texts: Why is the relay switched by a NPN transistor still on while the Arduino out is off (low)?

texts:
I have a circuit as shown below:

simulate this circuit – Schematic created using CircuitLab

Note:

In the above schematic some pins of Arduino Nano are not shown for simplicity purposes. Also, SW1 and SW2 are not switches but sensors as shown below:

Here is the arduino code:

//include LCD library
#include <LiquidCrystal.h>

//Initialize an LCD object
/*Pins should be mentioned in this order:
  Reset
  Enable
  Data4
  Data5
  Data6
  Data7
*/
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);
int upSensor = 11;
int downSensor = 10;
int continuousSwitch = 8;
int suddenSwitch = 9;

unsigned long counter = 0;

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

  pinMode(upSensor, INPUT);
  pinMode(downSensor, INPUT);
  pinMode(continuousSwitch, OUTPUT);
  pinMode(suddenSwitch, OUTPUT);

  //Begin the LCD interface
  lcd.begin(16, 2);

  lcd.print("MOTOR OFF");
}

void loop()
{

  if(counter == 1)
  {
    digitalWrite(suddenSwitch, HIGH);
    delay(1000); //1 Second
    digitalWrite(suddenSwitch, LOW);
  }

  Serial.println("upSensor: " + String(digitalRead(upSensor)));
  Serial.println("downSensor: " + String(digitalRead(downSensor)));

  if(digitalRead(upSensor) == HIGH && digitalRead(downSensor) == HIGH)
  {
    digitalWrite(continuousSwitch, HIGH);
    lcd.setCursor(6, 0);
    lcd.print("ON");
    counter++;
  }

  if((digitalRead(upSensor) == LOW && digitalRead(downSensor) == LOW))
  {
    digitalWrite(continuousSwitch, LOW);
    lcd.setCursor(6, 0);
    lcd.print("OFF");
    counter = 0;
  }

}

Everything is working fine except relay RLY2.

No matter if switch sw1 and sw2 are open or close, RLY2 is always ON. I mean RLY2's COMMON connection is always connected to NORMALLY OPEN Connection. If I measure the output from pin D9 of arduino, then I can see that it is changing according to the state of the switches SW1 and SW2. But the Relay RLY2 is always ON. WHY????

Update:

Before removing transistor:

I have added a diode between emitter and ground. Also changed the resistor R2 from 1K to 470E.

Voltages of Q2:

A. When D9 is HIGH:

Collector - Ground ----> 6.15V
Emitter - Ground ------> 0.70V
Base - Ground ---------> 1.40V

Collector - Base ----> 4.75V
Collector - Emitter -> 5.40V
Base - Emitter ------> 0.70V

B. When D9 is LOW:

Collector - Ground ----> 7.90V
Emitter - Ground ------> 0.70V
Base - Ground ---------> 0.65V

Collector - Base ----> 7.25V
Collector - Emitter -> 7.20V
Base - Emitter ------> 0.50V

I will remove the transistor, after Trevor checks above voltages and makes sure if transistor is sick.

Update2:

After removing transistor:

Voltages of Q2:

A. When D9 is HIGH:

Collector - Ground ----> 15.06V
Emitter - Ground ------>  0.15V
Base - Ground --------->  4.03V

Collector - Base ----> 12 V
Collector - Emitter -> 15.6V
Base - Emitter ------> 3.70V

B. When D9 is LOW:

Collector - Ground ----> 16.90V
Emitter - Ground ------> 0.12V
Base - Ground ---------> 0 V

Collector - Base ----> 16.8V
Collector - Emitter -> 16.4V
Base - Emitter ------> 0.15V

I have also measured the transistor:

Base - Collector    --> 647
Base - Emitter      --> 642
Collector - Emitter --> 1
Collector - Base    --> 1
Emitter - Base      --> 1
Emitter - Collector --> 1

So, from above mentioned readings, I think the transistor is OK. Am I right?

Update3:

I have put new 2N2222 after removing the first one:

Voltages of Q2:

A. When D9 is HIGH:

Collector - Ground ----> 0.76V
Emitter - Ground ------> 0.74V
Base - Ground ---------> 1.52V

Collector - Base ----> 0.74 V
Collector - Emitter -> 0.02V
Base - Emitter ------> 0.77V

B. When D9 is LOW:

Collector - Ground ----> 10.25V
Emitter - Ground ------> 0.70V
Base - Ground ---------> 0.73V

Collector - Base ----> 9.50V
Collector - Emitter -> 9.55V
Base - Emitter ------> 0.04V

Now, my diagram looks like:

simulate this circuit

Update4 (Working Diagram):

simulate this circuit


texts: how to identify transistor/IC by its model/product number?

texts:
How to identify(biasing/company/working sections) transistor / IC by its model/product number? or details ?Example: 2sc2078, 2n2219 etc.

Please help, i need to understand...

Thanks


texts:
could somebody explain me how does this audio amplifier circuit from old radio is working ?
I understand role of last transistors 413,417 and 415,419 but what is the point of T409 and T411 and other blocks ? Another question is why we feed input through differential amplifier ?
Btw do you guys know any good resources about old audio equipment design ?


texts: How to set forward voltage for a diode model in NGSpice?

texts:
I am trying to understand the documentation for the diode model, but I could not find how to set the forward voltage value.

Can someone help me simulate silicon diode that has a forward voltage of approximately 0.7 volts?


texts: Digital potentiometer analogue for high voltages

texts:
I have an RS-485-like (not a standard RS-485, but close to it) circuit with 35V+ voltages in it. I need to change resistance of the resistor, that installed parallel to my device data connectors A and B (in the range of ~120Ohms..5kOhms).

The main problem is that I need to do it in the run-time and do it with MCU. I know, that digital potentiometers aren't suitable for it, because voltage range of the resistor terminals should be in (Vss, Vdd) range. Are there any other ways to do it? Or it's impossible/useless and I should play with changing my circuit overall impedance (seems like impossible to me).

Update:

simulate this circuit – Schematic created using CircuitLab

As shown on the picture, I have U1 -- RS-485 similar optoisolated driver and need to control the resistance of R1 with MCU. The typical voltage ranges in the network can reach up to 35V+.


texts: Resistor values in transistor logic gates

texts:
I breadboarded some AND, OR, NAND and NOR logic gates (schematics below) using:
- 2N2222 transistors
- 10K resistors
- 4.7K resistors

Can anyone explain (or provide a link that explains) why 10k and 4.7K resistors are used?

I'm sure this topic has been covered before, but I just cannot find any relevant information, most likely due to Googling the wrong keywords...


texts: Axial ratio of a square microstrip antenna

texts: I am currently designing by CP microstrip antenna using CST. The picture is shown below. However, when I view the axial ratio plot, also shown below it is way above 3dB at 90 degrees. the patch is 31,95 by 31.95mm.  The resonate frequency output is correct which is 915MHz. I have tried varying multiple variables such as the length of the patch, length of the main feed, the distance between the branched feed line and the patch (quater-wavelength feed line). But the axial ratio does not change much. How can I alter the axial ratio to be below 3dB but keep the resonate frequency at 915MHz?


texts:
I have a rotary switch with 20 x 2 pins in a rectangular form, and I need to connect almost all pins, so I thought to buy a PCB board for that.

The problem is that the spacing between the pins is about 2.0mm which PCB boards I can't find on the internet...

Is there another way to connect all those pins?
I could, of course, make my own PCB board, but I don't have a that good drilling machine for those small holes.

What would you suggest? :)

Thanks


texts: I need an amplifier to measure the difference of voltage of 48V battery. As I were seaching, I found the AD8206 from Analog Devices with High common-mode voltage range from −2 V to +65 V operating but used mainly and recommended for current shunt applications. Can I still use this amplifier to measure the differential voltage on my battery?


texts: Differential amplifier with active load Sedra Smith

texts:
I'm studing differential amplifiers on Sedra Smith book, and I have come across the following circuit.

My question is: how can NMOS transistor \$Q_2\$ have a current \$g_{m2}\cdot v_{id}/2\$ if the voltage between its drain and source is zero? Now, I understand that this circuit is the equivalent circuit for small differential input signal. Thus, \$g_{m2}\cdot v_{id}/2\$ is a decrement component in the drain current rather than a real current going from source to drain. Still, I cannot understand why \$Q_2\$ isn't cut off with \$V_{ds}=0\$.


texts:
I've been scavenging for components on a deceased gadget and I've found a thermistor I'd like to use in the future. The problem is there's no serial code printed on it. Without knowing the manufacturer, finding the datasheet is going to be hard. I'm no EE, just a newbie. I'm assuming it is a thermistor because I've empirically verified that it resistance varies with temperature, and since it was inside  a cheap promotional gift I doubt they would have used a more expensive component. Here's a picture of it:

All I can tell for sure about it is that it is a negative temperature coefficient thermistor. I've taken a few measurements using my cheap multimeter and here are the values:

So my questions:

Have you ever seen one like this? Do you happen to know which brand (or possible brands) could it be?
Is there an online catalogue or DB so that I could identify the component just using the image and approximate resistance?
In case I failed at identifying it, could I infer the function given the plot? I mean, are these measurements consistent with the behaviour or a thermistor? (I was expecting a linear behaviour, but considering my results either one of the values is an outlier or the function is not linear)

NOTES:
First measurement was made with the resistor inside an ice cube (took several readings to be sure). I'm assuming the temperature here was close to 0ºC.

The last measurement was done with thermistor inside a glass of warm water. I measured the temperature using a digital clinical thermometer.

These two measurements are the most accurate readings I have been able to obtain with the available means at home. I'd have taken a few more readings using the clinical thermometer approach but it only shows me values in the range of 34-44 ºC, so they are too close to be useful. I was thinking about measuring again at boiling point (100ºC) but I've no means to measure the water temp at these levels. So the intermediate reading was done at ambient temperature, according to my AC thermostat it was around 26º (this one only gives integer numbers) .

My cheapo multimeter has an inherent resistance of measuring cables: 0.5 ohm and the precision is +-0.8%, but this is nothing compared to the errors in temperature reading so I doubt this info is meaningful.


texts: Is the RFSH signal really needed in a Z80 CPU?

texts:
The Z80 CPU has a RFSH (active low) signal used to signal when it's refresh time for dynamic RAM chips.
The Z80 datasheet states that RFSH alone shouldn't be used to generate a RAS only bus cycle in a DRAM, because at the time RFSH goes low, the address bus with the refresh address is not yet stable, so it is needed to wait for MREQ going low.
But during a refresh cycle, as MREQ goes low, neither RD or WR does so, making this the only bus cycle in which MREQ goes low but no read or write operation is signaled.
So, if the condition MREQ = 0 and RD = 1 and WR = 1 is enough to signal a refresh cycle, why Zilog engineers put that signal wasting a whole pin for it, when its function could be decoded with the already mentioned condition?


texts:
Could anyone suggest, why lifetime of Pb batteries is so short in UPSes?

