texts: Static Hazard in Specific Value or Any changes?

texts:
I have one solved problem, My teacher solved it as follows:

and says

  with B=C=D=1 for change value of 'A' from one to zero we have Static-Hazard '1'.

but I think we should say

  with B=C=D=1 for any change values of 'A' we have Static-Hazard '1'.

Which one is Correct? Any idea?


texts: For the Arduino Uno, should I use a 3.3V or 5V serial LCD?

texts:
I am just getting started with Arduino, so please forgive me if this is a stupid question.

I was searching for serial LCD displays, and found them in two variants: 3.3V and 5V. I looked on the Uno board to see which I should use, and found that it had power outputs for both.

So, which should I get? Or does it not really matter?


texts: Looking for a capacitor capable of driving a 12V / 7A valve for ~4 seconds?

texts:
Is it possible for a Capacitor to supply a servo motor with enough power for it to close the servo when power is disconnected?  I've got an application where I need to close a servo valve that takes 7 Amps (12 Volts) to run and it takes 4 seconds to close the valve. Voltage can vary between 13 and 7 Volts.

Any idea what Capacitor size I need to look at. I tried a 40V 5100uF capacitor that was sold as a battery replacement for a motorcycle but it discharges before the valve even moves.


texts:
My understanding is as follows:

For an isolated SMPS, we first rectify the input ac voltage, then convert it to a square pulse using a switching regulator. It is then stepped down using a transformer, and then again rectified.

For a non-isolated SMPS supply, I think we either first rectify it and then pass it through the switching regulator, or we first pass the input ac voltage through a switching regulator to get the desired voltage, and then rectify it to get a dc voltage.

I would also appreciate if anyone can please share a block diagram of a non isolated SMPS.


texts: Is it possible to induce negative/positive charge wirelessly

texts:
Sorry if this question doesnt belong here. I have no clue of what I'm about to ask.

I want to know, if possible, how to induce negative/positive charge on objects inside recipients? What I want to achieve is this:

Say plastic recipient A have a liquid and some metal objects inside.

We also have recipient B with the same caracteristics.

Now I want to have positive charge on everything inside recipient A and negative charge on everything inside recipient B without dropping  a cable inside each recipient.

I already have positive and negative charge being supplied on different cables. I want to know how to induce the charge wirelessly.


texts: Voh and Vol value in S32K142 Microcontroller

texts:
I'm having this S32K142 Microcontroller. 64 pin package.
I have some trouble with the logic level compatibility between the above Microcontroller and the A80604-1 Backlight Boost LED Driver.
Performing the IO Logic compatibility:
From the Table 19, In Microcontroller datasheet, we get the values of Vih and Vil.
Question 1: Why is the value of the Voh and Vol not provided? Can someone tell me how to find the value of the Voh and Vol pin (incase the GPIO is not configured in Open Drain fashion. I assume in the case of the pin being Open-drain the Voh and Vol will be determined by the voltage supply outside the pin from which the pull-up is connected.) ?
If I perform a Ctrl+F search "Vol and Voh), I see from the other tables that in certain places (Table 17 and Table 19), Voh appears to be (Vdd - 0.8V) and Vol appears to be 0.8V. Can we take these as the Voh and Vol ? Voh = Vdd - 0.8V & Vol = 0.8V ?
Question 2: I have an Enable Signal coming from the Microcontroller to the LED Driver.
From the datasheet of the LED Driver, I found the Minimum Input Logic Low for the Enable pin is 0.4V as below.

In the above case, if the Vol(max) of the Microcontroller is 0.8V and the Vil(max) of LED Driver is 0.4V, they are not voltage compatible right? Is my understanding correct or am I missing something?
If that's the case, how to solve this voltage compatibility issue?
And just by the way, how can the Vol of the Microcontroller be as high as 0.8V?
Can someone help to clarify the above 3 questions, please.


texts: Common base large signal transfer characteristics

texts:
simulate this circuit – Schematic created using CircuitLab

I'm trying to draw the large transfer characteristics for this common base BJT below. I redrew figure 1 to look like figure 2 so it can help better visualize what's going.
I want to plot Vo Vs Vi

I used KVL to come up with this equation
-Vcc + RLIc + Vo + Vi = 0

So then Vo = Vcc -RLIc - Vi

Ic = Is x e(Vbe/Vt)

Vo = Vcc - [Is x e(Vbe/Vt)RL) - Vi

My confusion is that the base is grounded. Does this now mean that Vbe = -Vi? Or is it that Vbe = 0 since the base is grounded?

If Vbe = 0 then Vo = Vcc - (IsRL) - Vi

Or Vbe = 0 -Vi then Vo = Vcc - [Is x e(-Vi/Vt)RL] -Vi.
Can you please tell me what's right here? Or maybe I get it all wrong then I will need some guidance.
Thanks!


texts:
This is a picture of the problem:

Can someone please explain to me, why is to \$V_1=V_2+10\angle{45°}\$
why not \$V_2=V_1+10\angle{45°}\$ or not \$V_1+V_1=10\angle{45°}\$? (It's circled in the picture.)


texts:
I got this IC in my circuit and I'm wondering if I could hook up a pull-up network to it, in the following way:
Since it's an RS485 transceiver, the input to it is differential. I need to know if I can input a non-differential voltage as an input to it.
My intention is to eventually determine the voltage that comes into the IC, if it's high then the cable is not connected and when it's low the cable is connected.
(for clearance - the voltage will be determined my an MCU input reading the high/low states).


texts:
In this circuit:

Assuming ideal diodes

We are required to calculate VD1, VD2, ID1, and ID2.

If I assume that D1 is off and D2 is on which is a wrong assumption (as I think). How I prove that it is wrong? how to calculate Vx to show that D1 should be on here?

Edit: I calculated Vx as following:

I = (9 + 6) / (22k + 43k) = 2.31 * 10^-4

V(of 23k resistor) = 43k * 2.31 * 10^-4 = 9.93 v

=> Vx = 9.93 - 6 = 3.93 v

Is that correct?

If I assume that D1 and D2 are both on, then the circuit will look like:

How can I calculate ID1 and ID2?
Can this resulting circuit redrawn to be easier to solve?


texts:
I'm new to electronics and am building a very simple circuit involving a peizo speaker, amplifier IC and LED.

Right now I run the peizo into the amp IC and then take the output to the led. With this when I bang the peizo on the table the LED lights up for a briefly. I'd now like to modify this so instead of the LED immediately going off I'd like it to stay on for a bit longer.

My thinking is to do this I need to use a capacitor and have the peizo trigger the capacitor to dump power into the LED. I'm stuck however trying to think through the circuit. How can I charge up the capacitor and then once fully charged stop the flow of power to the capacitor and then dump it out another path when the peizo triggers?

My thinking is I could use an NPN and have the peizo trigger the gate and then have the capacitor keep the gate open while it also dumps into the LED but I'm still not sure how to initally charge the capacitor.

edit: added schematic


texts: Voltage rating and tantalum vs ceramic capacitor on the output of a switching voltage boost stage

texts:
I am designing a PCB with a TPS61090 synchronous boost converter. The datasheet recommends a ceramic 2.2uF and a tantalum polarized capacitor on the output of the chip. They discuss calculating the capacitance of the polarized capacitor and the influence of the ESR on it. But they don't actually mention the voltage rating of that capacitor, and neither do the articles I found when googling. I am planning to output 5.2V on the output (to allow a small voltage drop due to downstream components) so the capacitor should be at least that. But I also read that you need to size your capacitors to double the max voltage, because the capacitance drops with voltage. So what voltage rating would people recommend for the tantalum capacitor? Would 6.3V be enough? Tantalum caps higher than 6.3V seem to get expensive quickly.
Secondly, adafruit makes a board that uses this chip and although their schematic says it's a polarized capacitor, it looks more like a large ceramic capacitor to me. Why would you prefer a ceramic capacitor over a tantalum capacitor or vice-versa for this application?


texts: Getting the optical power of a UV-LED using a spectrometer data

texts:
if it is possible can you let me know the way to get the radiated power of a UV-LED using the output data from the "Ocean optics- Maya pro 2000" spectrometer, or the calculations needed to calculate it from that data.
in the data sheet of the UV-LED the radiated power is from 2mW(min) to 6mW(max) at 40mA current, i uploaded a screenshot for the spectrometer data.
thanks in advance.


texts: Need help for a trouble with Keil C window

texts:
I tried to program STM32 with Keil C but when I try to "Set Path" to the library, there is a problem like this:

As you can see, the "Option for Target" window doesn't show all everything, there is something on the right side but I cannot see it. I tried with KeilC4, KeilC5, and the problem persist. I cannot zoom in/enlarge this window. I guess I need to adjust something in my computer but I don't know what to do. Can anyone help me? This happens to all the other windows in KeilC.


texts:
I was desoldering components from a power supply board for a printer and I came across this small component. It was pressed against a heat sink so I assume it is some sort of thermistor but I am not sure.
The text on the component is "5104BL6"


texts: How to interface this circuit with a 0-10v Theatrical Lighting Dimmer

texts:
I'm trying to build a circuit which allows an Arduino to control 6 channels of lighting from an old Strand Act 6 Dimmer.
These dimmers have 8-pin DIN connector on them like this specification. Pin 7 is +10V, Pin 8 is GND, and Pins 1-6 control the dimmers on channels 1-6. This is so that a variable resistor can be connected from GND to +10V, with its output going to one of the channels (so no powered controller is needed). However, I'd like to control 6 "variable resistors" from my Arduino using PWM.
I'm following this guide. My Arduino outputs PWM on 6 pins, each of which goes through its own filter circuit:

which produces a voltage between 0 and 10v at OUT. My question is: this 0-10V is relative to the Arduino's GND and +12V input power. Will simply connecting the OUT of each filter circuit and GND to the corresponding pin on the DIN connector work, or do I have to somehow make the 0-10V OUT correspond to the +10V/GND coming from the dimmer?


texts:
In the following circuit I have to find the output voltage, Vo, related to the input voltage, Vin. We assume that both diodes, D1 and D2, are the same and have a 0.7 V drop when they conduct and op-amps are ideal.

I am thinking that at start, before any input is applied, both D1 and D2 are reversed biased and no current flows in the circuit. When a positive input is applied (Vin > 0), op-amp 1 will immediately saturate at the negative supply (V -> V+), which means that V' will be negative and D1 will conduct when D2 will be reversed biased.

On the other hand, when a negative input is applied (Vin < 0) opamp 1 will immediately saturate at the positive supply (V- < V+)  which means that V' will be positive and D2 will conduct when D1 will be reversed biased. Then, in both cases, we will have a circuit with closed loop op-amps with negative feedbacks. Thus, by using Kirchhoff's law I can define the output voltage related to the input voltage knowing that no currents flow in or out of the inputs of the op-amps.

