texts: Why do some microcontrollers have such huge synchronization delays?

texts:
On the Atmel SAM-D21 series microcontrollers, many peripherals use a clock which is asynchronous to the main CPU clock, and accesses to these peripherals must go through synchronization logic; on peripherals whose clock is slow relative to the CPU time, this can add some really huge delays.  For example, if the RTC is configured to use a 1024Hz clock (as appears to be the design intention) and the CPU is running at 48Mhz, reading the "current time" register will cause bus logic to insert over 200,000 wait states (a minimum of five cycles of the 1024Hz clock).  Although it's possible to have the CPU issue a read request, execute some other unrelated code, and return 200,000+ cycles later to fetch the time, there doesn't seem to be any way to actually read the time any faster.  What is the synchronization logic doing that would take so long (the time is specified as being at least 5 ⋅ PGCLK + 2 ⋅ PAPB and at most 6 ⋅ PGCLK + 3 ⋅ PAPB)?

By my understanding of synchronization, a single-bit synchronizing circuit will delay a signal by 2-3 cycles of the destination clock; synchronizing a multi-bit quantity is a little harder, but there are a variety of approaches which can guarantee reliable behavior within five cycles of the destination clock if it's faster than the source clock, and only a few cycles more if it's not.  What would the Atmel SAM-D21 be doing that would require six cycles in the source clock domain for synchronization, and what factors would favor a design whose synchronization delays are so long enough as to necessitate a "synchronization done" interrupt, versus one which ensures synchronization delays are short enough as to render such interrupts unnecessary?


texts: Use BLE instead of RFID for race timing system

texts: I've never studied electrical engineering, although lately I'm been increasingly curious about race timing systems. According to the research done so far, usually they use RFID systems to monitor when the athletes cross certain points in the circuit. I'm been wondering if it would be possible to create a similar system by using the increasingly popular BLE technology. As far as I know, BLE beacons emit a signal every x ms, so right from this point I know the readings would not be very accurate when lots of athletes crossed the line at the same time. Anyway, for the points where the order of the athletes is not relevant, would it be a viable option? Thanks in advance!


texts: Designing a wide-range light detector circuit

texts:
I'm looking for a few hints in designing a light detector circuit.

Priorities are that the circuit is simple (both as in few parts and as in relatively easy to understand), rather cheap, and can give a rough estimate of the light level.
It should be able to clearly differ between night, early morning light, a cloudy day, direct sunlight etc. Much more isn't strictly necessary, but would be a very nice bonus. (This is for a simple greenhouse temp/light monitor/logger circuit.)
Analog or digital doesn't really matter (the board has a microcontroller with an ADC), but I suppose anything except off-the-shelf solutions are analog.

I'm not quite sure where to begin, or even what class of photodetector to use. Since bandwidth is completely irrelevant (I need a reading every few minutes), I would suppose that the more important spec is how wide a lux range they can handle.

I'd also appreciate some input on noise sensitivity. Given the (lack of) accuracy required, do I need to be careful with separate analog/digital grounds etc., so that the lower-end measurements are still OK?
External power will come from a switching supply, but there's a LDO first thing on the board. However the rest of the board is digital (microcontroller, temperature sensors, SPI Ethernet chip).


texts: I have a 2 A 12 V regulated power supply and I want to use it to emulate a 9 V battery for a breadboard

texts:
I have a 2 amp 12 volt regulated power supply and I want to use it to emulate a 9 volt battery for a breadboard. However, I need to protect the power source and the components used in my breadboard experiments: transistors, LEDs, etc. None of the components or circuits need more than a 9 volt battery could supply new.

I am asking this because I am concerned that the 2 amps of my 12 volt source is too much current for my breadboard and the parts that would normally be used only with a 9 volt battery.


texts:
I have this outline of a circuit designed to display a scrolling message.

I'm having some trouble understanding how it's supposed to work, so I'm just going to explain what I think I know and go from there. Disregard where it says "Mux later", I don't think we have to do that part of the project (at least not yet). The circuit is supposed to display a message chosen by me that simulates a scrolling effect.

The DIP switch simply switches between different 16 character messages. I'll be making two messages, so for me it will be just a switch that's either 0 or 1. This switch is connected to the EPROM which is where I start to get confused. From my understanding the EPROM is used to pick the message (depending on the value of the DIP) and to multiplex the output across the 4 displays. But how do I program the EPROM in such a way to accomplish this?

The 7 seg decoder will be a PAL designed to take a given 4 bit input and transform it into a corresponding 7 bit output which determines the character displayed at a certain point during the 2 bit counter cycle that's counting 00, 01, 10, 11. The EPROM multiplexes this message across the 4 displays in accordance with the digit drivers at the rate of the "fast clock" so that the displays look continuously lit.

How can we cycle through 16 characters with a counter that is only counting 00, 01, 10, 11? I think this is where the memory address comes in. My prof said that the simplest way to do it is by using an adder (we have 74283's). What exactly are we adding?

The picture shows an independent "slow clock" that is "added" to the 2 bit counter. Since we want to scroll through 16 characters, should the "slow clock" be a 4 bit counter? So at time 0000, bits 1 through 4 of the message are displayed. Then at time 0001, a bit is added and so bits 2 through 5 of the message are displayed. And so on. Is this correct? I feel like this is the right track, but I don't genuinely grasp the idea. We're adding a 4 bit number to a 2 bit number, but there are only 2 bits going to the EPROM. If there are only 2 bits controlling the output (plus the DIP switch, but that's constant for a given message), there are only 4 unique outputs. So how can you cycle through 16 combinations? Shouldn't it be 4 inputs?

Any input is greatly appreciated.


texts: Where has 150 Vac mains voltage been used?

texts: Interestingly, on the rear of this instrument from the early 70s, one of the mains input voltage options is 150 Vac (note that all of the remaining ones are not too unusual---100 V in Japan; 115 V in the older US; 127 V in some island nations; 220 V in the CIS and mainland Europe; and 240 V in the UK).  Any ideas on where and when such an obscure voltage was used?


texts:
I am puzzling over the purpose of ferrite beads and grounding on the PIC32MZ DA starter kit.

On page 34 of the User Guide it shows L2 and L3, and a separate Ground and power net.  It would appear these tie into planes.

The real reason for the questions would tend from an EMC standpoint, trying to understand the problem and what this may fix.  Also, I'd like to minimize pcb layers, but don't want to compromize EMC or DDR.


texts:
This electromagnetic relay will be used/wired in normally-open(NO) mode. It will be ON most of the time by a continuous DC control signal and will be open/OFF only when a fault happens(the control signal will go off and the relay will open and stop AC current).

In the data-sheet there is both mechanical and electrical life as below:

What is the difference between mechanical and electrical life?
Most importantly in my application the relay will be in closed position i.e it will be passing a motor driver's current most of the time. Can this relay withstand continuous rated current for half a day for instance? Electrical life has anything to do with it?


texts: I'm designing a readout circuit for an APD manifactured by Hamamatsu Photonics (datasheet). However, I've found myself lacking some information about exactly how would the device behave in my particular application. The datasheet supplies the gain M, the dark count and photon detection efficiency, but no information whatsoever about leakage and noise current, so I am unable to extrapolate what kind of current characteristics the device has. Particularly when constructing a transimpedance amplifier, I'd need to have an idea of the photodiode current at a specific light level (my goal is to work at low to no light) - how exactly could I find that out from the datasheet?


texts: Can there a be a situation where two way propagation model is important in GHz range?

texts:
I assume that applicability different propagation model for wireless channel depends on the frequency of operation and the kind of obstacles or channel under consideration. My question is can anyone give me a practical situation when the two way ray model is applicable when the operating frequency is say 5 GHz?
Link for the two way model is:
https://en.wikipedia.org/wiki/Two-ray_ground-reflection_model


texts:
I have question regarding the wiring of the output of PLC (mode: Omron CP1L). Below is the output wiring diagram.

The PLC is AC powered, and input are 24 VDC. As the image shows, the output has a "+" and a "-" that supply a DC voltage. 00-07 are switches with separate COM. I have programmed to ladder logic correct to trigger an output on 01. But when I check with a multimeter across 01 and COM, I see no voltage at all.

What am I doing wrong? Does the output of 01 and COM actually supply a voltage? If not, what should I do? I cannot find it in the documentation.


texts: Simple DIAC circuit which I do not understand - LTspice

texts:
Here is the circuit :

Here is the model and the parameters of the DIAC :

.SUBCKT DIAC DIAC_IN DIAC_OUT PARAMS:
+Tr=0.342
+Vbo=13.6V
+Delta_V=19V
+Ibo=15uA
*
*Tr:      Rise time (in µs)
*Vbo:             Break over voltage
*Delta_V: Dynamic breakover voltage
*Ibo:     Breakover current
C_C1         N02098 DIAC_OUT 1u IC=0
V_IDIAC1     DIAC_IN N01041 DC 0Vdc AC 0Vac
R_R1         N02098 TRG  {1.462*Tr}
D_D1         N06161 N01041 DZ19V
E_ABM1       TRG DIAC_OUT VALUE { IF(ABS(I(V_IDIAC1))>{Ibo},1,0)}
D_D2         N06161 N01060 DZ19V
D_D3         N10655 N01060 DZ14V
D_D4         N10655 DIAC_OUT DZ14V
S_S1         N01041 N01060 N02098 DIAC_OUT _S1
RS_S1        N02098 DIAC_OUT 1G
C_C2         DIAC_IN DIAC_OUT 10p
****************
* Switch Model *
****************
.MODEL        _S1 VSWITCH Roff=1e7 Ron=2.2 Voff=0.1V Von=0.99V
****************
* Diodes Model *
****************
.model DZ14V    D(Is=3.142f Rs=0.1 Ikf=0 N=1 Xti=3 Eg=1.11 M=.3282
+                               Vj=.75 Fc=.5 Isr=1.973n Nr=2 Bv={Vbo} Ibv=.14467 Nbv=1.093
+                               Ibvl=.1m Nbvl=1.2722 Tbv1=001433.3u)
*
.model DZ19V D(Is=6.994f Rs=5.612 Ikf=0 N=1 Eg=1.11 M=.2906
+                    Vj=.75 Fc=.5 Isr=2.088n Nr=2 Bv={Delta_V} Ibv=.17098 Nbv=1.2072
+                    Ibvl=2.002m Nbvl=1.1457 Tbv1=888.89u)
*               Vz = 18 @ 14mA, Zz = 37 @ 1mA, Zz = 11 @ 5mA, Zz = 7.9 @ 20mA
.ends
*
*********************************************************************
*                                                               Standard DIACs                                      *
*********************************************************************

*$
.subckt myDIAC DIAC_IN DIAC_OUT
X1 DIAC_IN DIAC_OUT DIAC params:
+Tr=0.342
+Vbo=13.6V
+Delta_V=19V
+Ibo=16uA
* 2008 / ST / Rev 1
.ends

where :

* This DIAC model simulates:
*Tr:      Rise time (in µs)
*Vbo:             Break over voltage
*Delta_V: Dynamic breakover voltage
*Ibo:     Breakover current
*
*All these parameters are constant, and don't vary neither
*with temperature nor other parameters.