3 years till 0 mAh - I've seen that several times, and some UPSes were not low-end (~250$)...

Are there any ways to make it last longer when designing new device?

Same for LiIon - if we rarely charge/discharge them, how long they could last? (I've heard things like '2 years of shelf-life and they are garbage')....


texts: How to display high frequency signals on a small display?

texts:
I'm working on a project to build an oscilloscope using the Arduino Mega2560. I've built the system using an 128x160 display, and I'm having difficulty showing a range of frequencies on the display.

The system I have developed measures the input signal with a 1ms delay between each measurement, doing this 120 times placing each reading in an array. I found I have to use a 1ms delay else it captures low frequencies too fast and will only show parts of waveform. Using this system, the scope only measures up to about 400Hz before Nyquist sets in and the waveform becomes distorted.

I measure frequency (top left) by checking the array and finding how many times the signal crossed 0. To stop the signal flying around the screen, i find the first value when it crossed 0 and draw the signal from there. Only 74 values from the 120 array are displayed.

Is there an mathematical way from the information given such that if frequency is above 'x' change delay, such that the system could auto range and measure upto 100kHz and display the signal on screen, is this possible?


texts: What does a reset of a PIC microcontroller via MCLR actually clear?

texts:
I'm working on a project that uses a PIC18F26K22 microcontroller, and it's behaving oddly.

Basically, sometimes if you kind of "bounce" on the reset line (I have a button on it, and I just kind of fiddle with it), it will reset and some of the interrupts will not be functional (in this case, the EUSART RX interrupt).

The reset button has a debouncing capacitor to ground, and a pull up resistor (10n/10K respectively).

I've tried adding some precautionary cleanup to the startup section of the source, but it hasn't helped. At this point, I have a manual watchdog that detects a lack of serial traffic, and manually triggers another CPU reset, at which point everything starts working correctly.

My assumption was that the registers on the chip were all reset to their "power-on" state when a reset was triggered (excepting perhaps the RCON register), but the fact that I can fairly reliably trigger strange behaviour by just resetting the chip multiple times quickly makes me think this is not true.

Is corruption of registers triggered by repeated reset a common (or even extant) thing with PICs? I'm mostly familiar with AVRs.

Edit: I considered switch-bounce, but the documentation for the MCLR input states:

  These devices have a noise filter in
  the MCLR Reset path which detects and ignores small
  pulses.

My assumption here was that reset pulses shorter then the minimum width (2 uS, for this part) would be ignored.

Further edit: I've actually looked at the MCLR line with a scope. It is both bounce-free, and entirely satisfies the minimum hold time (the shortest period I saw was ~50 milliseconds, the minimum hold time is 2 microseconds). It's not MCLR bounce.


texts: RJ45 dual LED green and yellow operating

texts:
Attached is a small section of USB to Ethernet converter design. RJ 45 Connector has one dual LED (see attached) Green and Yellow, backward connected, and drive via the LAN9500 chip pin27.

As per design look like only Green LED will trun on when nLNKA_LED/GIO9 goes low. and when nLNKA_LED/GIO9 goes high no LED will turn on. then how the yellow LED will turn on here?


texts: Can I use a power supply as a constant current source?(+general understating problems)

texts:
I beg you pardon if the question sounds trivial.
I have a Power Supply that can provide a outer voltage between 0 and 32 V , and an outer current between 0 and 10 A.
I would like to connect a resistance heating wire to this power supply, so that it should archive the maximal(needed) heating power.

1)If one uses a wire with the total resistance of 20 Ohm at a constant current of 3 A for 2h that one should archive 129600 J (Q=tRI^2), Is it correct?

2)The user manual of the power supply states that: "output voltage and output current can be set from 0 up to maximal value, both operation modes, constant Voltage(CV) and constant Current (CC) are selected automatically ()auto cross over."
If I am using the Constant Voltage Mode, at a voltage of 30 V and a resistance of 1 Ohm that the required current should than be 30 A, what the supply can not provide, and so it is not possible to built. Is it correct?

3) For maximal heating power I should choose maximal resistance and current , withing the technical possibilities of the Power Supplier?

4)Is there a equation that helps to estimate how hot will the conductor be after some time?

Thank you very much and have a nice day :)


texts: In the equivalent circuit of transformer is the shut branch placed before or after the winding impedances in the primary?

texts: I read a couple of books on transformers. A few have drawn the equivalent circuit with the shut branch placed before winding impedance while opposite was done in others. Which one is right?


texts: I have interfaced HB100 sensor with ATMega Microcontroller. It easily detects my hand movement upto 5-6 inches only. I want to extend range of the sensor so that it detect movement upto atleast 10meters. I see people use Dish antenna. For that it requires LNB, I have no knowledge of RF can someone please suggest how do I select LNB for HB100? Or any other way to extend the sensing range which can save me from LNB stuff? Thanks


texts: How to plot "voltage drop" across a specific component in LTSpice?

texts:
In the above circuit I can only be able to plot |Vr1+Vc1| = V1 in green plot and Vc1 in blue plot. I use the voltage probe in LTSpice and click on the lines to obtain the plots. If I click on the line between V1 and R1 it plots |Vr1+Vr2| = V1. If I click on the line between R1 and C1 it plots Vc1.

Is there a way to see also Vr1 (the voltage drop only accross R1) along with the others?


texts:
All MOSFETs (not JFETS)

Have I calculated the small-signal gain correctly?

IGNORE body effect etc. but not channel length modulation

I was basically able to get rid of M2 apart from its resistance.


texts:
I have a circuit where 2 DC motors are connected to 4 AA batteries and being controlled by an Arduino microcontroller.

Whenever the motors start, they starve other components in the circuit and it is enough to reset the Arduino (since it is essentially quickly being turned off and on). What can I do to help smooth out the current? Adding a capacitor on the power output didn't seem to help.


texts: Identifying Noise in 12AU7 Based Headphone Amplifier

texts:
I've been working on making a tube based headphone amplifier as a fun personal project.  The amplifier is based around this 12AU7 vacuum tube.  The project for the most part is following this existing design.  It's currently being powered by a 12V lead acid battery.  Here's the circuit diagram:

After assembling everything on a piece of perfboard and testing, it sounds great!
 However, there seems to be an intermittent noise that I can't seem to identify.  This noise is not always present; sometimes the amp will run fine for several minutes without problem, other times the noise will start and last only a few seconds, but sometimes it lasts for minutes at a time.  It appears independent of input. I have heard it while listening to music as well as when no input is connected.  Here's what it looks like.  This was created by recording the output of the amplifier using the line-in of my pc and analyzing the data in Matlab.

There are strong peaks at 60Hz (I'm in the US) in both channels which makes sense as the input comes from a 1m cable running across my desk.  What I don't understand is the popping.  It also appears to be worse in the left channel despite the two paths being identical.  This is only one sample, but the popping seems to be consistent across occurrences based on what I've heard and other samples I've recorded.

Here's what I've tried so far:

Removing the input.  Even with no input cable connected to the amplifier, this popping is still present.  This also means the noise is independent of the volume set by P1A.
Changing the tube.  The noise is present with the extra 12AU7 tube I have and even with no tube.
Using different headphones.  I typically use this amp with my Audiotechnica ATH-M40X with a 35 Ohm impedance but the noise exists with my cheap ear buds as well (8 Ohm I think).

This leads me to think that it likely has something to do with either the IRF510 MOSFET or LM317 linear regulator (which is acting as a current source).  I don't know enough about the noise performance of these components to conclusively put the blame on either of them.  If it matters, they both run very hot.  I can record some exact temps later if necessary.  I can't rule out the power source or passives as potential culprits, but again, this is beyond my knowledge.

Any suggestions?  What is the likely cause of this noise?  Are there things I can do to learn more about the noise and narrow down possibilities?  How can I get rid of it?


texts:
As far as i understand turning off a MOSFET too fast, is bad, as high drain-source dv/dt can cause ringing through:
a) biasing Parasitic NPN and:
b) charging the GS capacitor through DG capacitor, and thus turning on the MOSFET.

1- is my understanding correct?
2- if yes, then it won't be an issue in the circuit below, which uses a diode to turn off the MOSFET as fast as possible?
3- is that diode even necessary, considering there is only one low side MOSFET, thus no chance of shoot-through?


texts: How to determine annular ring width for thru-hole pads?

texts:
When placing thru-hole components on a PCB, how do you determine what the annular ring width should be?

For example, I'm making a PCB with a thru-hole switch whose contacts are 1.2mm in diameter. To me, an annular ring width of .4mm (so an outer diameter of 2mm and drill diameter of 1.2mm) looks "about right" for this hole size, but is there a general rule of thumb or formula that should be used to determine the width?


texts: Voltage input for charging NiMH Batteries

texts: I have 12 AAA NiMH batteries(1000mAH and 1.2V per battery) and I want to know what is the optimum voltage for charging them. I am using a simple Constant Current charger(LM317 and 68 Ohm Resistor(R in the circuit diagram). But i'm unsure on what the input voltage needs to be. My circuit doesn't have the diode.


texts:
Setup: a simple 3 bit incrementer that is both connected to a digital display and to itself

simulate this circuit – Schematic created using CircuitLab

Assuming that there is no clock to regulate the timing of outputs, what would happen?

If constant power was given to the circuit, I imagine the incrementer would start by outputting 001 to both the display and itself. But that 001 was based off an input of 000, which has now changed.

I am guessing that one of two things would happen: either (A) this state is a paradox and the incrementer continues to output 001 until it has no power, or (b) the display would continuously show a different number, changing at the speed it takes for the current to travel around the circuit.


texts: Two charged capacitors connected in series

texts:
simulate this circuit – Schematic created using CircuitLab

The circuit has the initial condition as shown in figure. What will Vfinal be when SW3 and SW2 are open but SW1 is closed.


texts:
I bought this cartridge heater for my reflow oven. Since this was rated for 220VAC I connected it to my mains through an SSR which is in turn controlled by the reflow oven firmware. The firmware goes into a 'learning' mode that tests the heaters and then adapts the duty cycles according to the rate of rising temp etc. There is a K-type thermocouple that measures the temp inside the oven.

When I connected it, and starting running tests, the heater became red hot and then literally exploded inside the oven (image attached). Is this normal for this style of heater? Should I bother trying to reach the manufacturer or is it something that I did?


texts: Value of 5-band resistor (current sense)

texts:
I have some blown current sense resistor and I don't know how to figure out the value of it. Resistor is blown so I cannot measure it.

