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I have an Arduino Uno and a Raspberry Pi that I'm using to control some LEDs in a computer case. Power is coming from a Molex connector from the computer's PSU. I want to place the Arduino and the Pi at the top of the case, but the power supply is at the bottom. In order to try and reduce the length of wire runs, I'd like to power one of the devices from the other.

When I supplied 12V to the Arduino through the Vin pin and tried to supply 5V to the Raspberry Pi via the 5V pin, I ended up frying the Arduino (too many amps?). I was wondering if I could do the inverse: supply 5V to the Arduino through the GPIO 5V pin, then provide 5V to the Arduino through the other GPIO 5V pin. According to the diagram here:

http://www.megaleecher.net/Raspberry_Pi_GPIO_Pinout_Helper

there are two 5V pins and five ground pins that I can use. I'd like to prevent against frying something else though. Will my idea work, or is this a foolhardy idea?

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    \$\begingroup\$ You could just power both devices off the same molex connector (5V rail) coming from the PSU. Since you are already running a cable from the PSU to the top of the case, I'm not sure why you would want to power one of the devices off the other when the voltage rail is already accessible where you need it. \$\endgroup\$ – Luc Sep 23 '14 at 16:17
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You likely fried the Arduino by supplying a high input voltage (you say 12V). The voltage regulator on Arduino UNO steps down voltage, e.g. 12V, by converting power to heat. Usually it work okay as long as there isn't much current being drawn from pins. I

R-Pi GPIO pins are rated at less than 20mA, and Gert Van Loos recommends using under 3mA/GPIO to remain within the design assumptions that were made for the R-Pi.

So NO do not try to supply power to the Arduino via any R-Pi GPIO pins except 5V. It is less clear how much current the 5V supply on the R-Pi GPIO socket can supply. In the absence of information, I'd assume it might be best to avoid it.

The R-Pi USB sockets are not supplied via the R-Pi's on-board power supply. Instead they come from its external power supply, and so it very much depends on the R-Pi's external power source on whether the Arduino UNO would overload anything.

Edit: R-Pi's USB and GPIO 5V are all connected to the external power supply via a 1A resettable fuse (polyfuse). That has the benefit that it protects the external power supply. It also limits the entire current drawn from the external power supply. In the case of powering an Arduino from the R-Pi, and nothing else, it should still allow the Arduino to consume up to 300mA, which should be plenty.

I'd suggest using a USB cable plugged into the RPi and the Arduino to power the Arduino, however the schematic shows the GPIO 5V has exactly the same power-supplying capability.

Be careful, some of the R-Pi external power supplies don't seem to have much 'headroom'. Where I work, students have problems sometimes because of this.

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  • \$\begingroup\$ The USB sockets do not use a converter but worth noting they go through the 1A polyfuse. (hence the default requirement for powered USB hubs) \$\endgroup\$ – Dan Nixon Aug 24 '14 at 13:50
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Yes.

The power consumption of a Arduino UNO is approx. 40-50mA/5volt. The 50mA is without shields and such.

The power consumption of a Raspberry Pi is approx. 700mA/5volt. 700mA is without USB devices, USB devices will add to the total power consumption.

So theoretically, a 750mA/5volt power supply will cover the consumption of a Arduino UNO and a Raspberry Pi.

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You probably fried the Arduino from excessive heat on the regulator. The regulator on the Arduino is a 7805 linear regulator. The linear part of the name means the it acts as a variable resistor turning the excess voltage into heat. You can calculate this by the voltage you are putting in, 12V - 5V (Output voltage) which equals 7V. Then 7V x (The current you are drawing in amps). If you are powering a raspberry Pi which draws roughly 1.5 to 2.1 amps so by estimating 2 amps draw, 7 x 2 = 14W of heat.

For a chip smaller than a your fingernail, that's a lot of heat. Most likely the 7805 overheated and fried leaving your Arduino and Rasberry Pi without power.

A better option is taking a 5V line from the PSU. No regulators, no heat dissipation. If you have no option but 12V, a switch mode power supply module based on the LM2596 is a good option, it can provide up to 3A, enough for a raspberry pi and Arduino.

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YES just use the raspberry pi USB port and connect the nano via micro USB I'm using the nano instead of an ADC(analog to dc input converter). works like a charm :-)

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  • \$\begingroup\$ ADC = analog to digital converter. \$\endgroup\$ – JRE May 15 at 16:27

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