What I think :
When Vc reaches the breakover voltage (32V), the DIAC begins to conducts, until the current is lower than the breakover current, ie 16uA. The current of the source voltage is able to provide 15uA due to the limiting resistor 60 Meg (this is a simulation). So it should conduct until the capacitor is able to provide 1 uA. And then wait again that the voltage across the capacitor rise to 32V. The voltage capacitor should "oscillate" over the time. Nevertheless, here what the simulation shows :

What is weird is that the capacitor voltage stays @ 32V whereas if the DIAC was not conducting, it should continue to grow until the voltage source. Nevertheless when conducting the DIAC have a "forward" voltage lower than 32V. In the model the forward voltage is equal to 32V - 19V = 13V.

Thank you very much and have a nice day ! :D


texts:
I want to design a 4 layer PCB with the following voltage levels. GND, 5V, 3.3V and 80V.
In the circuit there are some MOSFETs which are driven by 3.3V and MOSFET switch 80V (required current is very low uA level). Which makes overall on the pcb, there are 80V and 3.3V signals close to each other (At some places less than 20 mils).

For the protection I kept 80V at the bottom layer. And the other voltage levels and signals are on the top and second layer. And I keep the third layer completely ground.

I tried to represent the design with the simple picture below.

Now I am worrying about the DC break down voltage somewhere in my PCB. For such a circuit, where one different high and low voltage uses, I have not much experience. I am not sure about my structure, whether it is safe enough? Is there any article or source where I can find some useful information regarding to this issue.
Do you have any advice for such a PCB-design ?
If there is lack of information required for the question please ask.


texts: Who manufactures this chip? Looking for the data sheet. Top marking "QB52"

texts:
I'm looking for the datasheet of this chip. I don't recognise the manufacturer logo. Does anyone recognise this?
I tried a Google search for "QB52 Chip" but failed.


texts: Connecting phototransistors or photodiodes in series

texts:
I am designing a velocity measuring device and want to use 2 strings of 30 photo-transistors in series.

The strings are 15mm apart and are illuminated by separate collimated light sources.  The output of each string is a negative going pulse when any one or more of the photo-transistors in the string are blocked. This output goes to a comparator and then to a processor.

I am having problems with the slow and varied rate of transition when different PDs are blocked. This is affecting the velocity measurement. The rise time can vary from a few hundred micro-seconds to over a millisecond. I am considering putting a trans-impedance amplifier on the output of each string, so that I can create an output to the comparator and processor as soon as the first PD is blocked, and for the reaction time for the two strings to be equal. Or nearly equal.

I have chosen a TI device, OPA2380 for the 2 channels. I would like to ask for any comments on the design, hopefully to prevent me falling into a hole.


texts: What is this diode bridge used for in this circuit?

texts:
I'm currently trying to figure out how this circuit work :

I found this in a microchip documentation dealing with DALI (Digital Addressable Lighting Interface) protocol. The DALI protocol is mostly used to communicate with lighting equipment.
I can already understand what is going on for the most part but I'm still having trouble with the function of the diode bridge. I know that diode bridge are used to convert AC to DC voltage. But in this circuit, the input is already a DC voltage, so I'm wondering what is this diode bridge doing exactly?


texts:
I have breadboarded out this circuit and it worked perfectly once. I tried to transfer it stripboard and I have had so success with it again. The schematic is below.

The description of the circuit can be found here

The theory of the circuit is to ramp up slowly at power on, maintain close to VCC and ramp down at power off. R1 is supposed to adjust the output voltage, this will always be Vcc so I have just put a 1kΩ resistor here. I have put a 1MΩ in R2. When I do this the output of pin 7 goes straight to 2.75v. If I put a lower value in, around 300k it ramps slowly to around 2.75v (supply is 5v).

Here is my Breadboard.

I am coming to the conclusion that maybe I have cooked the chip as I am not able to reproduce the required result.


texts:
I am making a wifi scanner with ESP8266 and to display information I am using SPI based Nokia 1616/C100 display.

This time I am coding ESP8266 natively rather than using mcu + esp8266 (running at command firmware) combination.

On the ESP side I have successfully coded the hardware spi (HSPI) to spit out 9 bit values in the proper format (msb first, spi mode 0). I can see the data being sent on spi just fine.

However when I connect the LCD, there is nothing on it. Its just plain  white with backlight as if it's not even getting initialized. The initializatin code that I have used works just fine (with an AVR for a different project)

void LCD_NOKIA_C100_init(void)
{
//SET GPIO4 AS OUTPUT FOR RST LINE
PIN_FUNC_SELECT(PERIPHS_IO_MUX_GPIO4_U, FUNC_GPIO4);
GPIO_OUTPUT_SET(4, 1);

LCD_NOKIA_C100_RST_LOW;
//DELAY FOR 200us
os_delay_us(200);
LCD_NOKIA_C100_RST_HIGH;
//DELAY FOR 10MS
os_delay_us(10000);

//SOFTWARE RESET
LCD_NOKIA_C100_send_command(0x01);
os_delay_us(5000);

//SLEEP OUT + BOOSTER ON
LCD_NOKIA_C100_send_command(0x11);
os_delay_us(6000);

//PARTIAL DISPLAY OFF
LCD_NOKIA_C100_send_command(0x13);

os_delay_us(6000);

//INTERFACE PIXEL FORMAT = RGB (5 6 5)
LCD_NOKIA_C100_send_command(0x3A);
LCD_NOKIA_C100_send_data(0x05);

//DISPLAY ON
LCD_NOKIA_C100_send_command(0x29);

//SET GAMMA PROFILE
LCD_NOKIA_C100_send_command(0x26);
LCD_NOKIA_C100_send_data(0x08);
}

void LCD_NOKIA_C100_clear_screen(uint16_t color)
{
uint8_t h = (color>>8);
uint8_t l = (color);

//CASET (COLS = 0 TO 131)
LCD_NOKIA_C100_send_command(0x2A);
LCD_NOKIA_C100_send_data(0x00);
LCD_NOKIA_C100_send_data(0x00);
LCD_NOKIA_C100_send_data(0x00);
LCD_NOKIA_C100_send_data(131);

//RASET (ROWS = 0 TO 161)
LCD_NOKIA_C100_send_command(0x2B);
LCD_NOKIA_C100_send_data(0x00);
LCD_NOKIA_C100_send_data(0x00);
LCD_NOKIA_C100_send_data(0x00);
LCD_NOKIA_C100_send_data(161);

//RAMWR
LCD_NOKIA_C100_send_command(0x2C);

uint16_t i;
for(i=0; i<(132*162); i++)
{
    LCD_NOKIA_C100_send_data(h);
    LCD_NOKIA_C100_send_data(l);
}
}

I have a feeling that this is something ESP specific but I don't have enough experience with it to pinpoint it.

The TFT is connected to ESP8266 as follows

ESP8266  ---  NOKIA TFT

/RST ----------- GPIO4
/CS  ----------- GPIO15 (HSPI)
SDA  ----------- GPIO13 (HSPI)
SCK  ----------- GPIO14 (HSPI)


texts: Converting AVR assembly to machine code - addressing registers?

texts:
In AVR Assembly - I want to work out the machine code representation of the following:

ANDI r18,$10

I know the opcode for ANDI is

0010 KKKK dddd KKKK

And I know that r18 is the destination register (Rd), and that $10 (16) is KKKKKKKK - my intuition thinks that I should replace dddd with 18 but that is not possible with only 5 bits (unless I'm severely missing something here...) as 18 in binary is 10010.

I'm thinking I just replace KKKK KKKK with 0001 0000 - but I just don't see how I'm meant to address register 18 with only 4 bits.

The instruction set summary says that r16…r31 can all be represented with dddd which I would think means 4 bits also, so I know I've got something horribly wrong.

Any help would be great.

Reference: http://www.atmel.com/Images/doc0856.pdf - page 20


texts:
If reactive power means losses, why don't we correct the power factor and make it 1? For example, on marine vessels that I have been working on, the power factor is always 0.8. We could add capacitors in parallel, or over-excite a generator.

Why this is never the case?


texts: Can ESD damage a board that is not powered up?

texts:
I have a PCB in the field that is put in an enclosure box and is placed on a pole in an open environment.
My question is, if the PCB does not have the power supply connected, can ESD still damage the PCB or any of the sensitive components?

Please correct me if I'm wrong, but just like normal voltage signals that go from higher potential to lower potential, ESD would try to find the smallest path to ground.
So, even in the worst case if a lightning bolt does hit the pole, the charge would rather travel straight towards the ground than touching the PCB board (not powered up).


texts: Is it possible to hand-solder a BGA without solder balls

texts:
In an attempt to fix a short circuit on a BGA package, I ended up making things worse. The BGA is desoldered with some of the balls left on the BGA, some on the PCB, and some gone entirely. I don't have replacement solder balls or a stencil to replace them. Instead of ordering some, waiting and then reballing by hand, I'm considering pulling off all the balls and soldering the pins directly to the pads (preapply some solder to the pads and then use hot air). I haven't been able to find information about this online, so I assume that means it's not a good idea.

What is the benefit of the solder balls? Do they make soldering easier? Is it possible to solder the pins directly to the pcb pads? Between waiting for new solder balls to manually replace on the package (which I've never done before) and attempting to solder the bga directly to the pcb, which is recommended?

It's worth mentioning that another option is to buy another IC, since it's only $20. But I'd prefer to avoid that if possible.

Edit:

Unfortunately hand soldering without solder balls was more difficult than I expected. I tried this several times and was unsuccessful each time. Although I can't be sure about why it didn't work since I can't check the individual connections, the problem seemed to be that I wasn't able to preapply enough solder to the pads and pins since the metal contact area is so small. The height of the applied solder seemed to be consistent enough, so I don't believe that was the issue.

A possible alternative to get more solder would have been to spread solder paste over the pads. However, it's difficult to control the amount of paste with this method and it sounds like it would be asking for a short.

I think I'm just going to order a replacement IC. If the IC were more expensive, I'd probably try to reball by hand first.


texts: Am I able to make a comparator on optocoupler?

texts:
Initially I'm trying to make over current protection scheme. So if the R2 current (and therefore R2 + D1 voltage) will go higher than some certain level I should have a signal to break the circuit.

I'd make it with a comparator, but making a comparator with isolated output can lead to a relatively complicated schematic: in addition to comparator itself I will need isolator (optocoupler for example) and isolated DC-DC power source to feed the comparator: tall tale.

However if I don't need high precision, high speed and so on - it looks very attractive to made a whole comparator scheme using optocoupler only.

For the moment I made a schematic which basically works (comparing U(R2)+U(D1) voltages with some threshold), but pretty bad:

Blue line representing the forward current of the coupler LED.

Basically I need to make a signal if the R3 current will be higher than some threshold. The precision can be as bad as +100 -50%.