Well, I know about standard rules, unfortunately none I know applies to this.
Color bands are quite symmetrically spaced, and the silver band is in the middle.

Colors:
orange (or red?), green, silver, black (thicker), green (thicker)

I assume 1st and 2nd band is for value, 3rd is multiplier, 4th is tolerance and 5th is TCR.

Someone suggested that thicker bands represent tolerance and TCR.
Then it would be 0.35Ω, but black color is not specified for tolerance and green is not specified for TCR.

When I reverse order:
green (thicker), black (thicker), silver, green, orange (or red?)
Then it would be 0.5Ω, ±0.5%, 15ppm

Which one is correct? Or what is the correct procedure and value?


texts:
I am using this Microcontroller NXP MCU

I am trying to understand the RESET Section of the microcontroller.

1.On page 83, it is given as MCU reset is a bidirectional pin. So, It can drive other peripherals to reset and it can also be reset by other peripherals, right?

2.I was not able to find in the datasheet that this RESET pin is in open drain configuration? Can you please help me where to find this information for the pins?

How to check if the reset pulse duration is not long at power up?
What does WFRST mean? And how can I calculate the minimum current required to pull reset pin low?

I am unable to understand certain terms mentioned in the datasheet as this is my first project in microcontrollers. That's why so many simple queries. Sorry. Please help

Thanks


texts: MOS Amplifier Circuit - Lower 3dB Frequency Calculation

texts:
I am confused with the above problem as the output node is not specified. If the output node is drain, it will be common source and if output is source, then it will be common drain.
My question is that is it necessary to specify the output node to calculate lower cutoff frequency or the solution is ok ?


texts:
I am trying to build a simple JFET common source amplifier to get about 5-10 times gain for a signal I have coming from a microphone with an amplifier already in it, from ADA Fruit, here

I am working with a circuit just like below, but with the capacitor on the output removed.

I have tried various values, but currently I have RD at 10 KΩ, RS at 1 KΩ, Cs and Cin are are .1 μF, and RG is 1 MΩ. VDD is 5 volts. I tried two different transistors FQP30N06L here and  J310 here. From what I understand, this should give a gain of 10x.

I can generate a signal by whistling, and the preamp on my circuit gives about 100-500 mV sine wave output. However, my output signal from the drain is always smaller than my input signal.

I am not sure what is wrong here, any advice would be appreciated :)


texts: Weird behaviour of logical mosfet in proteus

texts:
I'm trying to drive a P-Mosfet logical from a 2-3Decoder 74HC238, the problem is whatever the Input to the MOSFET's gate, I always get a high output on the drain.

Kindly find the attached schematic, if there is a faulty mistake.

Q1 is the output,  DEM1 is the input from the 74HC238 ( directly connected )


texts: Synchronous buck converter in parallel with linear regulator

texts:
I'm looking at designing a circuit to provide power to a USB charging port (500 mA charge rate max) in a 12V battery-powered application.

I'd like the buck converter to be "off" when there isn't any USB device plugged in for charging, so as to save on battery life since most buck converters consume a few mA of input current under no-load conditions.

My thought was to have a voltage reference with series resistance in parallel with the buck converter that would regulate the output voltage to a value slightly higher than the set point on the buck converter (i.e. for a 5V output buck, the LDO would output 5.15V).

The idea is that the buck converter would go into "pulse skip" mode and stop switching until the voltage fell below back to 5V, which would never happen for light loads since the voltage reference would be holding this output voltage at 5.15.

As soon as a USB device was connected for charging, Rload would drop dramatically (say from 10Mohm to 10 ohm), which would cause Vout to drop from ~5.2V until it fell below the threshold of the buck converter's "pulse skipping" comparator, causing the buck converter to switch on once again.

Is this a sound plan?  Do Buck converters in "eco" mode with their output being held high by external forces work the way I have described here (i.e. can they be in "pulse skip mode" for days on end?)?  See below schematic:

simulate this circuit – Schematic created using CircuitLab

An alternative approach would be to monitor the output of a linear regulator with a comparator and series resistance and toggle the enable pin of the buck when the comparator senses enough current flowing as in the following schematic:

simulate this circuit

This would probably result in the lowest power consumption, right?  But what about the start-up time for the buck converter? Won't the startup time for the converter result in the voltage falling far below 5V before it can come online an compensate?


texts:
I have a solar panel hooked up to a 12 V battery that it powering a DC motor. What is an easy, efficient way for me to change the voltage across the motor. I would like to include a knob so I can change the voltage, and I would also like to include LEDs like a bar graph to show the relative speed.

Thank you stack exchange community.


texts: Create a robot arm using microcontroller

texts:
I am planning to create a robot arm using the MicroController.
The robot arm should move from the angle of 0 degrees to 60 degrees.

I am going to use this robot arm in my application to stop and allow the small small toy vehicles on a dummy road. This is for demonstration of my project.

What are the specifications that I need to keep in mind while choosing the Stepper Motor and MicroController.


texts:
I was reading an article in a magazine in which the following sentence is written about a circuit that generates a certain waveform on a load R (in which one of its terminals is connected to the earth - not the circuital GND - ):

"Never connect a normal oscilloscope probe to the ends of the load.  In fact, the oscilloscope's GND terminal is connected directly to the earth conductor and therefore you could make a direct short circuit between the circuit phase and the earth, with relative risks of explosion, electrocution or fire. You need to use a differential probe."

Can you explain me this on detail? I do not follow this reasoning. Why should the phase "touch" the earth voltage?

To clarify the problem, here there is a picture of the schematic (the load is connected to CH1 or CH2, while the input AC 230V enters x1):


texts: Detecting power loss in a microcontroller to save context

texts:
I am trying to detect sudden power loss in my micro controller to save its state before the MCU dies. I have been thinking to utilize one of my GPIO pin to detect the supply voltage and use a large capacitor (with a diode to stop reverse feeding into the GPIO) to get enough time to save the state. Below is my proposed solution.

simulate this circuit – Schematic created using CircuitLab

Note - My brownout voltage is 2.1V and blackout voltage is 1.67V. I have shown a load in the 5V section to represent some relays and LED's which are powered at 5V (not sure if this is relevant). Also the 10uF and 22uF are required for AMS1117 and 100nF is a decoupling capacitor.

My questions are

Is this the best approach for such cases?
Will it be better to use ADC pins instead of GPIO?
Is IN4007 the correct diode to stop reverse feeding (3.3V, max load is 470mA)?
Any other suggestions / improvements on the circuit?


texts: Can you safely "short circuit" 2 signals when they compete for the same pin to avoid having to use a multiplexer?

texts:
I'm developing for a very limited, 8 pin LPC810 microcontroller and have to connect multiple signals on a single pin. Obviously, if there's only 1 output signal on a bus, that should be OK, but what about 2 output signals? I have 3 such cases (1st signal listed is only used in programming/debug mode, while 2nd is only used during run time):

RS-232 TX output and push button - these are OK because I've read that RS-232 can be "short circuited" indefinitely by limiting the current (I measured ~30mA)
SWDIO/SWCLK (ARM serial wire debug) and GPIO output - this is my main inquiry. I know GPIO cannot be safely shorted, so for this to work, SWDIO & SWCLK must be current limited. Is that the case? I don't want to risk breaking my Segger JLink to find out.
push button (for enabling programming mode) and GPIO output - if these were to compete, the GPIO would definitely die. But I did find a way to put them on a bus without killing the GPIO: press and hold another reset button, which makes the GPIO output a GPIO input, and then press the button. This is kind of cumbersome - is there a better way?

Note: please ignore the correctness of 2 short circuited signals - I'm assuming only the cases where 1 signal dominates the other are actual use cases.

Update
Here's a diagram:

simulate this circuit – Schematic created using CircuitLab


texts: Shared feed/GND pad on Pulse W3011 antenna

texts:
This is my first post; sorry if I've unwittingly broken any rules or accepted conventions around here...

I'm using a Pulse Engineering W3011 ceramic GPS antenna. As is common with these small ceramic antennae, the feed and GND share a pad on the part. Without knowing what the internal structure of the antenna looks like, I can't tell if it's important that the feed-line connects to a certain region of the pad and the GND to a different region, or if the connections are interchangeable.

Referring to the figure below, observe that feed and GND (traces 1 and 2) both connect to the same metallized pad on the chip antenna. Now imagine that I've drawn the same copper pattern, but on the reverse side of the PCB, and we're looking at the layout on the computer screen, as one would do in your favorite EDA software. In other words, we're looking through the PCB so that when you flip the PCB over, the feed-line is entering the part from the left. So far, this is permissible because Pulse states that pads 1 and 2 on the part are identical and the part can be mounted either way. But the question I have is whether or not it's OK that the feed-line is hitting the pad in a different place than is stated in the document.

In other words, with the antenna placed on the copper as in the diagram, with antenna pad 1 on the left and 2 on the right and the copper on the top side of the PCB, the feed-line hits the top corner of pad 2 on the antenna. With the antenna flipped around so that antenna pad 2 is on the left and pad 1 on the right, it's really the bottom of antenna pad 1 that touches the feed-line. But if the copper is on the bottom side of the PCB, it's the top corner of antenna pad 1 that touches the feed line (or the bottom corner of antenna pad 2).

With that exhaustive explanation out of the way, does anyone know if it matters where on the pad feed and GND touch and, furthermore, if the positions can be swapped? I understand the basic concept that one side of the antenna forms a PIFA-type radiator, the other side connects to ground, and the slot in the surface between the two capacitively couples the two elements. But I just don't know how dependent the proper operation of the antenna is on the relative positions of feed and GND.


texts: Is this a triphase or monophase AC motor?

texts:
I have got this motor from a local junk yard.

It says it is a monophase motor, but its wiring looks like a triphase one. Please help me classify it.

It reads

  Monophase dual-value capacitor asynchronous motor

  Model ...

