texts: Can CMRR be computed given the open loop gain and closed loop gain?

texts:
So there are two formulas of the common mode rejection ratio (CMRR). I will mention the one that has the open loop gain. It is because someone asked me if the open loop gain and closed loop gain are enough to be able to compute for a CMRR or if there needs to be more given values.
CMRR = AOL / ACM

CMRR - Common Mode Rejection Ratio
AOL - Open Loop Gain
ACM - Common Mode Gain

But what if ACL was given instead of ACM? Are they the same? I think they aren't.
I think there is a relationship between open loop gain, closed loop gain and feedback that can be computed from this thread.
How do the open loop voltage gain and closed loop voltage gain differ?
But I don't know how that relates to the common mode gain for me to eventually get the CMRR. Is there a way to do so?
I guess for someone kind of lazy but knowledgeable, a simple answer such as "No, there has to be an additional given to solve for the CMRR" would suffice because the question might sound really stupid. That would probably be enough. But I would appreciate more explanations. Thank you.


texts:
I'm brand new at electronics, and brand new at Arduino. I know very little about eighter, so please bear over with me... :-) To top it of, this is my very first post here on Electronics.

I'm working as a frontend developer, and my first Arduino project is about controlling a slot car via a website.

I can turn an LED on and off, remotely from a website, and I have connected the slot car to the Arduino, like I connected the LED, but of course there isn't enough power to get it running very fast. I does run, but sloooow... :-) I used a digital multi meter and saw that there were only 2V in the tracks, compared to 14.8V when plugged in the wall.

With my very limited knowledge of electronics, I was wondering if I could plug the slot car into the normal power socket, and somehow control how much power that goes into the tracks with Arduino.

How do I do that? With a resistor? Or?

Thank you in advance.


texts:
I am trying to match a dipole antenna to a 50Ω source. Problem is that for my frequencies (VHF) the complex impedance basically circles the 50Ω point between VSWR 2 and 3 lines. Because of that matching with a transformer or a lumped component seems impossible. To get around it I decided to use some relays to switch in different capacitors and inductors to get a good match for every frequency with some switching.

Now I'm trying to optimise these components with QUCS. I started with four sources with four different matching components. All of them go to separate sinks with the same file name.

I am running default Optimization block to try to optimise these four matching components. The problem is describing the goal for the optimiser. I can't give a formula like "max(S11)", because that would optimise one component to be good at every frequency. But I don't know how to tell QUCS that the goal is to minimise "max(min(S11, S22, S33, S44))". I am able to describe the algorithm in code, but don't know how to write it down in QUCS equations.


texts: Load resistor on (very) old toaster circuit

texts:
So the other day, my family toaster which is roughly as old as myself (25yrs), burned down.

When I took a look at the circuit, I found out that some components melt down completely.

One of them is (or at least i think it is) the load resistor of the diode bridge.

I made a schematic from the components i could still read:

So the unknown resistor is RL. J3 is connected to the huge toaster wires (the ones that actually toast). those wires are then connected to the mains (230V 50Hz)

Would anybody have any idea on how to estimate the value of the RL?

(Also, Kudos to whoever can give me some hints for R1 and R2 as well)

Cheers!


texts: What is the simplest circuit which can automatically power on a V59 LCD controller?

texts:
Given a V59 LCD controller, what is the simplest circuit that would automatically power on the LCD once voltage to the red LED becomes present?  The goal is to automatically turn on the monitor once power is supplied to the LCD controller ( currently it does not and instead awaits for someone to press the power button controlled by K0 in the schematic ).

Specifications can be found here:  https://sites.google.com/site/lcd4hobby/6-lcd-as-pc-vga-hdmi-av-tv-display-tsumv59/ND-LA.MV9.P-2.pdf

  Page 7 shows the "Key Schematic" referring to K0 and LEDR

I'm assuming there would likely need to be a slight delay before closing the K0 circuit after voltage is detected on LEDR to turn on the monitor.

Would a capacitor for delay and a transistor for switching be able to handle these requirements?


texts: Solar Panels: Charge Batteries via MPPT Charge Controller *AND* Power PV-Direct Load At Same Time?

texts:
I have two 290 watt panels in series that are currently used to charge a 48V battery bank via a MPPT charge controller. The run from the panels to the charge controller and batteries is about 70', and I've got a PV-direct load (one or more DC fans) I'd like to run that is 30' in the opposite direction. I know the output voltage from the panels will vary widely, but assuming the PV-direct load (i.e. fan(s)) is able to handle that range is it possible for me to tie in to the existing +/- outputs from the panels (combined, something like 75V max) and run that over directly to a DC load (in addition to the run to the charge controller)?

My primary concern/question is how this might affect the charge controller (a Victron SmartSolar MPPT 150/35). I think the draw from the fan(s) would be quite low in proportion to the "power" of the panels, so would it just be that the charge controller would only "see" / experience a reduced voltage level coming in from the panels (e.g. what might otherwise be a strong 75V might only come through as 60V due to PV-direct load burning-down some of that potential energy)?

Is this kind of setup "allowable" / advisable? i.e. having a PV-direct load in addition to a MPPT charge controller "load", each on separate circuits. Would the PV-direct load side need its own ground connection?  BTW, I know the PV-direct load circuit probably can't be as simple as depicted below; for example at the least there would probably be a voltage monitoring relay ensuring the fan can only kick in above some set voltage and also a thermostat.

Thanks in advance!


texts: Adding a temporary load to a power supply

texts:
I have an isolated switching power supply which takes in 30V and outputs 55V 1.5A. It's a power source for a PoE+ powered device. When the device which is supposed to be powered is not connected (via RJ45), the only load present on the 55V rail is an LED which draws 6mA and the output voltage goes up to somewhere between 56V and 57V. When the powered device is connected (it draws ~400mA) I have a nice and stable 55V output.

Now, the transformer requires a minimum load of 20mA. So the question is, how can I add a temporary load on the output that would automatically disconnect when I connect my powered device? As mentioned above there is only a 6mA load, so I need to add a temporary 14mA load.

As the voltage increase when there is no load, I was thinking about adding a zener with a breakdown voltage of 55V in series with an LED and a resistor. So if the voltage was greater than 55V the zener would start conducting and I could adjust the resistor value accordingly to draw at least 14mA. However I couldn't find a zener with a Zv of 55V.

Any other ideas? I have limited space on the pcb so the component count/footprint is important.

Thanks in advance.


texts: Power over time for RC ish circuit in LT spice

texts:
I have a simple circuit in spice that I put a 0-5V step function into.  So basically as square-wave going in. Then I can get my current and voltage waveforms out, or do some math to get power.  But I really want to know say for 1ms how much power was used.  I just want to compare a few approaches and my comparison that other people on my team will understand will be Watts.  So I was thinking how many Watts were used in 1ms.

I'm thinking maybe I want to integrate under the power curve?  Not sure exactly how to accomplish that in LTspice so I'm asking for some advice.  I did read a little about the idt function.


texts: Why is there a positive temperature coefficient in a MOSFET?

texts:
When the temperature in a MOSFET increases: resistance increases and mobility decreases thus avoiding thermal runaway compared to BJT.

But what is the reason for increasing resistance and decreasing mobility in MOSFET?

I thought before that it will be opposite: as temperature increases, mobility of electrons will be excited(increase) no matter what semiconductor we have thus resistance will also decrease. Why does the opposite happens in a MOSFET?


texts: CMOD A7 Seeing Input Even When There is None

texts:
I've created a quantum-random number generator which is outputting random pulses to 8 IO pins on my FPGA. I've implemented the following input component to lengthen the ~10ns pulses to something my FPGA can sample.
architecture behavioural of input_synchroniser is

signal delayed_pulse:   std_logic := '0';
signal in_pipe:         std_logic_vector(in_pipe_len - 1 downto 0) := (others => '0');
signal pipe_head:       std_logic := '0';

begin

    FDCE_inst : FDCE
    generic map
    (
        INIT => '0'
    )
        port map
    (
        Q => delayed_pulse,
        C => din,
        CE => '1',
        CLR => pipe_head,
        D => '1'
    );

    input_synchroniser: process(clk)
    begin
        if (rising_edge(clk)) then
            in_pipe <= in_pipe(in_pipe'high - 1 downto in_pipe'low) & delayed_pulse;
            if (pipe_head = '1') then
                dso <= '1';
            else
                dso <= '0';
            end if;
        end if;
    end process;

    pipe_head <= in_pipe(in_pipe'high);

end behavioural;

Followed by some other components to implement the algorithm discussed in this question.
I then push this into a ring buffer which is read by my UART unit to output the data.
tx_uart: uart
    generic map(baud_rate => baud_rate, f_clk => f_clk)
    port map(clk => clk, reset => reset, tx_tri => rd_en, data_in => tx_data, tx_out => tx_out, ready => uart_ready);

    tx_buffer: ring_buffer
    generic map(ram_width => 8, ram_depth => buffer_depth)
    port map(clk => clk, rst => reset, wr_en => load_tri, wr_data =>byte_in, full => buf_full, rd_en => rd_en, rd_valid => rd_valid, rd_data => tx_data, empty => buf_empty);

    rd_en <= '1' when buf_empty = '0' and rd_valid = '0' and uart_ready ='1' else '0';

This all seems to work nicely in sim. However, when I read the data over the serial link something weird was going on and the data was not random as expected.
So I took my CMOD A7 off the RNG and put it on breadboard. Somehow, I'm still getting a serial output which makes no sense.
If I run my design on the simulator with the inputs disabled, I get no output as expected.
Any ideas what could be going on or what I can check?


texts:
I'm trying to convert a 5V PWM signal to 0-10V through an optocoupler to drive a VFD.
The output "0-10V" should be 0V when PWM duty cycle is 0%, and 10V when 100% (linearly !).
Here is what I've come up with:

So, when OUT1 is high (5V):

10mA should pass through U9 and saturate the photo-transistor
Q1 and Q2 bases are now 12V, so Q1 is opened, and Q2 closed
C2 charges through Q1 and RV1, voltage rises

When OUT1 is low (0V):

U9 transistor is closed
R17 pull Q1 and Q2 base to 0V, so Q1 is closed and Q2 opened
C2 discharge through RV1 and Q2, voltage fall

RV1 can be tuned to increase or decrease smoothing (depending on PWM frequency).

Will it works ? I would like to know if I'm heading in the right direction before ordering the parts !


texts:
I am designing an automatically played air instrument which consists of an air compressor, solenoid valves, a variety of pipes through which air flows and makes sounds, as well as an Arduino connected to a relay module for easily controlling the solenoid valves. When I apply electricity to solenoid valves, I hear (in addition to the usual clicking sound in solenoid) something like a popping sound (or maybe better described as a plop sound), probably caused by the sudden escape of compressed air. Is there a way to reduce this? I initially thought of driving the solenoid valves using PWM, so that it opens slower and the air makes less sound, but heard that this would not slow down the opening speed of the valve since solenoids cannot be slowed down... Any electrical or mechanical suggestions would be very helpful. The usual solenoid clicking sound is ok, I just need to reduce the air popping sound if possible...

