer and only cut the portion off where I insert and remove parts?

Question

I'm baffled as to what is really going on. I'm trying to make a circuit that can successfully program an AT89S52 everytime.

I made two versions of my circuit. In the first version, I didn't include the components in red boxes (resistors in red boxes before were wires) decouple each IC and it only had 1 100uF capacitor and 1 47nF capacitor (not included in schematic) for decoupling.

This is where things get crazy.

When my laptop lid was still intact with my laptop and I was using my first circuit, everything worked continuously. Sadly the hinges to the lid broke and now I have to use my laptop with an external monitor. I included a picture of my current setup. I then used the exact same circuit with the same software setup and everything else EXACTLY the same, and now I get continuous failures in programming (example: byte verification fails).

So now I took a hunch that maybe with the absense of the lid, the laptop is sending unwanted spikes to my circuit making my circuit think there's extra clocks.

I did some research and then I redid my circuit by adding components shown in red boxes. I did a double-filter setup on the clock line using RC filters (330 ohms for R and 10nF for C). I even made my software write one byte every 100 microseconds while I was on lunch and I still get errors.

The resistors feeding to the VCC pins of each IC are 0 ohms but I wanted to try ferrite beads so I tried them and they didnt work.

I also tried a parallel port extension cable and that gave worse results (couldnt validate signature).

In all other tests (minus those with the extension cable attached), the chip signature can always be read correctly.

Is there something I can do hardware wise to rectify this issue (before I install a new laptop lid) even if it means another capacitor?

The chip number of the other IC I used in my circuit is a 74HC125

Sample of layout used in test


texts:
I am using the BD9C401EFJ for 9V to 5V conversion (with enable pin pulled high). So - input = 9V and output = 5V.

I was just doing some experiments and saw that when I give no input, and I give 5V at the output side pin, strangely I am getting 5V on the input section. I thought that reverse flow of the current is not possible in a DC-DC regulator.


texts:
I'm trying to connect an led light strip in my car. The light strip is powered
via USB, however, just connecting it to the 12 socket with an adapter or a USB port would leave
the lights on all the time. So, I was wondering if it was possible to splice the
USB cable and put a mosfet in to be able to automatically turn the leds off. The source and drain be in between the 5 V USB power or ground and then
connect the gate to a 12 V accessory wire that is only hot when the key is in the
ignition, thus turning the LED strip on and off with the key being in the ignition.

Wondering if this is feasible or if anyone has any other suggestions for how to do this.

Thanks

Like so:


texts: Help identifying a transformer with yellow bobbin and clarifying its purpose

texts: I've a small yellow taped transfomer. It has 6 terminals and one of the input and output terminals are shorted. It has a number (14) on one of the sides. I'd like to know the input and output terminals and also the use of this transformer.


texts: Finding the current dissipated on each resitor

texts:
I'm given a question and part (1 asks me to find the total resistance of a 3.0 and 6.0 ohm resistor when I) in series and ii) In parallel. The answers to those are 9 ohms and 2 ohms respectively.

Now, part B) says that a 4.0 ohm and 6.0v battery of negligible internal resistance are connected in series with the combination In (a)

Now it wants me to find the current, p.d., and power dissipated on each resitor but I'm not sure how. I tried several attempt but they've not been successful.

Thanks.


texts: I am currently working on a project. We have a metal bar as test object and at each end we stuck a piezo disc. I am trying to use one piezo as a sender and the other as receiver or reflector. I tried sending signal and wait for the reflection. However, I do not get any visible difference in the oscilloscope. The idea is to create an impedance matching circuit on the receiver piezo and as it stop receiving then, it starts sending the signal back. Is it even possible?


texts: Is there a color code for relay housings?

texts: I have noticed that most relays have plastic housings that are white/natural, black, or orange. I have also seen blue, green, and clear housings. I am wondering if there is any meaning associated with this color besides marketing or availability of materials. For example, does it have anything to do with whether or not the device is fully sealed or perhaps its flammability? Or is it arbitrary?


texts:
I've been trying to make a program that would continuously read analog values from 3 different pins and then make a PWM signal corresponding to each of those 3 pins. So basically, 3 output PWM channels with different duty cycles corresponding to 3 different analog values. The problem is that all the PWM channels share the duty cycle from what i noticed, but if I ignore the ADC and just set duty cycle in code they work well.
Here's the code:

#define F_CPU 16000000UL

#include <avr/io.h>
#include <avr/interrupt.h>

void selectADCchannel(uint8_t channel);
void initPWM();
void setupADC();

int main(void){

    sei();
    initPWM();
    //start with 0'th channel; no channel selected needed
    setupADC();

    while(1){

    }
}

ISR(ADC_vect){
    //get current channel
    uint8_t currentChannel = ADMUX & 0x0F;
    //set output compare registers for current channel
    switch(currentChannel){
        case 0x00: OCR0A = ADCH;
            break;
        case 0x01: OCR0B = ADCH;
            break;
        case 0x02: OCR2B = ADCH;
            break;
    }
    //loop through channels from 0 to 2
    if(currentChannel == 2)
        selectADCchannel(0x00);
    else
        selectADCchannel(currentChannel+1);
    //restart conversion
    ADCSRA |= 1<<ADSC;
    }

void selectADCchannel(uint8_t channel){
    //0xE0 is 11100000
    //0x1F is 00011111
    ADMUX = (ADMUX & 0xE0) | (channel & 0x1F);
}