This schematic was built intuitively. I hope that I could make a better comparator of the optocoupler. Am I?


texts:
I am trying to use an A3916GESTR-T half-bridge to drive a brushed DC motor however I am running into several issues. The largest of these is the fact the output of the half-bridge does not match what I am expecting. The image included shows the output of the motor driver's terminals (OUT1A and OUT1B). The motor driver input 1B is being held low, whilst the other input 1A has a 50% duty cycle at a frequency of
~ 2 kHz (3.3 V). The motor driver is being supplied with 9V, so I am expecting an average of 4.5 V on the output.

At lower frequencies (~100 Hz) it works fine.
I have tried attaching a 47 uF capacitor to the power pins of the motor driver which has yielded no change in output.
Is there any reason this is only happening at higher frequencies? and what can I do to try and mitigate this issue.
Thanks.
2020-06-23 Update
I think a large part of my problem may have been hardware, and the waveform has improved after replacing the IC, however I am still not achieving a 50% duty cycle. The following images were sampled at 1 MHz.

Here is another image but the PWM frequency is at 20 kHz instead of 2 kHz

Is this due to capacitance on my PCB?
Thanks


texts: C++ AVR microcontroller optimization problem

texts:
I'm faced with a weird problem. I'm developing a program for AVR.

Microcontroller ATtiny85.
Frequency 1 MHz.
Programmer pickit2.
Software for programming avrdude on Linux.
Compiler avr-g++.
Optimization -Os (I tested with -O0, it doesn't work too).

This program must enable output pin PB3. But for some reason, it doesn't.
#include <avr/io.h>
#include <avr/interrupt.h>

#define NOINLINE_ENABLED 1

#if NOINLINE_ENABLED == 1
#define NOINLINE __attribute__ ((noinline))
#else
#define NOINLINE
#endif

// Error occurs only if SetLedState method has noinline attribute or function implemented in other .cpp file (also noinline).
// NOINLINE_ENABLED macros enables noinline for this method
void NOINLINE SetLedState(bool state) {
    if (state)
        PORTB |= (1 << PB3);
    else
        PORTB &= ~(1 << PB3);
}

class Test {
public:
    Test(unsigned int a) : a_(a) {}

    void Update() {
        // a_ for some reasons doesn't equal 5, but it's impossible.
        if (this->a_ == 5)
            SetLedState(true);
    }

private:
    // I don't know why, but error doesn't occur if I add first variable, which can never be used
    // unsigned int padding = 0;

    const unsigned int a_;
};

static Test *test;

ISR(TIMER1_OVF_vect) {
    // error occurs when method called from timer interrupt method
    test->Update();
}

[[noreturn]] int main() {
    test = new Test(5);

    DDRB = (1 << PB3);
    PORTB = 0;

    TIMSK = (1 << TOIE1);
    TCCR1 = (1 << CS10);

    sei();

    // no error occurs when method called from this place
    // test->Update();

    while (true);
}

I wrote some comments to explain why it doesn't work. I think the problem is in the optimizer.
Output PB3 doesn't enable if (and):

Test::Update method calls from timer overflow interrupt.
a_ class member has offset 2 and more.
SetLedState is no inlined or implemented in other *.cpp file.

Why?
Thanks in advance!
Edit:
Also, I tried to change the implementation of new C++ operator.
Earlier it called return alloca(size), but now I tried to call return malloc(size). And it worked. Also, this initialization works too:
static Test test_static;
test = &test_static;

Why it doesn't work with alloca? What is the difference with malloc and alloca AVR functions?


texts:
I was taking apart an old game-show buzzer system (like something they might use on Jeopardy) and I was confused by the a particular section of the circuit board:

I'm pretty sure the circular component labeled "W005G 840A" (datasheet) is a bridge rectifier. It is connected immediately after the power coming from the switch.

This board runs of a 9V DC wall supply, so why would they add a rectifier? It seems to me that all it would do to a DC voltage is drop it slightly.

I thought it might be used for some sort of circuit-protection, but I don't understand what they are protecting against. Wouldn't the 9V wall adapter prevent any harmful voltages from reaching the board? Also, if they are trying to protect against reverse polarity wouldn't single diode work fine?


texts:
I'd like to buy or build a UV exposure unit for the photoresist method of making my own PCBs.

Nice-to-haves:

adjustable timer knob
works for double-sided PCBs
US$50 budget

What are my options?


texts:
I have a project in mind based around a Raspberry Pi Zero. The case I am using has slots for two AA batteries so I thought I would use some of the AA sized Li-ion batteries.

The batteries I want to use are 3.7V 2300mAh.

The charge circuit I found is: http://www.banggood.com/37V-Liion-Battery-Mini-USB-To-USB-A-Power-Apply-Module-p-928948.html

Ideally I would like to have two batteries in parallel so I could get 4600mAh, but I know there can be issues charging and discharging in parallel, plus I have no idea if that charge controller will do that.

My next option is to just use a single battery with that charge controller, that seems the easiest. Although I cant actually find any reliable info saying this circuit can charge Li-ions, Can I use anything advertised as charging Li-po on Li-ion?

One other option would be to put the two batteries in series and an LM7805 to bring the voltage down to 5V, would this be suitable? I would use an external charger that way.

Sorry for the broad question, if I use google all I get are things for Li-po batteries, and if I look for Li-ion charge modules all I get are the external type.

I am pretty good with amateur electronics, but I've never worked with these before and I don't want to get it wrong.


texts:
I am going to do one project in labview
my requirement is to control the stepper motor in following way

while pressing one button in front panel  the stepper motor should run in one direction in  less than 30 RPM continuously.
 I have seen in USB 6008 specification we can only send digital I/O at 20mA.
But, my application require minimum one kg -cm torque, for that the stepper motor that I am having will draw more than 20mA...(probably 0.5 to 1 A)

and I don't know what exactly the stepper motor driver will do...
Can anyone elaborate the function of stepper motor driver ...?
Can stepper motor driver amplify the current pulses (digital output) to produce required torque?


texts: Can two normal batteries be connected by series and parallel, at fraction of second apart, so as to charge and discharge at the same time?

texts:
Two ordinary wet cell batteries can either be connected by series or by parallel.

What happens if I have a contraption that enables these connections to alternate between series and parallel cycles in such a way that, in one cycle (first cycle) it connects these two batteries in series.  In the next cycle (second cycle) it connects these two batteries in parallel connection.

The contraption moves fast (30 - 100 times per second) between series connection and parallel connection so that it becomes almost series/parallel "at the same time".

Can these two batteries in the first cycle (series) be arranged to discharge the battery and in the second cycle (parallel) be arranged to charge these two batteries?

If so, can we have the possibility of a battery system that can charge and discharge "at the same time"?


texts:
Well I've been stuck on this for a while, maybe 2-3 weeks at this point.  I'm just not sure what I'm doing wrong.  I'm trying to write to this spi flash part, and now I'm just running routines to erase, write, and read to try to isolate it but so far no luck.  Of course I've solved a bunch a bugs along the way...

Anyway I've got my WP line tied high on the board, and I've slowed the clock way down to 200khz, then I run my erase routine and it looks like this:

First I check the ID just for debug, that's the 9F command, then I set WREN with 06 command, C7 is the whole chip-erase, and then I check the status bit with 05 and it's clear.  This thing's chip erase time is only 35ms.

Now I reload my code and try a write:

First I set WREN with 06, check status to see that WREN is set with 05, it is, then send the page program command 02 to address 0x000000.  You can see I'm writing deadcafe as the first few bits.   Also not pictured here is after the write completes (one page or 256 bytes), I send the 0x04 command to disable WREN.  I have observed that and I did set the last four bytes of my page buffer to be 0xAA, 0x55, 0xAA, 0x55 and I saw them just before the CS goes high.

Now stop reload code and try to run a read cycle:

Send 0x03 as the read command and 0x000000 as the address, and... all 0xFF back from the device.

I can see the device responding to my read ID and set WREN commands so I know it hears me, and can respond.  I don't know what I'm doing wrong at this point.  I guess I'll go back to reading the datasheet, and trying some things but if anyone has any insight I'd appreciate the help.  It's shaping up to be another frustrating weekend working on this thing.


texts: How do I determine the curve of the transmission output on a torque-angular velocity graph for a DC motor?

texts:
I'm doing a homework problem that involves motor characteristic graphs. For this problem, I have a motor with stall torque of 8 N-cm and a no-load angular velocity of 80 rad/s. The motor powers a 4-wheel drive robot that requires an input of 60 N-cm from the motor to power all the wheels. Additionally, the robot has a transmission with a gear ratio R = 20 and is frictionless.

I need to find the point where the transmission output line intersects the horizontal "wheel requirement" line (= 60 N-cm) so that I can find the velocity of the robot at this point (called the operating point).

The issue I'm having is that I don't know the equation of the transmission line. All I know is that the \$t(0) = t_s\$ (read as "torque at angular velocity of 0 rad/s = stall torque"), \$t(w_n) = 0\$ (read as "torque at no-load speed = 0 N-cm"), and that \$t(w_i) = 60 \$ N-cm (read as "torque at angular velocity of interest = 60 N-cm"). Once I know the stall torque and no-load speed of the transmission output line, I can figure out the equation of the line and the angular velocity at the operating point.


texts:
I have switch mode power supply (SMPS) rated for 32V 50 watt. I plugged it in main AC, checked its output then unplugged it.
Then to put the SMPS back into its casing, to be on safe side I (tried too) shorted 400V filter cap but accidentally shorted it with something else, the SMPS stopped working after that
Upon diagnostics (randomly probing components) I found a Zener diode completely shorted (aka closed) in both directions and behaves the same way out of the circuit board.
Zener have no other markings other than 24 written on it so can I assume its breakdown voltage is 24V? Also, what other components might have gone bad because of it.
My (blind) guess: it is used for some over voltage protection because I didn't find any other bad component on input or output side, the UC3842 also appears to be fine.
The problem is, I cannot find any 24V Zeners on similar electronic circuits like SMPS or UPS kits, what else can I replace it with?
Update:

Note: The SMD transistor is so tiny that I only managed to guess its marking using optical lens.
The cathode of the Zener is connected to Vcc.


texts: How will temperature affect the output of a semiconductor diode?


texts: Are only standard footprints ever used? What if a manufacturer wants a devices footprint but the manufacturer doesn't list it?

texts:
They want a BOM like this but the part I want doesn't list a footprint. It lists the components dimensions and then you have to make the footprint yourself so I don't think there is a standard name. What do I put here?

Here's the part I need a footprint for.


texts: How to use simple generated clock in Verilog Code Vivado 2015.2

texts:
I am new to FPGAs. I am using an Artix-7 that comes in the Nexys4DDR, and I am programming in Verilog. I want to create a simple D Flip-Flop that will be triggered by a CLK of 50MHz. The CLK in the board comes in through pin E3 and it is 100MHz, I understand I can divide by 2 this clock in the Verilog code itself, but I thought I wanted to use a derived clock from the 100MHz. So I do this in the Constraint file:

Clock signal

set_property -dict { PACKAGE_PIN E3    IOSTANDARD LVCMOS33 } [get_ports { CLK100MHZ }];
create_clock -name sys_clk_pin -period 10.00 -waveform {0 5} [get_ports { CLK100MHZ }];
create_generated_clock -name clkdiv2 -source [get_ports CLK100MHZ] -divide_by 2 [get_pins REGA/Q];

How can I use the generated clock in my Verilog code? This is probably a very simple question, but how can I take the Q pin of the REGA and use it as my clock in the D Flip-Flop?, how can I complete this design? Do I have to instantiate REGA? If so, how? I have tried many ways, but none work. Thank you for your help.

module D_ff_behavior
    (
        input D,
        input CLK100MHZ,
        output reg Q
     );

wire clk_div_2;

always @ (posedge clk_div_2)
    Q <= D;

endmodule


texts:
I am writing an interface for a HITACHI SX19V001-ZZA that is a color LCD display. Please have a look at the datasheet (pages 13-14) to understand the references I am going to make.