(Below is the type of valve I am using; the pressure I use does not exceed 1-2 bars and I am using push-in connectors to hoses with 4mm inner diameter)


texts: AD9833 Problems with Arduino and SPI [Can't think of a good title]

texts:
Alright I'm about at my wits end, I'm playing around with a AD9833 to synthasize a sin wave. I have combed though all forms of forums regarding the AD9833 to no avail. This is the circuit I'm running.

EDIT: although the circuit says Fsync is controlled by PB0(pin 53) its actually connected to pin 36 as per the code

Another EDIT: Im doing this on a breadboard, which as I have read is a big no no, could this damage the part, or would it only introduce crazy interference.
.
I'm controlling the AD9833 with an Arduino Mega2560 and communicating with the SPI protocol, but instead of using the SS pin on the Arduino I'm manually controlling the Fsync pin, as I need to transfer 16bit.

// the sensor communicates using SPI, so include the library:
#include <SPI.h>

// pins used for the connection with the sensor
// the other you need are controlled by the SPI library):
const int fSync = 36;

void setup() {
  Serial.begin(9600);

  // start the SPI library:
  SPI.begin();
  SPI.beginTransaction(SPISettings(1000000, MSBFIRST, SPI_MODE3));
  // initalize the  data ready and chip select pins:
  delay(10);
  pinMode(fSync, OUTPUT);
  digitalWrite(fSync, HIGH);
  delay(10);

  digitalWrite(fSync, LOW);
  SPI.transfer(0x20);      //turns B28 - write 28bits to FREQ register
  SPI.transfer(0x00);
  digitalWrite(fSync, HIGH);
  delayMicroseconds(1);

  digitalWrite(fSync, LOW);
  SPI.transfer(0x4C);     //write 0x0C0F to 14LSB
  SPI.transfer(0x0F);
  digitalWrite(fSync, HIGH);
  delayMicroseconds(1);

  digitalWrite(fSync, LOW);
  SPI.transfer(0x70);     //write 0x30FF to 14MSB
  SPI.transfer(0xFF);
  digitalWrite(fSync, HIGH);
  delayMicroseconds(1);

  digitalWrite(fSync, LOW);
  SPI.transfer(0x00);      //Output sinewave
  SPI.transfer(0x00);
  digitalWrite(fSync, HIGH);
  delayMicroseconds(1);

  SPI.end();
}

void loop() {

}

The data is being clock in on the falling edge, and the clock is idling high.

This is 1MHz signal I'm using as my master clock, and its coming from a function generator.

This monstrosity is what I'm getting for an output. By my calculations the FREQ register should have 0x30FFC0F = 51.379E6. This means the output frequency should be about 191 kHz - which is a fluke I think becasue this wave form has a frequency of about 200 kHz

I'm sure the data registers are being updated as can be seen here when I enter the following SPI data

0x2000
0x4C00
0x7F0F
0x0000

I have checked my voltages and everything seems to be withing range

CAP/2.5V is ~2.49V
AGND to DGND 0V
VDD 4.95V from the arduino

My only thought is that I fried the chip when I soldered it to the breakout board, I have tried 2 already and am hesitant to put the 3rd on in as these bad boys are not cheap.

Are there any glaring issue that anyone can see? Ask for any other data if needed.


texts: What is limiting high frequency ultrasound from being high power

texts:
This is mostly just our of curiosity and I feel like I may be missing something basic, but what is limiting ultrasond transducers in the range of 500kHz-MHz from not outputting higher power like the low frequency high power transducers (20-80kHz)
Is it a materials issue? I can't find the answer anywhere.
Thanks


texts:
I am confused on how the specs of a DAC work together.

I am looking at this one: http://www.ti.com/lit/ds/symlink/dac7811.pdf
for a project and am wondering how the sampling rate (5 MSPS), the serial clock rate (50 MHz) and the resolution (12bits) all work together.

Where I'm getting lost is how the resolution and the sampling frequency work together. If my fs is 5 MHz, does this mean that I have 12 bits to represent 5M worth of values? Or does each single sample in the 5 M samples have a possible value from -=2^12?

This particular DAC has a 16 bit register with the first 4 being control registers, so what exactly goes into the last 12? They're binary values, so how can that accurately represent a signal being sampled at 5 MSPS?
I know that the clock can operate at a max of 50MHz, which is how fast the DAC can send packages back and forth from my micro-controller. Does this value have anything to do with sampling rate or resolution?

I've been all over google and wikipedia for this and have checked with other students who aren't quite sure either. Can anyone offer clarification?

Edit to add: here is the link to the Newark.com page for this part where it specified 5 MSPS
http://www.newark.com/texas-instruments/dac7811idgsr/digital-to-analog-converter-dac/dp/85K0568


texts:
Is there a way of telling if sei()/interrupts() or cli()/noInterrupts() was last called?

I need this to be able to enable interrupts, execute some code and set interrupts disable interrupts if they where disabled.

Here is some sample code:

void function_requiring_interrupts(void) {
    bool interruptsEnabled = getInterrupsState(); // what function / variable here?

    interrupts();

    // Code requiring interrups are enabled

    if(!interruptsEnabled) {
        noInterrupts();
    }
}


texts: Why a high voltage AC always present in SMPS AC to DC power adapters

texts:
I'hv seen every 2 pin SMPS AC to DC adapters shows a little high voltage respective to the ground on the out put, on both + and GND wires(or more if more wires present).

This voltage is high enough to light small neon bulbs or a line tester, but very low current, barely could be felt. This voltage vanishes if I connect the output to ground somehow, e.g. touch it while standing on floor bare foot.

As the size of the adapter increases, the AC voltage and current increases. When laptop adapters are powered from a ungrounded AC outlet, they gives reasonable shock from the 19V DC(or whatever else) output.

Perhaps this is the reason why many 3 pronged laptop adapter carries a warning CONNECT ONLY TO GROUNDED OUTLET Connecting to a grounded outlet magically vanishes the high voltage.

I am aware about the EMI filtering capacitor connected between high voltage and low voltage ground, I tried to solve this by removing them, but this trick is not working.

Why and how this mysterious AC voltage is created ?
Is it harmful to sensitive electronics components ?
Is there any way to solve this without grounding the DC output side ?


texts: what size battery storage is needed to provide 10A at 115v for 5 continuous hours

texts:
I have a two part question:

What size battery storage is needed to provide 10A at 115v (I meant 115v AC) for 5 continuous hours?
what size solar array (assuming proper alignment, etc.) would be required to charge the battery bank each day during the summer months?


texts: I am finding it difficult to understand how transistors which are transconductors can be used to design an Opamp which is a voltage amplifier. Silly question but has really been heavy on me. Thanks.


texts: So I learnt about phasors and phasor representation this week in college. I noticed that in every example problem that we did, one phasor was chosen as reference and the angle was taken as 0°. My question is :if we take that the reference not as 0°, but something else, would it be wrong? Why is the reference always 0.


texts: Clarification on terminology : RF Signal

texts: I frequently come across the term 'RF Signal' in circuits for ex in the below picture, please ignore the functionality of circuit not important.:  I understand RF means Radio frequency but what I dont understand is why use this terminology for electrical signals. When I see RF I always visualize an Electro-magnetic wave. Then why is it used for electrical data? In the above example why use RF IN or RF OUT (I can to a certain degree understand why RF OUT) ? I know they are electrical input and output.  I would like to know your understandings and hence expand my understanding.


texts: Can a LCD display work with swollen capacitors for a large period of time until briefly turned off?

texts:
I am trying to figure out why would my very old SyncMaster 720N stop working after turning it off for a very brief moment. I've already had issues with it, I had to replace some capacitors and then it worked fine for more than a year.

I'm not asking about how to fix it. My question is: is it possible that display's capacitors would swell some time during its 20+ days uptime without going to standby of turning it off, but the display would still work with swollen capacitors until briefly powered off? Or would actual swollen capacitors cause the display to turn off spontaneously? I'm just wondering if it is worth it to take it apart once more to look at the capacitors.


texts:
I've been trying to make a active load that would use a very small resistor, around 10mOhm as a shunt resistor. I've figured out how to make it, it's a common circuit, however since I need to use opamps to measure the voltage drop and drive the mosfet, I do require a negative voltage power source.
I've tried simulating the circuit in the picture below in LTspice.

However while it seems to work ok when powering one opamp, when powering the mosfet driving opamp and the opamp connected to the shunt to amplify the voltage drop to the volt range, it seems to not be capable of generating a negative voltage anymore and goes into the +V range.
Basically even though I thought opamp power rails don't really use any power, it seems the current draw is enough for the circuit to not be able to produce the negative voltage. Aka the load is too large.

I want to know if it's perhaps a LTspice problem, am I just not using the proper opamps (OP07) or is there a way for me to limit the negative supply current into the opamps. Or perhaps something else is drawing current that I'm not aware of.
Here is a picture of the circuit I'm talking about. The graph shows the output of the "negative" voltage power source shown at the bottom left side.


texts: LTSpice: Can I vary schematic temperature over time?

texts:
I'm trying to simulate a temperature sensing schematic with a latching function (meaning that the schematic should go to overtemperature mode at let's say 75C and go back to normal at 50).

I can do a temperature sweep function with the command .temp 25 50 75. I see that the schematic responding well (I see that the forward diode voltage going down with a rate of -2mV/C as expected). But this means that the LTSpice engine does regular transient analisis for each temperature I'm giving, which stays constant over all the simulation time.

Actually I'd beter do only ONE transient with a temperature changing over the analisys time. I could pick a voltage source to be a temperature set point or may be there is a SPICE command that will tell the engine what I actually want to do with a temperature?

I see some models that containing another one pin representing the temperature of the chip. It can be connected to the heat sink with a capacitors (standing for corresponding thermal capacity), resistors (standing for correcponding thermal resistance). This technique looks very powerfull and accurate, but I will definitely struggle to find all needed components with this kind of thermal model, do accurately all thermal elements including heat sources. I don't actually need all this accuracy right now - all I need is to verify that the thermal protection will work fine at some certain points.

Any ideas?


texts:
I'm looking for an ESD wrist strap and found that in many models you can choose between either a 4mm, 7mm or a 10mm press stud.

Why are there multiple sizes? Is one better than the other?


texts: Which wired communication standards operate at 2km range or above?

texts:
I am trying to find a standard (hopefully with a chip set) which can communicate over copper (twisted pair) for at least 2km, maybe up to 10km, using a baud rate somewhere between 10kbps and 100kbps.