void setupADC(){
    //enable prescaler (128 for 16MHz => 125kHz)
    //would probably work with 250kHZ for 8 bits
    //set ADPS bits in ADCSRA to 111
    ADCSRA |= 1<<ADPS2 | 1<<ADPS1 | 1<<ADPS0;
    //enable result shift to ADCH to only read ADCH (8 bits)
    ADMUX |= 1<<ADLAR;
    //enable interrupt
    ADCSRA |= 1<<ADIE;
    //set voltage reference
    //reference is AVcc
    ADMUX |= 1<<REFS0;
    //turn on ADC
    ADCSRA |= 1<<ADEN;
    //start conversion
    ADCSRA |= 1<<ADSC;
}

void initPWM(){
    //TIMER0 (8 bit timer)
    //set pins 5D(OC0B) and 6D(OC0A) as output
    DDRD |= 1<<DDD5 | 1<<DDD6;
    //set fast-pwm mode
    TCCR0A |= 1<<WGM00;
    //set non-inverting mode for both pins
    TCCR0A |= 1<<COM0A1 | 1<<COM0B1;
    //set prescaler to 256
    TCCR0B |= 1<<CS02;

    //TIMER2 (8 bit timer)
    //set pins 3D(OC2B) as output
    DDRD |= 1<<DDD3;
    //set fast-pwm mode
    TCCR2A |= 1<<WGM20;
    //set non-inverting mode for both pins
    TCCR2A |= 1<<COM2B1;
    //set prescaler to 256
    TCCR2B |= 1<<CS22 | 1<<CS21;
}

So, what the program should do, after initialization, read the value from one of the ADC pins, and then set the PWM compare register of the corresponding pin to the ADCH value.
Thanks.


texts:
Is it OK to use a zener diode in series?  Normally I see them across the output of a power source to limit the voltage to the value of the zener.

Putting it in series instead should reduce the voltage by the value of the zener, yes?  (so a 5V zener on a 12V supply would give a 7V output).

The thing is, I have a -12V supply and I need a -5V (or near, -7 will do - I have added a couple of Si diodes to drop the voltage a little more) supply from it - BUT - I don't want to lose the -12V supply (that is needed for other parts of the circuit), and I don't have any negative regulators, only positive.

I have tried it and it appears ok, but will it cause problems if I leave it like that?


texts: What happens if the secondary of an ordinary transformer is left open?

texts:
Let's consider a transformer. The ideal transformer equation is:
$$\frac{V_1}{V_2} = \frac{I_2}{I_1}$$
Suppose the secondary is open (that means \$I_2 = 0\$): it will result \$I_1 = 0\$. How is this physically possible?
I'd say that, also in case of absence of losses, there must be a current in the primary circuit. In fact, the primary circuit is a normal closed circuit, (voltage source closed on transformer primary winding), so I'd say that there will be the current that will flow if the secondary circuit does not exist.


texts: Why does a pull down resistor eliminate floating input

texts:
Ever since I connected a button to an Arduino for the first time, I've wondered how does the resistor prevent floating input from happening? I've read several answers to similar questions, seen videos and read forum posts:

https://www.quora.com/What-is-a-floating-input-gate
"We say it's left to float, which means it's in an indeterminate state: maybe high, maybe low, maybe somewhere in the middle. Worse, it may even change depending on other conditions in the environment." This just explains what it is. Which is fair, since that is what the person asking, asked for.

https://forum.arduino.cc/index.php?topic=378402.0
Same as above.

https://www.youtube.com/watch?v=wxjerCHCEMg
This video goes into a decent amount of detail about what causes floating input, i.e. outside electrical sources, and how to solve it, but does not address why adding a resistor eliminates this noise.

Everything I read on the internet just answers the same questions over and over again. I already know why you use a pull-down resistor ( or a pull-up resistor), to eliminate floating input and to prevent a short (in the case of a button). I already know that floating input is a result of electrical noise. But if someone asked me "so why does adding a resistor make the floating input go away?", I don't know how I would explain it to them, other than "it just does".

I wasn't sure whether I should post this question here, or in physics.stackexchange. I feel like this question is well within the domain of both sites, so I just picked one.

Edit: I do not feel this is a duplicate of What is a pull up and pull down? Because even though the information I am after is within the scope of that question, it does not provide it. I am not asking what a pull up or pull down is. What I'm asking is why does a resistor in a pull up / pull down eliminate floating input.


texts:
I'm back with yet another mystery.

Summary question:

Why would an input to a voltage clamped circuit de-stabilize and or elevate that voltage clamp's upper rail?
How do you properly clamp voltage using a lightly loaded LDO supply?

How I got here:
I'm in the middle of developing a sensor for use in the field.  I'm trying to make this thing robust, so I've added diode clamps to all the inputs with access to the outside world.  The diode clamps look like this (input is on the left side, and is fed into an xbee IO port):

The system runs off of a solar source etc so I've got a switching regulator (LMR1403), cascaded onto an LDO (MCP1802) to run everything.

While performing my due-diligence and testing the voltage clamps, I noticed something odd:

yellow = clamped line
blue = function generator input
green = regulated 3.3v:

The test input that I sent into the circuit was "raising" the power rail, thereby causing the voltage clamp to fail (since the diode only holds the input to the rail).  The test input was fed with a function generator, 1khz, varying amplitudes, but obviously amplitudes greater than 3.3v.

I simulated the circuit in LT Spice until I could recreate the problem.  I used a similar LDO from LT instead of from MCP.  I assumed (perhaps in arrogance?, but oh well) that most of the low-power LDO designs were fundamentally (hopefully) the same.  Below is my simulation.