My interface sadly does not work but I checked with a scope and all the timing requirements are met, although I am not very sure about the relationship between CL1 and CL2: the first is the "first line marker" while the second tells the display when to sample the 8 bit parallel input. What I do not understand is what the "first line condition" is, I mean, should CL1 be high while CL2 goes low (page 13)? Because that's not what I understand looking at the timing requirements.

That said, my real problem is another. CL1 pin has an input capacitance that is over 300pF while the other pins are around 50pF. I measured this with a simple tester so these values are not particularly  reliable, anyway when I connect the display to the FPGA the waveform of CL1 is everything but a rectangule, being a little bit under 100ns of rise and fall time, that is double the maximum allowed. My quick fix idea is to assign CL1 to two outputs of the fpga and connect both of them to the display CL1 input, just to see if my problem is its rise and fall time, or somewhwere else.

The generic question then is: is it safe to shortcircuit two FPGA output pins given that they are driven by the exact same wire in the verilog/vhdl/whatever description?

Some random infos: currently my CL2 frequency is 3.125MHz to achieve a frame rate around 27 FPS, CL1 is shaped exactly as per page 13, not meeting the rise and fall time as stated, it starts to rise when CL2 rises and starts to fall at the next CL2 positive edge. The frame sync (FLM) is pulled high when CL1 rises, and it is pulled low at the next CL1 positive edge. Of course CL1 and FLM are pulsed at the correct frequency, the first one every 240 CL2 and the second one every 480 CL1. The FPGA is an altera cyclone II (development board DE2)


texts: Electrical Circuit with Fourier Transform

texts:
I'm working in my Electrical Circuits homeworks. One of the exercises says: "Use the Fourier Transform method to calculate \$v_0(t)\$"
The circuit is this:

where \$v_g=36sgn(t)\$, and \$sgn(t)\$ is the sign of \$t\$ (it returns 1, -1 or 0). Well, my problem is the following. I consulted my table of Fourier Transforms and I found that $$V_g(\omega)=36\cdot \dfrac{2}{j\omega}$$
However, I don't know how to calculate \$\omega\$. I need it in order to calculate the \$V_g\$ and also \$Z_C\$. I know that, if, for example \$v_g(t)=A\sin(kt)\$ then \$k=\omega\$. But in this case I'm completely lost.

How can I do it? Thanks in advance!


texts: Removing noise induced by IC (Ground loop?)

texts:
I want to build a simple, portable, MP3 decoder + amplifier. I use a PAM8610 amplifier and a generic MP3/Bluetooth decoder.
When I power each of them from separate batteries (7.4V) it works nicely. When I power them from the same battery (7.4V) I have a LOT of noise, especially when I turn on the Bluetooth.
I put capacitors (3300uF and/or 100nF) on the battery. That didn't help.
How can I make these two circuits work together without using separate batteries?

Measured between the speaker "+" and the battery "-" (ground). The input probe is set to 10x attenuation.
Current consumption (MP3 decoder): 50mA in AUX mode, 70mA in Bluetooth mode, 45 in standby mode.
Current consumption (amplifier): 18mA
(without input signal)
Update:
Placing a capacitor on the battery didn't help. However, placing a 1000uF capacitor directly onto the power connector on the MP3 decoder helps a lot. The noise is at half now. Unfortunately, I don't know which pins are the plus/minus on the IC so I can connect the capacitor directly/closer to the IC. I tried also a 3300uF but the noise decreased with only 5-10%. Considering the size of the capacitor (100uF vs 3300uF), it might not worth it (for a portable application).
Even more, now (after installing the capacitor in the new position) the coil also helps a little. I will try with a bigger coil.


texts:
I've asked yesterday a question about choosing a mic, and I conclude that I need a mic  that can "hear" a sound louder than 160SPL , after Googling and reading wikis about mics, I still can't find a mic or a technology, that could serve my purpose. so my question  is which mic is appropriate for this kind of projects:

Dynamic microphone
Condenser microphone
Piezoelectric microphone
etc.

I'm asking this because in the datasheet of the mic there nothing mentioning that expects for the MEMS mics but the specified range was 135SPL which is not enough for the project.


texts:
I was reading the SGMII specification and the documentation of a Gigabit MII to SGMII converter (see MAX24287). I do not see a MDIO to control the registers of the PHY (Basic Mode Status Register, Basic Mode Control Register, ...) in the SGMII specification. Thus, I suppose SGMII is using the tx_config_reg to configure EVERY REGISTER (in the document, they only speak about the auto negociation process and how to exchange link patner abilities, not every registers).

In the MAX24287, there is also a figure that shows a MDIO link between the MAC, MAX24287 and PHY. So I am a bit confused :
Does SGMII allows to configure EVERY REGISTERS? Or only for the auto negociation?

Thank you


texts: Current monitor for a High frequency signal

texts:
I'm working on a current monitoring circuit for a high frequency current monitoring application as shown in the schematic below, the requirements are as follows.

Should be able to provide RMS current feedback, the differential amplifier output would be fed into an ADC
the AC signal feeds into a resistor which connects to ground

will the LM7372 connected directly across the shunt work for this application? or is there filtering required before connecting to the LM7372 to get the RMS value?

[Update] Signal input is 13.56Mhz sine wave ±15V, Bandwidth is <1Khz, also added the LM7372 circuit below

please refer to the updated LM7372 Circuit


texts: SFH6916-- SOP-16, Half Pitch Mini-Flat Package eagle library needed

texts:
I want to use SFH6916 ( Optocoupler, Photo-transistor Output, Quad Channel, SOP-16, Half Pitch Mini-Flat Package) in my circuit.

I am using Cadsoft Eagle for layout designing.

The package description of this IC is kind of different I searched on internet but could not find anything regarding the eagle library for this.
Where I can find the package and symbol for this??
Any kind of help is appreciable.
Thank You.


texts: Number of independent KVL equations in a circuit?

texts: Why, for a circuit with B branches and N nodes, the number of the linearly independent KVL equations for a network is: B-N+1 ?


texts: What kind of plug does this machine take?

texts:
I was in my attic and I found what seems to be a light projector, it appears to have no power as the on/off switch won't work, so I think it may be out of battery, the only thing I found related to battery was that plug on that back, I searched all around my house but didn't find any plug that would work with it.
Could you guys help me find out what plug it is so I can purchase one at my local store?

(European by the way, I don't know if that helps anything)

Images of the projector:

After brute forcing the fan open, this is how it looks like:


texts: Migrating Cortex Application from Development Board to microcontroller chip

texts:
I have been working on different micro-controllers and I am new to Arm cortex architecture.

I have developed an application on NUCLEO-F207ZG (powered by STM32F207ZG).

The application is supposed to run on stm32f207vc.

Currently, I have made separate projects in STM32 Workbench, one for development board and other for the stand-alone microcontroller.

This seems to be an ugly approach to me as it involves a lot of hassle in copying files from one project to another and then working around to successfully build the project, and I am sure I am not aware of certain good approaches.

Is it possible to run the same project for both microcontrollers? (I think there should be a solution as both are from similar series, with different memory capacities and pin count). One thing that I see is that I may have to make a change in linker script, changing the amount of RAM and ROM that the target device houses.

Looking forward to methods to be able to develop applications faster.

Below is the link to the datasheet. Both devices are listed in the same datasheet for being similar.

https://www.mouser.in/datasheet/2/389/stm32f205rb-956262.pdf

Thanks and advance


texts:
Are these rwo circuits  the same considering the right hand sides of them where it is parallel for the C&R and C&L(meaning the way i should obtain the frequency response?
And for the longer circuit how do i obtain the frequency response and the freqency for MAX amplitude response(im lost with the second one)


texts: Can I use a lithium charger for a bluetooth speaker with a NiMH battery?

texts:
I have a BlueAnt bt blast bluetooth speaker that I need a new charger for. It says DC 12V on the back by the power supply. I checked the manual and this speaker has a NiMH rechargeable battery. Can I use a 12v lithium charger for it? It seems really difficult to find any other kind. Also, the speaker has been sitting in storage for a couple of years and apparently you need to use NiMH batteries regularly for them to keep working. If it doesn't hold a charge, would it work if I left it plugged in?
Thanks!


texts: How does a transistor work as a switch; internally what actually happens?

texts:
I have searched about this, and wherever I see they mention two things:

How [the transistor] will be biasing
Q-point must be at the cut-off and in saturation.

But I want to know in the case of the "ON" condition of a switch, for a transistor, we need to make the emitter junction forward-biased and collector junction must be forward-biased; what actually happens inside? How it will be equal to an "on" switch?

When it serves as a switch for both "on" and "off," it has different biasing. How does it internally arrange this biasing, and gives this application as a switch?

Anyone here with in-depth knowledge and answers will be a great help.


texts:
I was given in a lab a 4-to-10 decoder truth table. I was wondering why it stops at 10 inputs. However, my circuit could hold up to 15 instructions.

So for instance, I built my circuit and it went from 0000 --> 1111. I have a picture of the circuit, however I don't know if it is useful to post it along this question. I'll edit with it if need be!


texts: Building a tester for 5VDC 2A power adapters

texts:
I am looking to built a tester for 5V 2A power adapters. I want to plug in the power adapter output lead and check for proper power output.

The wall plug outputs 5VDC at 2 amps. I also want to have a single LED to tell whether it has power or not.


texts: With the case of stepper motors, what correlates to the max RPM of the individual unit?

texts:
I'm looking at a few different stepper motors for an engineering project I'm working on, and I'm attempting to tease out any correlations that a stepper motor's stats would have with its maximum speed.

Voltage, current, micro stepping on or off, as well as the chip and driver all have an effect (I believe).

So, is there a way I could take a datasheet from something like the Anaheim Automation 17YPG Series High Torque Stepper Gearmotor and calculate the maximum torque and speed?

The sheet says:

Speed of the output shaft (after gearbox) = Motor Speed / Gear Ratio

But I'm unable to find a "motor speed" on the sheet.


texts: What would be the input current of buck regulator

texts:
I have a basic question about measuring input current. The buck regulator I have chosen
is rated to deliver 3.3V/2A from +12V input. My question is -

Is the input current 2A (load current) + few mA (needs for operation)?

Or because of stepdown from 12V to 3.3V, based on load current, the input current is 500mA + few mA?