Is this process right?


texts: How Dual MOSFETs are used in Power Management or Protection circuits?

texts:
I'm learning the basics of MOSFETs and came upon these common-drain, dual MOSFETs in single package, AFN8205:

It seems they are used for some specific applications (e.g. load switch) as noted by manufacturer. one of its common application would be the switch for DW01 battery protection IC. (the left portion of circuit containing the TP4056 charger are not considered in this question):

I had some problems understanding why the the 2 MOSFETs are used symmetrically and how they would turn on at all in this specific circuit. I tried to solve the circuit for the case for when the 2 MOSFETs are turned on for normal operation of the load (no overcharge nor over-discharge).
Both MOSFETs gates charged by control circuit:
In this case the GND of the battery should be connected to GND of the circuit. the current should flow through both MOSFET while they are ON so the internal diodes are not dropping voltage and wasting energy.

simulate this circuit – Schematic created using CircuitLab

The right MOSFET turns on, because the gate voltage, Vgs (from the control circuit), is bigger than 0V of the source or the battery's negative pole (assuming the gate threshold is reached).
The voltage at the common-drain would be ~0, equal to battery's negative pole and a tiny value considering the current flowing through Rds of the MOSFET. the Rds is <50 milli ohm for this particular MOSFET.
The load which is turned on by now because of the internal diode of the left MOSFET, and is getting a voltage of ~0+1V because of the forward drop of the left MOSFET's diode.
The left MOSFET turns on because of the assumption that the Vgs would be greater than threshold and ~1V of the source.

Here comes the problem. why the left MOSFET turns on when its drain-source voltage is "-1V"? the MOSFET only turns on when the drain source voltage is above a limit:

So, what's wrong?


texts: Altium. Can't apply a rule of plane connect to Polygon

texts:
Problem with Altium Designer!
I'm trying to use Plane Connect to Polygon with four conductors, but in existing PCB it dosen't work. (in new projects it working)
What could be wrong?

My actions: 1) Set Plane Connect rule. 2) Repour all polygons. (also i'm tried to repour selected polygon)

The rule:

The polygon (GND):


texts: Resistors in high-speed I/O trace when impendance mismatching

texts:
I am little bit confused over impedance matching when dealing with high-speed digital I/Os. I would like to share some perspectives in hope to clarify a few things.
Let's consider a digital output with a known impedance Zt=50 Ohm. If the transmission line (PCB trace) is designed with Z0=50 Ohm, then there are no ringing/reflection phenomena, beside the expected one.
Now, let's say that Z0=80 ohm. In that case, a series R of 30 Ohm is placed in the trace, and here my confusion begins. What exactly happens? By reading material, I have gained two perspectives, of which either one is wrong or both are wrong and I have completely missed the points.

Perspective 1: By applying a 30 Ohm R, then there is a correct termination because Ztt = Zt+ 30 =80 Ohm, which matches trace impedance.

But then, I question myself, why the 30 Ohm add to Zt and mitigate the problem, and not add up to Z0, and further amplify the problem? What's the difference of having a trace with Z0=110 ohm and a trace with Z0=80 Ohm plus a 30 Ohm series resistor? Also, with that logic, the series R should be placed as close to the output pin as possible, whereas I have see designs that place it in the middle or even at the end of the trace, next to the input pin.

Perspective 2: By applying a 30 Ohm R, you limit the output current, thus increasing the rise time which in turn increases the maximum conductor length before the undesired high speed phenomena affect the line.

In that perspective, the R can be place anywhere in the trace. Also, you essentially trade between rise time and max length. So, if you have a clock, let's say, with 200 MHz freq (5 ns period) and rise time of 1 ns, then it could have an impact on setup and hold times: now there is less pulse width time due the increased rise time, whereas in a correctly matched trace impedance the additional time could be used and the overall design would be limited only by the propagation speed of PCB material.
Additionally, if that's the case, then a series R could be placed based on the max length desired to be achieved: if, for example, Zt=50 Ohm, Z0 = 80 Ohm and rise time is 1 ns, in that case max length is ~4.5cm, then if the trace is 4.9 cm, a R=30Ohm is more than enough, so it could be lowered to 10Ohm, thus preserving some pulse width time.
To sum up, my question essentially boils down to these:
When I am placing a series R, am I doing impedance matching, am I doing a rise time increase or have I completely misunderstood everything?


texts:
I am trying to drive 8 strips of led WS2812 (5V) with a CPU STM32F030.
The output from the CPU is at 3V3. So, I used a 2N3906 connected to 5V with resistor. I've got no problem with that.

Now,I want to drive 8 strips of WS2812 with the same CPU, one strip at the time. Can I use a 74HC373 (@3V3 or 5V ?) connected to the CPU and 78HC08 (@5V) as showed.

Is there any other design to be used to drive the leds.

Thanks

simulate this circuit – Schematic created using CircuitLab


texts: Filling a 200 V capacitor from a 12 V battery

texts: I understand that AED (defibrillators) use a 200 V capacitor with a small amperage. I am wondering if it is possible to fill this 200 V capacitor using a 12 V car battery? If you could, you could create the rest of the AED in a box and use any car's battery to power it. Every car on the road would be a source for an AED.


texts:
I have been trying to use a zener diode and cannot get it to work as expected. I have been searching forums and watching youtube videos without any luck, so hoping someone can explain it to me

I want to use a Particle Electron to measure a 12v supply, the Electron accepts 0-3.3v so I am using a voltage decider which is working fine, I want to use a zener diode as over voltage protection to clamp it at 3.3v

I have purchased multiple packs of zener diodes (thought the first might be faulty/incorrect) but am currently using:

https://www.jaycar.com.au/3-3v-1n4728-1-watt-zener-diode/p/ZR1398

I am attempting to test the diode using the following tutorial on youtube:
https://www.youtube.com/watch?v=WdDFI1IRQds

I have a 5.1v supply (measured at 4.98v using multimeter), a 1K ohm resister and the diode, when I measure the voltage I get 2.15v. I expected this to be 3.3v (as the zener voltage of the diode).

Can someone please explain why it is 2.15v? I have attached a photo of the circuit. Thanks for the help in understanding it.

Updated Diagram after changing the resistor based on feedback.


texts: where can I find high gauge copper wires for an homemade induction heater?

texts: I am looking for something similar to this coil but for the life of me I can't find it "separated" from the circuit which I want to make by myself.


texts:
I have the following:

Two 12 volt batteries hooked up in series to supply 24 volts to a
a 120 watt LED lightbar.
One 12 volt battery that is hooked to a switch.
A relay that has a max operating voltage of 27 VDC.
(http://www.foocles.com/FLS821G-pd934013.html)

Can I safely supply the relay with 12 volts to "switch on" the 24 volt load to power the LED lightbar?

Thanks.


texts: What is the best way to isolate power hold-up circuit?

texts:
I an currently designing a hold up circuit for a computer and I need to keep this load isolated from other circuits that don't need to worry about a brief loss of power. The research I've done has lead me to a circuit like this with Load 2 being the circuitry I need to hold up for the power interrupt. (D1 D2 part numbers are not correct, I just couldn't figure out how to get rid of them)

simulate this circuit – Schematic created using CircuitLab

I need to hold this load up for 50ms. I'm short on space for this capacitor so the the forward voltage of these diodes is going to be significant factor. I have looked into Schottky diodes and for the current I expect to see for this load the forward voltage is ~0.5V. I have also looked at TI's SM74611 Smart Bypass Diode, which looks to be a power FET with some control on top of that, which has a forward voltage of 26mV. This would be awesome but the reverse voltage is 28V and I need a reverse voltage of at least 56V (derating specs).

What components would you recommend using for D1, D2 in this situation? Is Schottky the best way to go?


texts: Problems with dc motor driver design: Mosfet fail

texts:
I made a brushed dc motor driver. The motor speed is controlled with PWM (from an Arduino). The motor that I'm using draws 3 amps without load.

This is the schematic:

As you can see there are two N channel mosfet in a parallel configuration.

The first problem that I had was that when I tested the PCB for the first time R2 burned and Q2 was damaged (all three pin where internally connected). I though that Q2 was defective so I change it and the PCB worked perfectly.
Then I tested the same circuit, different PCB, and happened the exact same thing, R3 burned and Q2 damaged, that can't be coincidence. Right?

Then I ran the motor at max speed for around 2 minutes, and the circuit worked fine, no overheating at all.

When I test the circuit with load (in a rc tank) the Heatsink heat a little bit (as expected), but then one of the drivers failed and the motor keep spinning. A mosfet failed.

Any suggestion on how to make the circuit work reliably, without the mosfet failing?


texts: Amount of current after DC/DC conversion for PC/104

texts:
Let say I have a AC to DC adapter with output 19V 7.9A connected to a 150W DC to DC power supply board (PC/104) with input 14-30V and output 5V.

What is amount of current I'll get from the 5V output board? Is it 150W/5V = 30A or 7.9A?

Sorry if this is so primitive question but I can't find corresponding reference.


texts: Lithium thionyl chloride for GSM application

texts:
I'm trying o use a LiSoCl2 battery in a low power GSM application. When the system is in standby only the microcontroller(MSP430) is powered(3.3v) and the GSM(5v) and sensor(5v) is turned off. The whole system consumes 50uA. The burst current when sending data over GSM is up to 2A, but my battery provides a maximum 400mA of discharge current. Some applications use auxiliary capacitor, but most capacitors have high leakage current.
The converter used for provide 5v is LMR61428, when the system is in standby mode it is turned off.

What is the best way to avoid leakage current of an auxiliary capacitor?
Is there a way to enable the capacitor only moments before using GSM to prevent leakage current?


texts: Sampling with multiple ADCS using SPI Interface Raspberry Pi

texts:
I'm trying to collect data from the circuit I built using an SPI interface off the raspberry Pi. I would like to measure the current and the voltage of my circuit. and the signal I would like to measure has a maximum frequency of 1khz and is a square wave.

Would it be necessary to use two separate SPI interfaces to try and collect data simultaneously to calculate the current (Voltage across a resistor), or would using a single SPI interface with two slaves be sufficient? I was thinking that the clock frequency for my SPI interface is much greater than 1k so it would not really matter. Is that thinking correct?


texts:
I am working on design of a MPPT for charging batteries via solar panels. After doing some reasearch, I am a little confused as to how the boost converter can output a constant voltage, as well as limit the current flowing from the solar panel.

I get that you can use a PWM signal to basically output a constant voltage from a varying input voltage. However I am failing to understand how you can control the current coming from the solar panel when you do so, and how using a PWM signal on the boost converter can maximize the power point.

Can someone please explain in depth how a boost converter controlled via PWM allows you to not only output a constant voltage to the batteries, but also perform the function of an MPPT?