  Power 2200W, RPM 2800 r/min

  Voltage 220V, Frequency 50Hz

  Current 16A, B grade insulation

  Operating 45uF/450V, Starting 300uF/250V

  IP44  Implementing standard: JB/T9542-1999

  Serial ..., Date Aug 2008

  (Left) CCW, (Right) CW

  (Wiring Diagram)


texts: 19v Charger with 14.4v Battery: What exactly can I expect?

texts: Long story short: I have to replace the charger AND battery on my ASUS U53F-BBL5 laptop due to a combination of lost original charger and Best Buy can't read a laptop's model number for the correct charger. Now, I already ordered a charger, but looking back I may have accidentally ordered for ASUS U52F rather than U53F. I still have the absolutely worthless battery and I already have the ordered charger. Charger says 19V, Battery says 14.4V. I do not have the money to order another charger. So what can I expect the charger to do to my battery, and how badly? I.e. will it shorten total life before the battery becomes useless, will it just shorten how long a full charge lasts, etc. and to what degree?


texts: What voltage do you measure while implementing the charge algorithm?

texts:
So the charge algorithm for recharging a battery is (I will be using a lithium-polymer):

Pre-charge
Constant current charge
Constant Voltage charge

But I have learned that the open circuit voltage of battery is different to the voltage measured while charging.
So my question is what/which voltage do u measure while you charge the battery. How do u measure this. I have searched for this, before asking the question here. So if anyone could direct me in the right direction would really appreciate it.


texts: Altium interactive routing is always ignoring obstacles

texts: I can cycle through all the modes of interactive routing, but Altium doesn't seem to care. Any trace I lay will just step right over other nets that already exist, with no effort to push or avoid. A DRC error is instantly generated because of the short circuit this creates. Why is my interactive routing not working properly?


texts: So i read alot of data sheets regarding bluetooth modules and when i come acorss antenna section i find that term called effeciency. What is it for ? For example If class 1 bluetooth  with 100m range and 70% effiency. It means that effective range is only 70m or what.there is another term called gain is this one has direct relation to range too. Thanks in advance


texts: How do I read a simple touch sensor value from Arduino?

texts:
I suppose instead of  connecting to the LED it will connect to A3 on the Arduino for example but I'm  having a hard time making it work.

I don't know which point on the circuit should be connected to which pin on the Arduino. I seem to get values alternating between 950 and 1050.
My question is in general how this should be connected to the Arduino.


texts: Large Active Area phototransistors? And can solar cells be a replacement

texts:
Me and my friends are trying to build a laserharp driven by arduino as a learning exercise. Currently we are using a phototransistor to interrupt the laser light and play music.

However the activation area of the phototransistor seems to be very small and requires it to be placed quite precisely in the path of the beam.

I am unable to look for something like a large activation area phototransistors... if they exist?
Or is it possible to use some kind of lensing arrangment (which should be cheap) to focus light from a wider area to the transistor.

As another possibility, I would also like to look into solar cells. Since there area is quite adequate they are perfect for my application. However I don't know if their response time would be fast enough (close to phototransistor) and secondly from where do I get a single solar cell?
Since the laser is just a point on cell, using a solar panel is quite inadequate for my purpose.

More details: Sorry for not having them before.

I have one 8mW green laser (power is not precise, I hacked it out of a home projector.. but is getting my job done)

We incident the laser on a mirror, that is being rotated by a stepper motor. Currently 4 steps clockwise, and then 4 anticlockwise with a delay of around 4 ms on each step.
This produces 4 beams of laser from a single beam.

As a pick I am currently using a phototransistor with Vcc. on the collector, and an emitter grounded through the resistance with a floating base.

When the phototransistor is used to block one of those lasers, if the laser happens to fall on the activation area of the phototransistor then it gets biased and I can read that. This combined with the step number of the stepper motor lets me determine which beam is being interrupted(realize, there is only 1 beam at a time)

The problem is that since the activation area of the phototransistor is quite small, its inconvenient to get it in line of laser. This creates a non-interactive user experience. I need to remedy this.


texts: compatibility of Bluetooth module and Android devices

texts:
I'd like to connect a Bluetooth module to PIC to communicate with Android devices
what is the property that determines the compatibility between them , i could not find anything in the web from Android Bluetooth site , How to know if the Android device and the module i will choose will work together or not ?
Please do n't mention to me Names of modules that will connect , i'd like to know how i can decide if it will connect or not.


texts:
I'm trying to learn about interrupts using one of the Teensy USB boards. It's got an AVR AT90USB1286 chip on it. I'm using the code below, and I'm expecting my ISR block to get called and periodically flash the LED on pin 6. But nothing is happening. Can anyone see what I'm doing wrong?

#include <avr/io.h>
#include <avr/pgmspace.h>
#include <util/delay.h>
#include <avr/interrupt.h>

#define PIN_ON(n) (PORTD |= (1<<(n)))
#define PIN_OFF(n) (PORTD &= ~(1<<(n)))

#define LED_CONFIG  (DDRD |= (1<<6))
#define CPU_PRESCALE(n) (CLKPR = 0x80, CLKPR = (n))

#define OVERFLOW_INTERRUPT_ENABLE (TIMSK0 |= (1<<TOIE0))

volatile unsigned int overflow_count = 0; //Count of overflows

ISR(TIMER0_OVF_vect) {
  cli(); //Disable Global Interupt
  if (overflow_count < 0xFFFF) {
    overflow_count++;
  }
  else {
    PIN_ON(6);
    _delay_ms(500);
    PIN_OFF(6);
    overflow_count = 0;
  }
  sei(); //enable global interupt

}
int main(void)
{

    // set for 16 MHz clock, and make sure the LED is off
    CPU_PRESCALE(0);
    LED_CONFIG;
    OVERFLOW_INTERRUPT_ENABLE;
    sei(); //enable global interupts

    while (1) {
      _delay_ms(1000);
      //analogWrite(6, 10);
    }
}


texts: How to turn on a high output for every other high input

texts:
First appologies if my title sounds ambiguous, im fairly new to electronics, and some of the things I learned in school all those years back have escaped me.

I have a circuit that consists of a lipo battery, a magnetic switch and an electromagnet.

The electromagnet turns on when the magnetic switch is turned on by a nearby magnet.
However what I need is for it to turn on every OTHER time it detects a magnet.

I vaguely remember something about using flipflops for doing this. Am I right to assume this is the best way to approach this? Or am I going to run into problems? I want the simplest circuit possible. (ive previously used an arduino to do all this and increment a counter, but I feel this is a bit overkill).


texts:
I'm just looking at the BQ2407x range of Lithium-Ion charging ICs. One part in the range has an extra pin, TD, which disables/enables "charge termination". Here is the functionality description:

Sadly this only goes into what happens if you disable it, but doesn't really say what happens if it is enabled (i.e. I'm guessing normal operation). From my understanding, "termination current" is the current fed into the battery once it reaches the CV stage. As someone semi-new, I can't understand the point of disabling this. So my question:

Why would you want to disable termination current?

The only thing I could find (here) is that you can extend battery life by not charging it to 100% every time, which is what would happen if you disabled any current at the CV stage - but that article encourages reducing termination current, not stopping it entirely. Frankly, the product I'm designing doesn't need to be perfect/have extremely long life, so really I just want to know the consequences of pulling the pin low vs pulling the pin high.


texts: Voltage Requirement for Integrated Circuits

texts:
There are industry standard voltage levels for integrated circuits i.e. 12, 5, 3.3, 1.0, 1.05 , 1.08 and 0.6 volts and etc. My question is around why make it so complex to have this many voltage levels, why not just have one voltage level i.e 12 volts to be universally used across all IC's?
Potential answers that am expecting is around power drawn that involves current holding capacity, copper losses and etc but it would be nice to have a good explanation from industry technologist who have spent many years in electronics.

Best Regards
Yasir


texts:
I Have step down transformer that transforms 240V to 9V.

However, I cannot find out, which terminals are for input and which are for output. The turn ratio size is very similar, because it is covered.

How can input and output side be identified?


texts: What is the purpose of curved PCB traces?

texts:
I have seen traces like this enough times to begin wondering if there is a purpose and benefit. The only technical explanation I can come up with is that perhaps these curved traces increase the inductance between the end-points (for the type shown on the right of the IC) and decreases capacitive coupling for the type shown at the bottom. If this is the case, why would that be desirable? If not, what is the purpose? Also, I thought it was generally back practice to include sharp edges in the traces.

This particular screencapture is taken from the PCB of the new Raspberry Pi 2 B


texts: The problem is to find a modulo when a three digit number is divided by its last two digits. But the three digit number is received in a binary form. So I first want to change the binary form into integer form then use the mod operator.


texts: how to design an electronic circuit that convert a binary sequence to Manchester code

texts:
I want to design an electronic circuit that convert a binary signal to Manchester code. I have already put a XOR operator between the binary signal and the clock, I got the allure of Manchester but the the low level is coded with 0 V and I want it to be -V. How to do that ?

here is my circuit:


texts: I am looking at buying a chip holder for a chip that comes in the form of DIP28S according to different datasheets on it. However when I searched for DIP28S chip holders I could only find SOP28 chip holders, and the measurements of them would allow the DIP28S chip to fit in those chip holders. So my assumption would be that DIP28S is the same or very similar package form to SOP28. Am I correct?


texts:
I'm working on a project with the quite new STM32F429 in LQFP208 package.

I need to solder the first couple of prototype by myself for low budget reason. I choose this package so I could check myself if a problem is due to the routing/firmware or just a soldering issue.

In the project there are an LCD, a CAMERA, an ULPI and a 32b SDRAM bus plus some other slower interface.

The FMC BUS will be only used for SDRAM, no other memory is needed for the project.

The PCB stackup is a standard 4 Layer S-GND-VCC-S.

I need an advice for what would be the best approach to route the SDRAM/MCU interface.

Here there are 2 different design that could be done:

Left one will be the best to have very short traces, but it will not leave too much room for lenght matching,not really needed due to really low propagation delay for short traces).
The LCD/ULPI/CAMERA bus could be routed externally whitouth much problem.

Right one could be better, slightly longer traces but lot of room for lenght matching, and still no termination needed. The LCD/ULPI/CAMERA bus will be routed externally but they will meet the SDRAM bus in lot of point so vias count will be increased on theese bus and layout will be much more complicated!

EDIT:

Both sides assembly is a must because of some other compontents.

Could you explain which one would you choose and why?

EDIT2:

I choose the left one after populating the pcb, so there wasn't too much space for the right one.

This is the preliminary result.

Advice is still accepted to improove the layout:

EDIT3:

Added Power and Ground vias:

Thank you!


texts: How to get 12v 5amps battery setup for LED strip

texts:
I'm building an LED lightbox but I really want to avoid using a power supply/cable so I'm trying to figure out a way to do it with batteries.

The strip I'm using is http://www.amazon.ca/dp/B00D76XBU0/ref=pe_386430_30332290_TE_3p_dp_1
I'll be using about half the strip. I've got it setup using 2 9v batteries in series with a switch but I'm sure I need a resistor I just don't know how to figure out which to use!

Also does this look right?

   + 9v - + 9v -
   |    |-|    |
  (res?)       |______ -
   |                   STRIP
  (switch)____________ +


texts: 4g transmit from a tv antenna to an indoor antenna

texts:
We have a TV antenna on the roof, works on 5-2600 MHz.
Its cable runs from roof to my room, connected to the TV.