It seems that I've correlated at least 2 possible issues:

Insufficient resistive load.
Insufficient capacitance on the output rail.

If I mess with either of those in simulation (make them too small, or rather "too big" for the load) I can cause very similar situations to occur.  I checked with my circuit, and added more resistive load (circuit runs 30mA), and a MUCH larger output bank capacitor (I only had a 47uF ceramic on hand to swap out with the 1uF that was there) and both "solve" the problem at small input amplitudes, but both still fail for large inputs (20V p-p waves).  The wave is properly rectified for the ground loop, but fails to be contained within the regulated 3.3v.

In an attempt to triple check everything, I patched in a bench supply to the 3.3v rail and it behaved in a similar manner.

So my question is basically this.

How do you protect against lightly loaded circuits?  Like, say, a sleeping microcontroller that is only drawing uA.
Am I missing something fundamental in my voltage clamp design? (I hope so).
Should I not be using an ldo for this case?  I am starting to question whether I should just readjust my switching regulator to feed the circuit 3.3, but was worried that it would not be stable enough for XBEE operations.

Many thanks.  I am forever learning new things.
Matt

EDIT:

Design Rev #2.
I've thrown in a TVS diode for extreme spikes, then increased the value of R22 to limit the current intake through the circuit (thereby reducing the voltage raise).  Here's what I've got now:

I'll adjust C1 accordingly for how fast a rise time I need on the signal.  Thanks.


texts: Does a CR2032 take damage when connected to a 5V rail?

texts:
I've seen applications (Nintendo game cartridges, for example) that uses a coin cell battery for backup power to some RAM-chips (for savegames). When the ordinary 5V is gone, the battery takes over and lets the IC retain its contents.

However, won't the CR2032 (3V) take damage when connecting it to a power rail that contain almost its double voltage? Or is there some overvoltage protection within the coin cell that shuts it down when external voltage is applied?

Or how does it work?


texts:
Ripples from Mutable Instruments (open hardware) is a low pass 4th order filter. The schematic is found here https://mutable-instruments.net/modules/ripples/downloads/ripples_v40.pdf

Can I swap resistors and capacitors in the signal chain to create a high pass filter?
eg R10, C7 swapped with R8, C6

I would do this is Sallen and Key configuration but the inclusion of the OTA and VCA ICs makes me question what would be the right conversion.


texts:
These are the equations for finding lower cutoff frequencies for a BJT common emitter amplifier:

In finding the cutoff frequency, capacitor impedance must match the resistance so that output voltage from the resistor is Vout/sqrt2(half-power) .
However, why is that: $$f_B=\frac{1}{2\pi(R_s+R_{in} ) C_{C1} }$$

As illustrated above, Vout depends on the voltage drop on R_in only and not on R_s(or R_g). The voltage drop on R_s is wasted just like the drop on the impedance of the input coupling capacitor. Then why is that X_c must match the R_s+R_in if Vout only depends on R_in?
If X_c must match R_s + R_in, then Vout at R_s+R_in at cutoff frequency is Vout/sqrt(2) BUT that is the drop on BOTH R_s and R_in, the drop at R_in(where we are getting the output voltage for the base of transistor) is less than Vout/sqrt(2). This means the cutoff frequency is not right.
I can also say the same thing on the lower cutoff formula for the collector capacitor in which R_l is added to R_c BUT output voltage ONLY DEPENDS ON R_l(load resistor). If I use that formula, then the output voltage at load resistor will not be Vout/sqrt(2) since some of the voltage will also drop at R_c.... (I understood that at this part, I need first to convert the Norton current to thevenin so that R_c will be in series with R_l)
The book and the site says the same thing but I don't know what am I getting wrong here
Source: https://wps.prenhall.com/chet_paynter_introduct_6/0,5779,426214-,00.html


texts: Why am I receiving a Modem Status (0x8A) on broadcast messages (XBee)?

texts:
I am sending a Remote AT Command Request in broadcast (without ACK - frameID = 0x00), from my Coordinator API, to set the CB command to 1: this simulate 1 commissioning button press in software of the remote device in order to receive a Node Identification Indicator.

When I send the first packet:

7e 0 10 17 0 0 0 0 0 0 0 ff ff ff fe 1 43(C) 42(B) 1 66

I receive the following Node Identification Indicator frame:

7e 0 27 95 0 13 a2 0 40 aa d0 6 f9 5d 2 f9 5d 0 13 a2 0 40 aa d0 6 52 4f 54 45 41 44 4f 52 0 ff fe 1 1 c1 5 10 1e 7f

but, if I send the same Remote AT Command again (CB command with parameter 1), I get this two Modem Status frames:

7e 0 2 8a 1 74
7e 0 2 8a 6 6f

The first one means a Watchdog timer reset (1), and the other means a Coordinator started(6). I checked the voltage over my XBee and it's everything ok (3,3V), so is it not supposed to reset?. If I send the Remote AT Command again (a third time), I will get the Node Identification Indicator frame. And sending a second time (fourth time), I get the two Modem Status frames. Then, is keeping repeating..

Why this happen? I had to send twice in order to get the response I wanted.

EDIT

I am using XBee Series 2


texts: Unexpected current reading when powering LED from ATmega328p IO pin

texts:
I would like my LED to run at 40mA (max current for ATmega328p IO pin). The LED datasheet says that 2.2V is max forward voltage. I am trying to calculate which resistor to use.