I have looked at rs485, but this seems to max out at 1.2km even though I imagine dropping the baud rate might improve the range.


texts: What's the function the network outside a crystal oscillator connected to an IC?

texts:
Take a look at this:

Then general network is commonly seen when connecting an oscillator to an IC.  What is the purpose of this network?  Is there an article I can read on it?


texts: A Circular-Polarization Reconfigurable Meng-Shaped Patch Antenna

texts:
How are the pin diodes in this antenna with chinese character actually related to circular polarization ?
What are dimensions D and Fv in the paper?


texts: Stereo phone jack: purpose of terminals 1 and 6

texts:
Here's the datasheet

While I understand pins/pads 2-5, why it has 1 and 6 instead of having just single terminal? Is it like ground and protective ground? Where am I expected to connect 1 and 6? One of them is surely signal ground, but another?


texts:
I have a 7 segment display that has 4 digits. What will I need to make use of this? Can a single microcontroller handle the operation? I mean PIC16F690...I saw also a MAXIM chip that drives these kind of displays...is it absolutely required?

Here is a picture from the datasheet, I don't know why there are 2 pin diagrams?

Here is a link to the datasheet


texts: How to detect status of switch from serial (or other) port?

texts:
I have a switch and a headless Debian computer.  When the switch changes state, I want a script to run on the computer.  The switch has outputs for both NO and NC.  If possible I'd like to plan for a second switch, which also can be NO or NC.

The computer has:

Serial header (I have a PCI bracket but have yet to test it)
A plethora of USB ports
PS/2 ports

I've looked in to Arduino but it seems overkill for this.


texts: Hall effect output to a level voltage or other useful output

texts:
I am trying to take the output of a Hall effect sensor (latching or non) that is sensing magnets on a wheel and turn it into a level DC voltage that varies with the speed of the wheel. The only limitation I have is any circuitry must be analog. My ultimate goal is to make a speedometer with this information and I have a way of achieving that if I can get the Hall effect sensor converted into a varying DC voltage.
If you have any suggestions on how to do this, or  possibly alternative to it that is analog I would greatly appreciate it.


texts: Is there a ATtiny or similar microcontroller with a UART port?

texts:
I'm looking for a way to connect a sensor and control network to an Arduino, and I'm thinking serial communications through the UART port may be the way to go.

I've also seen the ATtiny chip, and I think that it, or another chip like it, could do very nicely for a node in the sensor and control network.

Are there any ATtiny or similar microchips microcontrollers that have UART ports?


texts: Changing terminal leads on a live battery

texts:
So somewhere along the line I made an idiots mistake that I'd like to avoid making again. I have a large 51.2V battery that's wrapped in shrink wrap and has wire leads soldered into a charging circuit that is soldered onto the terminals. The connections recently got crushed past being usable because one of our team members wasn't paying attention to where he was putting things. I thought that I would be safe if I only touched one terminal (i.e. one wire lead) of the battery at a time, but when I went to clip off the crushed positive connection I got a shower of sparks and a small heart attack. Thankfully I didn't get shocked, but I'd really like to figure out why it sparked so badly and what's going on.
We very carefully cut off the shrink wrap to take some pictures. Here's a folder of the pictures we took. Battery2.JPG is a picture of how each individual cell is hooked to the next one. The little red wire leads back to the charging circuit and connects as shown in Battery3.JPG. Battery4.JPG is an image of the battery as a whole. I suspect the spark shower has something to do with the charging circuit but I'm really not sure. Does anyone know how I can change the connections without killing myself?


texts:
I have an LED project with a pretty hefty power draw - 1.5 kilowatts. We're trying to figure out how to power this from a (large) 12 V battery bank.

We need to have the entire 1.5 kW output travel down a single pair of wires (slip ring).

Are there 12 V to 5 V DC converters that can do this?

I was originally thinking I could just wire together a bunch of smaller buck converters (such as these) but I'm learning that you need converters that can do "current sharing", and it's not clear to me how to identify 12 - 5 V converters that can do that.


texts: USB as a local bus in an embedded system

texts:
Is USB a reasonable choice for a local bus?

what are pros and cons?

what reliability concerns are there?

Bus spec device count ~4; peripheral devices are permanently connected to same PCB as host (soldered or via headers).

Some device are puny, e.g. serial port or temperature sensor, some are complex, e.g. an LTE modem or ethernet or wifi. Peripherals are such that are available as standalone USB devices or same chips are used in such devices. Linux is supposed to have all the drivers already.

Ideally I'd use only one bus (with hubs if necessary) for simplicity and eventually modifications without some components and with other low-speed components.

System spec ARM, Linux, DC powered, roughly equivalent to an Android tablet.


texts: How can I know the voltage input range of the CS5344 ADC?

texts:
I see that this ADC has a built in voltage reference, therefore I wont have to bias my audio signal as it goes into the ADC input. The thing that confuses me is however the full-scale input voltage listed in the datasheet:

So say my supply voltage (VA) is 3.3V, does this mean that the maximum unclipped input amplitude is equal to (3.3*0.56/2) = 0.924V? This just seems low to me.


texts:
I am using this LDO

Input Voltage is 14V
Output Voltage is 5V
Maximum Load Current is 150mA

Schematic :

I am observing two problems:
Problem 1:
Initially when I power on the LDO by given the input voltage but I am not providing an ENABLE signal to the LDO, I am getting a voltage of 2.65V at the LDO output for 5 seconds. Please see the below waveform.

Can someone tell me why this is happening? I am not able to find anything related to this in the datasheet.
Problem 2 :
This below test was done in thermal oven at a temperature of 95degC. The junction temperature of the IC would be even higher than 95degC.
I give a transient pulse from 16V to 18V for some 400ms and then back to 17V for some 600ms and the back to 16V. I give 3 pulses like this. The rise time and fall time of the pulse transitioning from 16V to 18V and then back to 16V is 1ms only. When I give this pulse at the LDO input, the output voltage 5V goes to 0V like shown below. The current was stable at 150mA but when this pulse is applied, it goes above 350mA and then to 0A and oscillates as shown below. Can someone tell me why this is happening?
I checked the LDO datasheet, but I was not able to find anything regarding this.

The above same test when done at 25degC:


texts: Decade resistance box with BCD-type rotary switches

texts:
I'm looking at building my own decade resistance box, but the typical rotary switches are... quite expensive. They seem to be the most expensive part of the entire project. Whether I choose a real rotary switch or a DIP switch or even a thumbwheel switch, the standard decade resistance box uses an SP10T switch that is either expensive or limited in selection.

I've seen a lot more switches that use a BCD output code, or a BCD complement code (example: page six of this datasheet, specifically switch functions 1 and 2. But I'm having a tough time wrapping my head around the connections. In an SP10T switch, you connect the 0 terminal to the "input", and the common terminal is the "output" (or vice versa), as seen here:

(source: EEVblog #212)

But a BCD switch makes multiple connections depending on the desired code. For example, if I set the switch to 3, then the common terminal will be shorted to positions 1 and 2. In a BCD-complement switch, if I set the switch to 3, then the common terminal is shorted to positions 4 and 8. Either way, I can't come up with an arrangement of resistors that would yield a resistance of 3ohms (or 30, or 300, etc).
This is the switch function diagram for the switches I have in mind, which might be a clearer explanation of the behavior I'm describing:

Sorry if this question is kind of confusing, I'm having a hard time explaining it myself! To summarize, does anyone have a connection diagram for a decade resistance box using BCD switches?


texts: How to find the inverse of a boolean function?

texts:
There is a practice exercise before my exam in mid april that says: find the inverse of the boolean function: F = AB + BCD + AD. What does this mean and how do I do it?

The answer is F = A' * C' + B' * D' + A' * B' + A' * D' but how?


texts: FET - confirm if both circuits are equivalent for medium frequencies

texts:
I would like to make an incremental model of the transistor for medium frequencies. I've tried to make the matrix. Could you confirm if the two circuits are equivalent for medium frequencies, please?

New circuit:


texts: Simple Reverse-polarity Protection for Automotive DC-DC Converter: FET or Diode?

texts:
I have recently decided to upgrade my old van by installing a few 5V/3A sockets using a 100W 12V-to-5V downstep buck that has no reverse-polarity protection. A little bit of searching here and elsewhere has led me to understand that I can facilitate that protection with either a diode, at the cost of a significant voltage drop and risk of reverse leakage, or a MOSFET set before the buck circuit. I've tried looking for appropriate p-FETs but have only found 7812s @1A/1.5A and variable I/O FETs that I understand would require additional components to configure.

Which of these techniques would be more appropriate to use for my purpose? If I use a p-FET, what should I be looking for to find the most appropriate one?

Thank you for your time.


texts: Choose the dimensions of the resistantors in this op-amp circuit with negative feedback to have a gain of 10

texts:
Here's the circuit:

Here's my attempt:

I already have the values for Ad. Is this right? I need to choose the values for R1 and R2 wisely I think.

What I don't understand  is the point of having R3 in there, and what would the value for R3 have to be taking into consideration what I said about R1, R2 and the gain. It is said to be ~R2//R1 but I dont know why.

What should I do compute the input impedance of that circuit (op-amp with negative feedback?) Can you guys give me any tips?


texts: New STM32L433 pins pull high??? Damaging opamps

texts:
I have an STM32L433, fresh from RS components. I soldered it to my board. PA6 is connected to the output of an opamp - INA181A1.
There are another 2 INA opamps on the board, connected to other pins.
I have now had 2 INA181s die (actually I am not sure they died, since I unsoldered the first and replaced it assunming it was broken... the second I unsoldered just the output leg and may have damaged it mechanically...). The board is not even programmed yet. There is actually not yet even a programming header...
The net between the opamp and the MCU is pulled high. If I hold the MCU in reset state (connect the debug header nRES to ground) the opamp-MCU net floats. As soon as I release the reset pin, it pulls high.
The other 2 channels to not do this! The other 2 channels behave exactly as expected!
There is no board error. There is >500kOhms between the net and ground/3v3 when not powered - this pull IS coming through the MCU. I observe there is ~50mA extra drawn from my power supply between when the MCU is held in reset and when reset is released.
Are my new chips pre programmed???am I missing some line in the datasheet/reference that says "PA6 will pull high when new"?
The boards were supplied without MCU and opamps and gate drivers. I have populated them myself. I have built 2 boards with F303CB chips, which work fine, using internal opamps, and 1 with L433CC. The pinout appears to be the same in terms of power, boot0 etc.
The schematics can be seen in https://github.com/davidmolony/MESC_FOC_ESC/tree/Rearrange_Vin - this is an open source EBike controller I work on in the evenings. I have been riding around with the F303CB version, pushing ~80phase amps and getting up to ~40km/h, so the board DOES work.
Edit:
Schematic
Offending opamp is op2, U9


texts: Looking for a USB/PCI controller that can replace a physical switch

texts:
I am looking for a component that I can drop into a circuit that will replace the functionality of a physical switch so that I can control it via computer, preferably via a standard interface (USB or PCI).