I am wondering if I could transmit 4g signal using another antenna, by connecting a splitter to the cable inside the house one end of the splitter to the TV and one to an antenna.

will this work?

by another antenna means, a simple bipole 2.4ghz antenna,
can be as simple as a diy bipole antenne


texts: How to choose the receiving end voltage for a transmission line using a short line approximation

texts:
I am confused as to how to choose the receiving end voltage for a short line approximation

For example if i have a 220kV transmission line at 50Hz at 60Km. At the end of teh line theirs a load of 50MW and the lines impedance is Z=5+6j. The question asks find the sending end voltage using Vs=VR+ZIR. I can do the calculations all fine etc. The problem i have is what would i select my Recieving end voltage to be?

Do i do 220kV or do i do something less than 220kV, does it matter at all if i choose less than 220kV since as the transmission line is 220kV does this mean the line wants to see 220kV along it (like example 220kV is seen in the middle of the line and the sending end is higher and recieving end lower?)

Hence i am confused as to what to choose for VR as its not given, all that is stated is the line voltage being 220kV for the transmission line. What does the transmission line voltage mean?

When i state i have a 220KV transmission line does that mean the end voltage of the line is 220kV

Note i know to get Vr its line to neutral voltage but to just get the concept what line to line voltage would be used

**

This question i state is made up by myself for understanding purposes

**

Thanks In Advance


texts:
I am using external ADC MCP33121-10 via SPI interface. I need to isolate this ADC from main procesor (Arduino Mega), so I used optocouplers.

The ADC worked fine without optocouplers but when I connected them, I can't get any readings. Then I found that the error was in speed (optocouplers couldn't transmit data this fast.)

I tried slower transmission speed in traditional Arduino SPI library, but it didn't work, so I had to write my own library.

Here is sample code:

unsigned int data=0;

  for (int i=0;i<14;i++)
  {
    digitalWrite(CLC, HIGH);
    delay(1);
    data=data | (digitalRead(MISO)<<(14-1-i));
    digitalWrite(CLC, LOW);
    delay(2);
  }

  Serial.println(data);

This code works fine without optocouplers too, but when I tried it with them, I get the error (described below).

(ADC input is connected to potentiometer and I am slowly increase and then decrease voltage with potentiometer.)

The output looks like this:

Do you have any idea what can cause this problem (those little spikes at bottom and in the middle?)

Edit:

Here is same code, same hardware, just without optocouplers:

(It's not linear, because I controlled potentiometer by hand, but it shows that those "magical spikes" dissepeared.)

Edit2:

The ADC is conected this way (the ic at the bottom is 1.8V generator, jumpers SJ7 and SJ4 are shorted and SJ6 is connected to VREF):

The optocouplers are connected this way:

(MOSI is used for other purpose)

UPDATE:

I found out when I touch the MISO pin (on ADC side) with my finger it just mysteriously started working. So I added on that pin small capacitor and I am finally geting correct readings.

Does anybody knows what my finger or capacitor did with that pin?? Why it started working?

Here is placement of that cap (left side):


texts: Uploading C program to the ARM core for execution through ethernet!

texts:
I want to write a c code on my local PC and upload it to ARM core on Zed-board for execution. I know we can do it using JTAG, but for obvious reason I want to use Ethernet interface.

I will be glad to explain more if i am missing the right words to explain my problem.

Many Thanks in advance!!


texts: Replacing USB power with simple power supply

texts:
I've bought a bunch of dlink wifi cameras for my home.  These all come with 5V wall wart psus connecting to the camera using what appears to be a simple 2 core cable terminated in a micro USB socket.

There are, of course, no power outlets close to where I would like to position the cameras.  So I have to extend the cables and, rather than terminating each in a separate plug, I was wondering if I could simply run a 5V pair supplied by a beefier psu, possibly with battery backup, around the house and hang all the cameras in parallel off that.

iirc though, proper usb devices do some kind of power negotiation at start up, which, presumably, would prevent them being used in parallel.  How might I determine if these cameras are simply using the microUSB as a convenient small physical plug, or if there's anything special going on?

This article (https://www.medo64.com/2016/11/100-ma-is-a-myth/) suggests I might be able to just ignore the whole thing anyway.  Is that realistic?


texts: How to design over voltage protection Crowbar Circuit?

texts:
I'm designing a Crowbar over voltage protection circuit with following specifications,

Maximum input voltage - 30V

Maximum input current - 5A

Output voltage - 5V

Output current - 5A

So I have chosen zener diode (1n4733A -> Vz = 5.1V,Iz = 49mA) and (2n5060 -> Vgt = 0.8)  components for my circuit.

According to the calculation I choose R = 16.3265ohms resistor.
But my simulation doesn't work as I expected.

(For more information I have attached screenshots of my Multisim simulation)

Could you please help me to solve my problem?


texts: What's the voltage used to power LEDs inside an LED light bulb?

texts:
I have opened an LED light bulb today, and there are two thick wires sticking out of the center to power the LEDs.

I know it will vary by design, but I can't find even a range of voltages, therefore I ask. What is a typical voltage used to power the LEDs in such an LED lightbulb ?


texts: Would anyone please explain why you don't need a controlled impedance board when you produce a PCB dealing with 50Mhz digital signal? I thought you might need a controlled impedance board, since 10Mhz is already fast enough to make problems 'in measurement'. If one measure such digital signal using an oscilloscope, the impedance matching is important. But why isn't it the case for PCB board production?


texts:
I am in big trouble with my power supply for Nixie tubes (IN 9 bargraph.)

I need 140V -160V (150V prefered) output voltage and 10x 12mA --> ~140mA current.  (~ 21W).

I tried to design boost converters but I wasn't able to get one with this amount of power. Does anyone have a schematic with such a boost converter?

I prefer THT components but if it is SMD there won't be a problem.

I also tried the idea with 2 transformers. One (50VA) 230V to 6VAV and one (50VA) 230VAC to 12VAC (secondary sides wired together). And I added rectifier and capacitors. But if I add a load (to reach 130mA ~ 1k2Ohm) the output voltage goes down from 160VDC to 120VDC.

So does anyone have an idea how to build a power supply with these power speficifications?

The load varies (min 0.5mA to max 130mA.)


texts: Noninverting schmitt trigger circuit LTP, UTP calculation

texts:
I knew very well how to work negative feedback using virtual short but this is the first time encountering positive feedback.
I think the feedback voltage here is \$\frac{R_1}{R_1+R_2}V_{out}\$. If so, this must be the reference voltage too. How is my textbook getting just \$\frac{R_1}{R_2}\$ ?


texts: Connecting / Soldering a Switch to Breadboard / PCB

texts: I'm pretty new to electronics and I have just found these toggle switches. But I can't figure out how the connectors on the bottom are called in the english language .. :) And also, is there a way to connect those to a standard breadboard (without soldering a wire to it)? And if you were to solder one on a PCB, how would you do it? Through-Hole?


texts: Reference Designs for Analogue & Digital Inputs to Microcontroller

texts:
I'm not so good when it comes the analogue end of electronics. My microcontroller has 0-3v inputs and I'm trying to get together a range conditioning circuits.

I know this I a reasonably broad question as the analogue design will depend on a lot of other factors, but are there any reference designs around for the following:

Analogue 0-3 volt

Now there'll need to be some over voltage protection and something for voltage spikes, but will that do?

Analogue 0-30 volt

Can I just use a resistor divider with some 1% resistors and hope for the best?

Digital 0-x volts

I guess here I'd be best to use an 'opto' based device that supports the required frequency?


texts: Solar: Reason For Joining Batteries/Solar Panels in Series

texts: I understand the concept of what happens when you do, but I do not understand the reason behind why some set-up require to double the voltage on the batteries, since the point is to store as much AH as possible. Is it for special devices that takes 12v or more, or it has something to do with better dealing with inverters?


texts: I have various power supplies in the range of 5 V DC to 19 V DC which still have about 60 V AC pollution in their output. This makes me get zaps from the attached devices quite often. Is there a way clean the output? I'm tired of getting zapped.


texts: What is the practical use of Laplace Transform?

texts:
I am trying to understand the electrical model of 3-phase Induction Model. The rotor of the motor is modeled as a variable resistor in s-domain.

I fail to understand how that works practically. Can anyone explain me the practical relevance of LT and its use in the IM modelling?

Your help is highly appreciated.

edit: This is the link of the IM model: When load increases in rotor of induction motor how does stator draws more current?


texts: STM32F0 Disco on-board "Cannot connect to target"

texts:
So I've already went through these topics:

"can-not-connect-to-target-using-stm32f0-discovery-board-as-st-link"
"STM32 & ST-LINK - SWD connector not working"

I cannot access on-board target with the on-board ST-LINK.

Things I have researched:

Computer can detect the on-board ST-Link via USB, but when trying to connect to the on-board target I get the same result from the utility as the first link - "Can not connect to target!" Also tested with the slowest CLK frequency and different modes - nothing.
I can see and have measured that the on-board target STM32F0308Rx does 3-4 resets while connecting and then I get that message from the utility.

I have reinstalled ST-Link Utility and manually reinstalled the USB drivers as well.
I am on Windows 10 Pro.
Also the on board ST-LINK got updated to V2.J33.S0 - maybe I need to downgrade ?

I can access the on-board target with an external ST-LINK V2 - no problems there - I can flash the target and run the code. So I'm guessing there's something wrong somewhere between the on-board ST-LINK and the target but I cannot put my finger to it.

I have double checked the connections from the on-board ST-Link to the on-board target - when jumpers are mounted, the connections are to the correct pins PA13 and PA14 - continuity check is OK.

I have tried to cross examine the Discovery board to the default PCBA pictures found on the internet, it SEEMS that no component is missing or added on the board (I didn't get this board brand new - so I'm not 100% sure what has been done with it).
I have all the PCB files at hand as well and so far haven't found anything out of place between design and PCB.

So I think I have exhausted most of my ideas. Anything else I should check ? Or should the target have smth to use the on-board ST-LINK ? I have fully erased the target flash with external ST-LINK.

I really would like to use the on-board ST-LINK - make sure the board is OK, as this saves me a bit of trouble (plan B is to keep using the external ST-LINK)

'###########' EDIT '###########'

I've done probing around the board and Found out that the on-board ST-LINK uC STM32F103 pin 27 is shorted to it's VSS pins. But only that GPIO.

The R14 resistor was also blown to open circuit as it seemed - so I'm assuming that the T_JTMS signal was blown on that micro - thus kind of rendering that chip useless to ever connect to on-board target. Other than that it works.