According to the calculations I have done, 3.3V (voltage of IO pin) - 2.2V (max voltage of LED) = 1.1V. 1.1/0.04 = 27.5 Ohms. I only had a 33 Ohm resistor and that would mean I should get 33mA. I got about 30 according to the multimeter, so roughly correct.

When I powered the LED from the IO pin, I only got 17mA. What's going on here? Should I decrease the resistor value until I get the 40mA I want, or is this dangerous for the chip?

Thanks.


texts: What does this symbol in the schematic represent?

texts:
I know the symbol at the bottom is ground, but I can't get what the other symbol is. It can be a single symbol of two arrows pointing at each other, or two symbols each one a arrow.

I also have the PCB for this schematic. It is nothing but two traces (1mm long) with a little gap in between. Is it a RF filter of some sort?


texts:
I've just started studying basics of signals and systems.
I have trouble understanding fundamental period of composite signals.The examples are below.
1) X(t)= \$\\2cos(t)\$ + \$\\cos(t/3)\$
I've found out the individual periods.T1(Period of Cost)=2\pi
and T2(period of cos(t/3))=6\pi

Now T1/T2=1/3 and the period of resulting signal is 6\pi

The author has stated that T1/T2 has to be a rational number always.
If not then the resulting signal is not periodic.And he says that L.C.M of 2\pi and 6\pi is 6\pi (I was confused here as LCM does not apply to irrationals)
And Why should the ratio T1/T2 always be a rational number?


texts: Modeling the elevator as a finite state machine

texts:
This is my first post here. Nice to meet you all!

I've read a related question here and am still having issues.

The task:

There is a building consisting of 7 storeys (indexed 0-6). Design a system that controls the elevator in this building.

Design details:

There are navigation buttons in each floor (up / down).
Inside the elevator there are buttons to select the destination. (For simplicity, can I assume that only one destination can be selected)
Seven segment displays indicate the position of the lift. These are present in each floor and inside the elevator.
There are LEDs to indicate the direction of movement of the elevator in each floor. (arrows, I presume?)
There are buttons inside the elevator to control the fan and lights. (Fans and lights are OFF by default . They turn on automatically if the lift is in motion).

What I've done so far :

System #1: Controlling the seven segment display

Let the elevator be in floor 'x'.
For the destination selection (say y) from inside the elevator, we use an encoder to obtain the destination floor in binary. We then pass it on to the controller which compares x and y and decides the direction of movement. As it moves, keep updating x and send it to the seven segment displays in each floor and inside the elevator.

System #2: Fans and lights. Default state : OFF. If the destination is selected, turn ON. Switch ON/OFF as per the passenger's choice.

System #3: The movement control unit (This is where I'm having issues):

Since we are modelling the elevator as a finite state machine, I have the following states.

Rest: (RST)
Moving up (UP)
Moving down (DOWN)

The following changes cause state transitions:

1.The elevator is called from one of the floors.

2.The destination has been reached.

3.The destination has been selected.

Case #1: The destination has been selected (y). If y > x (current floor) then UP. else if y

Case #2: The elevator is moving from say, the 3rd floor to the 6th floor. Someone at the 4th floor wants to go down. At the 5th floor, someone wants to go up. The obvious solution, halt at floor 5. go to floor 6 and then go to the 4th floor.

Issue #1: How do I handle the priorities ?

Issue #2: How do I store the information ? (I'm aware of flip-flops and related memory elements. Not sure about the finer implementation details)

Issue #3: How do I encode the states and create the state transition table ? (I'm not able to visualize it.)

PS: Since the question was worded ambiguously, I think it is safe to make some assumptions to simplify the problem.

Help would be greatly appreciated. Thanks in advance.

EDIT 1: For the movement control unit, there are 19 inputs (1 each from floors 0 & 6, 2 each from floors 1-5, 7 from inside the elevator) and 1 output signal to the motor (UP, DOWN).


texts:
I am making a PCB design of buck converter 30-50V to 12V using the Max5033 IC.
https://datasheets.maximintegrated.com/en/ds/MAX5033.pdf
This is the first time, I am doing a PCB design for a converter so I would like some guidance.(online I already read a few pcb design guidelines)

I am not sure of the location of C27 (the output capacitor).
At first, I had it on the lower side(same layer) of the IC to have it closer to the Inductor and especially the input capacitor for the return current path during on-time.
But then I visualized that the IC would be in the center of the loop for both the on and off time, thus I replaced it to the top side.
Is my reasoning correct?
In the datasheet they recommend to have star point ground connection. I have tried to make such a connection by connecting the ground of the IC (pin 3 and 6) to the input capacitor ground. But I am not sure if this the way to do and if this is the best location to make the connection. For example If I would connect it to the anode of the diode the trace would me shorter.
Is this correct?
Any more recommendations on the layout is highly appreciated.

NOTE: please do not comment on the component values as those might not be correct in the attached schematic

EDIT : Based on the answers and comments below I have made some changes
I have reduced the trace of the switching node and I increased the width of the traces which carry the load current , in particular the GND node.