The switch will eventually need to be controllable via a .net application.


texts: Can I use digital pots for my feedback resistors to a buck-boost regulator?

texts:
I'm working on a design, and this will be my first attempt at a buck-boost regulator.

I need the output to be variable because my application calls for different voltages under certain conditions.

The buck-boost regulator I'm considering is the LT8705

Most of the reference designs I've seen have used either a fixed output, or in some cases, I've seen where a potentiometer was added but never a digital one.

I  haven't yet decided on specific digital pot, but let's assume I decide to use this MCP4021/2/3/4 to replace the 392k and 10k resistors connected to the FBOUT pin on the right side of the image shown above. I haven't calculated what exact resistors I'll need so for the purpose of this question, assume that the digital pot's resistance is in range.

Max current through the resistors is 2.5mA. My max output voltage would be 28V. If I set my pot to be greater than 11.2kohm, the current would be < 2.5mA through it.

$$ R_{min}= \frac {28V_{max}}{2.5mA_{max}} = 11.2k\Omega$$

If this is true, then my next question is what considerations should I be aware from the following snippet from the datasheet

  ..set by an external feedback resistive divider carefully placed across the output capacitor.

What would 'carefully placed' entail ? Would placing this IC near the regulator potential disrupt its behaviour ? Any additional feedback would be appreciated.

Thanks!


texts:
I recently found one of those old rotary dial telephones in my garage and amazingly it still is fully functional (I tested it by hooking it to the phone line). As I have no use for it as a telephone anymore, what I want to do is to make it ring on demand, using parts that I have on hand. The ringing as achieved by a small "hammer" being driven by a coil and knocking the bells. I measured the AC signal using a multi-meter when the ringing occurred and it read around 50V, which I guess is RMS, so peak voltage should be around 70V... at least that made it ring in my case.

At first, I tried using a transformer I had laying around but it had a ratio of around 23:1, but it made the AC voltage too low for the ringer to work (mains is 230V RMS at 50Hz).

Then, I found out about the capacitive voltage divider, but as I played a bit with it in Proteus I discovered that it seems to need large capacitors in order to be able to drive any reasonable load, like a light bulb. Also, I think the current drawn would be too much for continuous operation.

Lastly, I started designing an oscillator to generate the sine wave from a DC power source (new plan is to use a regular 5V wall plug). I found an example circuit that designs a single supply Wien bridge oscillator, and by adjusting the resistors and capacitors, I was able to generate a 2.5V 20Hz sine wave in Proteus. As physical parts, I plan the op-amp to be a TL-074, and the capacitors regular ceramics (I do not have a lot laying around unfortunately, so I am rather limited there). Next, I thought of adding the transformer that I have in the mix, in order to get the high voltage I need for the ringer. That should give me 2.5V * 23 around 60V peak AC, which hopefully will ring the bell. My remaining question, besides whether all this is a good idea or not, is how to handle the power drawn by the ring bell? I modified the circuit so that the output of the op-amp goes into the base of a TIP41, and then the collector and emitter are connected to the PSU, and the transformer, respectively. Should this be enough to drive the ring bell? Does the phone line really supply that big of a current, beside the high frequency? I played a bit with my telephone and saw that the coil of the ringer is hooked to a giant capacitor. When the line "rings", I can manually ring the phone by tapping the tip and ring wires to one end of the coil and the correct end of the capacitor, but it does not ring if I connect the coil directly. Is that because the line does not feed that much energy and the capacitor "buffers" it? Pardon me if I am wrong, I am just trying to learn, I am a bit confused here and would really appreciate some help to make things clear for me. A useful resource I used for learning about how the telephone line generally works is here. I'd really appreciate any idea on this matter, a different perspective on how to achieve this, I am trying to find a good working design before I prototype it on the breadboard or perfboard because I do not have an oscilloscope and debugging this without one I think would be pretty hard.

I am attaching a screenshot with my current schematic and simulation in Proteus. Yellow signal is generated sine wave before voltage rise, blue is the wave after the transformer, while green is a reference 5V peak 20Hz sine wave, just so that I make sure that the frequency of the generated wave is indeed 20Hz, which seems to be the case.

Thank you very much.


texts:
Here is a screenshot from my 6-layer Stack-up board with this order (signal-GND-power-signal-GND-signal).
But I am curious if this is the best arrangement for layers, is it better to swap between L4 and L5 to have this order (signal-GND-power-GND-Signal-signal)?
This isn't a high-speed board(160Mhz) and no impedance control required, but there will be analog signals on L4.


texts: How to make a simple daylight on-off switch?

texts: I have a project planned where I want for some LEDs to turn on when it's dark and turn off when it's light. I have some transistors, diodes, and a photoresistor(and of course other basic components). The photoresistor has lower resistance when in daylight though. How do I 'NOT' this so that I can turn something on when it's night instead of daylight?


texts: How to convert Ripple Current spec to ESR?

texts:
It used to be that vendors like Digikey gave a cap's ESR value and not ripple current. Nowadays, it seems more report only ripple current and not ESR. What gives with that?

So what are we supposed to do with "ripple current" if we want to know ESR?  Many datasheets are not reporting ESR any longer. If a 4.7µF/250v electrolytic cap listed "Ripple Current = 146.2mA @ 10kHz", can we derive an ESR from that?

I see where ESR can be derived from the Dissipation Factor... but DF isn't reported for this cap either. Ideas?


texts: How do I calculate impedance of a (bypass) capacitor (for simulation)?

texts:
I wanted to build a simulation of bypass capacitors in Matlab, especially to play around with pairs of different valued caps.
So I thought I just take a model of a real capacitor as series connection of capacitor with a resistor (ESR) and an inductor (ESL) and derive the formula
$$Z=\mathrm{ESR}+j2\pi f\cdot\mathrm{ESL}+\frac{1}{j2\pi fC}$$
separating into real and imaginary part:
$$Z=\mathrm{ESR}+j\left(2\pi f\cdot\mathrm{ESL}-\frac{1}{2\pi fC}\right)$$
now take the magnitude
$$|Z|=\sqrt{\mathrm{ESR}^2+\left(2\pi f\cdot\mathrm{ESL}-\frac{1}{2\pi fC}\right)^2}$$

Now I programed the Matlab. first the fuction that calculates impedance of the cap at given frequency/ies

function [ Z ] = calcCapImp( f,R, L,C )
Z=sqrt(R^2+(2*pi*f*L-1./(2*pi*C*f)).^2);
end

The code to calculate and plot the impedance of a combination of two capacitors in Ohms and dBs:

clear all;
f=10000:1000:1e9;
Z=(zeros(size(f)));
for i=1:size(f,2)
Z1=calcCapImp(f(i),10e-3,700e-12,100e-9);%calculate first cap
Z2=calcCapImp(f(i),10e-3,1250e-12,4.7e-6);%calculate second  cap
Z(i)=(Z1*Z2)/(Z1+Z2);%Total impedance is parallel combination
end
loglog(f,Z);
ylabel('Resistance, Ohm');
xlabel('Frequency, Hz');
grid on;
figure;
Z=20*log10(Z);%convert to decibels
semilogx(f,Z);
xlabel('Frequency, Hz');
ylabel('Resistance, dB');
grid on;

While the results look plausible,

I fail to reproduce graph I have seen elsewhere.

In particular, the above code attempts to recreate Figure 2 from here (same range):

I get nowhere near as dramatic spike at ~10 MHz as on the above mentioned external figure (aprox 10 times/20 dB smaller)

Have I done the calculations correctly? Is there an error in my simulation?

EDIT: here the corrected code  and graph per The Photon's anwser below

function [ Z ] = calcCapImp( f,R, L,C )

Z=R+1i*(2*pi*f*L-1./(2*pi*C*f));

end

clear all;
f=10000:1000:1e9;
Z=(zeros(size(f)));
for i=1:size(f,2)
Z1=calcCapImp(f(i),10e-3,700e-12,100e-9);%calculate first cap
Z2=calcCapImp(f(i),10e-3,1250e-12,4.7e-6);%calculate second  cap
Z(i)=abs((Z1*Z2)/(Z1+Z2));%Total impedance is parallel combination, take the magnitude
end

loglog(f,Z);
ylabel('Impedance, Ohm');
xlabel('Frequency, Hz');
title('Impedance in Ohms');
grid on;
figure;
Zdb=20*log10(Z);%convert to decibels
semilogx(f,Zdb);
xlabel('Frequency, Hz');
ylabel('Impedance, dB');
title('Impedance in decibels');
grid on;

Now the result is practically identical to those used for reference


texts:
This is probably answered elsewhere but I can't seem to find it.

I have a circuit which uses a Mega8 to drive a couple of ICs as shown in the diagram below.

Circuit diagram http://img851.imageshack.us/img851/5741/dimmer.png

The ISP connectors in the diagram are:
1: MISO
2: VCC
3: SCK
4: MOSI
5: RESET
6: GND
Alse note that the 5V power supply is actually at 4.5V and the ISP's VCC pin is not connected.

I'm seeing the flip-flops being triggered almost randomly. If I connect a resistor between the ICs in series it seems to clean up the signal, and it doesn't matter if the resistor is 10R or 10k. Does this mean that I should always use a resistor when connecting ICs even within the same logic families?

It should also be said I use an STK500s ISP to program the mega8 which means that the circuit ends up with two ground. They seem to be differing about 0.5V. The power supply is at 4.5V so the highest potential is 5V? It's a little unclear to me how these things add up but both the mega8 and the ICs are within normal operating parameters if it's 4 or 5V.

Sorry if it's long winded. I'm not sure how to explain it better. My question concerning this is:

Am I right in thinking the resistor cleans up the signal? And if so how do I figure out the best size for it?
If the mixed ground potential is causing a problem how do I isolate the two ground potentials, since both need to be connected to the mega8 during programming?


texts:
I am trying to write verilog code to do sequence detector the the state diagram below. Input is a 2-bit signals and there're 3 state variables as in the image.
The goal is to detect the sequence (01)-(11). When this sequence is detected the output (1 bit signal) is 1.

I tried the code below but somehow it doesn't work expected. In my first test, if I set up reset is zero all the time then the output signal some part is correct and some part isn't.