OR is there any way to configure T_JTMS pin to some other pin with some FW wizardy ?
I could maybe also get a new bare chip, mount it on an adapter board, somehow get the ST-LINK FW (I think I saw some custom one on EEVBlog) and flash it with the external ST-LINK? dunno, maybe any other ideas ?


texts: How do you close a switch on a high-voltage network?

texts:
This is something I've been curious about for a long time. Let's say you're a utility trying to connect two segments of a distribution grid. Both segments will have about the same frequency, because they are both connected to the transmission grid, but the phase angles of their voltages aren't necessarily related to each other. I always assumed the procedure involved adjusting generators on one or both sides to bring those phase angles as near alignment as possible and then closing the switch.

A common AC distribution voltage in the U.S. is 7.2kV line-to-ground, though. That seems pretty unforgiving when you're trying to close a switch. If your synchronization procedure is off by even a tiny amount, you're going to see massive amounts of current flow.

Just to put some back-of-the-envelope numbers to it, let's say your synchronizing procedure is accurate to about 0.5%; maybe you're closing slightly out of phase or there is some small error in your sensors. That's still 36V across the switch, which we'll say has an impedance of 0.1 ohms. Now suddenly we have 360A at 7.2kV for 2.5MW. I know that's a transient current and both sides will get yanked into voltage agreement with each other, but that still seems like a lot! And that's not to mention that some networks are run at much higher voltages than 7.2kV. Is this just something utility switching equipment is built to handle, or are my estimated numbers off?


texts: Choosing the right capacitors and resistors for transimpedance circuit

texts:
I'm designing a circuit for a pulse watch. Therefore I naturally have an operational amplifier and a photodiode in my circuit.

The job that I want the transimpedance amplifier to carry out is to respectively amplify the signal which is picked up by the photodiode D1 and furthermore remove noise that I would otherwise get at V_OUT.

The intention is to connect V_OUT to an analog port on my Arduino, on which I then should be able to read the current fluctuations (or is it voltage - since an transimpedance doesn't translate current).

I'm a total beginner at this, but I think that I succeeded in mapping this correctly.

However, I'm unsure that the values I gave my resistors are correct..

Let me give you my reasoning for choosing the values I chose:

Since I don't have any "negative current" in my circuit, I raised the non-inverting voltage to 2.5v by dividing the voltage with R5 and R8 - I believe that's a reasonable voltage, since I then have plenty of headroom and wouldn't cause the wave to "clip".

Next, I plan to add an ATtiny85 MCU, which (as far as I can read) has a "typical" current of 30mA per I/O pin.

There is though a place in the datasheet where it says "Analog comparator input offset current", which has a max of 40mV, but I don't really know what the parameter means.

However, I decided to put a 200Ω resistor before the V_OUT, because then at maximum output I would get something like 5/0.2=25mA. Which should be okay, and thus allows for a finer granular reading opposed to if  I had e.g. a 1kΩ resistor, which would yield a maximum current of 5mA.

The photodiode I'm planning to use is: http://www.farnell.com/datasheets/8765.pdf?_ga=2.139995315.1420390384.1543406751-57595970.1536135582

And this is where things gets tricky for me. Especially, because I don't know which value to give R6, as the current across the photodiode will be dynamic.

Furthermore, I'm unsure about the capacitors.

My rationale tells me that C3 should have a relatively large farad value, as I obviously wouldn't want any noise from the gnd wire.

Also, my gut feeling tells me that I should just go with 0.1µf for both C1 and C2, but that's obviously not "optimal" in terms of limiting as much noise as possible.

To sum up:

Is this circuit correct? i.e. are my assumptions correct too?
How do I decide the values for C1, C2, R6 and C3?

And lastly, which DIP type amplifier would you choose for this job?


texts: Why does an op-amp perform poorly with no load?

texts:
I have a THS4221 evaluation module (THS4221EVM, schematic on pg 1-3) powered with a bipolar +/-5V supply.

My function generator (AtelierRobin F125) is generating a nice 1 MHz square wave, which I have verified with my GDS-1102A scope. I have the square wave hooked up to the input of the THS4221EVM, and am monitoring the floating output (VOUT in the THS4221EVM schematic) through the second channel of my GDS-1102A scope (high impedance input).

The output voltage on the THS4221EVM takes a long time (~250 nS) to settle at the final value after each voltage change in the square wave. It initially slews very quickly, but slows down as the it approaches the target voltage.

If I connect VOUT to ground so R5 (935 ohms) becomes the output load, and measure at U1_1, the output is as expected.

Why is the performance affected in this way when there's no load?

Strangely, TI's hookup diagram (pg 2-1 in the manual) for this evaluation board says to connect the output directly to a scope, but if the opamp doesn't work properly with no load, then why is it setup that way? Even with a load on VOUT, I have to manually probe the circuit to measure the opamp output since the VOUT connector is after R5.

EDIT: TI's hookup diagram makes sense now; I missed where the 'scope is referred to as a "50-ohm monitoring instrument". They expect the connection to provide a 50-ohm load, but my scope has a high-impedance input. A 50 ohm termination resistor would provide the load.


texts: What are these pcb connector type pads for?

texts:
My picture shows a prototyping board that I have.  Sorry that the contrast is not great, but there are two vertical rows of connector like pads down the left and right sides of the board.  They are oval. They look like they're for some sort of board connection, but there are no through holes.

If you solder wires to them, then what?  If you solder a connector wire to the board, and another leading to a component, they'll just come apart when trying to solder each other one.  I can't think of any suitable mechanical connector either.

What are they for, and are there any examples of their use?

Subsequently to this post, I've discovered that there are lots of these boards available at Chinese bulk buy sites (as my example below).  They come in all sizes right up to 150mm across. I use them a lot for projects, but still haven't discovered an appropriate use for the edge pads.  Others must also use them frequently, so...


texts:
Is it possible to measure the amount of water in a rubber water tank by using sound waves?

I want to make a non intrusive measuring device that attaches to the outside of a tank, and is able to approximate the amount of water in the tank however I don't know how to calculate what sound of a specific frequency will "sound" like given different mediums (e.g. sound travels faster in water than air).


texts:
I am still new on electronics (my background is software), I played around a bit with Arduino, and I am trying to advance on other microcontrollers like PIC, ARM, etc.

Can I rely on existing libraries to use peripherals like UART, I2C, SPI as I am used to with Arduino?

I googled around for a bit, and pages like this detail how I can implement UART on a PIC16. So I was wondering, does microchip (or any other microcontroller vendor) have libraries readily available which I can simply include as I was used to with Arduino? Or am I supposed to learn all the low level registers and implement them myself? (because that sounds quite challenging for a beginner like me).

Hope I won't get burned over this question, but couldn't find the answer googling...


texts: Microcontroller and decoupling capacitors on the VDD layer

texts:
I have a microcontroller design that is implemented using a two layer PCB. All the components need to be placed on the bottom layer due to the fact that there is a display in the top layer.

In short, I ended up placing all the components in the same layer as the VDD power. The initial design without copper pour intended to be like the following picture:

However, after placing copper pours, the result was this:

At first thought, I believed that there were no problems at all with the result: The capacitors where near and there were big traces to the processor pin. But as a second thought, I realized that it could be defeating the purpose of the noise suppression capacitors as I was now giving the noise source a low resistance path into the processor's power pin. Therefore, I changed the copper pours to avoid this low resistance path and forcing current to go into the capacitors leads as shown:

In essence, I'm asking anyone that has expertise in this matter to provide some comments and guidance about this design. Is there anything I am missing? I also don't see any problem with the fact that the processor is in the same layer as the VDD signal; if there is any problem, please comment.

EDIT

It is indeed a mixed signal plane. Pipe's comments makes every sense for me thus  I'm renaming VDDD plane to VDD.


texts:
I am trying to connect this mosfet driver:

To this circuit with 2 Mosfet (I can't use IGBTs):

I tried, but I don't know how to do it. I am doing the circuit with PSIM and I have to create all because PSIM don´t have comercial drivers blocks.

Could this driver works in this circuit without surpassing the maximum value for V_GE (20V)?

How could I connect?


texts: I read somewhere a few weeks back that a company is making SIM cards as IC chips for the "Internet of things". I can not find the article again or find anything about it on Google. Did I make this up?


texts: Necessary to lubricate old electric motor?

texts: I'm in the process of digitizing some old audio reels. The reel-to-reel player is very old and it tends to slow down after it's been on for a while. I was thinking that maybe the motor needed to be lubed up, but I'm not sure if that's correct. Any idea if this sort of motor should be oiled/lubed and the proper way to go about it?


texts: Piezo buzzer : transient audible noise when exciting over 20kHz

texts:
Let's 2 simple experiments, connect a piezo buzzer like this one to a bench amplifier driven by a function generator like this one. Driving voltage is 10V. Now excite it with a

linear chirp from 300Hz to 20kHz with a 500ms duration : you will
hear some noise, it's normal, we excite audible range
linear chirp from 40kHz to 200kHz : you will
hear 2 transient audible noise at the beginning/end of the
excitation. Loudness is small but we can hear it.

In second case, how can we generate audible noise when exciting over audible range with an analog signal ?


texts:
I have a wave and i can't know its formula
so i used Fast Fourier Transform (FFT) to make frequency spectrum for this wave to get all frequencies and amplitudes (in db) of this wave.

[1] i need to build the formula of this wave (time-domain) using frequency spectrum results and how to convert db of amplitudes.

[2] i can't know the phase for each equation because spectrum only give me amplitudes and frequencies, so how could i found the phases?