Can you comment on whether the grounding is correct?  (star point)
And I am bit unsure whether I should decrease the size of the trace of the LX pin. I have read that the switching node can act like a antenna, so the area should be kept small at the same time the application node says to use LX (among other pins) for thermal management.


texts: Do I really have to cast float to uint8_t if I just want to convert 203.0 to 203 at a microcontroller?

texts:
In computers, it's OK to use float as an argument where the argument should actually be a uint8_t
void myFunction(uint8_t myVal);

But what if I call this function myFunction(value); where value is of datatype float inside a microcontroller? The microcontroller have single precision included. The variable value have its range from 0 to 250 in this case.
Do I need to call my function myFunction((uint8_t) value) ?


texts: Resolution enhancement for a 2wire PT100 setup with ADC and no external amplification

texts:
I'm working on a PT100 based temperature probe sensor to read temperature difference between two points inside a pipe with flowing water, the requierements are:

1mK resolution over 0-45C range.
dual PT100 setup to detect calibration discrepancies.
0.1C absolute accuracy would be optimal but what is actually important is getting reliable differential readings between matched probes.
RS485 communication.

Restrictions I have:

The PCB can't be bigger than 100mm diameter to fit into the probe's head and since I need a 2xPT100 setup o don't have space for signal conditioning + ADC for both so I have to rely on high resolution ADC only.

What I have on the design table so far:

I'll be using a 2xPT100 DIN 1/10 for max accuracy (+-0.006 C error at 45C) with a 22 bit delta-sigma ADC (ENOB:21.9 but actually 20.9 since it uses two's complement output). This is the simplified circuit of one probe that show how both PT100 interface witch the ADCs and the MCU:

EDIT: Just to clarify, the PT100s inside each probe need to be compared against each other (in the MCU) so it can be detected when the probe needs calibration. Then temperature between probes must be compared to know the temperature difference between points.

For this circuit I get a signal that varies 12.6572mV from 0 to 45C (100-117.47 Ohm), then I get 2.27mK resolution and a 1.54mA current through the PT100, If
I wanted to go down to 1mK I only see two solutions:

Use a lower value for R1 to get more resolution and also lower Vref/Vex to adjust the  current trough the RTD

e.g: R1=500Ohm for 0.975mK resolution and Vref/Vex= 1.024V for 1.65mA

Keep the R1 and Vref/Vex values and get more resolution trough Oversampling and decimation method. The PT100 response time T90 typically is no less than 3 seconds so even with the 13SPS offered by the MCP3551 I think I should be able to get those extra 1.2 bits I need but I'm not sure.

Is there anything else I could do to improve the resolution?

I've selected the MCP3551 ADC because it's ENOB is pretty high 20.9 against all those 24bit sigma-delta ADCs out there that have no more than 19 ENOB,
and besides, It's just an 8pin SOIC IC so if someone can suggest a non massive ADC that outperforms this one I'm open to change it.

If you have any question about the problem, please ask, if I've left any important information behind or think I could elaborate more, please ask.

EDIT: I add the whole system sketch

EDIT2: I've been suggested to use  ADS124S06, It provides around 23 bit resolution without enabling the PGA,I could also enable the PGA and meet common-mode specs because this IC allows to connect the PT100s in parallel and use the voltage through Rref as level-shift. The downside is that it's a 32pin IC so routing it could be a nighmare...


texts:
I am interested in adapting this Jameco kit schematic to my own needs. I have run into an issue though. I am not sure how to lower the voltage requirements. This circuit is built for 12V, I would like to power it with between 3.3 and 5 volts, specifically from a lithium-ion battery.

My question is specifically about the various op-amps used in the circuit.

The MC33204P Datasheet says that the minimum supply voltage is 1.8V (+/- 0.9V) and the maximum is 12V(+/- 6V). I realize that this means that I can use a 3.3V supply, but how much do I have to change in terms of the resistors and capacitors, if anything at all?

The MC34072P Datasheet does not mention a  minimum supply voltage as far as I can see, although I may be mistaken.  One of the graphs showing supply current vs supply voltage, starts at 1V. Will this op-amp work as intended with the resistors of the original schematic? Will is work at all? Should it be replaced?

I do not plan on following the schematic past the transistors.


texts: How to change the frequency of PIC internal oscillator?

texts:
Internal oscillator of PIC16f884 doesn't change frequency in the following code:

#pragma config BOREN=0,IESO=0,FOSC=INTRC_NOCLKOUT,MCLRE=1,WDTE=0,CP=1,LVP=0

volatile unsigned char counter = 0;
void setup( void )
{
  ANSEL = 0x00; // all digital
  TRISD  = 0x00; // all RD is output

//
OSCCONbits.IRCF2 = 0;
OSCCONbits.IRCF1 = 0;
OSCCONbits.IRCF0 = 0;
OSCCONbits.SCS = 1;

while(!OSCCONbits.HTS);

//interrupt timer0
IRCF0 = 1;
IRCF1 = 1;
IRCF2 = 1;

}

No matter what values I assign to OSCCONbits.IRCFx the clock speed (as measured with a blinky light) never changes... The only other way that this could seem to behave this way, is if _delay were to somehow adjust for constant time rather than clicks, but I don't think that is the case.

EDIT: I am dumb...

why doesn't this work

int i = 0;
int *p = &i;
i = 0 // no matter what i change this to i is always one.... dumb
*p=1


texts: I need a pcb gps and a gprs antenna. But their size is very important. I'm thinking about fitting those into a leather dog leash. What can I use for this purpose?


texts: Which schematic should I use with CNY 70?

texts:
I have tried this three schematics (pictures below), and they all seem to be working mostly the same. So I can't choose which one to use, and what are the advantages/disadvantages. Any ideas ?
P.s. I use CNY70 as light sensor, and the MCUpin goes into Atmel AVR microcontroller digital input.


texts: Will reading serial flash memory wear it out?

texts:
I know that a flash memory has limited write cycles. Does it also have limited read cycles?