Is the 2A output current taken entirely from the input or step down conversion delivers 2A after consuming few mA.


texts: 741 vs MCP6004 for low power application

texts:
For experimental - educative purpose, I'm trying to control one 3-color led with the following circuit:

Power: single rail, 5v.
Signal generator: triangular 0-5v, 500 Hz (in next step, signal generator should be replaced by an op-amp circuit, could be a rectangular generator followed by integrator).
operational amplifier: 741 in comparator configuration. v+ from signal generator; v- from variable resistor R1=100 K .
red led with R2=160 ohms resistor (in the future, circuit will be triplicated for each color of the RGB led).

In this way, the triangular signal is converted to a WPM (width pulse modulated) where the width of the pulse is controlled via the variable resistor.

Problem: using a 741 op-amp the led intensity does a "jump" when reaching the low/high limits, probably due to its operational margin levels (741 seems not designed for 5v power supply).

Do you think MCP6004 can be used instead of 741 in this project to solve this issue ? (another possibility is TL974)

Thanks a lot.


texts: A simple circuit to toggle between LEDs based upon input voltage

texts:
I’m trying to design a circuit to test a certain component, so I want to have different pairs of red/green LEDs for indicating whether various parts of the component are working. Indication as to whether or not each component is working will be determined by whether or not a voltage is above/below a certain threshold.

I realize that I can do this with an op-amp/comparator or maybe a relay. However, I’m trying to avoid mechanical or bulky parts (no relay) and I’m not assured that I will have a voltage rail above/below the input voltages (so no op-amp?). Furthermore, since I know exactly what I need from the circuit (just lighting LEDs), I don’t need the nice impedances afforded by an op-amp.

I would like to do this all with some common transistors, diodes, or zeners, and I was able to get something kinda working, but I couldn’t avoid cases where either both LEDs were on or off unless I made the circuit very dependent upon the betas of the transistors.

How simple of a circuit can be made which, for example, given a 12V rail, will toggle between two LEDs when an input voltage crosses, say, 11V? Can it also be done with only a 5V rail?


texts: How to create a Program Log in Readable format

texts:
Im looking for a way in which the program can log specific errors/conditions(user-defined) as and when such conditions occur, and while the code is running I can give command to read it and interpret it in a readable format such a .txt or .xls etc.

What I have thought so far is implementing something like this in my code:

Create a circular buffer
When a specific error occurs, write the details into the circular buffer
Create a routine that always monitors for a request over UART(or any other comm port)
When request is received, send the data over the Comm port.
Interpret and populate the received data into a excel sheet(maybe using python).

Are there any other better ways I can create a Trace Log?

Is there a way such that even when an error occurs, and the code is stuck, I wont be dependent on the code functionality to read the Trace buffer entries(so that I can analyze at what point in code flow the code got stuck)


texts: copper layers of different sizes inside PCB (KiCad)

texts:
I am trying to design a PCB where the device is sitting on an elevated pedestal (or island) on a PCB, like the image shown here.
I have spoken to a PCB company about how to achieve this, and they suggested adding 2 copper layers to form the pedestal, as shwon in the image below.

(I understand that in KiCad, all copper layers are going to be sandwiched between mask and silk layers.  So, in 3D view, the PCB will still appear as a think rectangular box)

So, I went back to my KiCad PCB file and added two copper layers on the bottom. Then I realized, there does not seem to be an obvious way to manually define the boundary of each copper layer.  I think KiCad assumes that the dimensions of the copper layers are the same as 'Edge.cuts' layer.

The closest I could think of was doing what I wanted was 'Add filled zones', as shown in the images below .

However, you can see that, since KiCad assumes the bottom 2 layers have the same dimensions as other copper layers, they also have all the vias and through holes outside the filled zones.  The filled zones in my images represent the desired size for the bottom 2 copper layers.

Is there a way to adjust the size of each copper layer inside a PCB?


texts: Create electromagnetic waves using Lc tank circuit

texts:
Electromagnetic waves are produced by the motion of a dipole and suppose we have  top and bottom points then the negative and positive charges must oscillate between those 2 points.
However an LC oscillator does exactly the same thing if you consider the poles to be each conductive plate of the capacitor.
Are electromagnetic waves produced during the oscillation of charge in a LC oscillator?


texts:
Wireless RF Serial Link 865-869MHz 2KM range (WIR-1186) is what I am using for my project's wireless meter reading.

It works fine. My doubts are that the same module used for nearly for same purpose has signals that may cause collisions. Is there a way to solve this problem?


texts: Why can some devices ignore the USB 10uF inrush limit?

texts:
In general, USB recommends that the maximum capacitance placed on the end of the device is 10uF, in order to reduce the "inrush current" when the device is plugged in. While it is possible to use special circuitry to reduce the current drawn, some products somehow manage to use large caps with a simple fuse or ferrite.

For example:

PupDAC (C22 is a 1200uF cap!)

Sparkfun USB supply (100uF)

How can these devices, and many others (which should work as they are sold commercially) manage to place a large cap on the USB input without any problems?


texts: Can source transformation be used to internal circuit (source) while finding thevenin equivalent of the source?

texts:
At first, I'm very sorry because I don't have money for circuit lab so there is not much visual circuit that clarify my steps

I have practiced source-transformation as well as Thevenin equivalent separately but this is the first time I combine them in one circuit. Does doing it like this still cause no difference as doing it separately? For example, this circuit I am trying to find the Thevenin equivalent

I don't know how to calculate the short voltage between a-b terminals with this design so I intend to simplify it by using source transformation and circuit transformation.

To be more detailed, I will transform the \$Y\$ circuit \$8\Omega-12\Omega-5.2\Omega\$ into \$\Delta\$ circuit then the \$30\Omega\$ Resistor will finally parallel with the \$\frac{12*8+5.2*12+8*5.2}{12}=\frac{50}{3}\Omega\$ Resistor which make the

$$R_{eq}=\frac{30+\frac{50}{3}}{30+\frac{50}{3}}=\frac{75}{7}\Omega$$

Then I will transfer the \$10A\$ current source which is parallel with \$\frac{75}{7}\Omega\$ resistor into equivalent voltage source whose value is \$10*\frac{75}{7}=\frac{750}{7}V\$

Since \$500V\$ voltage source is parallel with \$\frac{12*8+5.2*12+8*5.2}{5.2}=\frac{500}{13}\Omega\$ resistor. I will ignore this resistor because it will not change the load's behavior. Now two voltage source is in series as well as two resistors. Just using voltage divider to calculate the Thevenin Voltage and deactive all source to calculate the Thevenin Resistance

So the circuit is finally simplified that Thevenin Voltage and Thevenin Resistance can be calculate. But what I am not sure is if this way of simplification ok. Will there be any change in the load comparing to the origin circuit.


texts: Suggestions for DC/DC converters with digital control

texts:
I am under quite some time pressure and I need to put together a document about how several DC/DC converters (preferably buck) with digital control compare to each other. I am pretty clueless, I have already pored over tons of datasheets, but I got little useful data, most of the converters out there have analog control. (Maybe I'm just so bad at finding anything on the web...)
What I need is something like the UCD74106 from TI. It should have an external PWM input which can come from e.g. a microcontroller.
The specs I am looking for are:

V_in = 48 V
V_out = 1.3 V to 24 V (programmable)
single input/single output
can be paralleled
any power range

It would be nice to have datasheets with efficiency curves. Something like 'typical efficiency is blah-blah %' is not very helpful...

EDIT: Other examples of what I have in mind: NDM1-12-120 and NDM1-25-120, both from CUI

EDIT 2: I need the efficiency curves to see how the converter behaves at partial load. Also I am interested in finding the (approximative) load current at which the maximum efficiency is achieved (usually below rated current).

And yes, I need digital control! This has been explicitly stated in my assignment... The idea is to be able to reprogram the converters whenever necessary and to make them SMB/PMB capable.

I listed the datasheets to show, what I have found so far and to give an example of what I would like to have. Unfortunately 3 are not enough... I'd need a dozen or so.


texts: Which Eagle part to use for this 2-pin Screw Terminal?

texts:
This is my first EAGLE design and I'm looking to add some a number of 2-position screw terminals (3.5mm pitch) PRT-08084.

Problem: I can find the EAGLE part for the 3-position variant named as M03SCREW_LOCK from the Sparkfun EAGLE library. However I cannot seem to find a part called M02SCREW_LOCK.

Will M023.5MM_LOCK be suitable? What should we be looking out for to be sure it's suitable?


texts: Not gate with 3 LEDS attached after NPN transistor

texts:
I want to build a circuit that turns 3 LEDS (L1,L2,L3) on if the button isn't pressed and turns a different set of 3 LEDS (L4,L5,L6) on when the button is pressed.  Only 1 of the sets of LEDS should be able to be lit up at a time though so pressing or releasing the button will turn off the currently lit up set.  I built and assembled this schematic:

When I don't press the button L1,L2,L3 light up properly.  When I press the button L4,L5,L6 light up, but L1,L2,L3 don't turn off.  How can I go about getting L1,L2,L3 to turn off when the button is pressed?


texts: Why does this Bridge Rectifier claim to have no [Diode] Forward Voltage drop

texts: I was, "OK, this is feasible"... But then I traced how it worked and it simply blocked current through Drain and Source when a P and N pair are reverse biased; then when the other P and N pair are forward biased current flows through Forward Diodes; then alternatingly... Then it's the same, one is just using diodes to Bridge Rectify. Worse still, MOSFETs generally don't have a low diode voltage drop... Or maybe I'm missing something here....


texts: Writing USB Joystick for PIC18F using MikroC

texts:
I'm using PIC18F2458 as USB Joystick HID. The program works, but I have few problems.
Right now, The USB is not detected If I write less than 5 values ( Throttle, X,Y, 4 buttons). The current problem is If I'm using an analog sensor for the throttle, other axis x,y getting read too, because they are going to be read from analog input and of course there is noise, so whenever I use a rotary resistor on the throttle usb input, I get other axis written too.
How can I fix that issue ?
second issue how would I add two throttle for the usb descriptor ?
Here is the current code:
unsigned int average(int channel)
{
 int samples = 16;
 unsigned int sum = 0;
 int i;
 for (i = 0; i < samples; i++)
 {

     sum+=(Adc_Read(channel)>>2)-128;
 }
 sum = sum/16;
 return sum;
}

void analogo() {

    usb[0] = average(1);   // Get 10-bit results of AD conversion
    usb[1] = average(9);
    usb[2] = average(8);
}

void main(void){
                              // Disable comparators

 ADCON1  = 0x05;                         // Configure all ports with analog function as digital
 TRISA.RA1 =1;
 TRISB.RB2=1;
 TRISB.RB3 =1;

 HID_Enable(&readbuff,&writebuff);       // Enable HID communication

 //vl6180x_configure();

  while(1){
  analogo();
  USB_Polling_Proc();

    writebuff[0]=usb[0];         // throttle
    writebuff[1]=usb[1];        // X axis
    writebuff[2]=usb[2];        // Y  axis
    writebuff[3]=0xFF;        //button  0xFF
    writebuff[4]=0xFF;        //button POV 0xFF

    HID_Write(&writebuff,5);