Thanks


texts: Problems with proteus simulation of register

texts:
I tried to simulate universal register in proteus software, for that purpose, I used 4052 component as a multiplexer (two of them actually, since one such component consists of two 4 to 1 multiplexers) and 40175 as a set of D flip flops. However, when I create this circuit, this is the warning I get:

Unfortunately, I failed to determine where \$V_{ee}\$ pin is actually located and what is the problem with it, but this is what happens with simulation:

As you can see, some sets of switches don't have their state (not even undefined), yet on the other hand, some of them seem to work just fine. What could cause this problem? Any help appreciated!


texts: Always plugged in solution with battery backup

texts:
I am trying to design an micro-controller based solution which is always plugged in and has a battery backup in case of power failure. I am using an SMPS power supply rated 15V, 1.4A which is always plugged in, a low voltage regulator with BC547 to regulate charging and an SLA battery rated 12V, 11.2Ah as a backup. Below is the circuit I am trying to build.

simulate this circuit – Schematic created using CircuitLab

Few questions I have are

I need to have a reverse polarity protection for the charger and load and stop any current from flowing back to the charger when there is no power. How to achieve this? I tried to add D1 and D2 as shown in the circuit, however it looks like D1 will not help in reverse polarity protection for the charging section.
Can this solution float indefinitely without damaging the battery? or should I use a solution with relays (i.e one for charging cutoff and another for backup switchover)


texts:
I'm building a battery powered device and I want to make sure, that no current is drawn from the battery, if USB is plugged in (while charging). I know that I could solve this with two diodes, but every 100mV counts in this project, so 0,3V voltage drop would be too much. Current draw is +-1A.
Is it a good approach to do this?:

The switch simulates the USB Plug-In
I'm asking because I think the P-Channel MOSFET then passes current to the battery, due to the body diode.
If it's true, I need another MOSFET to block the other direction, but is it worth it then? Or would 2 MOSFETs in series end up in the same voltage drop as a shottky diode?


texts: How to build an arbitrary (one-shot) pulse generator?

texts:
I need a circuit/IC that can generate a single pulse with a variable pulse width (I would want a minimum of 50 ns but if that is not possible the next minimum can be 1 μs, and even if that is not possible then the final minimum can be 5 μs, depending on the achievable minimum, correspondingly the max can be 5 μs, 5 ms, 25 ms respectively) and variable amplitude with both positive and negative pulses in a range of ±5 V (practically the operation would be in ±2 V range) with a resolution of at least 10-20 mV. The variables need to be digitally controlled (preferably) but this is not a requirement. The current output can be a maximum of 2-3 mA.
So I have searched a lot of the pulse generator ICs (monostable) available from different websites and companies (analog devices, data delay, maxim, etc) for 4 days now and I don't have anything that is the proper solution. All of them have variable pulse width and  ± pulses which is good but the amplitude is the same as supply voltage and is not variable which is not good for me.
Here are the links to a few of the pulse generators I have searched for:
LTC6993
DS1040
Data delay devices 3D3608 & 3D3612
The closest I have come to some potential solutions (might be wrong) are:
A. Pick any monostable multivibrator (such as LTC6993) and do either of the following for amplitude downscaling:

Use an 'AC voltage divider' or a 'Capacitor voltage divider' as mentioned in this answer. But I am not sure if this is the right way or if I should be careful about something such as drive current or capacitance of the pulse generator IC.

Use the output pulse (with an amplitude of 3.3 V / 5 V) of the monostable pulse generator to control the gate of a MOSFET with a lower drain-source voltage (typically 0.5-2 V) generated by a DAC.

B. Use a DAC to generate the (one-shot) pulse directly, I am not sure if it is possible to do this accurately (like a 1 μs pulse). If it possible, what kind of sampling rate/settling time/speed specifications I am looking for?
Thank you for reading everything. If you have a solution/advice (in form of a component, circuit, or a suggestion) please let me know, I would really appreciate it.


texts: Switching between two completely independent circuits

texts:
Background: I have built a 2S 7.4V battery out of two 18650 batteries. I have some TP4056 (5V 1A Micro-USB) charging modules lying around. I would like to use these the TP4056 modules (one per 18650) to charge the batteries but from the information I've found, having any connection between the two batteries is not a good idea while charging.

Therefore, I'm looking for a switch that would only switch on one circuit at a time. Either the serial connection b/w the batteries, or the charging input to the TP4056s.

Something like this:

What exactly is such a switch called (if it exists)? Is there a more elegant solution to this?

Excuse my noobness.

Update:

With a DPDT switch (thanks @Solar Mike!), does the following circuit make sense?


texts: Some questions from a first PCB design attempt

texts:
This is my first PCB design ever and I used DesignSpark's PCB software.

After simulating in LTspice I've drawn it in schematics as:

And converted to a two layer PCB and manually routed.
Here is the PCB:

Finally I checked with "Design Rule Check" of this software and according to the software: the design has no error now.
First I had Drill Backoff errors. I had to make power tracks thinner.

I have many questions regarding the procedure but here is some of them:

1-) How does the software decide the trace widths, I didnt even set any currents. Or should I ask: How can I set the track widths here?
I checked with LTspice and the max currents on the power supply's GND and power supply's Vcc as 5mA.
How should I set the track widths here? If I set the widths randomly how can I know the PCB machine will be able to make it??

2-) I'm not using any surface mount components. Do I really need solder mask?

3-) Do I need copper pour or ground plane? I work with frequencies less than 1000Hz.

Again I cannot find answers to these details on basic tutorials. I would be glad to have your input or suggestions.


texts: Will noise floor dominate the ADC resolution?

texts:
A 16-bit data acquisition board input range can be set to various ranges like +/-10V or +/-0.5V ect.

If our input signal’s range is +/-0.3V with a noise floor of 1mV does it make sense to set the range to +/-0.5V instead of +/-10V?

For +/-10V range the ADC resolution becomes 20/(2^16)=0.3mV. And for +/-0.5V range the ADC resolution becomes 0.015mV. But our noise floor is 1mV.

Can we say the DAQ input range here doesn't have any effect on the overall resolution?


texts: How to recharge a battery with a manual battery charger

texts:
What are the best practices for recharging a 12V lead acid battery with a manual recharger.

I have a 12V lead acid battery (7.2AH/20HR MK ES7-12 (PDF)). I've read the advice here on how to check the battery level (I have ~12.2 V under no stress, and when powering the system it still currently reads ~12.2 V on the DMM).

When it starts to run low, I'd like to know how best to recharge the battery. I have a manual battery charger (Schumacher MC-1). I realize the manual part means that I cannot just plug the battery in and walk away. How best to monitor the charge? With what frequency? What likely problems should I be aware of?


texts:
I designed a -very simple- circuit powered by a 12V battery.
I would like to add a sd card connector (its type is of no importance right now) on that circuit.

But I am concerned by the datasheets I find on the net:

first. No operation voltage?
second. How could I possibly feed a huge 250VAC RMS with my circuit?
third. 100 VAC max is approx 70V DC (100 * 2sq2). Way too much as well.
fourth. According to Ohm's law, I could put a 24 ohms resistor and be good.

I am pretty sure I miss something because one find those in every SoCs.

Could we make those fit my circuit anyway? (how?)


texts:
I have been scratching my head for a few weeks about the behavior of my circuit (attached). In this circuit I give a arbitrary known input signal to drive a current through R1 which is a thermistor. I then use an instrumentation amplifier to measure across points A and B to calculate the thermistor resistance. Unfortunately when I give the circuit a positive voltage it will clip, but for some reason the negative voltage does not clip. I have looked at the datasheet and confirmed that the opamp can produce the necessary current (\$\pm\$10mA) and I have given sufficient supply voltage (\$\pm\$12V).  I have observed that the clipping does go away with low input voltages i.e. (\$\pm\$1V).  I believe I am missing something trivial but I just can't seem to find it. I have also observed similar behavior with the other ADA4077 opamps in my circuit. I have removed the instrumentation amplifier and isolated the circuit completely and measured the waveforms using an oscilloscope observing the same behavior. I would really appreciate the help guys. Thanks in advance.

The circuit of interest.

Left: The waveform of the input (Yellow) and the voltage measured between A and B (Red). Right: The waveforms of the input and the measured wave at A to ground(Green). The measured waveform at A to my understanding must be really close to zero so this was most intriguing.

ADA4077 DATASHEET


texts:
Most early solid state portable MW AM radios used a ferrite rod antenna.

Some valve receivers like Phillips in the late 1950s used ferrite rods also. The early Germanium RF transistors were not too good by modern standards. Good sensitivity could be had with a large ferrite rod. As better RF transistors improved front end gain, the ferrite rod got smaller and performance was fine.

Sure a larger ferrite rod will pick up more signal. Is RF voltage proportional to core area?
What is the effect of rod length?
Is there an upper limit to all this when the rod is very large?


texts: method to handle concurrent GPIO interrupt sources?

texts:
I have two GPIO interrupt sources running in two separate threads:

GPIO pulses following line frequency(60 Hz)
button press

How can I use both these interrupts concurrently, considering my controller(ESP32) multiplexes all GPI0 peripheral interrupts into one CPU interrupt?

Currently, the program allows only one of them to work at a time.

Thanks


texts:
I'm trying to understand why with this very easy schematic, I got with my multimeter:

5.2V between the 5V pin of the USB breakout and GND: OK
0V between the GND of the LDO and the GND of the USB breakout: OK
0.9V between the output pin of the LDO and the GND: I do not have 3.3V.

How can I solve this problem? I have tried with both capacitors like in the test schematic of the datasheet but same issue.

Ref: LE33CZ


texts: Matching Networks on Narrowband Multistage Low Noise Amplifier (LNA)

texts:
How does the inter-stage matching network of a narrowband LNA compare to that of a wideband LNA for the same multistage design? I've read somewhere that narrowband LNA does not necessarily require a matching network between the stages and can be ignored when the design consists just of identical single-stage design in cascade.

Shouldn't the matching network be necessary for matching the impedance of the stages? Or, does it serve another purpose?

Here is the link: Design, Analysis and Optimization of Multistage LNA at KU- Band.


texts: Using a Peltier element to power an Arduino

texts:
I got myself a Peltier element and want to use it for an IOT project.
What is the best way to use the Peltier in order to power an Arduino or something similar every few minutes? (For my project it would be enough if I could charge a supercap and just power an ESP8266 board every 30 minutes.) Is a joule thief and a super capacitor the best solution or should I use something better?
P.S.: A small step up module would, at least in my opinion, be a waste of energy and won't be that useful. Or am I wrong?


texts: How to implement a negative edge triggered D-flipflop using using level triggered D-flipflops?

texts:
Say here's a negative edge triggered D-flipflop with its timing diagram with random binary signal.

And on the other hand, here's a level triggered one:

How do I implement the negative edge triggered D-Flipflop with a Level Triggered D-Flipflop? what should be my approach?


texts: What kind of diode to use with ADC inputs

texts:
I am looking for diodes to protect my ADC from over voltage conditions. From what I have researched so far, I know that I need schottky diodes hooked up from the input to the ground and the input to the VCC line, but I am confused of what properties of the diodes that I need to consider.

My ADC has a max input of 3V, and has some internal protection, but I have read that it is not good to rely on the internal protection circuitry. What kind of diodes properties would I need to protect my circuit, if someone accidently hooks up a 5V or a 12V input?

The diode properties that I am confused about are things like forward voltage, reverse voltage, etc.


texts:
Loop antenna's are often solved for magnetic field and we perfectly know how they behave towards magnetic coupling as shown in this image :

However, I am looking for the electric field lines pattern of these antenna's, I was thinking of a diametrical E vector "turning" with the current, creating some kind of circular polarization, am I right ?


texts: Can I change 1000 uF, 16 V for 1000 uF, 10 V?

texts:
Few days ago my main monitor did not turned on. I opened it and discovered three capacitors, of 1000 uF/16 V each, in bad shape.
Since all stores here in my town are closed due the quarentine, I'm trying to find these capacitors in old electronics not working that I've found here in my house.

