This example shows how to control a mains lamp using a 240V relay board and an Arduino Uno. The idea is to randomly flicker the light on and off, similar to an old strip light when it becomes a bit old, or the starter is failing.
WARNING: Don’t mess with mains electricity, unless you are very confident about what you are doing. Mains supply can kill. If in doubt, get a qualified electrician/engineer to assist you.
Controller Board
The controller board is a cheap off-the-shelf 4-port 240V, 10A relay module. For this example I have just used an Arduino UNO to control it, though I will eventually replace this with an ATTiny85 as I need only 4 ports. The relay module is similar to this:
4-port relay module
Originally, I powered the relay module through the Arduino using the 5V output, but this affected the operation of the relays, and led to erratic behaviour – the input lights for the relay would flash on and off, but the relay would not change state. So instead, the relay board is powered using a separate power supply, and is connected to the Arduino using only the inputs and a GND connection.
Arduino Sketch
The C code for controlling the is simple: generate a random integer between 8 and 11 (those are the port numbers on the Arduino that I have used) and use that generated number to toggle the state of a associated port. Do this over and over …
[code language=”css”]
#define INTERVAL 50
#define RELAY1 8 // Relay 1 is on pin 8, etc.
#define RELAY2 9
#define RELAY3 10
#define RELAY4 11
int switchState[4] = {0, 0, 0, 0};
int randomNumber = 0;
void lightSwitch(int state, int lampNumber);
void setup() {
// Relays are on pins 8 – 11
pinMode(RELAY1, OUTPUT);
pinMode(RELAY2, OUTPUT);
pinMode(RELAY3, OUTPUT);
pinMode(RELAY4, OUTPUT);
// The relays are active low, so pull them low to close the switch
digitalWrite(RELAY1, LOW);
digitalWrite(RELAY2, LOW);
digitalWrite(RELAY3, LOW);
digitalWrite(RELAY4, LOW);
void loop() {
// Randonly switch on and off a set of 4 lights
// On this cycle generate a lamp number
int randomNumber = random(20);
// Now toggle that lamp
if (randomNumber >= 8 && randomNumber <= 11) {
toggleSwitch(randomNumber);
}
//Serial.println(randomNumber);
delay(INTERVAL);
}
void toggleSwitch(int switchNumber) {
if (switchState[switchNumber – 8] = ~switchState[switchNumber – 8]) {
digitalWrite(switchNumber, HIGH);
} else {
digitalWrite(switchNumber, LOW);
}
}
[/code]
Here’s a video of the lamp controller:
You can hear all four relays switching on and off, which adds to the effect.
To Do
- Test this on the strip lights.
- Make board with ATTiny85 and voltage regulator.
- Place relay module and controller into an enclosure.
- Find cheap 240V – 12V power supply to power the relay module and ATTiny.