   }

}

and the Descriptor
const struct {
  char report[USB_HID_RPT_SIZE];
}
hid_rpt_desc =

     {0x05, 0x01, // USAGE_PAGE (Generic Desktop)
     0x15, 0x00, // LOGICAL_MINIMUM (0)
     0x09, 0x04, // USAGE (Joystick)
     0xA1, 0x01, // COLLECTION (Application)
     0x05, 0x02, // USAGE_PAGE (Simulation Controls)
     0x09, 0xBB, // USAGE (Throttle)
     0x15, 0x00, // LOGICAL_MINIMUM (0)
     0x26, 0xFF, 0x00, // LOGICAL_MAXIMUM (255)
     0x75, 0x08, // REPORT_SIZE (8)
     0x95, 0x01, // REPORT_COUNT (1)
     0x81, 0x02, // INPUT (Data Var Abs)
     0x05, 0x01, // USAGE_PAGE (Generic Desktop)
     0x09, 0x01, // USAGE (Pointer)
     0xA1, 0x00, // COLLECTION (Physical)
     0x09, 0x30, // USAGE (X)
     0x09, 0x31, // USAGE (Y)
     0x95, 0x02, // REPORT_COUNT (2)
     0x81, 0x02, // INPUT (Data Var Abs)}
     0xC0, // END_COLLECTION
     0x09, 0x39, // USAGE (Hat switch)
     0x15, 0x00, // LOGICAL_MINIMUM (0)
     0x25, 0x03, // LOGICAL_MAXIMUM (3)
     0x35, 0x00, // PHYSICAL_MINIMUM (0)
     0x46, 0x0E, 0x01, // PHYSICAL_MAXIMUM (270)
     0x65, 0x14, // UNIT (Eng Rot:Angular Pos)
     0x75, 0x04, // REPORT_SIZE (4)
     0x95, 0x01, // REPORT_COUNT (1)
     0x81, 0x02, // INPUT (Data Var Abs)
     0x05, 0x09, // USAGE_PAGE (Button)
     0x19, 0x01, // USAGE_MINIMUM (Button 1)
     0x29, 0x0A, // USAGE_MAXIMUM (Button 10)
      0x15, 0x00, // LOGICAL_MINIMUM (0)
      0x25, 0x01, // LOGICAL_MAXIMUM (1)
      0x75, 0x01, // REPORT_SIZE (1)
      0x95, 0x0C, // REPORT_COUNT (12) 2 bits added to switch report count
                  // so bytes are even. Bytes must be even.
      0x55, 0x00, // UNIT_EXPONENT (0)
      0x65, 0x00, // UNIT (None)
      0x81, 0x02, // INPUT (Data Var Abs)
0xC0 // END_COLLECTION
  };


texts:
I wanted to know if there is commercially available Diacs with Breakover Voltage of 20V or less. I tried to find in the internet but always ending up to Diacs with Breakover Voltage of around 30V or more.

I just want to build some circuit that has feature of activating it when it overcomes some "threshold" voltage. That is why I want to use the breakover voltage characteristic of Diac. The circuit should be done using my 24 V DC supply.

If there is no such thing, please provide me an alternative to it.


texts: Selecting 36V, 12V and 9V from 3 different PSUs

texts:
currently i am designing a system in a machine. One of the feature is it can select power supply between 36V (overvoltage), 12V and 9V (under-voltage). Max current would be 300mA @ 12, while 9V which considered as under-volt operates only 90mA.
Previously i have designed by using Relay module. And these relays are controlled by MCU.
However, now i am considering to use MOSFTET. which in my understanding, MOSFET have a longer lifespan than Relays.
Therefor, i am seeking help from you guys to help me in choose which MOSFET is considered OK with the operating power given as above, and also, how should i design the MOSFET Circuit?
your help and support is much appreciated.
Cheers!


texts:
I am a beginner to computer engineering and electrical engineering, and I have watched the entirety of Ben Eater's 8 bit breadboard computer series so I decided that because I understood that well, that I would try and design my own 16-bit CPU inside of Logisim. I have seen many posts on this website as well as some documentation for 16-bit SRAM chips, and I can't seem to find the answer to my question anywhere.
In Logisim they don't have 16-bit byte-addressable memory, so I wanted to make some so that my CPU could access it just like it is accessed in real life. The problem I am running into is that I simply don't know the behavior of 16 bit SRAM when it comes to writing data (this may be because I am missing some assumption that everyone else is making).
CPUs generally have a way to write either a byte to RAM, or a word to RAM, if they are 16-bit.
If I have some RAM with a 16-bit data bus, and I write a 16 bit value to RAM, then it will write the high byte to addr, and then the low byte to addr + 1 if we are using big-endian format.
16-bit SRAM has two signals, one for writing the upper byte, and one for writing the lower byte. When both are active, then the SRAM writes a 16-bit value like my scenario above.

However I can't find out anywhere, what happens when either the upper byte or low byte signals are active.
If I enabled writing to the low byte, and I specified address addr would the low byte of my data bus be stored at address addr or addr+1? I ask this because, what happens one one tries to write the high byte of the data bus by only activating the high byte write signal? Does the high byte of my data bus get stored at addr?
Do I just get the choice of writing the low or high byte of my data bus to address addr or do I need to shift my data down or up to get it to actually be written to addr?


texts: What is the signal carrier in a coaxial cable?

texts:
I'm confused about coaxial cables being called waveguides and the role of the outer shield being to cancel the waves. Is it the alternating current that carries the information (with voltage receivers on the receiving end) or is it the alternating field (with some antenna-like apparatus at the receiving end where voltage is generated by the alternating field)? In this latter case the field waves are not cancelled, after all(?)
If it's all about currents though and the EM waves are just side effects, then is the shield the return path of the current?


texts:
I am designing an electric vehicle controller for a university project. The motor driver varies the speed according to an analog voltage (0V-12V).
My queston is, should I use a digital potentiometer followed by a buffer or a DAC to change the digital signal output from the microcontroller to an analog voltage for the motor driver, I found both close in terms of cost and complexity, and the resolution of the digital potentiometer is good for my requirements.
So which would be better? Did I miss an important point of comparison?
Thanks


texts: I'm looking for a circuit breaker that interrupts the circuit when current drops to zero

texts:
I am looking for a switch that only keeps contact while current is running. Once the current drops to zero the switch opens contact. Something like a circuit breaker that trips with no current. It should require the user to press the switch again after tripping.
This is for a low voltage (24V) and low current circuit (<1A). Is there a name for this component?

If there is no off-the-shelf component that can do this I wouldn't mind assemble it from other components, but at the moment I'm not sure how to do it.


texts: How to troubleshoot a (possibly fried) ws2812b led strip

texts:
I have a 4.5m, 60led/m Ws2812b strip, hooked up on a raspberry pi running hyperbian.
Raspberry works on its own psu, and I have a meanwell 5v 18a for the leds with common grounds.
The setup was working great for some time until I decided to inject power at the end of the strip as it had some dfferences on high brightness whites.
I soldered the extra 5v and ground at the end of the strip and it worked wonderfully.
While trying to cable manage, the 5v+ wire got loose and short-circuited something. Probably the signal line?
I should note that the end of the strip is very close to the start, so that loose 5v could have touched anything.
Since then I cannot get the leds to work.
I multimetered along the strip, it seems to have a constant ~5v power everywhere.
I have tried a second raspberry pi (in case I fried the gpios on the first one) but I get the same behavior from the second rpi too
What are the steps to figure out if it's fried or if it's repairable?
Thank you.


texts: Connecting a higher-current power supply to a lithium-ion charger will damage the battery. Why?

texts:
I am not asking how the battery gets damaged, because that answer is straightfoward.

What I am asking is why lithium-ion chargers allow batteries to be damaged by excessive charge current in the first place.  My understanding is that all lithium-ion chargers already support current limiting features in response to battery temperature (e.g. as part of "JEITA compliance"):

So why don't the chargers also enforce the maximum charge current, regardless of the wattage of the input power supply?

UPDATE

Putting the question a bit better: considering the huge number of handheld devices that integrate the charger and the battery, why don't charger ICs offer the ability to set a maximum charge current to be enforced?  Why don't device manufacturers want to protect their batteries in this way?


texts:
I have a question about LED lamp:

Quantum Board

It has 16 strings of LEDs connected in parallel. Each string consist of 18 LEDs connected in series. It's supplied with constant current source (with max current 2800mA, what is much more than safe current for single LED/led string.) I know that connecting LEDs in parallel is not the best solution because of imperfection of LEDs while manufacturing and as a result inequality of currents through every string. But I see that is quite common solution for such lamps.
I have several assumption how it is possible:

using LEDs with very similar parameters (Vf), using LEDs with same binning. But actually, according to datasheet Samsung LM301B leds have 1V of Vf variation even inside every binning group. Possible in practice this variation is much lower.
very good thermal dissipation due to metal-core PCB

Could anyone explain how does it works? Are my suggestions the keys for the answer? Is putting a series current limiting resistor for every string and using CV source a more robust solution and why not do it in this way?


texts: What guage is the super thin wire in headset cable (e.g smartphone)

texts:
What is the gauge of the thin wires in a headset? I can tell they are stranded (not solid) and coated with paint on the insulation. they appear to be finer than the 24 awg that is in an ethernet cable.

I need to repair a micro drone and want to use super fine wire. I found some hookup wire at store that is 26 or 28 awg but it has super thick insulation. kind of defeats the point.


texts:
I am interested in making my own cheap (somewhat disposable, or permanently attached to prototypes) probes for my oscilloscopes.

In complex circuits, and dense PCBs sometimes it may be difficult to attach all these (standard)probes, test points may not be available, the connections may induce great ground impedance distorting the signals, etc...

The solution I came up with it to solder some coaxial cable to a BNC connector, and solder the cable directly to the "interesting" trace on the PCB, making a more robust connection (no hooks to detach, very annoying), greatly smaller grounding leads. Permanently attaching the probe will result in a perfect prototyping/developing board, always providing all the signals, ready to be connected to the scope.

How may I accomplish this? The signals may be in the MHz range (10-30MHz for example).

I was thinking of standard 50-ohm coaxial cable, is there anything better? Should I terminate it?

For 1:10 probing I thing a simple voltage divider is enough. Is that true?

How about capacitance compensation? How to generally reduce the capacitance of the probe?

Anything else to keep in mind, about the probes? Or any other way to accomplish the above goals?


texts: Determine input resistance of a DMM using a voltage follower

texts:
In my electronics lab we constructed a voltage divider that consisted of two \$1\$M\$\Omega\$ resistors and measured the voltage drop between the two resistors and ground. We supplied \$15\$V and calculated the voltage drop via the voltage divider equation to be \$15\$V\$/2 = 7.5\$V. We measured the voltage and it was around \$5\$V. My professor explained that this erroneous reading was due to the high resistance interfering with the measurement.

We then fed the voltage from the voltage divider into an op-amp acting as a voltage follower and again measured the output voltage. We now saw the expected \$7.5\$V.

