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I have a RPi 2 and my circuit involves an Arduino connected to it using Logic level converter. I want my Arduino to act as a watchdog for Pi that will receive a signal timely from Pi and if not received, send some signal to Run pins on Pi to reset it. How to implement the same? Following is my circuit diagram:

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1. Reset

The Pi 2 has a reset pin. According to this article it's a two pin header (unpopulated holes only) located between the display socket and the ACT LED. Supposedly, it's also labeled "RUN". Shorting these pins pulls an input pin of the BCM low, and thus resetting it.

So, to emulate this with the Arduino, it's only necessary to figure out which of the two pins is ground and which is the actual input pin. Then, simply connect the input pin to some digital output of the Arduino. Set high to keep the Pi running, pull low to reset. Mind the 3V3 logic level of the Pi though, use appropriate level converter, essentially the smallest of an switching transistor would suffice. This transistor would typically be operated in open-collector (or open-drain) mode. Note that this circuit is inverting the logic signal. The Run pin actually has 2 clamp diodes a pull-up resistor and capacitor connected (at least that's what we know about the model B, Rev 2.1).

2. Power cycle

Look for a so called high side switch here, e.g. utilizing a P-channel FET. To get an idea how this could work see here.

  • Yes, the reset worked. There are 2 pins. I had an idea of the pins but couldn't figure out how to use them. Out of the two slots labelled 'Run', the slot with a square boundary is the actual input pin. If I send a LOW signal to the same, it will reset the Pi. So now I have a monitor in Arduino that expects a ping from Pi every 10 minutes and if there is no signal received, it will send a LOW signal to logic level converter which will convert the Arduino voltage to Pi voltage and reset the Pi. Man, I am in love with this community. Thanks a tonne :) – Ric Nov 29 '15 at 5:38
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    You would be better to use an open-collector (or open-drain) driver as I originally suggested. Use of a level converter is overkill. The Run pin actually has 2 clamp diodes a pullup and capacitor connected. – Milliways Nov 29 '15 at 6:36

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