Am I missing something obvious that otherwise controls the current from the cells?

Here are some of the resources I have been reading if they are any help:
http://ww1.microchip.com/downloads/en/AppNotes/01211A.pdf
http://ww1.microchip.com/downloads/en/AppNotes/00001521A.pdf


texts: How to simulate a comparator in Simetrix/SIMPLIS

texts:
I am trying to generate a square wave using a comparator and I am trying to simulate the whole circuit using the software Simetrix/SIMPLIS. This is the circuit I am using:

The first part uses a resistor and a capacitor to get an exponential from the square wave source, as we can see in this simulation result:

Now, with voltage divider on the inverting input of the comparator, it should take that exponential voltage, and generate a square wave that goes to 5V when the exponential is higher than 2.5V, and that goes to 0V when it is less than 2.5V.

However, the simulation does not show this on the output of the comparator. Some big spikes in the order of kilovolts arise, as we can see here:

I thought that something was wrong with the simulation itself, so I tried to fix it placing a resistor at the output, just like this:

And it looked like it worked because now the spikes disappear. However, the output never saturates to 5V as it should do, although it has the squared shape I was looking for but it is too tiny:

Does anyone know why is this happening? Is it something related to the components or the simulation/schematic itself?


texts:
I want to connect K pin (or LED-) of LCD to the NPN transitor, so i can control it. The question is how can i calculate resistor value? I found this schematic online, do you think it would work?

Backlight supply voltage is 3V, current is 16mA.


texts: Implicit declaration is invalid warning for __set_BASEPRI() function in Keil

texts:
I'm trying to use a __set_BASEPRI() function in Keil to set up interrupts in STM32F407 but it doesn't work when I compile the code and  the IDE shows warning "implicit declaration of function '__set_BASEPRI' is invalid in C99". Functions __enable_irq()  and __disable_irq()  work fine. How do I make it work?

Also weird, when I click on "Go to definition" on all these functions, the IDE cannot find the source file for them even though cmsis_armcc.h is included in the project.


texts: Why are the parts more expensive than a Pro Micro?

texts:
I have just started studying electronics and I am having a good time. In the past my experience would have been to use cheap boards, such as the Pro Micro.
What I find confusing is that parts, such as an oscillator, is often more expensive than a cheap $3 Micro Pro, which could have done the same thing with a few lines of code!
What are the benefits of using electronics parts, when a cheaper development board could do the same thing?


texts:
For solidwork/photoshops and many other softwares, they come with a "history" or revision log. You could always easily go back to the previous step of components or check how it changed.

Is there such thing for Eagle? There are tutorials out there, but it could only visualise the change, using it with GIT + looking through the codes to get the changes or indicating version no. and last update date as a form of version control.

Is there a way to say, for each component, there is an activity log on it? (i.e. R20 changed from 100 ohms to 300 ohms etc......)


texts:
USB2 is limited to 500mA. If you want more current you need an external PSU to pump in more juice. What would be the proper way to add another 5V PSU to the system?

Connect the 5V from the PSU to the 5V of the USB?
Ignore the USB 5V and use only the PSU 5V?

In most cases (Well, 100%) the voltages are not the same and this might cause unwanted currents. GND of the USB and PSU must be connected though.


texts:
I came across a picture ( shown below ) comparing the SNRs of FM and AM. There was also some explanation of the FM threshold effect and how the threshold effect is the reason as to why the FM graphs start at about (S/N) of 17dB.

The explanation here - http://www.allsyllabus.com/aj/note/ECE/Analog_Communication/Unit8/FM%20Threshold%20Effect.php

Would just like to ask, what is the FM threshold effect and why is this the case? Why does the carrier-to-noise ratio matter?

Thanks!


texts:
I have several power sources (up to 4) going into a circuit and I would like to be able to power it with "automatic" selection. I have looked up power OR-ing and diodes are dissipating more power than I can spare so it was suggested to use P MOSFETS because they have a lower Z.

The problem is that I can't seem to make them work even in simulation and I see a significant voltage drop. Can anyone spot the error?

EDIT: Additional information:

Input voltages might be 3.3V or 5V with +/- 5%.
Current consumption from the sources can not exceed 5mA.
Power source selection is done while the sources are plugged in and are not expected to change during the operation of the device. When the usage is done the sources are simply unplugged.
The solution sought after is passive in order to be low cost. $2 is parts is fine, $5 is probably not.
Output voltage should not be under 3V.

simulate this circuit – Schematic created using CircuitLab

The main difference between my question and the one suggested as having a possible answer is that I have 4 power inputs, not 2.


texts: Problems extending a 12V power lead to an RGB-LED strip

texts:
I need advise on the following problem: I am connecting a 5 metres WS2812B based RGB-LED strip to an extension cord. This is a 12V version, where two LEDs are coupled in terms of their addressing and IC. There are 100 addresses and 200 LEDs. I am generating the control signal from a Raspberry Pi.

I connect the ground of the Pi's GPIO and the ground of the external 12V power supply (a strong 150W laptop power adaptor)
I connect GPIO 18 out (3.3V) to the DI of the LED strip
I connect the 12V to the LED strip
This works

Now I want to insert an extension between power supply and Pi on one end, and the LED strip on the other end. I bought a 3x 0.75mm 20 metres cable for that. (Here is the product description in German if you are curious).

I inserted two wires between the 12V power supply and the GND/12V pins of the LED strip
I inserted the third wire between GPIO out and the strip's Digital In.
This doesn't work

Simply powering the strip seems fine; all LEDs go on. If I run the modulating program on the Pi, the first three or four LEDs are erratically flickering, that's it. Now I tried all sorts of combinations to figure out what is going on. For example,

I inserted a LLC to lift the digital output signal from 3.3V to 5V. Makes no difference. Does not work.
I extended only the power but connected the digital signal directly without extension. Makes no difference. Does not work.
I extended only the digital connection, leaving the power supply directly connected to the strip. This works.

This result was very surprising to me. I kind of feel relieved that I won't have trouble extending the digital signal, but now I'm baffled why the power extension apparently doesn't work. Using a volt metre, I saw that over the 20 m, the voltage drops from 12V to 9V. However, compensating by setting a higher voltage at the adapter, e.g. 15 to 18V to measure around 12V on the other end, did not change the situation.

My question is: What is the reason for this problem, and what should I do to properly extend the power connection by 20 metres? Is this simply a fault of the diametre, or am I looking at the wrong type of cable? Because even a standard 240V euro cable only has 0.75mm diametre. (In German this type of cable is called H03VV-F). The cable needs to work in outside space.


texts:
I'm looking to make a USB HID enabled device with an AVR that I would hopefully sell, but I know that the USB IF gets finicky about how exactly USB is implemented in commercial products. I want to keep it all Arduino IDE compatible, so right now I see that I've got two basic options:

Use something like the ATmega32u4 used in the Leonardo to get hardware based USB support
Use v-usb on something like the ATMega328p to get software based USB support

I like the idea of the 32u4 but would like to make the product a kit and surface mount is not very kit friendly. I would prefer through hole.

v-usb is definitely doable and would let me use a through hole chip (the 328p)  but the USB implementation would eat up flash space.

Here's my main question though, with either do I have to get a USB vendor ID?
I was thinking maybe just going with the 32u4, assuming that it would already have an ID built in and I was OK with the device representing itself as an AVR, but some things I have read lead me to believe I would still need my own ID and pass that to the chip.
I would imagine I'd absolutely have to have one for v-usb but is a software implementation even technically valid and allowed to have an ID. v-usb seems to ship with an ID that's marked for educational use and they ask you to not distribute it... but is that only for commercial stuff or could I use it as long as it's just for a kit?

For the most part I would prefer to do what I can to avoid needing one at all since I can't exactly afford the several thousand dollars it would cost.


texts:
I am trying to do a project that involves proximity detection. I need a few devices omnidirectionally detecting each other at short distance (under 20 feet). It seemed to me that sub-1Ghz RF is the way to go. I got a few MRF49XA transceivers. The datasheet for the chip provides a reference balun circuit schematic, but considering my requirements, I wonder if I really need one and if I do, can I get a pre-made balun IC rather than building my own. All I need is for the devices to be able to detect each other at around 15-20 feet range, hopefully with the lowest possible analog RSSI value and get to highest RSSI when right next to each other.

I do not have EE education and I am very new to the field, so if the question doesn't make sense or requires more information, please be patient with me.


texts: Better Transistor Inverter Using Ground Signal?

texts:
I'm getting close to finishing my brand spanking new gate control design.  I sincerely appreciate all the help I've received out here.

My latest challenge is to extinguish an LED when a circuit is grounded.  To do so, I require a simple transistor inverter.  However, I could not find anything that uses a ground signal.  So I had to come up with one.

The parameters of the circuit are that the input signal has to be a ground, the circuit power has to be 12V, and I am trying to stick to transistors (I could probably use CMOS, but I'm trying to design the entire thing using transistor logic - it's been a great learning experience).  This inverter is also powered by solar/battery, so current draw (particularly when active and LED is out) is important.  The best I can do is 213.26 uA.  Here is my design:

(Simulation link)

All 3 transistors seem to go into saturation mode when they are forward biased, and go into cutoff mode when they are not.  I'd like to reduce the current draw, but I don't think it's possible and still maintain exactly 10 mA on the LED when it is lit.  Is there a simpler design that I am missing?  Am I overlooking the obvious (yet again)?

As always, any help is sincerely appreciated.  I can't wait to finish this design and start building it.


texts: The Maxwells Equation giving the value of Magnetic field (B) for stationary and moving coils are having different variables. How is the third equation possible with such 2 cases?


texts: Mosfet array as FPGA power consumption model

texts: I would like to use an array of power mosfets as a model for an FPGA (i.e the mosfets will represent the FPGA as a model for the power dissipation).  For example if the total estimated power consumption of the FPGA is 150W and the max current 180A,  Would it be best to have a parallel or series array of mosfets for such a case?


texts: Why are active loads used for transistor amplifiers?

texts:
I get it that voltage drop across active loads are less compared to passive loads and at the same time they offer high small signal impedance thereby increasing gain.

I cannot understand why DC voltage drop across them is lower compared to passive loads like resistors.

In the book "Fundamentals of Microelectronics" by Prof. Behzad Razavi, it's written that active loads don't follow Ohm's law like resistors. Okay I agree but still I don't get why the DC voltage drop across an active load will be lower.


texts:
Hei,

Wondering if any of you have experience on secondary li-ion batteries (not battery packs) that comply with IEC 62133 certification?

I can't seem to find abundant amount of batteries covering such certification. Can you lead me in a right direction where to buy such batteries?