From this knowledge I must calculate the input resistance of the DMM and I'm not exactly sure where to start. Is it acceptable to view the first voltage measurement as a voltage associated with a resistance, say \$R+R_{\text{int}}\$, and the second voltage measurement associated with \$R\$, since this the voltage follower pretty much negates the input resistance of the DMM? I feel like I'm on the right track, but I'm not sure where to go next.


texts: Is it safe to not power this USB to I2C chip when USB isn't plugged in?

texts:
I am working with someone on a data logger based on an MSP430. Since it operates on battery power, we want the device to use as little power as possible. We are planning to use this chip (FT201X) to interface the device with USB in the next revision. When the chip is running, it draws considerable current, and when it is in standby mode, the current drawn (125µA) is still more than several other components on the board, so it seems like it would decrease battery life nontrivially, which isn't desirable since the chip doesn't do anything when it's not connected to USB. Most of the time the device will not be plugged in to USB. The device has its own I2C bus connected only to the MSP430, so disabling the bus might work, but would add hardware to handle the pull-ups.

My question is whether it is safe or not to leave the FT201X unpowered (that is, only powered by USB, and unpowered by the circuit) for normal use and only let it power up when USB is supplying power. I'm concerned that the I2C lines, which each will have a 1K pull-up resistor to 3.3V, might damage the chip when it has no power. The data sheet says that the inputs have an internal resistance of 75K, but the SDA might be the problem. Am I right in assuming that this is a bad idea?

Additionally, what other options might I have? Is it possible that I could power VCCIO but not VCC? That might be my favorite option if it's possible. I suppose other options include connecting the pull-ups to FETs or, I suppose, powering the chip always. Are there any better ways?


texts: Choosing a RJ45 to WIFI adapater for use with Embedded Server

texts:
I wanted to build the classic web page that turns on and off an L.E.D.  My plan was to use one of the Atmega line of micro-controllers with an enc28j60, which seems to be a popular solution to this sort of thing.  However, there is one complication.

I wanted it to work over wireless (this would ultimately be used to monitor some hydroponics in a non-commercial environment.  Maybe control a modified remote control helicopter, for kicks?)

I was going to use a RJ45 to wifi adapter, but frankly, I'm having some trouble working out the details.  (Let's assume I can power it.)  Is using an RJ45 to wifi in stack with an Ethernet controller really a good way of doing creating a wireless embedded server or is there another well-documented chip my googling and forum browsing hasn't realized?


texts: Does source transformation in circuit analysis work the other way around?

texts: We all know that the source transformation shown in the first picture below is valid. But does it also work in reverse, as shown in the second picture? (because I use proteus to draw second picture, so you are regardless of value of current,voltage and resistor in second picture)


texts: Second order RLC circuit problem about signs

texts:
Consider this circuit. Which is a second order RLC circuit.

The problem asks for value of \$\phi\$ from the initial conditions.

I took the first derivative of the equation by hand but as you'd see signs doesn't match with the solution of the problem.

How did they find this answer from the equation above?

I suppose they neglected the C term for simplicity for current equation.

Update :

After solving the other part of the problem which asks for A I recognised that the differentiation is correct. But the solution would be \$\phi = \tan^{-1}(-\frac{\alpha}{\omega_d})\$

Only I couldn't be sure whether one of the sides of the triangle could be \$-\alpha\$


texts: control multiple leds using only 2 connection wires

texts:
i want to control 5 led bulbs using just 2 wires .depending on some condition i want to turn a led with a specific color from 5 led set and only one led should on at a time.

here is a small explanation .

in my house we use water tank .if water level is max i want to show it by turning on specific color led.if water level is fine ..weak.. i want to show another color led on the motor switch .but distance between motor switch and tank is very big so i can't really use 6 wires for control 5 leds.

so what I'm asking is is it possible to control 5 leds just using 2 wires ? i'm thinking about pulse technique.for example if level is max i send a specific pulse/bit pattern so using small circuit determine which led should turn on. but for that i think i need 3 wires( 3 wire is also ok but led amount can be vary -10 led may be) .what is the cheapest and easiest way to do this ??i'm really new to electronics. if i can do this without using bit pattern it's lot better because detecting bit patterns quite complex to me. thanks


texts:
I’ve been given a faulty Yamaha RX-V765 Receiver.  Parts are no longer available for this unit, and I’m trying to convert (i.e. hack) it directly into a Power Amp.

I have been able to get some audio out of the unit using a standard Line input source, but it is of poor quality and nowhere as loud as it should be.  I have to admit that I am pretty much out of my depth (but want to learn and also not spend any money).  I'm only guessing where the pre-amp circuitry ends and the power-amp input starts.  For debugging / starters I am working only on the Front Left (i.e. "FL") channel.

Link to the schematic for the main circuit board that I am working with.

I have annotated the above schematic with where I am adding an input source as per the image below:

(The Orange dot is the signal from the audio, and the Green dot is ground.)

A video showing what I am getting at the moment is available here. This has been recorded with the input source at the maximum volume (which is too quiet for what the amp should be able to do and is also distorted).  The Red lead in the zoomed in video corresponds to the Orange Dot.

The full service manual is available here.

Any help as to where I should be connecting the input signal would be most appreciated :-)

Thanks in advance.

Update:

Tested the DC voltages across all the main output transistors and they are all fine.  I'm also getting the nice slight hum out of all speakers (i.e for channels) which makes me think that the actual Power circuitry is fine.  When I repeated my input signal injection for FR rather than FL I got the same result (very low volume with some distortion).  This made me think that something must be wrong in circuitry that is common to both - so started looking for readings around the "star ground" circuit.  This is what I've found so-far - erroneous readings around one of the Voltage Regulators "IC102".  (My readings in Green - those supplied in the Yamaha Service Manual in Red.)

Oops - the voltages below are incorrect, see Update 2 Below

It's difficult trying to get readings with both the main board and one daughter board installed (for the speaker output), so I'm going to extend the leads so I can get the daughter board out of the main enclosure (but still electrically grounded where needed).  Hopefully then I'll be able to get some more readings.

Update 2:

It was only after I got good access to the underside of the main board that I realised I had the pin-out of IC102 wrong.  (I thought I was reading "IN" but was actually reading common.).  The corrected voltages are as below:

Update 3:

IC102 turns out to be a standard -12V 1A regulator.  I've replaced this using a good one from my local electronics shop - now the readings around this area are better, but there are problematic voltages downstream from this area.  Around Q1072, Q1073 and Q1074 the voltages are now fine - but around Q1067 and Q1070 the voltages are incorrect.  (Note: I wasn't sure what B/C/E readings I was measuring on these transistors because I was tired/lazy; I just noted the three voltage readings on the pin-out.  The values provided in the square brackets for these components may therefore be out-of-order.)

With one of the speakers connected, when I try to measure the voltages on Q1070 (with my properly grounded meter) I get an audible "buzz" when measuring one of the pins.  This seems to be the only place on the board where this happens so far.  I'm not sure what this means, but perhaps it means Q1070 is bad ?  (Two of the voltages around Q1067 look okay, but not the third.)


texts: Audio Switching Circuit - Ground Loop Noise Problem

texts:
I'm building an adapter to connect an RJ9 headset output to a 3.5mm jack output(TRRS, mic included). I have designed it so far to use DG409 (4:1) analog multiplexers to choose what lines are connected to what (for example Pin 1 on the RJ9 connector will be connected to the Sleeve of the 3.5mm jack (TRRS). This is done by connecting one of the AUX outputs to the 1 side and choosing which of the 4 outputs to output to.

NOTE: the DG409's that I'm using have two MUX's in one chip so I'm basically grounding all the inputs/outputs of one of the muxes for each chip as I only have use for one PER chip (i'm using 4 chips to route 4 signals, Left (only mono audio needed), MIC and 2 GNDS)

The 4 outputs (on each chip) have a 1MOhm pull-down resistor on each of them while the inputs have different size pull-downs (don't know why I need this to output the audio properly). The Speaker channel has a 4.7kOhm pull-down, the MIC channel has a 220Ohm pull-down and the 2 GND lines have a 100kOhm pull-down.

I am currently powering/controlling everything off of the Hummingboard (which is outputting the audio) and trying to use the dual supply function (+/- 5V supply). I am supplying negative voltage via the use of a voltage converter (LTC660) which is also getting its power also from the Hummingboard.

Currently I'm testing it by outputting audio from a Hummingboard which is travelling through the analog MUX and being outputted to a RJ9 connector which is connected to an IP phone, and I'm listening to the output speaker on the IP phone.

Issues that I am seeing:

(1) Noise on the output - there is a distinct hum that I hear on the speaker when audio is playing through. There are peaks occurring at the 50Hz harmonics.

(2) the ground connected to the voltage converter (-ve voltage provider) is 2-7mV higher than the ground on the Hummingboard. NOTE: I also have connected 5 op-amps to be used as buffers (RC4558, so 10 buffers really) to the +ve and -ve voltage supplies.

NOTE: Because everything is powered/outputted from the Hummingboard and thus everything is sharing a ground. The audio GND and circuit ground are the same.

QUESTIONS:

(1) Is the voltage converter's higher ground potential the cause of my AC hum?

(2) Could the use of capacitors in series with the audio signal lines help alleviate this problem? i.e. use 10uF or 22uF caps before inputting the analog MUX's? I've been looking at some audio switching schematics and they seem to use capacitors in series for the audio signal lines sometimes

High Level Schematic

As you can see I'm trying to choose where to output the SPK and MIC lines from the AUX to the RJ9 connector. For the SPK line, mux 2,3 and 4 are not outputting signals to the lines connected to the the mux 1 output line, thus they are an open switch.

Here's an image of the frequency analysis of the noise recorded on the MIC line.

As you can see the 50Hz harmonics are still prevalent.

NOTE: I am passing the audio GND lines through the analog multiplexer as well to choose what pin it is outputted to. Hence the GND line is seeing a small resistance in series (17Ohms) due to the switch being open. Is this possibly the cause of my AC hum/ground loop, as a difference in ground line resistance will be present? Or is this resistance small enough to be ignored....

Also could it be that if my buffers are outputting voltages slightly lower than what was inputted (due to the +/- 5V dual supply not being high enough) this could cause AC Hum?


texts: Calculating total power draw of device (camera) and accessories

texts:
I work with cinema cameras and at any given point the camera will be adorned with a number of accessories e.g. Monitor, Follow Focus Motors, Cinetape etc which are being powered by ports on the camera itself.

My knowledge of electricity and power is fairly limited at the moment but I want to learn how I can calculate the total power draw of the accessories and the affect they will have in reducing battery life.

As an example I work with the Arri Alexa frequently and as per the manual this accepts input of 10.4V to 34.0V. If the power drops below the 10.4V it will shut down. the camera is usually powered by 24V or 26V batteries.

When I add a monitor or other accessory how to I calculate it affect? Also, how does wattage and amperage have an affect here. I understand that voltage is akin to pressure but struggling to visualise the equivalent behaviour of Amps and Watts.

