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Button Hacking based on 4N35

2018-01-15 18:30  
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Button Hacking

4N35

A lot of interactive installation projects I’ve seen rely significantly on high power computers to do even simple tasks. Triggering audio to play is a common situation.  Often it is cheaper and sometimes more reliable to hack dedicated low power devices such as mp3 players.  For this task, optoisolators are your best friend. Using these chips you can keep the device you are controlling safely on its own circuit, and you “electronically press the buttons” to start and stop the player.

Observe the following circuit:

4N35

This is a basic circuit for hacking a button to be controlled electronically. We are sending a control voltage from a microcontroller (or logic circuit of choice) into a 4n25, 4n35 or similar optoisolator. Internally it lights up on one side, and a light sensor on the opposite side allows pin 5 to flow into pin 4.  If pin 5 and pin 4 are connected to the two sides of a microswitch like the “play button” in an mp3 player (S1 in the image above), then whenever you send a digital high into the optoisolator, it will essentially hold the button down. With this setup your player device will also still function as usual with its physical buttons. Rad.