I have only found this which seems to have passed by IEC 62133:
Lithium 14500 Rechargeable Cell: 3.7V 800mAh (AA size, 2.96Wh) - IEC62133/UN38.3 Passed

Capacity should be above 1000mAh and max package 18650.


texts: how to make a W potentiometer from a log or linear pot?

texts:
My circuit needs a s-curve type of pot, that is a W pot but i cant find it in a store.

How can i make a W pot Either using a log or a linear pot?

w pot graph

W pot=G pot
Does anyone have a G pot graph?


texts: High voltage output from CCFL backlight transformer?

texts:
I have an old television inverter board I've been meaning to turn into a power supply for a  plate-deflected oscilloscope CRT *. I'm not really an expert on transformers, however, and though I have pinouts and datasheets for the transformer in question (4006A), I can't figure how I would recreate the conditions needed to create the HV output. I've seen schematics on creating CRT drivers from a different kind of CCFL transformer, but none with one like the one I have here. Can a transformer expert help me understand how I'd implement a transformer like this?

Corrected from "mag deflected CRT".


texts: Hall effect vs Current Transformers as Current Sensors

texts: I am trying to clarify the difference between some current sensors, would i be correct in stating that Current Transformers induct the flux of collapsing magnetic fields caused by AC, but cannot sense DC, while hall effect sensors direct the magnetic field onto a semiconductor so they detect both AC and DC?


texts: main program run like an infinite while loop

texts:
I'm working in PIC24F microcontroller. My main program doesn't have infinite loop, but it is run like an infinite loop.  Before I test the code with infinite while loop (while (1)), but when I remove the while loop, it's still running like an infinite loop. What's the problem?

Thanks


texts: Can't figure out what connector is that. Orcad 9.2

texts:
I'm trying to reproduce this as I'm learning to use orcad 9.2 but there is that CN1,2,3,4,5 connector I can't find in any of the pre-installed libraries.

Can anyone tell me where can I find it and under what name?

I gave it some thought and I thought it's some pin connector for a power supply. (that is not contained in the circuit board, something like a breadboard type connector?)

Edit: this is the original, it was in a .pdf document and I screenshot the photo. If I had access to it, I would have double-clicked to find out.

I did take into account that it might be a custom component or a test pin and I would waste someone's time by asking, but I want to be sure, I keep searching.


texts: Why is the LED not lighting with the correct color?

texts:
On a simple circuit containing a tri color LED (Part Number: 5988740302F) when power is applied the LED only lights up Green but should be Blue when 5VDC is applied. To explain the troubleshooting, 4.4V was measured across the +5V node and ground. On another circuit (the good circuit) the LED is lighting correctly (Blue) and the measured voltage is 4.6V.
More troubleshooting: On both circuits When the cathode of the Yellow LED is shorted to ground, the LED lights up Yellow.
Is it possible that something in the circuit is driving the voltage down? There are other parts of the circuit that driven by +5V.
Forward voltage (from datasheet): 3.2V Blue, 3.2V Green, 2.2V Yellow


texts: personal safety - preventing electric hazard

texts:
I usually have AC mains powered devices/circuit on my desk, and I rarely taste AC current by accident:)

Could anyone suggest to me what kind of protection I should use for personal safety against electric shock? Would an isolation mat under my table be enough? What are the considerations when selecting a proper item and installing it?


texts: Without C3 this Colpitts oscillator won't oscillate - why?

texts:
The pictured Colpitts oscillator circuit will not oscillate on a plug-in protoboard without C3 and its connection to ground in place.  In LTSpice the circuit oscillates with or without C3 and its connection to ground.

The LTSpice circuit oscillates at about 928 kHz and the protoboard at about 900 kHz.

I am trying to understand why C3 is necessary on the protoboard.  The protoboard has a lot of stray capacitance and inductance and I have a number of long leads on the components.  Perhaps that has a lot to do with it.

From a theoretical point of view, the "tops" of R1 and L1 have a AC path to ground through the DC power supply, V2.  The higher impedance path through C3 seems to me to be superfluous.  The protoboard  is connected to an HP dual power supply.


texts:
I'm trying to figure out a way to make a ground signal last longer on my car. I'll explain what is happening and what needs to be done.

I'm hooking up an factory alarm on my car. It uses a negative trigger to trip the locks, I got everything working like it should, you hit lock button on the key fob, it locks and hit the unlock button and it unlocks. The only thing I'm trying to figure out is how to arm the theft system with the door closed..it only arms with the door open, then you have to shut the door.

Everything is tied in with the door switch...

The lock button has 12v constant but when you hit the lock button on the key fob it sends a negative trigger and drops the voltage to 0V for half a second which locks the car.

Door switch-When the door is open it is grounded..when the door is closed it gets 12V constant.

I tried tricking the car into thinking the door was open when I hit the lock button when the door is closed but the ground signal only last half a second and I need it to last about 3 seconds.

I ran a jumper wire from the lock wire to the door switch and placed a 1n4001 diode in the jumper wire to only let the ground signal pass to the door switch when I hit the lock button but it only last half a second. In order to arm the theft system I need the door switch to be grounded for atleast 2-3 seconds then get the 12V back.

To make this long story short, when I hit the lock button it sends a very short half second ground signal to the door switch but jumps back up to 12V..I need it to last about 3 seconds, then jump back up to 12V.

Remember the lock has 12V constant power when you hit the button it sends a negative trigger and drops voltage to 0V for a quick half second..just need it to last 2-3 seconds then return back to 12V.

What can I use to accomplish this? I was thinking a time delay relay but it needs to be triggered by a ground signal using the lock button.


texts:
If we have an OR function with two terms, like $$a \vee b$$ it can be written with only XOR like $$a \oplus b \oplus ab$$

RULE: $$a \vee b = a \oplus b \oplus ab$$

But what if we have three terms, like $$a \vee b \vee c$$ How can that be written with only XOR?

What is the equivalent of the RULE above for three terms?

What about four or more terms?


texts: Clarification on solder mask aperture in PCB?

texts:
I'm using a 0.5 mm pitch FPC connector in my circuit. I was using a DRC with a 4 mil stop mask value. This resulted in a stop mask layer in Eagle (tstop) that looked like the one below:

Based on my understanding that the shaded regions will be areas where no solder mask is applied and concerned that this would lead to potential shorts and difficult in soldering the pins, I manually set the stop areas of the pads to leave more space like below:

Is my understanding of the stop layer correct? If the shaded areas overlap does that mean there would be no insulation applied there?

I know this probably varies between board houses but what thickness of solder mask between pads is ideal to prevent any chances of tearing or defects? I read in a few places that you should leave some overlap of the stop mask over the pads to account for solder mask shifting but I'm concerned that adding any kind of overlap with the 0.5 mm pitch pins would leave only a sliver of solder mask left between the pins.


texts: I measured the input capacitance of a MOSFET and found it was greater than an IGBT. Why is this? Is it due to the Miller capacitance seen in a MOSFET?


texts: Different data type volatile unsigned int to const char ,

texts:
I have to reply via SMS the value of a variable if the password is sent to arduino by help of sim900. I am able to switch an led on successfully. Now I want the arduino to reply to me the variable value but I am getting typecasting problem.

Here is the code I am using:

#include "SIM900.h"
#include <SoftwareSerial.h>
#include "sms.h"

SMSGSM sms;
//Number of pulses, used to measure energy.
volatile unsigned int pulseCount1_Wh  = 0;
volatile unsigned int pulseCount1_kWh = 0;
char number[]="8763983139";
char message[180];
char message1[180];
char pos;
char *p;
const int ledPin =  13;

void onPulse1()
{
    //pulseCounter
    pulseCount1_Wh++;
    if(pulseCount1_Wh == 6400)
    {
        pulseCount1_Wh = 0;
        pulseCount1_kWh++;
    }
}

void setup()
{
  // KWH interrupt attached to IRQ 0  = pin2
 attachInterrupt(0, onPulse1, RISING);
 Serial.begin(9600);
 pinMode(ledPin, OUTPUT);
 if (gsm.begin(9600))
 Serial.println("\nstatus=READY");
 else Serial.println("\nstatus=IDLE");
};

void loop()
{
 pos=sms.IsSMSPresent(SMS_UNREAD);
 Serial.println((int)pos);
 if((int)pos>0&&(int)pos<=20){
   Serial.print("NUOVO MESSAGGIO, POS=");
   Serial.println((int)pos);
   message[0]='\0';
   sms.GetSMS((int)pos,number,message,180);
   p=strstr(message,"testpwd");
   if(p){
     Serial.println("PSWD OK");
     digitalWrite(ledPin,HIGH);
     p=strstr(message,"LEDON");
     strcat(message1, pulseCount1_Wh);
     strcat(message1,"PIN");
     sms.SendSMS(number,message1);
     delay(100);
     if(p){
       Serial.println("LED ON");
     }
     else{
       p=strstr(message,"LEDOFF");
       if(p){
         Serial.println("LED OFF");
         digitalWrite(ledPin,LOW);
         delay(100);
       }
     }
   }
   sms.DeleteSMS((int)pos);
 }
 delay(5000);
};


texts: Powering circuit with alternative and/or concurrent power sources

texts:
I have one of these led projectors which is normally powered by the embedded motion sensor.

I want to be able to power it manually by a switch button. I need to do this in both alternative and concurrent mode. By alternative I mean that the projector is turned on either by the motion sensor or manually by myself; by concurrent I mean that it is turned on by both at the same time.

In order to achieve this I can follow two these strategies:

simulate a motion detection by providing the control circuit with the same signal provided by the motion sensor;
power the projector directly.

I have opened the device and have found out the following:

the projector is powered by a 22-25VDC power supply provided by the control circuit.
out of the motion sensor come out three wires which are fed into the control circuit. I have yet to investigate what do each of this does.

In both cases the difficulty I have is protecting the existing circuit from voltages and currents generated by the power I supply myself. I think this could easily happen in the concurrent mode.

How do I deal with these two inputs?


texts:
The circuit above has 4 IDEAL diodes and there are 16 cases to check.
Is there any shortcut to fiqure out which case to check first (to guess which diodes are on or off)?


texts:
I have a device (an ADSL modem) that when plugged in to an ac adapter does not seem to do anything (power light stays off).

I would like to know how to measure voltage for an ac adapter to make sure it is working. I have multimeter, but when I connect the inner and outer rings of the supply, it does not register any voltage (I assume it probably needs some load in order to give a voltage but I am not sure).

Output rating is 12 V / 1.4 A.

I tried with a different ac adapter and it also did not register voltage. Yet while measuring a AA battery it shows correct values, which leads me to believe that I am not doing something right.


texts: 2 x 2 n-channel mosfets in series: does my circuit has any flaws?

texts:
For a hobby project I would like to switch between two power supplys.
The load are two motors which can also be switched on and off separatly. The two motors are BLDC controllers in reality.
I am only in developing phase so no test arrangement was done.