However, when I set a reset at the rising edge of clock, the output is always zero and two registers state and next_state is always unknown.
Could anyone tell me what is wrong with it and how to fix it?

module SeqDect(rst,clk,ip,op);

output reg op;
input clk, rst;
  input [1:0] ip;
reg [1:0] state;
reg [1:0] next_state;

  parameter [1:0] s0=2'b00;
  parameter [1:0] s1=2'b01;
  parameter [1:0] s2=2'b10;

always @(posedge clk, posedge rst)
begin
if (rst)
  state=s0;
    else
  state=next_state;
end

always @(state, next_state)
begin
case(state)
s0:
if (ip==2'b01)
  begin
    next_state=s1;
    op=1'b0;
  end
  else
  begin
    next_state=s0;
    op=1'b0;
  end

    s1:
  if (ip==2'b11)
  begin
    next_state=s2;
    op=1'b1;
  end
  else if (ip==2'b01)
  begin
    next_state=s1;
    op=1'b0;
  end
  else
  begin
    next_state=s0;
    op=1'b0;
  end

    s2:
  if (ip==2'b11)
  begin
    next_state=s2;
    op=1'b1;
  end
  else if (ip==2'b01)
  begin
    next_state=s1;
    op=1'b0;
  end
  else
  begin
    next_state=s0;
    op=1'b0;
  end

    default:
  begin
          next_state=s0;
          op=1'b0;
  end
    endcase
end
endmodule


texts: Nmos-bjt darlington pair dc bias. [Homework Help]

texts:
I have a homework assignment I need some help with.

I wanted to know if someone could tell me if I'm doing the dc bias calculations correctly, if not, could someone nudge me in the right direction.
I'm not talking about the ac analysis, only dc.

Here is the question

Here is my attempt


texts: Designing a latch with no constant power supply

texts:
I am trying to design a latch for an energy harvesting application with a very low power system.  Basically I have a setup with a 3.3V regulated output driving a circuit, which is run off a capacitor being charged by an energy harvesting system.  If the system ever turns off because it runs out of energy, I want a switch to prevent any current from flowing from the 3.3V output to the circuit.  This turning off can be detected by the output falling below 3.3V or from the charge across the capacitor dropping below 4V.  I then dont want to close the switch again until the capacitor is charged up to 16V, at which point the system should start drawing power.  Something that may be useful is that the output will always be at 3.3V when the capacitor is charged to this level.

I am having trouble with this because there is no true constant voltage supply and the system needs to be low power.  I also may need the system to stay on for long periods of time once the switch closes.

Some form of comparator with hysteresis of a few volts could work? but I do not know how I would get this to happen without some Vcc input.

As an update, I attempted to use a comparator tied to a latch that I thought would stay on until there was no power to it, but it does not seem to have worked.  any advice on getting this to stay on until it dies?
https://www.circuitlab.com/circuit/67e536/possible-latch-mide/


texts: replace buttons in voltage-divider with mosfets

texts:
I have this voltage divider (each press of a button generates a different voltage)

I want to be able to enable the buttons with a +5V signal. I tried to replace the buttons with 2N7000 n-channel mosfets, but somehow I don't get the right voltage at "buttons".
How should the mosfets be attached? Would it even work?


texts:
I want to detect a laser using a normal photodiode (Datasheet), but I am not sure whether it is robust enough, as laser (lower than 5mW) emits high energy photons.

Can I shine on such a photo diode constantly with a laser (<5mW) without being afraid of damaging the sensor?
What would happen, if the light would have to much energy? Would it just stop working or could it even burn?


texts: Could black-and-white CRT-based television sets be damaged by holding a magnet to the screen?

texts:
I know that it is possible to cause permanent (or at very least lasting) damage to some color CRT-based TV set by holding a magnet close to the screen and distorting the picture. SPECIFICALLY: it is possible for magnet activity to leave behind (semi-)permanent colour-blooming damage to the picture. But was there ever any kind of black and white set (again, CRT-based) where the same or similar was the case?

DETAILS
(The following took place over 40 years ago, in the first house in which I ever lived.)
When I was a kid, I remember being intrigued when I first heard about CRTs, electrons, magnets, etc. I was particularly fascinated by seeing a teacher demonstrate what happened when you held a magnet near to a TV screen and so I decided to try that for myself on our TV at home. However, my initial delight at seeing the picture bounce around under my control quickly changed to fear and dread at what my parents would say when they found out. The reason was that after I withdrew the magnet, although the picture returned to normal in terms of shape, I was left with a distinct purple shadow or "bloom" in the area where I'd been experimenting. Fortunately it was in the corner, not too obvious, and in fact faded away within a day or two. So I was never discovered. But still, it was weird. Subsequently I read that the problem was, I hadn't noticed that my teacher had demonstrated on a black and white TV, whereas my TV at home was a colour set!

However, in a recent discussion with my parents, during which I 'fessed up (well, it's been over 40 years...I figured it would be OK :-) ), I was told that it couldn't have happened as I remember -- at very least, not in the place I said it did -- because according to them, we never had a colour set while living in that first house. My mum insists that we only got our first colour set after we had moved from that house to one in the next town.

A few things could be going on here:

I'm mis-remembering where I was at the time; it was house 2, not house 1.
My mum is mis-remembering where we had our first colour TV; it was house 1, not house 2.
Neither of us are mis-remembering location, but I'm mistaken in my belief that only colour TVs were vulnerable to magnet-induced colour-blooming damage. (At least some) B&W sets were too.

Can anyone enlighten on option 3?


texts: What circuit will allow reverse polarity and continue to work?

texts:
I am looking for a circuit that will power my device with 12-24v no matter the polarity, the device will use around 1a maximum.

I know a bridge rectifier should work but I cannot deal with the voltage drop.

So if the supply is connected in reverse the device will continue to operate.

I need this because the wiring it will connect to cannot be changed, both conductors are the same colour, the connector is polarised and there is a good chance that the connections in the connector could be reversed.

I have looked up reverse polarity protection circuits but they just protect rather than make it work.

Has anyone got any example circuits or could tell me the terminology to search for?


texts: Heat Cable: directly powered with 230V AC vs. 12V DC with step-down efficiency

texts: Is it any less efficient to drive a 12V version of a heat cable from a step-down buck than directly powering a 230V version of it directly from the wall?


texts: Transmitting PWM binary at 400kbps (or 800kbps)

texts:
I need to send a string of bits to a chained set of RGB LEDs, each of which have their own controller IC. The datasheet for that IC, the WS2811, is here.

The protocol is quite simple: each bit, both 1 and 0, are sent as a high and a low, with different mark-space ratios, and are then strung together.

At 400kbps, the mark-space is as follows:

Binary 1: 1.2us high followed by 1.3us low (each +/- 150ns)
Binary 0: 0.5us high followed by 2.0us low (each +/- 150ns)

The data can either be sent at 400kbps or 800kbps. I'm not bothered which one I use, but I expect 400kbps will be easier to implement. (At 800kbps, the above times are halved.)

My question: How could this best be implemented? I'll probably be using a 20MHz (5MIPs) 8-bit PIC MCU to determine what data is to be sent, and I'm looking for the equivalent of a USART IC that the MCU could rely on to transmit data with the above encoding.

Possible solutions

There are three ways I envisage sending that kind of data at that speed:

Finding an IC / ASIC which is dedicated to this purpose.
Using a second MCU dedicated to receiving data from the primary MCU, and converting it directly to the above PWM encoding.
Building a dedicated transmitter out of TTL/CMOS logic ICs or similar.

For point 1, I can't find any IC that will do it. Do they exist?

For point 2, I have ideas for how it might work, but no solutions so far. One solution: Bit-banging would be very hard, having to be written in assembler given timing requirements. Another solution, although not capable of achieving the 100ns resolution for timing of the PWM signal to match the specs in the datasheet, could configure the USART on a PIC MCU to transmit synchronously - except each 4 bits transmitted would just be a hacky way of sending one PWM bit. So to send 400kbps PWM data, the USART would have to be capable of 400 x 4 = 1.6Mbps. Then, to send a PWM binary 1, the USART would send HHLL, and to send a PWM binary 0, the USART would send HLLL. This would only barely satisfy the +/-150ns timing requirements, a margin of 25ns. And I haven't found a PIC that can transmit that fast serially anyway.

So at the moment, option 3 is my only option: build dedicated hardware out of logic ICs. For example:

Construct a 25-bit shift register to output the PWM, required for a single bit. Then circuitry which fills the register accordingly depending on whether a binary 1 or 0 is to be transmitted. And since this would still be very intensive on the MCU, I would add perhaps an 8-bit latch which the MCU could write to, and allow further circuitry to process the 8 bits one at a time, for each one encoding the bit into the 25 bit shift register as a PWM cycle.
As above, but replace the 25 bit shift register with a monostable that outputs either a long or a short pulse, and another which loads a new bit every 2.5us.
Using a memory IC which acts as a lookup table, so perhaps (with extra circuitry) could be given a byte to transmit from the MCU and return data that a circuit could translate into serial data as the PWM output.

In short, I can't find a good solution! It seems like an awful lot of work for such a simple problem. How would you do it?


texts: How can I vary the output voltage of a "smart" USB charger?

texts:
I have a Raspberry Pi 3 system that I need to be small, light, and portable. It uses a USB Wi-Fi adapter that plugs into one of the ports on the Pi.
The adapter is quite particular about its supply voltage, and will not initialize if its supply voltage is below 5.0V.

The Pi and adapter draws about 400mA. I've found that my standard 5V 2A power supply for the Pi puts out 5.0V, which results in about 4.85 at the USB port.
I have another 6-port USB "high power" USB charger, but it is also well-regulated to 5.0 volts output.

By powering from a variable bench supply, I've found that a supply of 5.3V results in 5.1V measured at the Pi's power connector, and 5.0V available at the USB ports on the Pi. This is acceptable to the adapter but not very portable.

Rather than having to create some sort of customized supply to provide the 5.3V, I'd prefer to use a commodity "high power" "smart" USB charger (Anker, etc) and provide whatever type of circuitry is required to cause the supply to provide 5.3V.

This is a problem that was solved decades ago (in the general case) with remote sensing power supplies, but USB chargers approach it differently - more about current limiting than voltage control.

Is there any smart charging variant that enables output voltage regulation based on resistor values on D+ and D-?


texts:
What does "rated current" refers to in the capacitor data sheet? Is the current that the capacitor can supply?

I always assumed that it is the current that the capacitor can source. Is that correct? Also why the rated current is always specified at 125°C? How to calculate the rated current at different temperatures?


texts: Why are my op-amp (LMC6484) output signals not independent of each other?

texts:
I am using a quad op-amp (LMC6484) in a non-inverting circuit. Using only one of the 4 op-amps I was able to amplify Vin = 80.3 mV to Vout =1470 mV. Rin=2.66k Rf=10k. V+= 9V… V- = -9V

My problem is that when I use the other 3 op-amps using the same resistances, the output voltages are not independent of each other. When I change the input voltage on one of the signals, it alters the signals on the other 3 output voltages. (I am using 4 photoresistors connected to 160k resistors, which is connected to the same 5V Arduino pin and ground in order to give me the initial low input signals. Also when I say changing the input voltage, I mean covering one of the photoresistors with my finger.)

