Arduino and PIC communications/signaling question

I need some help with a project I am working on for myself. I am a software guy who knows enough to get in trouble with EE.

I am using a Arduino to set a digital output HIGH or LOW depending on a complex set of circumstances.

What I am trying to do is get that HIGH/LOW signal from the Arduino into a PIC 12F683 that is close enough to run a wire to and for the PIC to act on the HIGH/LOW. There could be multiple PIC's that will do different things based on the HIGH/LOW.

Can I wire the Arduino's Digital out to a GPIO on the 12f683 that is else where running from a different power supply?

Thanks in advance for the help!

Bob P.

The issue will be whether the ground potential on the two boards is exactly the same, and whether any noise is picked up on the wires connecting the two boards. If they are being fed from the same power supply and it is a low noise setup then you might be ok.

It might be easier to use a simple opto-isolator on the PIC board, drive the LED from two wires (GPIO/VCC or GPIO/GND) on the Arduino and keep the two wires electrically isolated from the rest of the PIC board. There are multi-channel opto-isolators available and they can drive logic inputs with a single pullup/pulldown resistor. With this scheme, the grounds from multiple Arduino boards sending signals to the PIC would also be isolated from each other which may be an issue later.

OK let me see if I understand you.

Coming from the Arduino I would need 2 wires, 1 my high.low and the other the ground.

On my PIC board I would have a opto-isolator that has one side connected to the arduino's 2 wires and the other side connected to the PIC.

Could I get away with the high/low wire from the Arduino and use the ground from the PIC?

Thanks

No, you need a potential difference to transfer information. If you just connect the GPIO wire you will get nothing but noise on the other end (usually).

If there is a common ground then you can use that ground as the second wire, but you will be better served by just running two wires from the arduino (don't forget the current limiting resistor, just like any led).

OK thanks!

I'll run 2 wires from the Arduino, I was just being cheap. And yes the resistor will be there too, just like any other led.

I haven't messed with photodetector's yet, anything special like resistors needed there too?

If you don't need anything fast (>50Khz), you can use a cheap quad optoisolator like the LTV-847 (http://www.us.liteon.com/downloads/LTV-817-827-847.PDF) [I assume you want a DIP package]. Connect the collector (the one without the arrow) to +5V, connect the emitter to ground through a 1K ohm resistor, and connect the logic input to the point where the emitter is connected to the resistor. If you can live with 5Khz frequency response you can up the resistor to 10K and save a little power.

You want to drive the LED with about 10ma and it has a forward voltage of around 1V, so use a resistor around 400ohms if you are driving it with a 5V arduino signal.

Thanks Dean! You've given me everything I need now.