I want to control my fog machine with an Arduino. Has a simple button that is used to activate the machine. I want to press this button using an Arduino digital output pin, but the fog machine is operating on its own electrical circuit. How do I use the Arduino to activate this machine?

I a few other machines with buttons that I want to wire into an Arduino, so is there a generic solution?

  • As krol says - a relay is liable to be what you want. Relays like these ones cost between $US1 and $US1.70 per relay and use 5V power supplies to operate them PLUS wil accept Arduino output signals top control them. I have found that specific seller reliable and the products good. Shipping is usually free and delivery to me (in NZ) takes typically 2 to 3 weeks. [I have no relationship with them except as a satisfied customer]. – Russell McMahon Feb 27 '15 at 2:41

You can interface with the fog machine's button by:

  1. Use a Relay (this will isolate the fog machine's circuit from your Arduino's)
  2. Use a Servo to physically press the button on the fog machine

I believe those would be the simplest and most generic.

  • Krol - see my "answer" - you may add this material to yours if you wish. – Russell McMahon Feb 27 '15 at 3:06
  • @RussellMcMahon good expansion. – krol Feb 27 '15 at 13:29

Please do not upvote this answer.
This is an expansion of @Krol's answer. Krol may incorporate this material in his answer if he wishes.

The image below shows a typical relay module which is able to be driven by logic level / GPIO signals from typical microcontrollers.
The relays have 5V coils and there are optocouplers and drive transistors between the input and the relay.
Inputs are active LOW - ground to turn on.

These are available by mail from China for under $2/relay (under $1/relay if you buy 10 modules with several relays in).

They are NOTIONALLY opto-isolated as well as having relay isolation between input and contacts. BUT the PCB layout and relay design is such that mains to input clearances are poor. They will PROBABLY NOT kill you or your controller but they may - as is the case with much other items manufactured afar off at ludicrously low prices.

I have found the seller/manufacturer whose logo appears on that photo to be a reliable supplier of well made products. (Being well made does not overcome "dangerous design" as above.

Note that the above warning applies to most buffered relays you can buy on the hobbyist market and also top consumer products that have not been put through formal testing (UL etc). This relay board would fail UL testing - as would most others.

enter image description here

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