Datasheets of most serial flash memories (like SST25VF series) mention endurance cycles. Does this endurance mean read + write cycles?


texts: Can I run an electronic piano using a power bank?

texts:
I have a Yamaha P-140 electronic piano. Looking at its power adapter, I see the following info:

Input: 230V~ 50Hz 170mA
Output: 12V (strange symbol here, something like an equal sign =, but with dots in the lower line) 1.5A

I have a new, massive power bank with 45000mAh that I can charge laptops with, so it has a lot of adapters. And I wonder whether it could be used to run the piano as well? Its specs:

Switchable output: 12V / 3A, 16V / 3A, 20V / 3A

What do you think? To me (as an absolute newbie to this topic), the option 12V / 3A looks very close to the needed 12V / 1.5A, but maybe it would require to match perfectly? Or 3A is the max, and 1.5A would fit nicely? I really have no idea.


texts: driving a relay with transistor and Opto-isolator

texts:
I am very new in electronics. I am controlling a relay with stm32 micro controller.  For the isolation I have used a 4N33 opto-isolator. As my relay coil needs around 250 mA, I used a mps222 transistor. I figured that the logic gets inverted when I used the gpio as the source voltage for the opto-isolator led. I just used a pull up instead and connected the other end of the led part to the gpio. Gpio is  open drain, I will drain around 3mA in the pin.
I do not have the R2 resistor grounded at this moment.
My problem is if in case my stm gets disconnected then my relay will be turned on - which I want to avoid. Could anyone please tell me if adding this R2 will fix the issue?


texts: Strategies for managing code size - PIC18 XC8

texts:
I'm new to embedded C development and I'm looking for some general principals/guidelines for managing the size of the generated code.

In my specific example I'm using XC8 on a PIC18F4550. My code so far uses about 13% of the space. Once I use "time.h" and 1/2 functions from it, the usage jumps to 45%! I realise that the free XC8 compiler does not optimise but I'm still very surprised to see just how much space is used.

What I'm looking for a tips / staring points along the lines of

Alternatives to the standard libraries that implement on small targeted subsets of the functionality. E.g. a date/time lib. i.e. are there repositions I can get useful routines from?
How to see what is using all the space. (Listing/map files - and tips for analysing them)
Any other tips / resources.

EDIT:
I found a nice implementation without using stdlib here: https://codereview.stackexchange.com/questions/38275/convert-between-date-time-and-time-stamp-without-using-std-library-routines

The general question still stands though. Are there guidelines, good repository sources etc


texts:
in university we had our internal program called HLCCAD - it was very nice, and now I need to do design & debug some digital circuit and wondering what is current state of art software for that kind of things (price is out of consideration for now)?

I.e. I want to visually place components, and then simulate it.

Manually writing VHDL code & looking at simulation traceouts of specific nodes is not enough.

Any suggestions?

Update: Found Logisim - this is exactly what is needed. Are there any commercial alternatives with more horsepower?


texts: Set DDR and PORT registers based on pin number (AVR)?

texts:
I'm writing an initialization function on an ATTiny441 to set the data direction register (DDR) for Port A or B based on the physical pin number.

So far my implementation seems a bit clunky.  Below is the initialization function in nrf.c that I'll call in main.c:

/* nrf.c */
#import <avr/io.h>
#import "t441.h"

bool ce_port_a;
uint8_t ce_bit;

void nrf_init(uint8_t ce_pin,
              uint8_t csn_pin)
{
    /* Map CE pin */
    t441_map_pins(ce_pin, &ce_bit, &ce_port_a);

    /* Set CE to output */
    if(ce_port_a) DDRA |= BIT(ce_bit);
    else DDRB |= BIT(ce_bit);

    /* Clear CE */
    _nrf_toggle_ce(0);

    /* ... */
}

In the same nrf.c, here's the function used to toggle the CE pin:

/* nrf.c */
void _nrf_toggle_ce(uint8_t direction)
{
    /* Set CE */
    if(direction) ce_port_a ? SET_BIT(PORTA, ce_bit) : SET_BIT(PORTB, ce_bit);
    /* Clear CE */
    else ce_port_a ? CLEAR_BIT(PORTA, ce_bit) : CLEAR_BIT(PORTB, ce_bit);
}

(Note the SET_BIT() and CLEAR_BIT() functions are defined elsewhere, but I assume that they're descriptive enough.)

And, finally, here's the function in t441.c that maps the physical pin number to a Port and bit number:

/* t441.c */
uint8_t t441_port_b_map[4] = {0, 1, 3, 2};

void t441_map_pins(uint8_t pin_num, uint8_t *port_pin_num, bool *port_a)
{
    if(pin_num < 6)
    {
        /* Pin is on Port B */
        *port_a = false;
        *port_pin_num = t441_port_b_map[pin_num - 2];
    }
    else
    {
        /* Pin is on Port A */
        *port_a = true;
        *port_pin_num = 13 - pin_num;
    }
}

Question: Is there a simpler or more elegant way to approach this?  I'm somewhat concerned with program memory usage but mainly with code re-usability -- e.g. having to significantly change things if using a microcontroller with more than two IO ports.

(I'll move this to Stack Overflow if appropriate.)


texts: Why is this solenoid valve consuming so much power?

texts:
The circuit below drivers a pump and a valve, the pump works fine, the valve consumes much more current than I'd expect.

The valve is rated 2W at 12V (600mA) i'm more like 15W. The PUMP_DRIVE signal isn't PWM, interestingly using a PWM signal with D = 0.5 doesn't even turn it on.

