It would help if you describe the project you are trying to implement.
The project is working now but it gets "confused" once in a while. I have a wireless motion detector on the front porch that triggers an LED flood light and also triggers a display in the TV room. The flood stays on 90 seconds and the display stays on for 5 seconds. They are 50' apart [display and flood] and operate on 9vdc.
The flood is operated by a small relay triggered by a 555 timer in "one shot" mode [90 seconds], and the display is operated by a 555 timer "one shot" [ 5 seconds] that triggers another 555 timer in "astable" mode [pulse every 200 nanoseconds] which sends the pulses to a 4017 decade counter which sequences 10 superbright LEDs [various colors] for 5 seconds. It is a display to alert my wife that someone is at the front door while she is in the TV room.
Occasionally if the person at the front door continues to move about briskly and continuously keeps triggering the motion detector - the timing sequence "gets confused" - this is why I want to do the triggering with relays - so I can isolate the two controls electrically.
Confusing but it works well - I just want to simplify the trigger that starts it all. Have the motion detector trigger the aurdino uno, Yes I have uncoupling caps, pull down and pull up resistors on both triggers. But am forced to operate it all off one power supply at present so it can be shut off.
The Arduino would solve the backfeed/inductance/spooks in the system by the two relays.