Build Instructions

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• 1

  Step 1

  The "stages" of this project are:

  1. Smartphone connected to wifi
  2. Old audio amplifier (pc speakers or bluetooth speaker)
  3. Comparator and relay circuit (made by you!)

  The objective is to energize the relay to switch anything (in this case to connect the two wires that signal the garage door opener)

• 2

  Step 2

  First you need to locate the output of your audio amplifier and remove any bootstrap or filter capacitors connected to it. You should see about 3V DC when the sound is not playing and about 5V DC when the sound is playing. Remove the speaker connection as well so that all the current goes to the comparator input.

  Find the ground on your amplifier and connect it to ground on your protoboard with your 5V source.

• 3

  Step 3

  Construct the simple LM311 comparator from http://www.learningaboutelectronics.com/Articles/LM311-voltage-comparator-circuit.php
  

  Instead of connecting an LDR and the 33K resistor, connect only the speaker output of the amplifier after removing the speaker itself and the capacitors.

  Instead of an LED in the output, connect the coil of the RAS0510. No resistor is needed.

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