What am I doing wrong? Do I need to add current limiting?

Solenoid Valve


texts: What is the polarity of this barrel plug with a double circle?

texts:
Related but doesn't answer my specific icon: How to tell polarity expected of a DC barrel jack?

I have a dell laptop barral plug adapter, and I can't tell from the graphic whether the tip is positive or negative. It looks like the tip has nothing, and there are two outer shells, based on the icon, but I don't think that's how I'm supposed to read it.

Can someone tell me how to interpret the polarity?


texts: The meaning of Cross and Auto Correlation Matrices

texts:
I have to make some system where I have an input signal (i) and and feedback signal (f) and from this I create a autocorrelation Matrix (ACM)  where ACM = i*i and cross-correlation vector (XCV) where XCV= f*i.

From this I get a set of linear equations ACM*x= XCV and I need to find x.

With the x I can update some filter taps and ensure the signal is manipulated enough to ensure it is not distorted too much, hence that x is used to pre-distort the signal.

I understand how it works but not why.

Does anyone have any information on how using the matrices like this we get meaningful coefficients, what exactly do those coefficients represent?

What is the purpose of autocorrelation and cross-correlation.  Basic questions, just starting some stuff with DSP.


texts: Cancel latching hall effect sensor effect

texts:
I want to use a hall effect sensor to detect when a door is close or not; the sensor would be in the door frame, and a little permanent magnet would be on the door. However, I learned that the sensor I got is latching: at first it outputs 0, when I bring the magnet in the right direction it turns 1, and when I remove the magnet it stays 1.

For my project, I want the sensor to turn HIGH only when the magnet is close to the sensor. To solve this, I could probably get a different non-latching hall effect sensor, but I wanted to know if there was a way to do this with the current sensor I have.

I thought about using a 2nd magnet that would by default make the sensor output 0, but would not be powerful enough to compensate the field generated by the magnet on the door.

Better ideas? Is it worth it?


texts: What is the significance of 111 in clock speed?

texts:
Never really thought about it until recently, but it looks like the number 111 appears very frequently in clock speeds and such: the first example that comes to my mind is one of the handheld game consoles that came with 333mhz CPU (usually downclocked to 222 for battery life), and RAMs also sometimes come with clock speed that are multiples, or at least close to that of 111 (333 for PC2700, 2,666 for DDR4 2666.)

To me, the numbers that are powers of 2 seems very logical, but 111 really looks like it just came out of nowhere but I can still find them rather often. Is it just a pure coincidence, or is there any historical or mathematical background to it?


texts: Is it safe to apply voltage to the output of UA78M33CDCY regulator?

texts:
I'm working on a project where I want to program a dsPIC33E. My board integrates an UA78M33CDCY linear regulator and I want to program the controller by powering the target from PICKit3.

Is it safe for the regulator to apply 3.25V from the PICKit to its output?

I mention that the regulator is connected as recommended in the datasheet (with two decoupling capacitors), without any additional components and the board is powered only by the PICKit. The functional block diagram of the regulator is given at page 10 of the datasheet.


texts: Ethernet RJ45 diagnostic port beside LSA+ block

texts:
I have a remote logging device that has an LSA+ block on the PCB for a 100Mbps Ethernet cable to the router, 50m away. Right beside the LSA+ block is an RJ45 socket, which the document says is "for local diagnostic purposes that is directly in parallel with the LSA+ block, so don't connect to both ports simultaneously".
When I first arrive on-site, it is easy to unplug the remote end of the Ethernet cable from the router before going to the logger, connecting to the local RJ45 port, do the diagnostics with the front panel, and restore everything before leaving again. But while I'm connected to the local RJ45, I can't help thinking that there's this 50m antenna for each of the four RX/TX wires that is just inviting interference. I mean it works all right, but still...
I'm thinking I could easily make a little RJ45 socket box with termination resistors that I plug onto the remote end of the Ethernet cable after unplugging it from the router. But what value(s) should the RX and TX resistors be, given that there's no ground reference?
Or is this a truly unnecessary step?


texts: How to shorten the width of a single pulse

texts:
I want to shorten the width of a single pulse to 50ms or 100ms width. For example, a circuit generates a positive pulse of duration 1 sec and I need to reduce its width to 50ms, synchronized to the rising edge of the input pulse. How can I do this?
Thanks


texts:
I have the following schematics:

If I have a scope probe on VIN, everything works very well. VIN is an amplification of the input and the ADC reports it very well: good accuracy and no delay. But if I don't put the scope probe on VIN, the measurement is problematic and if input drops VIN takes a lot of time to follow. In other words, the scope makes work the circuit. Any idea what I should modify?


texts: Auto Switching Between Battery Power or USB with a SPDT Switch

texts:
It is hard to fit everything in my title so please read ahead to understand the whole thing. I am trying to design a circuit that can meet a few requirements but having a lot of trouble trying to make it work.
The design uses a SPDT switch to either power on or off a device.
When the SPDT switch is turned on, the device will be powered from either a 3.7V LiPo battery or USB power depending on whether the USB-C port is plugged in or not.
When the USB-C port is plugged in and providing the 5V, the battery will be recharging from it regardless whether the SPDT switch is on or off.  The battery will also stop providing power to the device when the USB is plugged in and the device is turned on.
If there is NO USB-C plugged in and the SPDT is turned on, the battery power will provide the nominal 3.7V to a 5V boost IC before providing the power to the device. But the battery cannot provide current flowing back into the recharge circuit (i.e. prevent the battery from trying to recharge itself).
I thought of one way that might work using a combination of enhancement and depletion N-channel MOSFET. A picture of it is attached below.