I did not found the three capacitors with the original values that my monitor board require but I've found three capacitors of 1000 uF/10 V each, and visually they look fine. Can I use them? Which are the effects of switching from 16 V to 10 V capacitors with the same capacitance?
I'll test them soon as my electronics tools that I bought arrive in my house (I'm a beginner with electronics and still studying the basics).

I've also have found capacitors of 470 uF/16 V, just in case this information be important.

Thank you very much!


texts: Question About the Ground Wire on Aux Attachment Circuit for my Car

texts:
This is a specific question about a specific circuit, but I'm trying to use it as a learning experience as I'm still new to electronics and need to take practical knowledge where I can get it.

I recently purchased a box online that plugs into the cd-changer port on my stock Honda car stereo and will allow me to use any RCA stereo source as an input. It's got one plug on it and an exposed wire coming off of the box-side of the plug. The included diagram has this single hanging wire labeled as "Chassis ground when using portable device" and the step-by-step instructions say "NOTE: Chassis ground BLACK/WHITE wire ONLY when installing a battery operated audio device. (i.e. MP3 Player)"

I'm reading this as "if the AUX device you're using is not connected to the car battery, you need to ground the box," but my question is: why? Why would I have to ground the circuit box only when the AUX device is not using the same power source? Would it hurt to ground the box when the AUX is connected to the car battery? I'm not really interested in this specific device, but the principles involved in the decision.

P.S. This is the box.


texts: Is there a circuit that conserves energy of multiple power sources?

texts:
Say I have several batteries. To start all the batteries are "dormant"; there is no current running through them. Starting with the first battery it runs current through it until it dies, wherein the next battery is activated and so on and so forth.

Is there a circuit that can do this? Would a circuit with batteries in series or parallel work?


texts:
I have a trackpoint from a thinkpad keyboard with a trackpoint mounting a PTPM754DR microcontroller, what I'm trying to do is to find the usage of various pin on the trackpoint board and connect them to a teensy 2.0 that already controls a keyboard (I'm using this firmware https://github.com/tmk/tmk_keyboard), what I've found on various sites and forums like geekhack are info from other trackpoints with a different pinout, I say so because I've traced at least the mouse buttons and saw the vcc and ground that have bigger traces than the others, how can I find the purpose of other pins? I cannot connect that keyboard back to a laptop.

Here is some images of the trackpoint and what I was able, probably, to trace


texts: How to charge a capacitor using repeatable damped sinusoid current signals?

texts:
I am trying to charge a capacitor using repeatable damped sinusoid current signals from a piezoelectric bender - Result of the free vibration of the piezo beam(Current source plus piezoelectric capacitance in parallel). The current from the piezo bender is rectified and used to charge a capacitor. I have simulated it Matlab/Simulink but it yields a weird behaviour when the input is a damped sinusoid current signals. The voltage across the capacitor never reaches the open circuit voltage but grows indefinitely.

This is the expected behaviour (From a sinusoidal no-damped current input):
Graph1: Voltage Across Cp1(Piezo Bender)
Graph2: Voltage Across Capacitor that is being charged.

However, this is what I get (The voltage across the capacitor never reaches the open circuit voltage but grows indefinitely):
Graph1: Voltage Across Cp1(Piezo Bender)
Graph2: Voltage Across Capacitor that is being charged.

Would you have any suggestion on how to fix this problem?
Thank you very much for your help in advance.
Best wishes,
Lucas


texts:
I am trying to read from the SGX MICS-6814 gas sensor. The documentation has 2 small sections on how to read the output:

From the datasheet:

From the FAQ document

To start with they show the resister order differently. But mostly I don't quite understand what they are saying about switching resisters. I am using a 16bit ADC and they don't really give any indication how to work out what load resistor/s to use. Can anyone at least explain what the theory of what they are trying convey?


texts: What makes RF transmission so efficient?

texts:
I'm a layman in this field. I have a question about RF transmission.
How does the data transferred by RF waves (for example in mobiles, wifi) reach the users accurately in spite of losses during transmission?


texts: Help identifying surface mounted component

texts:
While replacing the damaged screen on my wife’s Pixel 3a, I damaged one of the blue components below the FPC connector that connects the LCD assembly to the main board.
Can someone tell me what these most likely are? From the white dot, I'm assuming something with polarity?


texts: I was looking at a schematic provided by TI for a PoE power supply, and I had questions about certain resistors. What is the purpose of R5,R6,R7, and R8 in this schematic?


texts: Why is there a system controller and a microcontroller in the same FPGA?

texts: I am starting to dig into the FPGA world. While exploring the FPGA SmartFusion2 architecture I found out that there is a microcontroller (ARM Cortex-M3) and at the same time a system controller. Why is there a need for both? Can't one of them replace the other?


texts: How to force USB device to drain 500mA Current for charging?

texts:
I designed an AC-DC converter circuit(220VAC to 5VDC@700mA) to create a smart phone USB charger.

The Transformer that I used in my design can supply only 700mA current.

I searched the Web and noticed that the specification for the USB 1.0 and USB 2.0 says that they can provide 500mA which in my case is just fine, but on the other hand the USB charger of the most of the SmartPhones support 1A current.

I'm wondering if there is any way to inform the USB Device (in my case smart-phones)to drain up to 500mA current?

Perhaps some specific configuration on the D+ and D- pins.

I'm afraid that if the USB Device drains current up to 1A, in some cases it will damage the circuit and USB device.

The attachment contains the schematic


texts:
( RCS =  radar cross section )

FEA wasn't mentioned in the acronyms or keywords list.


texts: Circuit for 3 stage lead acid battery charger controlled by microcontroller advice

texts:
I designed the circuit below as a mashup of different ideas.
It is a lead acid battery charger controlled by a microcontroller. The relay allows the micro to select between the constant current circuit and the constant voltage circuit. The micro can also select between 2 constant voltages (14.6V and 13.5V). The micro can read the current and voltage being applied using the INA240 for current and a voltage divider for voltage. Each of these signals is fed into a 555 timer which generates a Pulse-Position Modulation signal, which the micro can read (the micro does not have ADC inputs). The requirement is for low cost parts (although the INA240 is not cheap). It also has a simple switchover circuit based on schottky diodes.
Would you mind looking at the design and tell me if my logic is sound?

Update: After reviewing Bruce's comments, all very valid, I decided to redesign the circuit. Below is v2


texts:
I am designing a circuit for a PCB that will incorporate an ultra-sound sensor (HCSR04.)

The sensor needs 5V for supply and its input pin also requires 5 V. The MCU that I am using has pins that can only send 3.3 V.

I thought I could use a 3.3 V output pin and connect it to the sensor like the picture.

But now I am skeptical about it.

I think it will only send 3.3 V to the sensor pin. Should I switch the pin location so that the 3.3 V pin (PC7) is connected to the resistor instead, and place the 5V pin is where PC7 is? Or is there a better way?


texts:
I have a material and I want to measure the voltage and current through it over time. Unfortunately I only have an automatic voltmeter and the resistance of the material changes over time. Because I can't measure the current and I don't know the resistance I created a circuit to measure this. See image below.

R1 is the material with variable resistance (disregard the 2kO). I choose a known resistor (R2) and measure the voltage through that. I also know the applied voltage. This way I can figure out R1 as well as the current through the circuit.

The current is I = V2 / R2

The voltage is V1 = Vtot - V2

The resistance is R1 = (Vtot/V2 - 1)*R2 or R1 = V1 / I

My question: will this work? I did the math and it should, however, I have done some tests and it is not working as expected. Should R2 be a value close to R1? Will the voltmeter affect the current path and create a parallel circuit? I need to know the stuff that someone who has some experience with circuits would know.

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simulate this circuit – Schematic created using CircuitLab

]1]1


texts: i want to use heaters to heat small area

texts: Hi I want to heat an area of .5sqare mm to a a temperature of 100°c to 110°c and many such squares will be user in a matrix close to each other, do anyone have idea about any small heater which I can use in my application.. Please help. Thanks...


texts: What does it mean when my car inverter's labeling says "Neutral Floating"? Is it safe to use?

texts:
I recently came across a fairly old car inverter. It plugs into a 12v DC lighter socket, and outputs 115 Vac at 60 Hz, and has a normal American outlet on the side of it (with a ground pin, which seems questionable) and is rated for 100W continuous or 150W peak. This tool could be very useful to me, mainly to run a laptop in the car (when someone else is driving, of course). The output is also non-sinusoidal, but, as far as I understand, that does not matter for switch mode power supplies, and all of the things that I want to power in the car run on switch mode power supplies.

More concerningly, however, it says "NEUTRAL FLOATING." My understanding of electrical engineering tells me that this means that the neutral wire isn't attached to anything, except maybe a capacitor. This may still work with lower current loads (perhaps up to 100W based on the labeling, although that seems high) due to the capacitance on the neutral wire, but it would also cause the device that I am using to start floating above 0V on its neutral or ground side, a dangerous situation. It seems, however, that such a dangerous device would not be legal to sell in the United States, where I am pretty sure that this was bought (it is very old, so I don't know exactly).

As such, it seems like I am misunderstanding what "NEUTRAL FLOATING" means. What does it actually mean? Is it safe to use my inverter, or do I need to buy another one?


texts: Is there an IC which converts I2C/UART/SPI (or any standard communication interface) commands directly to DALI2 format?

texts:
Is there an IC which converts I2C/ UART/ SPI commands (or any standard communication interface) directly to DALI2 format? DALI seems similar to 1.2k baud UART in a sense, but is encoded in Manchester format and has its own start/stop bits. I'd like to reduce SW development for DALI driver bit-banging if possible by using a DALI-capable chip.
Thanks in advance!


texts: Understanding inductors with non closed/looping iron cores

texts:
Toroid inductors make sense to me. The magnetic circuit is closed. However, I do not understand inductors that just have a magnetic core in the center (like this one):

Considering that the inductance for an inductor with an air gap is:

If the air gap is at least the size of the iron core, wouldn't the air gap define inductance way more than the iron core?


texts: I am currently building my first coilgun.  I already have MOSFETs rated at 100V, and 50V 470uF capacitors I can wire in series to obtain 100V.  I know this voltage will not result in a very high velocity projectile.  What I am wondering is if I can switch the charging circuit between multiple capacitors, charging them separately, and then discharge them in series which would result in a higher total voltage.  By doing this I would only need to buy one high-voltage switching element.  Is this feasible, or am I way off here?  What would such a circuit look like?