I developed the following circuit, which I am not sure about if it works flawlessly:

U4-7 are highside MOSFET drivers with an integrated charge pump to achieve voltages above VCC.
R7, R8, R15, R16 are pull-down resistors to avoid floating potentials on the driver input and R1, R2, R9, R10 have the same function but at the output of the drivers.
Q1-4 are my n-channel power MOFETS (V_GS_max = +/-16V)
R3, R6, R11, R14 are restricting the maximum gate current
and R4, R5, R12, R13 I think are necessary to ensure that V_GS is never above 16V despite the source potential is floating (e.g. if Q1 is on and Q3 is off)

Some facts:

Maximum power-supply voltage: ~25V
Maximum current: ~50A through Q1/Q2 and ~25A through Q3/Q4
Q1 and Q2 can not be on at the same time (software-wise)
Q3/Q4 are PWM driven the first second after startup (to reduce the inrush current of the BLDC capacitors)

So my questions are:

are there any considerations for stable operation?
are there any maximum ratings which could be exceeded (especially
V_GS or crossflows)?

I would appreciate your advices!

EDIT:
I updated my schematic drawing with new MOSFET drivers some unnecessary pull-ups removed and some additional capacitors for voltage stabilization:

The problem with transverse currents if one battery has a lower voltage than the other is in a new thread:
MOSFET-switching between two power supplys: how to avoid transverse current?


texts: How to measure CAN_H / CAN_L of a CAN Communication using an oscilloscope?

texts:
I'm trying to set a CAN Communication between an MCU (Inside Renesas board that have a CAN interface inside) and CAN Transceiver (Vector CANcase) which is connected to my laptop via USB.

I want to check if the communication is passing (If frame messages are being transmitted / received) in the bus.

I found that I have to check the CAN_H / CAN_L signals using an oscilloscope but i need to know the circuit / wiring.

Since i have to measure the differential : Do i need to use a separate channel for each and then use the oscilloscope to substruct one from the other (I have Tektronic MSO 2024B wich is supporting Math function) ?

From what I have understand when a communication is running I should read CAN_H = 3.5V and CAN_L should be 1.5 and when not the difference should be 2.5 .

I have another question: the MCU gives the possibility to output CAN Tx/Rx signals in GPIO pins: How can I measure them in this case : should be the same as CAN_H and CAN_L (Altough I don't know the difference between CAN Tx/Rx and CAN High/Low)

Please share your suggestions on how to do this :) Many thanks.


texts: Atmega128 ISP programming, unable to read device ID

texts:
I am trying to program a Atmega128.
ISP programming
First I used AVR dragon, I can read the target voltage, but when I go to read the device signature, warning comes

  Unable to enter programming mode.

  Please verify device selection, interface settings, target power and connections to the target device.

I am using AVR studio 6.
I have programmed other Atmega128 with the same AVR dragon, but still I tried to program by using STK500. Its of no use as I got the same warning.

I have searched in google, but I did not find any solution.
sCK, RESET, MOSI, MISO, VCC, Ground all connections are perfect and I have put bypass capacitors between Vcc and ground of Atmega128.

Even I replaced the IC with new Atmega128, but the result is same.


texts:
I am trying to create an induction loop detector by following this http://www.allaboutcircuits.com/projects/metal-detector-with-arduino/ but apparently something is wrong on my side or I missed something.

I have soldered a PCB with a BC338, resistors and capacitors and I bought ENAMELLED COPPER WIRE to create the loop.

Connected all together but when I try to get any metal close by, nothing happens, there is not actually "clock" sent to the Arduino. Only if I power at 12V and I short quickly the coil wire to the pin I get a pulse for a second.

At 3.3 and 5v I get nothing, the voltage across the two pins of the coil is 0.035V and nothing increase when a put a metal close by.


texts: Wirelessly activate devices using light weight and low-power solution

texts:
I have several circuits which I need to turn on and off wirelessly.
The rules are:

They are placed inside a transparent small box (about 50x50x50 cm)
The control unit\transmitter can be placed anywhere outside the box, and has no power\shape\size\cost limitations
I have about 10 circuits which need to be turned on and off individually. Each circuit has it's own set of batteries (3 x 1.5v) and consumes about 1.7mw
It has to be very low weight - less then a gram
Very low power consumption - on the orders of milliwatts

I have two directions, but not a good way to implement any of them.
The first is to use IR with modulation, and the second is to use RF.

Any ideas?
Thanks.


texts: band / cylinder style heating element wattage calculations

texts:
The question concerns band or cylinder heating elements, which are designed to clamp around a hollow cylinder and heat whatever is flowing through it.

I'm looking for information on how to calculate the wattage required to heat room-temperature air (let's say 75F) to 475F if the air is flowing at 100CFM through a 4" diameter tube which is 10" in length. The voltage is 120 but 240 is a possibility as a plan B.


texts:
Let's say I have a sinusoidal signal of amplitude 5V and frequency 100Hz. I need an accuracy of 0.1% in the digital signal.

How to determine the ADC parameters required?

Do I need to apply an offset first?

How is the process different than that for DC?


texts: Implementing Push button as ON/OFF Toggle

texts:
Here is the flow:

1) Push button once to start the motor.
2) Push button again to stop the motor.
3) Push button again to Start the motor.
. . .and so on

I am trying to implement this with flip-flops but cannot figure out the correct logic.
TIA


texts:
I interfaced SD card (with SPI) with an C8051f931 successfully. Now my next task is to interface  an SD card with FPGA. So basically the FPGA will issue commands to the SD card for reading etc. In case of controller I used C programming where to send any particular command I used to write in some register. Writing to those register will send the data to the sd card.

How do I proceed in the case of FPGA. How do  send any SPI command using FPGA? A friend of mine said to send command you will have to write a FSM for this purpose.

Can somebody through more light on the exact procedure I have to follow. By the way I have some knowledge of VeriLog and I can pickup advance concepts  easily.

Update

I got sequence of operations I have to perform to access SD card. This is very much clear to me. But for what I have to use FSM?


texts: Simplest circuit to reliably produce two voltage peaks, then nothing

texts:
I'm trying to make a circuit with basic components and simple IC's that starts low, produces two pulses of high returning to low in between, in ideally a square wave though anything that doesn't bounce around between peaks should be fine, then returns to low indefinitely.

Duty cycle and frequency don't really matter, though the pulses must be a minimum of 0.2s wide with a specific 2.3s spacing between them, and ideally the spacing between them would be easily changed, as this is the most important variable I'm trying to play with.

What I've tried so far

Op amp and two RC circuits to produce repeating sine-like wave — Doesn't stop
555 circuit in astable mode — Doesn't stop
555 circuit in monostable mode — Doesn't repeat

Note: I'd like to ideally avoid the 555, but if that's really not possible it's not too much of a concern


texts:
Is the output current of an emitter follower out of phase with input current? In the book Electronic devices and Circuit Theory, the current gain, Ai, is negative. It depends on direction on output current Io.

you can see that output  current Io, is going from ground to resistor. The polarity of Vo is changed.Because from the diagram we see that Vo is taken between emitter and ground with polarity + (emitter),  -(ground). Im confused about this. Can anyone confirm what really the direction of Io is?


texts: Latching Relay That Follows +12VDC Trigger and Uses No Power Unless Switching

texts:
I have an application where I have a +12VDC circuit that I need to use as a trigger for a latching relay.

So, when +12VDC is present, the relay would SET.
When +12VDC is not present, the relay would RESET.

However, I need to have no power consumption when the system is quiescent (i.e. power draw during switching is fine, but there can't be a power draw during non-switching times).

I've tried a few things, including wiring the latching relay coil through its own output contacts (so that the latching side only received a ground when the relay was in the unlatched state), however this doesn't provide enough time to latch the relay.

Any ideas would be greatly appreciated.

P.S.  I'm using an Omron MY2K DC12, but happy to change to something different.

Thanks.


texts: Analysis of Closed Loop Transfer Function

texts:
I am trying to understand how to solve a homework problem I have. It states: Analytically show that closed-loop system is stable for all values of K.

By looking at the block diagram, I know that this is of course negative feedback with proportional control as the controller. Below, you can see my plant's transfer function and what I came up with for a closed loop transfer function.

\begin{array}{l}
G(s) = \frac{1}{{{s^2} + 4s}}\\
H{(s)_{closedLoop}} = \frac{K}{{{s^2} + 4s + K}} = \frac{{N(s)}}{{D(s)}}
\end{array}

I know that the poles here indicate whether the system is stable or not. Now I am not sure how I am supposed to show that every value of K satisfies stability because if I choose a vale such as K=-12, this will land a pole in the right half plane of the s-plane.

Did I mess up on getting the closed loop transfer function? Am I not understanding the question? Any hints on this one is appreciated!


texts: Is it reasonable to use a current limiting diode in place of a fuse?

texts:
I'm trying to source some fast-blow 5mA or 10mA fuses but Littelfuse has discontinued the only reasonably affordable ones I have found.  My circuit when operating properly will not output more than 2mA, however I'd like to ensure if it fails nothing will go over 5mA or 10mA.

Could I substitute something like this current limiting diode instead?

This is the circuit


texts:
These days you can't read anything about electronics without hearing about the dire consequences of omitting ESD protection from your designs.

It seems this wasn't always the case. If you look at most older designs (late 90s and earlier), you hardly ever see ESD protection components on I/O ports - even when CMOS ICs are involved. Why is this?

One might assume that modern ICs are more vulnerable than older processes. I don't think there's much truth to that though. Looking at the datasheet for a typical 74HC gate, they specify a maximum HBM of 2kV. This is the same as a modern MCU or FPGA.

I could understand designs using 74LS gates omitting protection, but I also see lack of protection when 74HC or CMOS LSIs are used in older designs. And having looked at more recent datasheets for 74LS parts, even those are specified only up to 2kV HBM.

Is it just that we have a better awareness of ESD now? Or could it be that you can actually still get away without ESD protection just as they did in the 90s? Is there a minimum level of ESD robustness required by law for consumer products, that wasn't enforced in the past?


texts: Why is buffer received over USB is not aligned on transmitted buffer length?

texts:
I stream some data from STM32H7 USB (VCP) -> to PC, and after stream is finished I just send "end\0". And on PC side I just look at the start of received data block and if there is "end\0", I just wind up PC program.

