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Calculating resistor value for transistor

There's not quite enough information in your question to give a definitive answer, but let's go through the design steps so that not only can you figure out this one, but you might be better equipped ...
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10 votes
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TP1/TP2 equivalent for Raspberry Pi 3 B

The official schematics show that: PP1 and PP2 are 5V input from USB PP35 is 5V after the polyfuse PP7 is 5V after the input circuit PP3 through PP6 are GND They are to be found on the bottom side ...
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9 votes
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Get reading of RPI supply voltage

I do not think there is any Pi circuitry to return the current supply voltage. As far as I am aware the under voltage circuitry is a piece of hardware which triggers at 4.65V. So you could ...
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7 votes
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Raspberry Pi's reaction to 7.2 Volts applied to a GPIO pin?

No. Take it on the bright side. You have learned one thing never to do to a Raspberry Pi.
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7 votes

FM transmitter antenna length

Welcome to the Raspberry Pi SE site! Your question may be judged as off-topic for this site (not saying it will, but it may be), but personally, I'm happy that you've asked it. I say that only because ...
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7 votes
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Raspberry Pi 4 - Booting with 3 USB attached Harddrives causes Crashing

I'm assuming these are USB drives, and are powered from the Pi USB port(s). You're probably exceeding the power supply capacity of the Pi and/or the power supply. Hard drives require a fair amount of ...
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6 votes

Rpi Reading MCP3008 10 bit ADC Result Problem

Those resistors are in fact too high. Section 4.1 "Analog Inputs" (p. 17) and figures 4-1 and 4-2 (p. 18) of the datasheet are of special interest: For the A/D converter to meet specification, the ...
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6 votes
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What happens to the GPIO voltage after shutdown?

The Pi has 3 "components" the CPU, GPIO and Video Core which are relatively independent. Even when the Pi is shutdown the Video Core continues to run, and the GPIO pins retain their state; ...
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5 votes

TP1/TP2 equivalent for Raspberry Pi 3 B

Thanks to @Ghanima's great answer I made markings on those +5V points:
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5 votes
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Undervoltage symbol

Powerbanks are not made for powering electronics. They are made for re-charging batteries. This is important because these two tasks have some requirements that are at odds. Most significantly, in ...
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5 votes

Powering a sensor using an external power supply board

Yes, (in general) in this case you should wire the ground terminal of all devices in your circuit together. This provides the necessary common ground reference voltage for them to interoperate. Your ...
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5 votes
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Rpi Reading MCP3008 10 bit ADC Result Problem

Question Use MCP3008 to measure voltage of range 0V to 4.2V. Use a voltage divider with 2.7MΩ / 8.2MΩ to step down value for Rpi but not working. Resistor values too high? How to ...
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5 votes
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Voltage dropped significantly on GPIO 4 with a relay coil

There is nothing wrong with the GPIO, it just can't supply enough current for your coil. If the coil has just 24Ω, at a 3,3V the GPIO would need to supply 137mA. This source at raspberrypi.org says ...
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5 votes

What happens to the GPIO voltage after shutdown?

This howchoo post shows how to connect an LED to show the status of the Pi. The LED is steady on when the Pi is running, and off after shutdown. Briefly: Add this line to /boot/config.txt, and ...
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4 votes

Supply voltage 5V issue from Raspberry Pi 3

The subject of ADC error is both wide and deep. Engineers have built careers on studying, quantifying, measuring and resolving ADC error. If you "Google" terms such as adc error analysis, or adc error ...
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4 votes
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GPIO Voltage tolerance for input

There are no formal published data, but the following summarises what I have been able to discover. Electrical Specifications of GPIO I would NOT apply 3.6V to a GPIO pin, but if the voltage does not ...
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4 votes

Connection of 220V Doorbell to Raspberry Pi GPIO

The statements "220V power" and "I'm very new with electronics" raise concerns. The only responsible advice I can give to anyone who isn't a licensed electical contractor is DON'T. Try something ...
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4 votes

Why my gpio input changes the internal resistance when running the python code?

Adding a resistor in series will not drop the voltage. It will simply reduce the current. Fortunately you seem to have limited the current to a level which the Pi's GPIO protection circuitry can ...
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4 votes
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Powering a sensor using an external power supply board

Everything looks fine. Yes, you need to connect the Pi ground to the ground of any sensors you connect to the GPIO. It doesn't matter if they are powered by the Pi or by an external power source. ...
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4 votes

How to increase voltage of USB ports on the Raspberry Pi 3 Model B?

Short answer: no way. Long answer: USB ports can only output 5 Volts. It's true that your screen came with (citing the product page you linked) 1 * USB to 3.5 DC Power Cable but that cable is ...
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4 votes

Get reading of RPI supply voltage

As noted in Raspberry Pi Power Limitations (which you referenced) The newer Pi(3/2/B+) have a voltage monitor chip (APX803) which triggers at 4.63±0.07V. The Pi3B+ Pi3A+ use a MxL7704 chip to manage ...
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4 votes
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Convert 12V to 5V to power RaspberryPi

I use buck converters that convert 12VDC to 5VDC to power most of my raspberry pi computers. There are many available but be sure to check the amperage output. Most come with a USB A 5VDC output and ...
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3 votes

Turn a Raspberry Pi into a voltage tester

Question Let me first summarize the OP's question. He has a 220VAC water pump. He knows that a 555 IC can tell AC current on by blinking a LED. His question is how to let Rpi talk to 555 to find ...
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3 votes

Is 5V out on the Pi Zero W unregulated?

Not entirely. There are two Q&A you should read: 1, 2. The first Answer tells us that the voltage output from the USB supply is regulated iaw the USB standards, and therefore needs no further ...
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3 votes

What is the correct (internal) voltage range for a RPi 4?

It is NOT a "voltage reading" (because the Pi has no analog capability) this is reporting the voltage configured. The Pi like most modern CPU adjusts voltage/clock to optimise performance. Don't ...
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3 votes
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Use Raspberry with two devices that require 3.3v pin

You can connect as many wires as you want to a 3V3 pin (pins 1 and 17). Similarly you can connect as many wires as you want to a 5V pin (pins 2 and 4). Similarly you can connect as many wires as you ...
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3 votes

How to add Capacitors to Raspberry Pi

You need the supercaps to be in parallel to the power supply, not in series. However, before fixing your circuit, mind a few things: If you simply connect your supercaps between 0 and 5V, most power ...
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3 votes

Voltage monitoring of battery pack (i.e. before voltage regulation)

One option would be to use an MCP3002 ADC (2 channel analogue to digital converter). Use a voltage divider circuit (2 resistors) to convert your battery voltage to a voltage range upto 3.3V. Feed this ...
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3 votes

Voltage monitoring of battery pack (i.e. before voltage regulation)

The PiCheckVoltage project may be stale for a reason. It strikes me as a bit over-complicated for the situation you've described. However, parts of the code may be useful. Here are some alternatives ...
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