Have one Uno signal another to take an action

I would like to have a Arduino Uno Rev 3 operate two servos then signal another Uno to start a procedure which runs 2 dc motors. Can I set an output pin on the first uno to high and then have the second uno read that high at a digital pin?

If I can do this, should I connect the grounds of the two unos with the grounds for the motors? Should I use a common 9v power source for both unos?

Answers to the first two questions are yes and yes. As for the common power supply, it'll work either way, either with a common supply or with separate supplies. Important to keep the grounds connected though.

If 9V source is a square battery, you will be disappointed with servo performance. Should plan for 1A capacity to drive the servo(s).

Hi, it seems you are happy with wiring the two arduinos together, why do you need two arduinos?
One arduino will do all that you ask.

Tom… :slight_smile:

Just a caution to keep in mind if one ever does wire two arduinos together as in a digital output pin to a digital input pin, use a series say 1K resistor to help prevent damage if you ever get the pinMode wrong or otherwise end up with two digital outputs wired together with one at a HIGH and the other at a LOW by mistake. Resistors are cheaper then arduino boards. ;)