This is STM32H7 code:

#define DMA_BUFFER_SIZE   2048
#define SIZE 2048

unsigned short int buffer[DMA_BUFFER_SIZE] __attribute__((section(".fast_buffer")));

// "end\0"
buffer[0] = 0x6E65;
buffer[1] = 0x0064;
buffer[2] = 0x0;
CDC_Transmit_HS(buffer, SIZE*sizeof(unsigned short int));
GPIOH->ODR ^= (0x1 << 2);
while(((USBD_CDC_HandleTypeDef*)(hUsbDeviceHS.pClassData))->TxState != 0);

PC side:

#define NUMBER_OF_DATA_UNITS 2048
unsigned short int lpBuffer[NUMBER_OF_DATA_UNITS] = {0};
unsigned long nNumberOfBytesToRead = NUMBER_OF_DATA_UNITS*2;
unsigned long lpNumberOfBytesRead;
for(;;) {

  QueryPerformanceCounter(&startCounter);
  ReadFile(
    hSerial,
    lpBuffer,
    nNumberOfBytesToRead,
    &lpNumberOfBytesRead,
    NULL
    );

  if(!strcmp((char *)lpBuffer, "end")) {
    CloseHandle(FileHandle);
    // we are finished
    break;
  }
  else if(lpNumberOfBytesRead > 0) {
    //write received data to the disk
  }
}// for(;;)

Sometimes the last data buffer that I get starts not with my "end\0" string, but with other data and my "end\0" string is somewhere in the middle of the last buffer, so I can't finish my routine properly. Why is this happens?

I transfer 2048*2 bytes in one batch from STM32 and receive 2048*2 bytes on PC side.

Maybe someone could just kick me in the right direction about how properly do things like that?

Edit:

I think I can just scan each block, but this is looks like unnecessary thing, and the gist of the question will be the same. Why sometimes my received buffers is not aligned on 2048*2 bytes length?


texts: How can I convert an irregular PWM signal with a duty cycle of 95 to 99% to an analog signal?

texts:
For the purpose of measuring particulate matter (PM) in air, I am trying to set up a DAC system for the PM sensor Shinyei PPD42NJ (info here and datasheet here).

I've been trying to just use a low pass filter to get an analog voltage, but I'm not sure how to calculate the appropriate capacitance and resistance. Concern: if I use the low pass filter, will past measurements affect the current measurements (unless the capacitor can be reset every time the voltage is sampled)? How often would I sample the voltage if the frequency of the LOW pulses are sometimes as low as .5 Hz?

The parameters of the PWM are Negative Logic, Digital output,Hi : over 4.0V(Rev.2) Lo : under 0.7V. Here is a picture with Channel 1 showing the usual behavior of the signal versus time.


texts: Stability (phase margin) analysis in real feedback circuits

texts:
So I had a bright idea of using negative feedback to control offset current in my data acquisition circuit.  Sure, you could do this in software, but removing the offset at the input stage would reduce the swing and allow more gain in the pre-ADC amplifier without saturation, thus improving SNR.

So I designed this feedback loop, and my company built it.  And it oscillated at about 50kHz, which probably comes as no surprise to most of the experts, because the only stability analysis I did was to triple-check that I had negative feedback.

The actual loop includes a sample-and-hold amplifier (this section, which includes \$C_{\text{track}}\$ and both \$R_{\text{track}}\$ resistors, has been proven in a previous iteration), but oscillation occurs only during the track phase, so I've reproduced the loop as it exists during the track phase.

The core idea is that the feedback loop should force the two inputs of OA2 to the same voltage (well, the output voltage divided by OA2 open-loop gain), so that \$V_{\text{out}}\$'s offset voltage is forced to \$V_{\text{offset}}\$.  Then the sample-and-hold switches to hold mode and I acquire \$V_{\text{out}}\$.

I studied gain margin and phase margin in school, but I'm haven't had any recent practice with that and am not really sure how to go about creating a Bode plot for this real circuit.  OA1 and OA2 are a OPA2376 and OA3 is a OPA340.  There are additional connections for supply bypassing, etc., which I left off because I don't think they're relevant to the signal path.  But feel free to ask about those if there's a reason they would matter to stability.  And the \$I_1\$ supply represents the current from the sensor, which isn't really an ideal current source.

How does one develop a Bode-plot for circuits such as this using non-ideal op-amps that contain important poles in addition to the ones created by my passive components?  Just read the ones from the datasheets and superimpose

I'm worried because the oscillation frequency is so low and close to my desired passband.

Am I right to think that the phase shift problem is caused by the op-amps' corner frequencies below 10Hz?  If I use a resistor feedback network, I will truncate the open loop gain, moving the corner frequency to the right (where the open-loop plot intersects my new gain)?  And the phase shift will also start at a higher frequency?

My impression is that both OA1 and OA3 have unity voltage gain (inverting), due to the existing feedback.  Which leaves OA2 as the problem.  What would be a good feedback loop for OA2 to stabilize the overall loop, while keeping the offset error small and settling time no more than \$250 \mu s\$ (because then I have to switch into hold mode)?  Or should I be adjusting \$C_{\text{tia}}\$ and/or \$R_{\text{track}}\$ instead, to move my existing poles instead of creating new ones?


texts: Why noise when increasing amplification of last cascade of transistor amplifier?

texts:
I've made small amplifier for hand-made electric guitar - it is just two transistor cascades - and I've found one curious effect when increasing amplification. Some annoying noise (just typical electric interference from nearby devices) appears if I raise amplification on the last cascade, but not if on first.

And I don't understand why is it so.

Now here are details:

The amplifier is necessary because my hand-made pick-up has comparatively small coils (in comparison with normal electric guitar).

Here you see the amplification of each transistor is determined by relation between resistor in collector and in emitter.

E.g. with values shown, first transistor amplifies 1100/39 = 28 times, while second only by 1100/220 = 5 times.

If I increase amplification by changing 220 Ohm resistor to 68 Ohm - i.e. roughly 3 times - I get the noise described above - it occurs when the hand is close to or touches strings.

However there is no such noise if I raise amplification on the first transistor instead. I.e. I changed 39r to 4r7 and got louder but still clean sound.

Well... How does it happen?

Below is the picture of the whole assembly for better idea - power is from two batteries, to exclude noise from power supply...


texts: are there 2 basic-type of CRT deflection-yoke coil?

texts:
Deflection coil inside TV, deflects the electron-beam, using magnetic field. However this-deflection is not as simple as electrostatic deflection.

What is the actual mechanism behind working of deflection-yoke coil? I mean in which direction or spatial-arrangement it produce the magnetic fields?

(I searched web for several days, but I could not find anything helpful or clear.)

In web, I found 2 basic mechanisms.

1.

This- image is obtained from http://www.gradllc.com/images/Def.pdf .

2.

 and

(Left one from http://obsoletetellyemuseum.blogspot.in/2010/03/deflection-coil-and-yoke-in-crt-picture.html , Image URL http://4.bp.blogspot.com/-1I5viFFbMWI/TXpTYhh9xjI/AAAAAAAAGzc/0R4qpHjBWlk/s320/DEFLECTION-9.jpg); and righ-one is from https://www.google.com/patents/US3192432 ; with URL https://patentimages.storage.googleapis.com/pages/US3192432-1.png
 .

Are they different thing?  also,

(https://en.wikipedia.org/wiki/Deflection_yoke)

What are the work of pair of coils marked  with arrow? Is it an example of the 1st type ? (appears so from winding direction)


texts:
I have a design with a high voltage and a low voltage part. Between the two I need to have a creepage distance of 8mm. Some optoisolators I use in my design are not wide enough on the PCB footprint, so I need do mill a slot into the PCB. Below is a sketch of the area with the milling in red.

I specified the clearance between high voltage net class and low voltage net class in altium to 8mm. That rule helps me a lot with placing the components, so I would like to keep it. I know that Clearance is not equal Creepance, but on most of the board it is just right, as the PCB is dead flat.
Unfortunately, around the opto component, the rule does not hold. I am closer than 8mm, but that's OK as i will mill the PCB there.

Question:

How can I correctly model the difference between Clearance and Creepage in Altium? As far as I know there is only Clearance in Altium, Creepage is not modeled. How do you handle that? I know that my design approach is not uncommon. Are there best practices?

(the component selection of the optoisolator is not in the scope of the question and can be assumed to be correct and without alternative)


texts: Implementing line propagation delay compensation for BiSS master in software

texts:
Following up on a question I asked some time ago: Simple Implementation of BiSS C interface for a position encoder. I have implemented a simple BiSS master (point to point) to communicate with an encoder. At frequencies below 2 MHz and short cable length, the software is working perfectly using SPI module on PIC microcontroller.

However I tried high speed (3 to 10 MHz) and a 10 m cable, which should work. I stumbled across a propagation delay issue. It appears the protocol needs an implementation of cycle by cycle delay compensation.

I tried an approach in which I depend on the start sequence (ACK and Start bit) and I shift the result by 1 or 2 or 3 bits depending on how many clocks was the start bit late. But it does not work all the time, the problem seems to be that the data might be shifted by any fraction of the clock (ex.: 1/8, 1/4, 1, 1.5) so MISO is not decoding at the right time all the time.

Does anyone have thoughts on proper way to implement such function in microcontroller? (I can add a couple of discrete componets and logic gates if necessary) but not an FPGA.

*EDIT ( Screen shot from oscilloscope ) using standard SPI functions *

Screen shot from oscilloscope when directly puting data in SPI buffer without wait or any function whatsoever

Screen shot when using Buffered mode , 2 spi writes . Note the signal is clean , but the oscilloscope probe and ground pin was not idle when taking the photo..


texts: Is there a clever way to prevent a window comparator from oscillating?

texts:
Here is my schematic

It's basically a crude battery level detector (I am very aware that this isn't the best way to guage battery life, I'm not here for that) it's not crucial that it is super accurate.

Problem

When the battery voltage is near 4.05V or 3.45V the output of U9 oscillates and two LEDs are on at the same time, LED1 and LED2 or LED2 and LED3 respectively. Datasheet here

It is necessary that only 1 LED is on at a time.

Solution

I have found one solution but I am asking a question here to see if there is a more elegant or clever one (hopefully). Board space is ridiculously important here and my solution really doesn't fit well despite being only 4 components. The biggest problem is I want to be able to rework it into existing boards, and my solution is ugly and time consuming (4 cuts, 4 jumps).

I made U9 into two schmitt triggers with 100mV of hysteresis. Yes it works, but it makes the schematic ugly and adds 4 more components.

Hopes

My thoughts were maybe there is an off the shelf comparator that has built-in hysteresis (don't know how to search for this on digikey) or maybe you clever guys on EESE have a better solution.


texts:
How do I find the Thévenin voltage in this diagram?

In parallel the voltage remains the same, so should it be 10 volts across AB?

