How to send trigger to external device

Projects General Guidance
1

Dear All,
I premise that I'm completely new in using Arduino.
I'm interested in programming an experiment in which Arduino can provide "trigger" events to external Devices (an EEG -electroencephalogram and Digitimer current stimulation) simultaneously.
Basically, from my understanding, Arduino should open some pins (which cable are connected to the devices) and provide a signal to these devices. The Arduino should provide these triggers in a loop-fixed time, but just understanding (and code suggestions) how to send the trigger is enough.
Moreover, do you know if it is possible that arduino provides the same trigger at the same time in both device?
Thanks in advance!
Best,

Matteo

2

One line can signal two devices simultaneously. You can also do register level IO that will switch all outputs in that bank at once.

3

Post moved because this clearly not a a tutorial it is a question.

4

There is one major flaw in your idea, you must not run the pins on wires much more than a foot. Also it must be compatible with the input you are connecting to. Is it a switch, if so what is the voltage. Simplest would be to use a relay. You can get a duel relay board for less then $5.00 US. You may have to shield it to immunize it from the radiated emissions from the equipment.