Here is my logic behind it. UVCC is the VBUS line from the USB port.
If the UVCC line is 5V (when the USB is plugged in), there is enough voltage from the divider (R1 & R2) to turn on Q1, allowing the USB 5V to connect to the LiPo battery recharge/protection circuit. It will also turn off Q2, cutting off the 3.7V nominal voltage from the battery to the UVCC line. Q3 will turn on and Q4 will turn off. Thus, allowing UVCC (5V) to go directly to the device when the power switch is on.
When the USB is NOT plugged in (UVCC < 4.2V), Q2 will be turned on and allow the LiPo Battery to provide current. Q1 will be off to prevent the battery from trying to recharge itself. Q3 and Q4 will be off and on, respectively. Thus, the battery current will flow into the 5V boost IC before going to the device.
I’d appreciate any feedback on this design as well as any suggestions of other circuit design that can meet the requirements described above.
Thanks!
EDIT: Here is a truth table to help understand the requirements


texts: Why is my instrumentation amplifier's gain non-linear?

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I am using an AD8226 instrumentation amplifier as the pre-amp in a circuit which uses a micro fuel cell oxygen sensor to measure oxygen content in a gas stream.  The pre-amp is configured in single ended supply mode, with a 5 V supply.  Gain resistor was chosen to give a gain of ~80.

The output of the in-amp is then passed through an active low pass filter and to a microcontroller's ADC, but I don't believe this is relevant to the problem.  Everything discussed here was done with the preamp outut (O2_PRE node in the diagram) floating and only connected to a multimeter.

When testing this circuit with the sensor I found that the gain was nice and linear - up until a certain point where the gain dropped off (this point was at about 20mV input/1.6V output).

To eliminate any issues with the sensor I replaced the sensor with a voltage divider made up of a fixed reisistor and a multi-turn linear pot:

With the resistor network I observed the same problem (see further down for a plot of the inamp output).

To further eliminate any issues with the surrounding circuitry I wired directly up to the AD8226, using my bechtop supply as VCC.  Giving the circuit seen here:

This showed the same behaviour as seen in this plot:

('mainboard' refers to the output when the voltage divider is used to drive the original circuit, 'breadboard' gain is slightly lower as I used a 630R gain resistor)

The AD8226 data sheet specifies an output voltage swing of 0.1 V to +VS−0.1 V in single ended mode.  I am measuring the output into a high quality multimeter (ie. high impedance), although I did observe the same results when I added a load resistor of 20 K. I have repeated the results with multiple AD8226 devices.

Can someone explain why the gain would be falling off above a differential input of ~20 mV given that I seem to be staying well within the output limits?


texts: Are these circuits equivalents (caps in parallel with VCC)

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I need to put 2 capacitors for decoupling in parallel with the power (5V).

In some guide of my project I did found schema "A", in other schema "B".

Are both equivalent and in parallel? Or only the schema A is parallel and B is in serie? (In Eagle board, but not in schema, I did omit GND for simplicity)

Thank you very much


texts: Solutions to reduce start-up currents from multiple DC motors

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I have some DC motors (8) which are connected to the same power supply (Murata, 12V, 20A), each motor needs 1A and is driven with a MOSFET. When I start these motors at the same time (a need for my application), I have a big start-up current. The voltage falls and the automatic over-current control of the power supply is triggered.

How can I properly start these motors at the same time? Does it need a bulk capacitor? Which size?


texts: PWM motor controller to switch down voltage on a boat

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I'm planning to use a bank of 4 x 12V batteries in series on my boat in order to provide 48V to power an electric DC motor. I also need 12V power for things like lights, fridge, etc. I thought of hunting around for a 48V to 12V buck convertor to provide the required 12V for my appliances. However someone suggested I could use inexpensive PWM motor controllers which would allow me to adjust the voltage down.

http://www.ebay.co.uk/itm/331044576419?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

As these are only rated at 15A current I suppose I could use 2 or more depending on my currency needs. So  could put the lights on one controller, then the fridge on another, etc. Does this sound viable or am I going down the wrong path?


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I have some errors during debugging I2C chip. I took an oscilloscope and found some strange artifacts on the log:

Maybe somebody has a suggestion about such questions?
1. What are these strange spikes at the beginning of each clock cycle?
2. Why SDA data ground level have different values?


texts: Electromagnet interference with motorcycle

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I just got a sport bike which the frame is aluminum the engine is aluminum the swing arm as well. Basically this bike is made up of mainly aluminum and plastics with very little steel or any other metals. I have run into the age old problem of getting caught at traffic lights and not triggering the sensors in the pavement. My understanding of how those sensors work is they are nothing more than just a large metal detector and since aluminum and plastic don't do well with metal detectors, I get stuck at the lights waiting for days for it to change or hoping a car or truck pulls up to trigger the light.

My solution to this is to mount a 20kg pull electromagnet to the bike and turn it on while sitting on top of the sensors to trigger them.

So here is my question to this (multi-part)
Is this just a moronic thing to even attempt and a waste of time?
If it is not a waste of time, then do I have to worry about shielding the magnetic field so that it only goes downwards? I'm afraid the strength of the magnet may cause issues with the electronics on the bike, but I may just not fully understand electronics and magnets (which is why I am here).

Sorry for my long winded question
I am providing a link to the electromagnet I have below.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270624517539