I am given that since \$R_3\$ and \$R_4\$ are not connected on one end, they do not carry current. Therefore, they cannot have a voltage drop. The voltage present between points A and B is the voltage drop across \$R_2\$.


texts: Replacing LED with Flashing LED in a circuit

texts: I am currently building a FRED Photopopper but instead of using flashing LED can I use normal LED? I don't get what is the difference between these two in the circuit. If the FLED cannot be replaced, is there any equivalent circuit for a FLED?


texts: How does series feedback pair work? (the art of electronics)

texts: I'm studying AOE but i can't figure out how this circuit even works(also i'm confused if Q1 and Q2 make a sziklai pair). any help with the circuit description will be great.


texts: Laptop battery pack rebuild; what cell discharge rate?

texts:
Currently I am looking for eight new 18650 battery cells to rebuild my iBook G4 (A1055) battery pack. Because I can't find for what discharge rate the original cells are rated, I'm not sure which cells to pick. The original cells are Panasonic CGR18650CA (datasheet is for a slightly different type, I know), but in the datasheet is not specifically described what the maximum discharge rate can be. There is a mention of actual capacity vs discharge rate, the highest being 4080mA given as an example. Is there a general 'safe' rating for laptop battery pack cells?

The cell type I am planning to buy is the Samsung ICR18650-26H. This cell can have a discharge rate of 5200mA.

Here is a schematic of the cells as connected in the iBook G4 battery:

simulate this circuit – Schematic created using CircuitLab


texts: What happens in the secondary winding if there's no spark plug connected?

texts:
The circuit below (minus the transformer and SCR) is used to detect the existence of a flame using the concept of flame rectification.  Based on the circuit here:  Pilot Light Flame Sensor

I have already proven this out, and it works awesome.  Instead of the probe used in the link above, I chose to use a spark plug.  This was done on purpose, as now I would like to add a spark transformer to automatically light the flame.  So, now the spark plug will be used not only for sensing the flame, but for ignition as well.

I added in a spark transformer (1:1000) and SCR to my diagram as an initial concept, but have some concerns:

1) When the spark is activated, it will be in the 10kV range.  Could this damage my sensing circuit, or will the high voltage only be seen at the spark gap?  Maybe I need a zener diode or TVS at the input of my sensing circuit?

2) If the voltage isn't able to jump the gap and spark (if the spark plug wasn't functioning properly or pulled out of the circuit), what happens to the energy?  Would this end up damaging my sensing circuit?

PULSE: This is a pulse coming from an audio transformer on another page.  This is essential to the sensing circuit from the link above.

SPARK: This is a signal from a microcontroller to initiate ignition.


texts: Determine the Y parameters of two port network. help me check what is wrong with my answer on this question


texts: Component/design recommendations for high power RF switch IC for 1-50 MHz

texts:
In trying to design the circuit, I've been researching the components that are available, and most appear to be focused on the 1-4 GHz range, but some work with lower frequencies.

Is there a solid state component (perhaps an RF switch IC?) that will handle 1KW at HF frequencies? The closest I've found is the SKY12208-306LF which only handles 50W so many would need to be combined.

datasheet: http://www.skyworksinc.com/uploads/documents/SKY12208_306LF_202077C.pdf

The need for the RF switch is to switch in and out inductors and capacitors in an L network.  Most designs seem to use relays, but I wanted to investigate solid state switching options.


texts: What is the circuit formation in this electric blackbox?

texts:
It should be a simple question from my exercise book, but I could not find the solution for some reason.

As illustrated, in an electric blackbox, there is one switch (k), one 3-volt battery, three 1-Ohm resistences, a diode. Now observe the blackbox with a voltmeter and a conducting wire.

When k is off (disconnected, or the switch k is off), UAB = 3V, UBF = 3V, UDE = 0V, UAF = 0V

Connect D, F: UCD = 0V, UAF = 1.5V

When k is on (connected), UEF = 1.5V, UDF = 1.5V

Connect C, A: UED = 0V = UBD

Disconnect C, A, connect E, D: UAB = 2V

I think that to allow UAB to be 2V (when k is on and E, D connected), the circuit diagram at that point has to be equivalent to either of the below two:

However, I can not find any formation which would show the voltage readings mentioned in the question, when respectively k is on or off (with nothing else connected).

Does this question even have a solution?

Note: One may assume that the sign of the voltage can be ignored.


texts: Multimeter misuse by shorting a 220 voltage through it

texts:
I intended to measure an AC voltage, but I forgot the multimeter on the resistance position (200 Ohm scale). I've shorted the 220V through the multimeter.

The fuse is not damaged, neither the bridge, but it is not working anymore for AC voltage, it gives wrong measurements for DC voltage, and the resistance scale seems to function only on the highest position on the scale.

Can I throw away the thing?


texts: Half-wavelength lossless transmission: magnetic energy and electric energy balance

texts:
I'm studying transmission lines and came up with a problem about a lossless transmission line that has a length equal to half the wavelength of the line.

My book computes the complex power at the lines generator and it comes up with pure imaginary number. That means active power is zero and reactive power is non-zero.

Now, from Poynting Complex Theorem that means that the Joule power dissipation is zero (makes sense because this is a transmission line) and that the difference between the average magnetic energy and the average electric energy inside the line is non-zero.

However, my book remarks that the average magnetic energy is equal to the average electric energy through the line because the line has a length equal to half the wavelength.

How is that physically possible since we have a non-zero reactive power? Am I missing something? Is the book trying to imply some thing else related to a half-wavelength transmission lines?

I would like to have some clarification please.


texts:
I have this schematic:

which supposedly makes the two LED flash alternatively with a period of 1.5s
The thing is that the one connected through the NPN transistor flashes, but in it's "off" state, still has about 6V going through it, and the other one doesn't flash and it's always powered with 12V.

I double checked my connections, everything is fine.
I don't need resistors for the two LEDs because they are at 12V


texts: Why isn't my PC recognizing my serial stream from my Arduino Uno?

texts:
I installed the instrument control package to Octave and have the Arduino IDE sending a single character to the computer every 100 ms. The device is transmitting on COM3 but the software still doesn't recognize that COM3 is still being used and gives the message error "serial: Error opening the interface: No such file or directory". What could be the issue? I know my computer doesn't support GPIB.
Arduino Code:
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
Serial.print('A');
delay(100);
}