I am running the output signals through an Arduino Mega and monitoring their values in real time.

When I run the signals from the photoresistors without an op-amp, I get independent signals.

How would I make it so the output signals from the op-amp are independent of one another?

(Image source)


texts: 90 degrees phase shift in AC servo motors

texts:
IEEE Article1 and
IEEE Article2
In both of these links, its stated that main winding and control winding in an AC servo position motor are 90 degrees displaced from each other. Why is this so? Any explanation is appreciated, thanks.


texts: Is it possible to detect cellphone IDs in an enclosed area

texts:
I'm working on a project where I need to be able to identify different cellphones in an area.
Ideally I need a way to identify when specific cellphones enter and exit a range - this could be IMEI or Mac addresses (or any other unique ID).
I know that this is possible with wifi to get the MAC but it depends on the phone being set to autodiscover open networks - is it possible by using some RF device/scanner?


texts:
I am interested in finding the impedance as a function of frequency of the \$n^{th}\$ circuit in this series:

simulate this circuit – Schematic created using CircuitLab

(By request: this is intended to be a model of the internal impedance of a battery.)

I've tried simulating this circuit in LTSpice, which worked well. However, I can't easily change \$n\$ that way: I have to manually edit the schematic to increase the number of branches. I want a more general solution, where I can plug in values for \$n, R_1, R_2, R\$, and \$C\$.

How can I attempt to find an analytic solution for the impedance of this circuit? Are there any tricks that might help here?
If an analytic solution is impossible (or too ugly to be useful), what kind of techniques can I use for a numerical solution? I believe there will be a way to calculate this with some sort of loop and a bunch of complex-valued math.


texts:
I have an external LED on my alarm system (outside at my garage) that indicates the status of my alarm system. The LED is solid green when the alarm is off and all zones are closed (no movement). The LED flashes in green when there is an open zone (some movement). When the alarm is activated the LED flashes in red.

The LED is connected to 3 wires. The one wire is +3V, the other -3V and the last is ground.

My requirement is to add a buzzer to my alarm at the location of the LED using the power coming to the LED. The buzzer should beep once when I activate it, and beep twice when deactivated. I plan on removing the LED to accommodate the buzzer. If required to drive the buzzer, there is a 220V mains close to the LED.

So my question is how can I design a circuit to use the +-3V as a control signal to activate a buzzer as described above. Any help would be appreciated.

Table of voltage states:


texts: Rechargeable battery Charging another device calculation

texts:
Based on the same device and 2 AA size rechargeable batteries from this question - Rechargeable battery calculation

Now, the device is used to charge a small 5 inch tablet that have a 3600 mAH battery.

By theory, the device using 2 AA size rechargeable batteries will have a total of 2 x 1900 = 3800 mAH.

Compare to the tablet battery which is 3600 mAH, it should be able to fully charge the whole tablet.

However, when the device with the 2 AA size rechargeable insert and use to charge the tablet, it only manage to charge a max of 20% before the device start blinking and could not charge anymore.

So, the 2 AA size rechargeable batteries of 3800 mAH is only able to charge the tablet for a value of (20% x 3600 mAH = 720 mAH)

So, there is a huge difference of 3800 mAH (the 2 AA size rechargeable battery) minus 720 mAH (the amount it can charge the tablet) equal to 3080 mAH.

So, does it mean that the 2 AA size rechargeable battery of 3800 mAH have only 720 / 3800 = 0.19 (or 19% efficiency to charge a item)?

But the theory say that the 3800 mAH (2 AA size rechargeable batteries) should be able to handle the 3600 mAH tablet battery.

A side note - the 2 AA size rechargeable batteries took 1 hour to charge the the tablet and it only can charge up to 20% of the tablet battery (which is topping up 720 mAH to the tablet battery)

Is there a problem with the circuit or the theory is wrong?


texts: Setting the internal oscillator speed on PIC12F1822

texts:
I'm trying to get a PIC12F1822 to run at 32 MHz. Here are the relevant bits of code:

__CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_OFF & _CLKOUTEN_OFF & _IESO_OFF & _FCMEN_OFF
__CONFIG _CONFIG2, _WRT_OFF & _PLLEN_ON & _STVREN_OFF & _BORV_19 & _LVP_OFF

MOVLW   b'11110000' ; 32MHz HFINTOSC

BANKSEL OSCCON
MOVWF   OSCCON

BANKSEL OSCSTAT
btfss OSCSTAT, HFIOFR      ; Is internal oscillator running?
goto $-1
btfss OSCSTAT, HFIOFL      ; Is internal oscillator locked?
goto $-1

BANKSEL TRISA
CLRF    TRISA

BANKSEL PORTA

ON
    BSF      PORTA,2          ; 1 cycle
    GOTO    OFF               ; 2 cycles

OFF
    BCF      PORTA,2          ; 1 cycle
    GOTO     ON               ; 2 cycles

I'm getting a 1.33MHz square wave from PORTA,2, meaning that the clock is running at 8MHz... The PLL is definitely working though, as if I switch it off, the freqency drops to 333KHz (2MHz)

According to the debugger (PicKit3), OSCCON is getting the correct value.

The chip is running at 5 V.

Any ideas?


texts: LED still glowing with a capacitor in series

texts:
simulate this circuit – Schematic created using CircuitLab

I have a 470ohm resistor, 22uF capacitor and a 5mm LED in series (same sequence as described), connected to a 9V DC battery. I was expecting the LED to fade away but it didn't, it continues to glow with full power.

I am not able to understand why, your inputs will provide clarity.

Edit:

I realized that the polarity of capacitor was reversed. I corrected it and am now getting the expected result. However, I'm still confused as to why the LED was lit when the capacitor was reversed.


texts: Attempting to adapt a 4.5v flashlight for 120v AC use

texts:
I'm very new to learning electronics and have a project in mind. I have a battery powered light switch with 2x12 led strips that I want to adapt for light socket use. It runs off of 3 AAA batteries. The resistor pictured is Red, Black, Silver, Gold, .2 Ohms if my math is correct.
My problem is, I am not sure how to find the forward voltage for the leds without a voltmeter. I am thinking of using a DC power supply from another led light bulb to drop the voltage as well as rectify it.

I know this is probably not the best project to take on for a first but eh it's worth a shot, any help is greatly appreciated!


texts: Can I replace a NIMH rechargeable pack with a resistor if I only want to run plugged in?

texts:
My kids have a pair of IKEA night lights ("spoka") where the internal battery packs have died.  I'm debating replacing the batteries (3x AAA NIMH, marked 3.6V so in series) and have looked at this answer but since we've pretty much only ever used them plugged in, that seems like it might be better to just bypass the battery pack.

The lights worked with the the battery leads shorted, but there was an inline fuse on the old packs, and the circuit board gets uncomfortably hot.

One guess is that if I put a resistor there rather than shorting it, it will limit the current and keep things from burning up.  At the same time, I've got very little sense what size resistor to try to convince whatever very simple battery management circuit is in there that there's a full pack.

I do have a basic multimeter if it makes sense to measure the current or voltage across the battery charge leads.

The PSU is a cheap 5V, 500ma.  (edited: incorrectly wrote 200ma)


texts: Running an Arduino from a dual 12V power supply

texts:
I build a regulated dual +/-12V power supply with common GND myself as specified in http://musicfromouterspace.com/analogsynth_new/WALLWARTSUPPLY/WALLWARTSUPPLY.php. Now I would like to run an Arduino from that power supply.
Can I simply use two resistors (140 and 100 Ohms) to create a voltage divider (with or without an opamp buffer), or should I use a 5V voltage regulator?


texts: How to wire digital voltmeter/ammeter to measure arduino battery consumption

texts:
I'm not sure if you can tell but I'm a bit of a beginner, I want to wire up an digital voltmeter/ammeter combo to measure arduino power consumption.

I found the following device which seems suitable however i am unsure how to wire it so it is self powered.

If anyone could advice on the correct wiring that would be greatly appreciated!

Thanks


texts: What electrical design reasons are there for making rechargeable batteries non-removable?

texts:
There are lots of consumer devices that run on rechargeable batteries and have those batteries non-removable without disassembling a device. The most notable example is I guess an iPhone.

Making a battery non-removable has these advantages:

simpler case - no need for the door that would otherwise need to be strong enough to survive careless operations by the user

better case sealing

tighter packing of the battery into the case allows for more space for other components or smaller case

users are forced to use service shops that can generate money for the manufacturer through "authorization" programs

Yet none of these reasons seems to have any electrical design basis.

Are there electrical design reasons for making rechargeable batteries non-removable?


texts: Purpose of an Electronic Speed Controller(ESC)

texts:
I need to implement a brushless dc motor and I know the motor needs to need constant control to ensure that consistent torque is applied to the rotor.

What control does the ESC provide and what control is up to the engineer?

(I will be using scalar control) My understanding is that the engineer determines at what time power needs to be applied to ensure maximum torque while the ESC manages the flow of current to its respective coils. I know that a sensored motor uses the Hall effect to provide info on the rotors position, so I assume I can provide microcontroller to read the hall sensor input and then determine the angular speed of the rotor, but I feel this isn’t very robust.

Is there an easier way to approach this problem?


texts:
Why is the current through 1K resistor higher than Ib (Base current) even though the base-emitter path is less resistive than 1K?

Schematic


texts: Eagle - Custom pad shape for SMT inductor

texts:
I'm trying to make the following footprint in Eagle for an SMT inductor:

I understood how to make D-shape pads and similar, but this is driving me nuts: my idea was to enclose a pad into a polygon with 6 vertices, so I could bend the lower central segment into the arc with the radius shown above in the figure.
I've tried to do this in many ways but I can't figure out how. I've also thought about importing some dxf or svg, in order to draw it with a more drawing-friendly software like Inkscape. Any ideas on how to obtain this shape?


texts: Use RS232 - RS422 Converter with Encoder

texts:
Problem
I am trying to communicate an incremental encoder (TTL/422) with a PC, however, the PC is modern (correct me if I am wrong, It is a Sabertooth Z77) and doesn't have parallel ports...
I found a RS232 - RS485/422 Converter from Sintech, model: STM-8522B. And wondered if It could communicate with USB or VGA or even RJ45.
However, The encoder has the outputs: A, A/, B and B/. That are just outputs of 5V and my fear is to burn it with this converter, because the encoder just send signals and the communication is used bidirectional.
Question

Is it possible to read the encoder output from the PC with this converter?
Will it burn the encoder?
Is there another way to read the output?


texts:
According to wikipedia; a solar micro-inverter is a plug-and-play device used in photovoltaics, that converts direct current (DC) generated by a single solar module to alternating current (AC).

I can understand the benefits of having micro-inverters on every panel increases efficiency for a number of reasons; owing to moving AC is more efficient than DC and their MPPT capabilities.

