Need circuit for arduino to reset Raspberry Pi.

What kind of circuit do I need to use an Arduino Nano to interface to the Raspberry PI GPIO to ground a pin ?

I'm using " /sys/class/gpio/gpio"$SHUTDOWN_PIN"/value" in a script to detect the values on the GPIO pins.... I'm just not sure how to physically interface the two devices . For example do I have to implement a level shifter or can I connect the directly ?

I'm sure this has been asked many times but I cant find an answer, and I don't want to blow up another raspberry Pi/Nano.

What voltages are you running the devices on?

It may be a matter of simply using an NPN Tr as an open collector switch to the R Pi pin.

Weedpharma

The arduino Digital Pins are 5 volts and the R Pi has 3.3 volt inputs on the GPIO pins.

As the voltages are different, you cannot simply connect them. A simple isolator using an NPN Tr will do the job.

Use a R of around 4k7 from the output to the base of the Tr, connect the E to gnd and C to the reset pin. When the output goes high, the Tr will take the reset low.

Weedpharma

Do you want to "Reset" (as in your title) the Pi, or do you want to tell the Pi to "shutdown" (as in the script variable quoted)?? Those are two very different things. The reset stops whatever is in progress on the Pi and restarts Raspian. The shutdown signal is used to STOP Raspian and leave it stopped.

To use the shutdown signal, use Weeds suggestion. To reset the Pi, use a MosFET to short the two reset pads in the upper right-hand corner of the Pi board.