Human Trigger

The Human Trigger

Project Goals

  • Trigger a low/high voltage application safely

  • Up to 6 people to complete circuit with a delay

  • Unlock a drawer, turn lights on/off up to two devices (Opto Isolated Relays)

  • Plug and play functionality

  • Create a custom PCB and provide an easy to understand tutorial

The Circuit – Parts Needed

1k Resistor
Arduino Nano 3.0 or equivalent
Single or double channel relay.

It works with the Arduino UNO as well.


  1. Attach a wire to A0 on your Arduino going to a 1k resistor then out to a bare wire this will be the input side of the circuit. Note: Depending on your environment you may want to try a few resistor values.

  2. Connect a wire from A5 to the positive side of your led on the and the signal side of your relay board. On the negative side of the LED add a resistor this is your output side of the circuit.

  3. Now attach a wire to ground and leave the other side bare

  4. Remember to provide 5v power to your relay board from either an external power supply or the arduino.

Wire Connections

A0 --------—-Resistor --------------- Trigger Sw A
GND --------------------------------  Trigger Sw B
A5 --------------------- + (Anode) LED ------ Relay Signal 
- (Cathode) LED --—-Resistor------GND------- LED GND
5V ------------- Relay Positive +
GND ----------- Relay Negative -

Reference the image below for visual connections.

The Code

Simply copy and paste this code into the Arduino Environment and upload the code. Touch both ends of the wire if everything is wired correctly you should see the LED and the Relay turn on simultaneously. If your Human Circuit keeps triggering by itself you’ll have to play with the Sensitivity on the first line of code (const short Sensitivity = 5;) I got mine stable at about 100. You can also play with the resistance value to stabilize false triggers.

// FMD Human Circuit Relay Trigger Board
// Open Source and available to use in any project

const short Sensitivity = 5; // The lower the number the more sensitive. change this to prevent false triggers;

void setup() {
  pinMode(A0, INPUT); 
  pinMode(A5, OUTPUT); 
  digitalWrite(A5, HIGH);

void loop() {
  short value = analogRead(A0);
  digitalWrite(A5, (value > Sensitivity) ? HIGH : LOW);
  delay(1000); // increase or lower this number for Output on time 1000 = 1 second


This is the completed PCB All the outputs for the current code is broken out to screw terminals and header pins. The input is further to the left to prevent noise from the other components on the board. The system can be powered via USB or the 12VDC – 24VDC power jack. All other unused pins are broken out for tinkering/ code changes. The Prototypes are currently on order check back later for more information on this project. This PCB is being re-imagined and will be available in the Fatal Mentality Shop some time soon.

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