The question that I wanted to ask is, how do you create micro-inverter strings?

Let's say you have 10 panels rated at 300 watts, each tracking their maximum power point. Now each micro-inverter outputs 110v AC.

That's 10 panels each outputting 110v AC. How do you combine those AC output?


texts: Where from the second half-wave of rectified voltage comes in full-wave rectification?

texts:
I know it may be sounds silly! But I can not figure out where from it comes - the second half-wave (let's say positive) in full-wave rectification. Is there any key to understand it? I mean: there is only one cycle at a time, and we currently see it's positive half, but when the cycle going down to minus V, where from the second positive half-wave appears?

I may guess where it comes from in the case of two secondary windings with common center where the signal of the second coil acts in anti phase 180° (I'am right?). But when there is only 1 secondary winding, what is the trick to double the frequency?


texts: Interface Self power Sensor with Particle Photon using 4-20mA current receiver

texts:
Is it possible to use 4-20mA self powered sensors using current receivers ? If not then what will be the best way to use these sensors and interface it Particle Photon to monitor the readings?

Note:- 4-20mA current receiver is new device and easy to use with IOT device and I am giving try with particle

Experienced suggestions on this will be helpful.


texts: Pros and cons between SMPS switched-mode power supply and heavy line-frequency transformer

texts:
I just found a huge 18V 1A heavy line-frequency transformer. In comparison, I also have a relatively tiny 32V 3A power adapter from a printer. So I notice the size advantage. but what else? Should I keep my 18V 1A huge power brick?

What are the Pros and cons between the modern SMPS switched-mode power supply and old school heavy line-frequency transformer?


texts: Increase range of an analog voltage output

texts:
I have a sensor that produces an analog voltage on output that can vary between 1,2 V and 1,4 V. As soon as my A/D converter on my Arduino would be not so effective with only 0,2V of variations, I would like to expand this range.

If I'm not wrong, there should be a way to subtract 1,2 V from my analog signal, so I will have a range between 0 and 0,2 V and amplify the signal, let's say, 10 times so, the new range will be 0 - 2 V, way better for reading from a microcontroller.

Now, I don't know what's the name of this type of circuit and, most import, how much they consume because my system is a very low powered circuit (400mA).


texts: PWM with Oscillator does not dim LED display as expected

texts:
I have a fairly successful attempt so far at driving an LED display with an Arduino Mega 2560. The Display sequences work well on their own and the Arduino seems to be doing its job sending the patterns. The part where I am struggling with is I am trying to control the intensity of the display with PWM. I am using an NE555P timer based mostly on the information here:
555 Oscillator Tutorial

The end goal is to replace POT1 with a rotary switch to select several pre-determined brightness settings via resistors as well as a location for a photocell to provide auto dimming to adjust to ambient light. I need an external oscillator as opposed to the PWM on the Arduino board because I am planning on using an Atmega chip by itself instead of the whole Arduino when more are made.

The problem I am having is that no matter how I attempt to regulate the PWM, it has no effect on the brightness of the LEDs. They stay lit with the same intensity regardless of the timer adjustments. I have a single indicator LED attached to the timer in front of R48 that dims as expected without any problem. It is the LED array that doesn't seem affected and it outputs with the same intensity regardless of the oscillator. It would seem to me, that being that the entire voltage in should be regulated by the pulses, that they would have to dim unless they are drawing power from somewhere else. Does that seem correct? I tried replacing Transistor 17 with an FET to see if maybe it was the switching speed of the 2N2222 not being quick enough but there was no change.

Would I be better off using a different timer or do I simply have something hooked up wrong? Is there a way to isolate the voltage in to the LED array better? I am fairly stumped as to why the LEDs are unaffected by the PWM. On the schematic the connection to the Arduino Mega2560 are represented by the "Digital" labels. Any input is appreciated, I have tried switching it around but haven't had any success.!!
Update: I have made changes to the schematic based on some helpful suggestions. There are still no changes to the brightness of the display though.
Update 3:

Having problems getting the images to insert...


texts: Hello i was just wondering if someone could explain to me why the shunt regulator is used in this circuit. I get the zener diode keeps the 12 v constant to the motor but does it have to be there? Couldnt just the resistor be used in place without the zener diode to drop the 24 v to 12 v? Also only 1 motor is on at time


texts: I am testing the proof of concept for an IOT smart watch. Is there an algorithm for calculating Blood Pressure if the smart watch is on the person's wrist? From the algorithm I can determine what sensors I need to collect the variables needed by the algorithm?


texts: AM modulation stage for small transmitter

texts:
I am trying to build an AM radio transmitter. I have built a Colpitts oscillator with a 7 Vpp output and an audio stage with a 1 Vpp output. I am trying to build the amplitude modulation stage I am using a circuit like this.

But my output on R3 looks like a mixer signal instead of a modulated one and is getting clipped.  what is causing it to do this? And what would be a solution to get amplitude modulation? Any resources or help would be appreciated. I would like the amplitude modulation stage to not use IC's if possible.

====================================================================

Ok here is my new schematic with a varying resistive network (as suggested below)

I am still not seeing the intended results, any ideas?


texts: Looking for a explanation/cause of lithium polymer battery failure

texts:
I'm hoping that someone on the EE StackExchange could give me some insight into what is going on with some lithium polymer batteries that I have under test.

The question I am trying to answer is: what conditions/causes lead to the type of failure mode described below?

The Setup:

I have a fixture that automatically charges and discharges a group of candidate batteries while logging battery voltage so that I can gauge battery operation and usable life. The fixture uses an MCP73837-FCI/UN Lithium Ion/ Lithium Poly charger IC to charge my batteries at a rate of ~65mA. Once they are all at full charge (4.2V or so - I go by the status flags of the MCP73837), the fixture disconnects the charge IC from the power source via a relay, connects into a load circuit, and begins discharging against a load that varies between 30mA and 80mA duty cycled at 80% at a rate of 74Hz (see below). The load is independent of battery voltage.

Once the batteries all reach a voltage of 3.4V, the batteries are disconnected from the load circuit, connected into the charging circuit, recharged and the cycle repeats.

The Batteries:

I am testing 3 different lithium polymer batteries in my setup:

A 120mAh battery that has a production history measured in years and is deployed in the field in thousands of products.
A candidate 250mAh battery that so far exhibits no issues with my test regimen.
A candidate 200mAh battery that has exhibited failures across 3 samples.

The Problem:

After about 10 or so charge/discharge cycles, 3 samples of the 200mAh battery began exhibiting poor battery life. Physically, the affected batteries increased in size (thickness) by 20-30% from their pre-evaluation measurements and have noticeable ruptures / rips in their pouch (picture of affected battery included below):

The batteries seem to have rigidly increased in volume. This does not seem to be just a battery outgassing event.

Other useful information:

None of the other batteries under test exhibit this failure mode.
The affected batteries have an integrated battery protection PCB at the leads that ought to protect against accidental shorts, overcharge, overdischarge etc. (The protection circuitry consists of the DW-01 IC + The 8205 Dual MOSFET)
These batteries are not being compressed / under mechanical stress during testing.
The batteries had read about 3.9/4V prior to being subjected to the charge/discharge protocol described.
I have another fixture with a nearly identical charge/discharge setup where I have a 3.2V depth-of-discharge threshold instead of a 3.4V depth-of-discharge threshold and none of my 200mAh candidate batteries exhibit this failure mode even after 40+ charge/discharge cycles.

Some insight into this phenomena from someone with some general lithium polymer / battery testing / battery chemistry expertise would be very much appreciated.


texts: I have read a couple papers that mention nominal SNR in Massive MIMO. In the places where I have seen it, it says it is the SNR of the User when M = K = 1. This means that it is the SNR when the the number of users is 1 and the number of antennas is 1. Does that mean when they say nominal it is just the basic SNR equation? The Massive MIMO blog talks about it here.


texts: Crackling sounds when both speakers are connected?

texts:
I have finished my amplifier using the LA4597 chip following the schematic below.  So far everything's working fine.

However, I noticed something. Some songs crackle the speakers (probably because of their frequencies). But if I disconnect one speaker, the crackling sounds disappear on the other. I tested it to both of the speakers to check if one of them is blown or damaged but nope, both speakers sounded clean whenever the other one is disconnected. Btw, the volume was the same on every test that I did.

What is happening? Can this be resolved?


texts: How to determine the value of an SMD coil?

texts:
I am trying to repair one PCB where an SMD coil seems to be burned out.

I would like to replace this component, but I have no idea about how to determine the value of this SMD device, because it is not marked.

How can I get this value?


texts: Getting Rid of Annoying Buzzing Sound from Multimeter

texts:
my multimeter has been bugging me with this buzzing sound that turns on and off while I'm using it. I think it has something to do with its autoranging feature, but I couldn't find the manual for this one and have a mind to get rid of the buzzing if it won't stop.

The model is a Craftsman 19736. I opened it up and discovered the culprit: a spinning thing with a blue and red wire going to it in the back case. Do you know what it's for and if it's OK to remove?


texts: Optical encoder triggers false interrupts

texts:
I have a hobby project with four-wheel mobile-robot-platform, where I have attached two optical wheel encoders, that are further connected to micro-controller:

(Source: https://www.dfrobot.com/wiki/images/b/b9/FIT0029_Encoder_Schematics.png)

The micro-controller handles the encoder input by using two interrupts, that are set up to trigger for rising-edge. In general the setup works OK.

However, the problem is that every now and then false interrupts are detected, which makes tracking the position impossible. Here is an example sequence of time differences between the interrupts for a specific wheel: 0.059 0.059 0.060 0.061 0.064 0.063 0.058 0.006 0.064 0.062 0.060 0.025 0.034 0.058 0.060.

The time difference is rather contrast around 0.06, put then suddenly the interval is split to two interrupts, summing together to around 0.06. I'm also observing much shorter intervals, but these are easy to remove by just detecting the too short interval.

The splitting of interval, might be related to sawtooth like profile of the encoder, i.e., when the voltage drops, due to reaching hole region, it causes some sort of short oscillation generating false rising edge. I have tried to reduce the problem by using a Schmitt trigger, which inputs are connected to low-pass filter (10kOhms, 9nF, and 20kOhms and 9nF combinations tested, not sure if these are optimal?).

This greatly reduces the short intervals but the longer ones are still a problem. The setup contains lots of wiring which are also potential sources of interference.

I would be grateful for any suggestions how to remove the false interrupts.


texts: Boolean expressions from Bubble Diagram for D-flip flop entries

texts:
I am supposed to get boolean expressions for the two D-flip flops involved in this state diagram but I am stuck.

