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 to solve the next transistor question that occurs to you.
Ohm's law expresses the relationship among resistance (R), current (I) and voltage (V): V ...
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 of the PCB near the Micro USB (power in) connector (that is on the top side of course).
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 powering electronics it necessary for the supply to be responsive to rapid fluctuations in current draw, but the exact opposite is true with regard to ...
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 discriminate between two values, more than 4.65V or less than 4.65V.
The only justification for this answer is I remember dozens of posts where people have asked the ...
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 radio applications for the RPi don't seem to get a lot of coverage here - which suggests to me that folks are missing out on one of the best application areas ...
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 charge holding capacitor (CSAMPLE) must be given enough time to acquire a 10-bit accurate voltage level during the 1.5 clock cycle sampling ...
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 that the maximum current it 51mA for all GPIOs together and 16mA per GPIO.
You can connect the GPIO to a transistor that can supply the necessary 137mA.
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 correction, you'll find enough highly technical and/or scholarly information to keep you occupied for quite some time - for example. But the bottom line is ...
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 exceed Vcc + diode voltage (~0.7V) damage is unlikely. I would use a serial resistor in any event.
If you know the voltage may be excessive use a resistive ...
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 involving lower voltages first.
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. You need a common voltage reference so both ends know what's high and what's low.
The resistor divider is fine. There are many examples on-line. This is ...
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 voltage divider needs to go from 5 vdc to 3.3 vdc. There are two considerations in setting up a voltage divider:
a. it provides the proper voltage, and
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 useless for a 12-Volt device like your screen.
To me, it looks like they threw the cable in just to "complete" their offering someway, without paying any ...
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 that way you can use the microUSB for power thus having fuse protection My RPi Zero computers for my weather station
as well as my RPi3B+ camera are all ...
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 handle. However you are risking destroying the Pi when you connect any voltage more than 3V3 to a GPIO.
One way to produce a safe voltage for the Pi GPIO is to ...
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 the pump is on or off.
I am guessing how 555 detects AC current.
As soon as the AC current passes a wire, electromagnetic field is created. ...
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 calculate the resistor values?
MCP3008 ADC operation is indeed very complicated. You need to go through the long answer below a couple of times, ...
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 regulation on the RPi. So, I'd say the answer to your question is, "the 5V pads are regulated iaw the USB specifications and standards".
The second Answer is ...
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.
Add this line to /boot/config.txt, and reboot
Connect the TxD pin (GPIO pin 8) to the positive lead of a 2 or 3 volt LED.
Connect a ground pin (e.g. GPIO pin 6) to a 330 ohm resistor, ...
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; only the CPU is not running.
The 3.3V is supplied by separate circuitry and will be present while ever the Pi is connected to a 5V supply.
The best way to reliably ...
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 want to a ground pin.
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 supplies / batteries will have trouble starting your system, since a discharged capacitor is essentially a short circuit. Most power supplies handle shorts ...
The default state of pins is given in http://www.panu.it/raspberry/
The default Device Tree settings configure most pins as inputs, some with pullup others with pulldown.
Pins set as input cannot be said to "have a voltage", except for the high value pullup resistors they are in a high impedance state. Any voltage you measure is a artefact, and depends as ...
Why not just connect Pi ground to one relay contact and a GPIO set as an input to the other. Then set the internal pull-up GPIO resistor. The GPIO would then read high when the relay is open and low when the relay is closed.
You need no other circuit components.
The Pi's GPIO are to set logic levels (on or off). They are not designed to be a voltage reference.
The 3V3 rail is regulated. You'd have to see the specs for your Pi model to find the actual regulator used. I doubt if it is calibrated or particularly stable.
I assume that the LED is a 100mA type?
And from the PN2222 data sheet we assume the gain of the transistor is 100 or so. This means the transistor current will need to be arround 1mA, and the GPIO voltage is 3.3v.
Using Ohms law, 3.3/0.001 = 3k3, or if you take into account the bias voltage, (3.3-0.6)/0.001 2700 ohms, and this would be my choice.
You will still be exceeding the maximum voltage of the GPIO (admittedly not by much).
There is no allowance for tolerances; ±5% for resistors, ±2.5% for external power. Good design always makes allowance for worst case values.
There is also NO NEED; GPIO will be low if <0.8V; high if >2.2V so I suggest you design for 2.3V
The ACTUAL threshold for GPIO ...
I believe the Pi will be fine with that arrangement. The voltage (3.4V) is slightly larger than the official 3.3V limit. The excess current will be easily handled by the GPIO protection circuitry (excess voltage 0.1V, resistance 4700 ohms, current 21 microamps).
Remember the resistance values may be +/- 20% anyhow.