Octave Code:
pkg load instrument-control

if (exist("serial") != 3)
    disp("No Serial Support");
endif

#s1 = serial("\\.\COM6")   % Open the port
pause(1);                    % Optional wait for device to wake up
testport=serial("COM6"); #open
pause(1);
#{
set(testport,'baudrate',9600);
set(testport,'bytesize',8);
set(testport,'parity','n');
set(testport,'stopbits',1);
set(testport,'timeout',50);
#}
```


texts: how to express y(t) as function of x(t) from a given two signal?

texts:
is there a simple way to answer ?
I couldn't do it by finding the equation of the two signal and then proceed like any problem in math


texts: Is it possible to use static electricity to grab paper and then release paper by discharging?

texts:
I need to build a device that can transport bits of paper one sheet at a time. I was thinking of using electrostatic force to attach paper to the rod, stick or whatever. The rod will then move the piece of paper to a different positon where it will place it precisely at the correct coordinates and then release.

I know of course it is possible to use static electricity to attach paper to things, however I don't know if discharging will release the paper? Probably a stupid question, but I've never really seen it done before.


texts:
I'm currently in a microcontrollers class, one where we use the PIC18F4550 and must use the C18 compiler (something Windows oriented and used for grading). I'm trying to install this on Mac OS X, and am running into difficulties.

I can't find a valid C18 compiler that works on Mac OS X. Instead, I find a XC8 compiler, which Microchip says is a complete replacement. But, when I try to compile the code below, it gives me an error, and this code is widely used in my class.

#pragma interrupt low_isr       // both lines generate errors
_asm goto low_isr _endasm

Yes, I have found a C18 compiler, but it's only for Windows. Despite how hard I search, I can only find the XC8 compiler. Online forums indicate that the C18 compiler for Mac OSX has been taken offline.


texts: USB Serial Adapter Unintentionally Powering RS232 TTL Converter

texts:
I have a programming setup where I plug in a GoldX USB cable plugged into my programming laptop (in this case a MacBook Pro). Cable picture:

This is plugged into an eBay sourced RS232 TTL converter:

Which I plug into my testing board. Everything works fine, most of the time... Except I've noticed that occasionally, when I plug in just the cable to the converter board, without connecting to my circuitry, the IC is powered. The LED turns on, and the VCC pin reads ~ 2.1 V. Note, the leads on the chip pins are connected straight to the meter; that isn't clear from the photo.

But, this doesn't happen every time I plug in the cable. Occasionally it works as expected, where the LED is not powered until I connect VCC and GND to the testing board.

I tried with a couple different programming computers, and the problem seems to be worse when powering from my MacBook; about 50% of the time when I plug in. I tried 10x on another laptop, and an ATX desktop and didn't see the issue with 10 attempts on each. Not a ton of data, but relevant.

My gut instinct is buying the RS232 to TTL converter from eBay left me with a knockoff MAX3232 chip that is misbehaving and leaking one of the data lines back through VCC. I'd be fine leaving it there, but then why would the behavior be so different when connecting the GOLDX cable from my macbook versus a different programming computer? Or, maybe thats just the issue -- the behavior will be completely inconsistent, and I shouldn't try to find an expected output from a given input.

TLDR: Should I just assume the MAX3232 is counterfeit and move on?


texts: When is a lower gain transistor preferable? - Letter suffix on bipolar transistors

texts:
Some transistors are available with a letter suffix indicating hFE.

Eg. BC547 is available as (typ. @Ic = 2mA):
- A => 170
- B => 300
- C => 520

I understand why you would choose C, hFE being high sounds good as that is what we use a transistor for: amplification.

But why would I want to use an A postfixed transistor? Are there any good reasons to specifically using these?


texts: Question about mounting two LED strips in parallel, one properly and one reversed, and using a switch to switch between the two

texts:
I work in a bar and we want to install UV lighting with UV LED strips. Currently, we have a simple circuit that consists of a 12V transformer and wires which go all around the bar, with regular white LED strips placed at key locations.

Now, buying another transformer and running another circuit would cost some money and also would be a lot of work, so I was wondering if we could reuse the circuit already in place, since the regular lighting and the UV lighting should never be used together at the same time.

The idea is to add next to each of the existing LED strips a new UV strip, then wire it in parallel with the existing wiring, but in reverse. Then, add a switch next to the transformer that reverses the polarity of the wires coming out of it.

This way, only one set of strips would be active at a time, and they can be easily switched, and the installation would be quite easy and cheap.

Would this work?

Also, if both sets of LED strips are about 60W each, and the transformer is 72W, it would not be overloaded, since the current that flows through the inactive LEDs is next to none, is that correct?


texts: Our plant has a 3 phase line to line connection when I test the voltage from line to line in the supply side of the main breaker it reads 230 volts but when I test line to ground, line 1 reads 196 volts, line 2 is 111 volts and line 3 is also 111 volts. Are these readings ok? When the main breaker is turned on, the reading from line 1 to ground is 0, line 2 to ground is 230 volts and line 3 to ground is 230 volts.


texts: Custom Heating Element with power controlled by Arduino

texts:
I'm looking for guidance on building an arduino-controlled heating element. I like to have a rotary encoder switch control the over heat delivered to the device.

Because heating is such a power drain, I'd like to connect the device directly to the power source, but run it through a relay that is controlled by the Arduino. I've attached the design below.

In general, I have two categories of questions:
 1. Power Management
 2. Heating Element Design

Power Management Questions

How can I use AC outlet and manage via Relay? Please give me the brief overview of mindset there.
What precautions should I take?

Heating Element Design

My plan is to take a nichrome rod, (or any other high resistance rod), and wrap it in nichrome coil. I'd then like to encase this rod/coil in a cover. When plugged in, The coil will heat up, thus heating the whole unit.

Is there a simpler approach? ie, connecting the rod directly to power? I could just build an encasing around that.
Is nichrome the right choice?
Are there any pre-made materials that look like this? I need it to get red hot.


texts: Multiplexer output is unstable and inaccurate - what am I doing wrong?

texts:
I have an Arduino project which takes three variable voltage inputs (in the range 0.43V to 0.63V) to a 4051 multiplexer (FAIRCHILD SEMICONDUCTOR CD4051BCN).  Each input is selected sequentially and passed through an OpAmp to the Arduino and on to the PC for logging and analysis.  DC5V is taken from the Arduino.

I can control the multiplexer input voltages fairly accurately for testing purposes with a variable resistance and multimeter, also I can test the OpAmp is working ok and stable.

My problem is that the output from the multiplexer is hopelessly unstable and varies by +/- 20% or more from the input voltage and does not stabilise over time.

I have tried change the sampling rate and allowing more time for the output to settle before reading it - but no good!

As an electronics newbie I may have picked the wrong multiplexer - there seems to be a load of products available but not clear to me which is best for my application.

Any insight or guidance appreciated.


texts: Will a step-down module increase amps and keep power supply steady on other 'branch'?

texts:
I don't know much at all about electronics, so this is a very basic question that I'm struggling to figure out, even with the help of Google.
So the scenario I want to achieve is this:

I have a 12V/1A converter plug (which can go lower in voltage, same amps I think. I guess I could also get a different one).
There are two devices that need powering from the same source. One [5V, 2.1-3A] and one [12V, 1A].

Could I just split the output of the wall converter and feed one 'branch' into a Step Down module, to transform the power supply to something that fits the 5V device?
The module I'm looking at (Amazon link) has these specs:

Input: DC 3V-35V (Input voltage must be higher than the output voltage of 1.5V or more).
Output: DC 1.5V-35V the voltage is continuously adjustable, the max output current is 3A.

I've read that if I make the voltage lower, then the amps should go up in linear relation to that?
Would that be true for a down stepper too?
I also think I read somewhere that doing this kind of thing can cause power supply fluctuations on the other 'branch' that might be damaging. Is this correct?
Grateful for any advice!


texts: Most cost-efficient way to implement USB full-speed host?

texts:
I need to a device which can act as a USB host to send various chunks of static binary data periodically to a full-peed USB serial peripheral of FT232 type (RS-232-ish UART).

I was thinking maybe using a microcontroller that supports USB host and accessing a serial flash for the binary data.

It'll be a custom board (vs. modules) and I need to keep the part count as low as possible.

Am I approaching this the right way?  Any recommendations that fit these requirements?  I'm afraid I'm not sure really where to start on a project like this..


texts: What problems exist in making USB splitter cables?

texts:
I have a use case for a mobile phone and OTG device that all use the micro USB connectors. Typically the OTG device is designed to be plugged directly into the phone, however this prevents the phone from staying on charge as charging and the OTG device needs the same port. I naively bought a cable with USB female split into a male and female micro USB port. The assumption was all pins would connect, power could be provided from the USB female to both the phone and connected device while the device and communicate on the data lines.

The cable I bought however does not do this, it only powers the phone (and only some phones at that), but does not power the device. No cable I can see can do what I need despite it seeming to be the trivial setup.

Is there some obvious reason why the cable I describe would be a bad idea?

More Information:

I am using one of:

Sony Xperia Z
Sony Xperia J
ZTC Nubia 5 Mini
LG Nexus 5
Google Nexus 9

as host. The device is the Seek Compact Pro thermal imaging camera and the cable is this one from Amazon: https://www.amazon.co.uk/gp/product/B00V9XS4V4/ref=od_aui_detailpages00?ie=UTF8&psc=1

Is there any glaring compatibility issue here? I am somewhat ignoring the Seek Thermal advice on compatibility as it seems they don't know much about it.


texts:
I am now building a power supply for a 100W LED light. Right now I already got 32V DC from my DIY Power Supply, with 3A current. I try to enable my PS to dim the light by regulate the voltage to the light. I am looking to be able to reduce the voltage to around 28-32V. I tried use a 10K pot in series with the light, but it burned. I can't use PWM because I need the light for studio illumination and PWM will filcker the light.

here is the circuit that i build.

any suggestion to achieve my goal?
thanks

IDEA
EDIT: here is a stupid idea. lets say, i can create 32V DC and 25V DC, and connect them both to left and right leg of pot respectively, then connect the output from the middle leg of the pot. will I be able to adjust the voltage between 32 and 25 V ?


texts: Question about comparator MAX912 latch enable

texts:
http://www.hep.uiuc.edu/cleo/trig3/boards/tile/vme021d_data_sheets/max912.pdf

I am using this MAX912 as comparator. There is a latch enable in this circuit which according to the datasheet, output is latched when LEA is TTL high or floating and latch is transparent when LEA is low.
I have two questions about this latch.
1. I am using a pull down resister and connecting Q- to latch enable (LEA).  Output Q is high (initial state) until input state changes. Q- will change from low to high and enable the latch. Can this circuit serves as a one time voltage detector? I only want it be triggered once.

This chip is in TTL logic. Someone mentioned that there is a current limit for logical low for TTL. What value should I use for this pull down resister?


texts:
If i have a 2to1 mux together with logic gates like this:

I can simply create a karnaugh map and test the different values of XYZ and get a function.

From this i get the function f = x'z + yz + x'y

However in the next task, I am supposed to look at this 4to1 MUX

And decide what inputs to use to achieve the same function f = x'z + yz + x'y

The four different alternatives I get to choose from on each input are:(0,1,Z,Z')

In the task I am also told to create a new karnaugh map for this 4to1 MUX.

I just don't get how I am supposed to think about the inputs to get the same function, or maybe I have misunderstood something.


texts: Finding Voltage and Current across a capacitor. Will you check my work?

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Question:

Work:

I have decided to approach this question using a differential equation for practice, but I keep getting an equation that doesn’t seem right. The reason I think this is because for part b, I keep getting -inf or inf for my current or voltage. That obviously can be right. Would you mind checking my work and seeing where I went wrong? I am using KCL with the linear ode method.


texts: Physical Layer: How do how frequency sources work?

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This is likely basic: but how do the source that rapidly generate 0-1s thru a channel "work" so fast? If it is a electric signal that is the source [as it is I believe even for fiber optic where a source converts electric signals to light pulses to be transmitted along the fiber]: how are these high frequency signals generated?

I am thinking that there must be some "moving part"/mechanical part that "vibrates" so fast:  but can we really have mechanical parts vibrating that fast? Or is there a frequency amplification from the mechanical to electrical that happens?


texts: High-side current sensing with a rail-bound instrumentation amplifier?

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I know that current shunt monitor ICs and high common-mode voltage differential amplifiers like the INA117 and AD629 exist but I'd like to know if it's possible to use a regular instrumentation amplifier where its input range is bounded by its power supply (e.g. AD623, INA177) and pre-attenuate the common-mode voltage using discrete or semidiscrete components.

I thought that using a voltage divider on the input and then compensating the gain factor proportionally would work if the in-amp has a high enough CMRR for the desired input range. I vaguely suspect that it's not that simple. If so, are there other (better) options to do this? I read something about using a current mirror but I don't really understand how that applies in this case.


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We have an ATMEGA162, and have connected an SRAM to it. We do not use PC5, that is the 13th address bit. What are we to do with this pin? When we connected it to ground, we got no errors in the SRAM. When we connected it through a 1k resistor, we got some errors.

What is causing this? We think this is a problem since if we put on an address that has the 13th bit high, that would cause a short circuit, which is not good.


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I want to add fine and coarse adjustment to a power supply for both voltage and current control, for fine tuning I'll need four potentiometers either 10 turn or regular ones. I was thinking to trim two of this pots to reduce the cost and space and I came up with this idea:

simulate this circuit – Schematic created using CircuitLab

Basically converting an 8 bit PWM to voltage and using it as voltage reference, above circuit is the same as this one:

simulate this circuit

And the problem with above circuit is; if we set the coarse pot to output it's maximum voltage, it's like the coarse pot isn't in the circuit anymore and therefore we can't get any fine tuning.

In this question @Spehro Pefhany suggested a voltage divider "network" for coarse and fine tuning.

How can I combine digital(DAC) and analog(POT) to achieve coarse/fine tuning?


texts: Modify pot to lower value while maintaining full range?

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So i have a bunch of 100k pots. But i need a few pots that goes up to maximum of 100 ohms. I have tried to put resistors in series with the pot to limit the range and it does work, but the pot gets to sensitive and about 80% of the pots range is useless.

Is it possible to do anything about this or do i have to buy one for my needs?

I'm asking because i have around 20+ 100k pots. So it seems pretty dumb to buy a new one if i can "modify" them. All the pots are linear ones.

Thanks!


texts: Dual Input Voltage source single output question

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I am trying to make a circuit that will have 2 power sources. One will be be a main and one will be a battery backup. When backup or main is disconnected I want to make sure that the supplies are not being put into the other. (like a battery backup circuit) However most of those that i saw use 2 diodes. Ones on each of the positive rails.

I have wondered why not use mosfets to do this as they have a diode built in. But I can't seem to understand the datasheet. It seems that source to drain voltage is -1.5v so I won't be able to do it in this case. But I thought that power mosfets are used in some circuits this way. Here is my circuit. I have 2 irf9520 p channel mosfets I can use. I want them to also work as reverse voltage protection and in their current configuration I know they will work for that. But I'm not sure if this configuration will cause an issue with that also.
I have kept away from the diodes as they cause to much of a voltage drop. The load takes 7v minimum and the battery backup does not last that long so I would prefer that method.

I believe I'm not reading the datasheet right. Can anyone tell me if this will work ? If it will not work can you help with an explanation and possible a circuit to be able to do this. Thanks.

Load current draw is between 25ma and 200ma. Being held mainly at 170ma.