I have come up with a truth table (except for output y which I don't understand) for the state diagram but I don't understand how to get the actual expressions of D0 and D1.
The hindsight says: D1 = 0, D0 = Q1'Q0'+xQ1Q0+x'Q'0 but I don't know how to get there, I'm struggling with the truth table

How do I do it? This is my truth table based on S0, S1, S2 and S3:

\begin{array}{ccc|ccc}
 & PS & & & NS \\
D0 & D1 & x & D0 & D1 & y \\
\hline 0 & 0 & 0 & 0 & 1 \\
0 & 0 & 1 & 0 & 1 \\
0 & 1 & 0 & 0 & 0 \\
0 & 1 & 1 & 0 & 0 \\
1 & 0 & 0 & 0 & 1 \\
1 & 0 & 1 & 0 & 0 \\
1 & 1 & 0 & 0 & 0 \\
1 & 1 & 1 & 0 & 1 \\
\end{array}


texts: Quartus Minimum Propagation Delay Report doesn't show up

texts: Does anyone have any idea why minimum propagation delay report doesn't show up after compilation? It doesn't happen in every project, sometimes it's included in compilation report sometimes not. This is really confusing.


texts: I need help to identify this old SMD device

texts:
I'm working on a circuit and I can't find information on this component (see picture).
This hybrid circuit is part of an old industrial PSU. It is a PFC circuit based on UC3854 but I don't know if the device I'm trying to identify is directly involved in power factor correction.

What I know is:

The SMD code is "5393". I have some of this chip and the number at the bottom changes from one component to another.
Pin 4 is GND and pin 8 is VCC.
Judging by the connections, it would appear that pin 7 is an output. Pins 2-3 and 5-6 may be inputs.
The package is a sort of SOIC, the body is approximately 4.40 mm x 5.16 mm, like the Panasonic SO-8D or Renesas PRSP0008DE-B (JEITA P-SOP8-4.4x4.85-1.27).
The device may be a Japanese device. Or may not. :-)
This equipment is from the first half of the 90's.

Here is a draft, which briefly describes the connection:

Seeing this circuit I think the right side could be a comparator; on pin 5 there's a sort of reference voltage related to the "19V" (auxiliary PSU voltage?) compared with the 380V (DC voltage before the switching section of the PSU) on the pin 6. While 380VDC are OK the hypothetical comparator output on the pin 7 keeps on the pass transistor Q1 (I suppose this is a kind of enable signal to the power switch drive section).

Also the left side is like a comparation between the 380VDC and VREF (generated by UC3854), but I don't clearly understand the output circuit.

If my assumptions are right the device could be similar to some dual comparator like AN1939 or LM393 but I can't find any evidence that there is a device named or marked "5393" similar to these devices.

Anyone could help me?


texts: How to get the Bode Plot of both magnitude and phase?

texts: I want to know if there is any instrument which gives the Bode plot of both magnitude and phase simultaneously? For instance, a CRO displays the waveform as soon as we connect its probes to a given circuit. Is there anything same for the Bode plot?


texts: How to wake up SIM800 module from sleep, after entering sleep mode 2 (AT+CSCLK=2)?

texts: I want my SIM800 module (I interfaced it with Arduino Uno) to enter sleepmode-2 (I used AT+CSCLK=2 command). My question is, how do I wake it up from sleep? I tried giving various AT commands but I cannot see anything on the Arduino Terminal.


texts: How do I calculate what resistors I need for RGB LEDs with 3.7V?

texts:
I have a total of 4 x RGB LEDs.

I am hoping to power these as well as a RFduino BLE module with a 3.7V lithium rechargeable battery.

I was just wondering how I would go about calculating the resistors needed for these RGB's?

I'm confused because I've seen this example of using 150ohm for Red and 100ohm for Blue and Green.

I guess I'll have to eventually get my head around resistance. There's a great app called Circuit Playground, but I wasn't 100% sure on what the forward voltage and supply voltage (Vf) meant.


texts: Moving the code and interrupt locations in Arduino

texts:
I need to be able to choose between two Arduino apps running on an atmega 1280 (megaavr) at boot time.  Therefore I need to move one of those apps to a different location in program memory, and I need to move the interrupts to that location as well.

I already have a method of executing the correct interrupts (with the help of the bootloader) in any location in memory.

However, I don't understand the build process enough to see where the linker decides where to place things and how to move both the program and interrupt sections to new memory locations.

Where is the location of the interrupt vector defined?
Where is the location of the program defined?

The current builds are performed using Arduino 22. While I'd prefer to modify build scripts or files in that environment, if needed I would consider moving it all over to a makefile build process and out of the Arduino environment.


texts: Heathkit IP-27 bench PSU min. stays at 0.18V and there is a +0.1V for all the readings?

texts:
I've recently acquired a Heathkit IP-27 bench power supply. The supply itself works quite fine except that the minimum voltage it can be turned down to with the coarse adjustment is only 0.18V, doesn't zero out. It wouldn't go down any further. Lets say for example I set to 10V, it is actually 10.18V when measured with multimeter. I tried the calibration procedure but still the issue persists. Is this due to a fault with the device or is it just that the PSU is just like that?

I've attached a link to the manual for the IP-27 for reference. The only additional mod I did was add the zener+capacitor for protecting the transistor when changing the voltage knob as per the manual.

http://www.rsp-italy.it/Electronics/Kits/_contents/Heathkit/Kits/Heathkit%20IP-27%20power%20supply.pdf


texts:
"The MAX6960–MAX6963 are compact cathode-row display drivers"
What does cathode-row mean?


texts: Servo motors: does neutral position imply a 50% PWM duty cycle?

texts:
I'm working on a project using a Savox SB-2290SG servo motor. The datasheet I received is only 3 pages long, and includes limited information on the control interface. I've posted the relevant datasheet snippet below.
While the datasheet does list the acceptable range of pulse widths, it never mentions the overall duty cycle or PWM frequency. For example, if I want to command this servo into the neutral position, I know I need a pulse of 1500 microseconds, but how long should I wait between pulses? Another 1500 microseconds? 3000 microseconds? 10,000 microseconds? It doesn't appear that that PWM wave I need is fully defined by this datasheet.
Does 'neutral position' imply a 50% duty cycle? Is the datasheet missing key information? Or am I misunderstanding something about how to control servo motors?

Update: I reached out to the manufacturer, and they informed me that they use a 333 Hz frequency during their testing.


texts: How do we have the \$E=\frac{1}{2}L_1I_1^2+\frac{1}{2}L_2I_2^2 \pm MI_1I_2\$? Can anyone show me its proof?

texts:
What is the total energy that two inductors store?

Solution

\$R_{th}=(12||6)+6=10Ω\$,so \$I=\frac{90}{10}=9,I_1=9\times \frac{6}{12+6}=3,I_2=9\times \frac{12}{12+6}=9\$.

So the energy that two inductors store is

\$P=(\frac{1}{2}\times4\times3^2)+(\frac{1}{2}\times6\times6^2)-(1\times I_1 \times I_2)=108J\$

What confused me is this part:

\$-(1\times I_1 \times I_2)\$

I can't understand why we should write (\$1\times I_1 \times I_2)\$

1.It seems that in this situation,the formula for this is

\$E=\frac{1}{2}L_1I_1^2+\frac{1}{2}L_2I_2^2 - MI_1I_2\$, \$M\$ is mutual inductance

How do we have this formula? Can anyone show me its proof? I am very curious that why do we have \$MI_1I_2\$ in the formula  because it seems that we didn't use the formula below:


texts: How to make a constant current sink in the pA-nA range

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I am tasked with making a constant current SINK for a testing device. It must outputs 4 separate values, -10pA -100pA -1nA -10nA. I need the current to last for at least 10-20 seconds, preferably up to 100 seconds if possible. These current values are very small so I won't be able to use a simple current mirror with transistors.

The reason I need to make this device is it needs to be much smaller than a test bench instrument, think handheld, and only needs to work for those specific current values. I also do not know the load, this is a source, it shouldnt matter?

So far, all I have come up with is to use a voltage ramp to charge a capacitor (Ic= C dv/dt) so it can output the current. I would use a mechanical switch to change the capacitance value so the ramping time stays the same and the current can be changed  between the 4 values. The waveform would need to be a sawtooth so as to ramp back up in ~1 second. I don't know how to make a sawtooth or really any voltage ramp myself and need it to be linear so as to get the proper current from the cap.

Please give me any suggestions and ask questions about whatever else I forgot to tell you, I'd like to figure this out soon.

EDIT: hopefully its a bit more clear


texts: Proper Component Testing (Specifically Resistors)

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What is the best practice for testing small components such as resistors / capacitors before shipping? I buy these in bulk, and while it is easy to catch the duds that have already failed, sometimes there are components that spontaneously die in the field. What is the best way to simulate a few hours or dare I say days of rigorous use?

If there is a recommended book full of these practices, I would love to know about it. (perhaps in the wiki?)


texts: Thin film resistors & power derating curve

texts:
please take a look at the pic,
what would happen if ambient temperature goes over 180C?
would it still be functioning as a resistor at 180C even it can't dissipate anything anymore?


texts: Need to identify this 3-pin Connector to a small amp. It's a Pre-Amp input

texts:
I could use the neighbouring 3.5mm stereo jack for sound input, but those connections are flimsy.

It's a 3-pin connector, 10mm long, 6mm wide and 7mm high with alignment slots on all sides but the back (see picture).  I could not manage to measure the pins.


texts:
I am a honey bee researcher and I want to build a temperature sensing system to monitor the temperature changes in the three dimensional space within the hive body using 5 sensors on each hive frame (25 sensors on the frames), five sensors on each side (20 sensors on the sides), and 5 sensors on the top and bottom of the hive (10 sensors top + bottom). There are 55 sensors in total.
I need to collect the temperature at each sensor as well as the average temperature inside the entire hive. During winter, when the hive can be as cold as -23.3 C, the cluster temperature (~100 bees and the queen) keeps the temperature within the cluster at ~26.7 C. If the cluster breaks, the bees will freeze to death. I want to track their movement through the hive (the cluster is in constant motion).

Several engineering students have attempted to solve this problem to no avail. This project is more than 10 years old.

Essentially, I need to create a grid that will allow me to track the temperature in a 3D space. I will be connecting the sensors to a Raspberry Pi and I will connect the system to a remote transmitter / receiver.


texts: Transistor circuit swap out motor for crude induction coil

texts:
I have a motor, which is the fan from inside a computer, is controlled by a BC237 transistor as in the diagram. The transistor is controlled by a signal from an Arduino. The signal comes on for 5 seconds and then off for two and this repeats. The motor then comes on for a few seconds and goes off as expected.

I replaced the motor with a crude coil of wire wrapped around a plastic pen cover inside which is a nail, with a magnet attached to the flat end. And the nail moves as expected when connected directly to a 3V battery. But not when the coil replaces the motor.

So why is the same thing not happening when I replace the motor for the coil?
I thought this has something to do with self inductance.
Is there anything I can do to solve this problem?