Thanks in advance.


texts: circuit test is performed on low voltage side ,and reading are given of high voltage side

texts: There is a question in vk mehta in which open circuit test is performed on low voltage side ,and reading are given. of high voltage side and magnetizing branch ,excitation branch current is  asked.how is this possible?


texts: Should I switch the transfomer input or output?

texts: I am installing a remote receiver switch into my outdoor lighting circuits and wonder should I leave the 230-12volt transformer (500va) permanently supplied & install the switch module on the 12 volt output or would switching the 230 volt input be best.


texts:
I feel a bit silly here. I managed to build a complex multi-board block of digital logic, but I can't figure out how to plug in a wire...

My plan was to buy a simple set of standard square-pin connectors, solder those to my PCB, and then connect to it with some ribbon cable. Well, I mean, I need 4 wires, so actual ribbon is maybe excessive. I thought I could just poke 4 separate wires on there.

Anyway, I purchased some 4-pin headers, and some 4-pin IDC plugs. Reading Wikipedia, I was under the impression that "IDC" means you just mash the wires in there and the blades are supposed to cut through the insulation, but... well, I can't get it to work at all.

I tried just smooshing the wire in there, but it easily falls out again. I tried pressing it down with the end of a screwdriver, but it still comes out, and the insulation is clearly still perfectly intact. Heck, I even tried stripping the ends of the wire and soldering it in there, but that didn't work either.

Am I supposed to use some kind of special tool to insert the wires or something?? How is this stuff meant to work?

The actual item in question is

https://uk.farnell.com/amp-te-connectivity/3-640440-4/housing-22awg-4way/dp/1098455

It plugs into the header just fine, but I can't figure out how to put wires into it. Supposedly it works with "AWG 22" wire, and the datasheet for my wire says it's "AWG 23", which I believe is meant to be thinner, so...


texts: Is this solution of linear circuit correct?

texts: Is this solution of linear circuit correct ? Have I applied KCL and KVL correctly?


texts: Radio triangulation on millimeter scale plausible?

texts:
(For this question, let's throw away the skepticism of what's possible or practical today and instead focus on what's plausible in the future. This is all theoretical, but here's the idea:)

We'd like to design future nanobots (≈5-10µm in size) that navigate around in the brain in mass quantities (a million or so of them) to apply therapeutic stimulation. In order for them to know where they are, one idea was to use RF triangulation. Essentially, a helmet with RF beacons would be placed on the patient's head, and then the nanobots could somehow use those beacons and a nanotube radio to determine their location in the brain. Assume that the bots have some processing capabilities.

If we placed some beacons around the patient's head, would the close proximity of those beacons allow the bots to find their location to within, say, a millimeter or less? Would direction be possible as well? How many antennas would be required?


texts: Large blue arc from capacitor when shorting it - how deadly was this situation and how much energy was inside?

texts:
I was working on a transient circuit and I applied a 8kV, 2 ohm voltage transient on its input with a rise time of 10us and fall time of 50-100uS. It comes from a transient generator off mains so can provide an excess of 5kA if required.

(Stupidly) I was touching the circuit, and decided to do another test and everything seemed okay. I for some reason thought this time I better just check these caps are discharged and got an insulated test lead and shorted the capacitor out. It flashed this massive blue arc and made a loud bang as it did. Obviously, it made me realize how lucky I am and im still a bit sketched working with the circuit now.

I wanted to get some details from the community about how close to death I really was there, how much energy predictably would of been in the capacitors and energy it would of taken to be deadly?

I will provide some circuit details below:

simulate this circuit – Schematic created using CircuitLab

The transformer's secondary was shorted. It has 1 ratio of 1:1 and has 750u. It presents 0.2 ohms of impedance and has an inductance of 750uF. The capacitors are low ESR surge capacitors rated a 500+ volts. I dont know their ESR but its in the region of 1-2 ohm.


texts:
Currently trying to construct an RF Receiver and Transmitter circuit, however I've run into a little hump.

What I am expecting to happen is, the LED in the receiver circuit should turn on when the switch in the transmitter is pressed.

However, I'm observing the opposite. That is, the LED is on and when the switch is pressed, it turns off.

Is there some way of reversing this so the opposite happens?


texts:
I'm having a problem designing a circuit to interface an LF398. On it's data sheet it says that it needs +5 and -5 volts, but I only have +5.

My questions are:

Can I put V+ on 5V and V- on ground and still have a viable circuit and how would this constrain my input values?
Is there a way I can get both 5V and -5V without using another IC?

As a plan B, I could use an voltage inverter to get the -5, but this would require another dedicated IC. The samples that I'm trying to hold will be in the -1 to 1 volts range.

A little background: I'm building a pulse oximeter for a class project. We have 2 flashing LEDs that reflect off of skin into a photodiode that is connected to a microcontroller for processing. The series of events should be: LED flash -> Photodiode -> S&H -> Micro. The S&H IC should sample when that specific LED is high.

RM: LF389 does nort exist - changed to LF398


texts: Why is the oscilloscope in Multisim software showing more voltage than the source?

texts:
The Multisim oscilloscope shows around 13V peak despite the voltage source being 12V peak. I was expecting 12V. The diode voltage drop is set to 0.1v  when forward biased.

Am I missing something?


texts: Use two 250V series cap in APFC instead of single 400V

texts:
I have a EVGA 500W PSU with an APFC which is causing spike noises, presumably from the APFC or main switching as they both run in sync controlled by the CM68000TX combo apfc switching PWM chip

Noise (about 700mV every 16uS) comes in when APFC turns on, even on the 5VSb line. (5VSb line is smooth until PSU turns APFC and everything else on, noise on all 12v, 5, 3.3 lines etc.)
Also when I load the PSU with e.g. a 10Ohm resistor on the 5V line, the Power Good output goes low for about 270mS. Voltage levels averages are kept somewhat ok, but I believe the PG is rebooting the PC "randomly"

Now I have measured the original 400V 270uF and is giving me less than 240uF so I have in hand two 250V 470uF caps, can I connect these in series for testing purposes?

I'm a bit concerned if it being 200 extra uF would cause any issue, or may be something else I don't know.


texts:
I'm trying to read multiple ADC value one after the other using the continuous scan method. I have fallowed quite a few tutorial and example, but nothing seems to work for me. I am using the STM32L100C-Discovery board. Here is my code, I'll be grateful if someone can tell me what I am doing wrong. Everything seems to work fine, but when I try to evaluate the voltage, I only get wrong values... If I put 3.3V on PA0, adc1 gets me a value of 1500 so around 1.4 V which makes no sense. The value on adc1, adc2,... are all quite different as well as they are floating pin.

int main(void)
{

HAL_Init();

MX_ADC_Init();
int adc0, adc1, adc2, adc3, adc4, adc5, adc6;
while (1)
{
        HAL_ADC_Start(&hadc);
        HAL_ADC_PollForConversion(&hadc, 40);
        adc1 = HAL_ADC_GetValue(&hadc);
        HAL_ADC_PollForConversion(&hadc, 40);
        adc2 = HAL_ADC_GetValue(&hadc);
        HAL_ADC_PollForConversion(&hadc, 40);
        adc3 = HAL_ADC_GetValue(&hadc);
        HAL_ADC_PollForConversion(&hadc, 40);
        adc4 = HAL_ADC_GetValue(&hadc);
        HAL_ADC_PollForConversion(&hadc, 40);
        adc5 = HAL_ADC_GetValue(&hadc);
        HAL_ADC_PollForConversion(&hadc, 40);
        adc6 = HAL_ADC_GetValue(&hadc);
        HAL_ADC_Stop(&hadc);
}

And the ADC_init is :

static void MX_ADC_Init(void)
{

  ADC_ChannelConfTypeDef sConfig = {0};
  hadc.Instance = ADC1;
  hadc.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;
  hadc.Init.Resolution = ADC_RESOLUTION_12B;
  hadc.Init.DataAlign = ADC_DATAALIGN_RIGHT;
  hadc.Init.ScanConvMode = ADC_SCAN_ENABLE;
  hadc.Init.EOCSelection = ADC_EOC_SEQ_CONV;
  hadc.Init.ChannelsBank = ADC_CHANNELS_BANK_A;
  hadc.Init.ContinuousConvMode = ENABLE;
  hadc.Init.NbrOfConversion = 6;
  hadc.Init.DiscontinuousConvMode = DISABLE;
  hadc.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
  hadc.Init.DMAContinuousRequests = DISABLE;
  if (HAL_ADC_Init(&hadc) != HAL_OK)
  {
    Error_Handler();
  }

  sConfig.Channel = ADC_CHANNEL_0;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_4CYCLES;
  if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sConfig.Channel = ADC_CHANNEL_1;
  sConfig.Rank = ADC_REGULAR_RANK_2;
  sConfig.SamplingTime = ADC_SAMPLETIME_4CYCLES;
  if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

And so forth until ADC_CHANNEL_5 and ADC_REGULAR_RANK_6.


texts:
The only limitations I can think of are:

Comparator/Schmitt not gate output swing time, and
Transistor switching time

simulate this circuit – Schematic created using CircuitLab

BTW, these are parts i have, and thus probably aren't optimum.

It's supposed to do 3v3 @ roughly 200mA


texts:
I have a PCB with an RF module that is built on top of another PCB. If you look at the picture below you can see that it is almost identical to what I have soldered on top of the PCB.

The difference is on the top and bottom of the RF module board. I have some solder pads that are offset into the RF module PCB board, so they aren't exposed at the edge of the board.

I can't get direct heat to the solder pads.

What exactly do I need to do so I can desolder the offset pads?

Are there any kind of special tools I need?


texts: Is there any easy and systematic way to analyse circuits containing opamp and multiple diodes?

texts:
simulate this circuit – Schematic created using CircuitLab

For instance the circuit above.I need a more systematic procedure then hit and trial.
Diodes have a cutin voltage of .7V and show ideal piece-wise characteristic


texts: Programmatically turn on PIR device with Arduino

texts:
I have a D203S PIR sensor operated device.

I want to simulate motion detection with my Arduino and then let the device operate as normal.

I have seen that shorting the PIR sensor for a couple of seconds does the trick. I suppose that with Arduino I would need to use a resistor. I think the resistor should be as high as possible, say 100 Kohms, in order to draw as little current as possible from the device. Would this approach interfere with the device circuit? Can shorting the PIR sensor damage it in the long run?

Is there be a better, more energy efficient, solution?

Addendum:

Please find below pictures of the front and back of the PCB along with a schematic of the add-on circuit. In the pictures, I have indicated the relevant portion of the PCB with a red square and each contact I am shorting with a line.

simulate this circuit – Schematic created using CircuitLab

Addendum2:

I have managed to find the datasheet for the D203S PIR sensor used on the board. On page 4 the manufacture provides an example circuit, which I am enclosing below.

By looking at it I think that by shorting PINs D and S, I am powering the portion of the circuit starting with R2 and interesting Quad Op Amp LM324, which otherwise would be powered only when D203S detects motion. In the light of this, I think the key to avoiding damage to the D203S PIR sensor is making sure that the new current generated when connecting pins D and S flows into A and not into S - see schematic below. In order to achieve this I think a good approach would be to modify the circuit as shown. I would prevent current from flowing into S when turning the device on programmatically with Arduino, but then the LM324 would not be activated by the PIR. How should I proceed?