Electronic – arduino – Multiple channel independent AC dimmer using Arduino

acarduinodimmertriac

I want to build a 8 channel, independently controlled AC dimmer using Arduino. I have successfully tested a single channel dimmer but i am stuck in expanding it to 8 channels. The circuit I am referring is as below
single channel dimmer circuit

The arduino code i am using is as below

/*
AC Voltage dimmer with Zero cross detection
Author: Charith Fernanado http://www.inmojo.com
License: Creative Commons Attribution Share-Alike 3.0 License. 

Attach the Zero cross pin of the module to Arduino External Interrupt pin
Select the correct Interrupt # from the below table:
(the Pin numbers are digital pins, NOT physical pins:
digital pin 2 [INT0]=physical pin 4 
and digital pin 3 [INT1]= physical pin 5)

 Pin    |  Interrrupt # | Arduino Platform
 ---------------------------------------
 2      |  0            |  All
 3      |  1            |  All
 18     |  5            |  Arduino Mega Only
 19     |  4            |  Arduino Mega Only
 20     |  3            |  Arduino Mega Only
 21     |  2            |  Arduino Mega Only

In the program pin 2 is chosen
 */

int AC_LOAD = 3;    // Output to Opto Triac pin
int dimming = 128;  // Dimming level (0-128)  0 = ON, 128 = OFF
/* Due to timing problems, the use of ‘0’ can sometimes make the circuit 
flicker. It is safer to use a value slightly higher than ‘0’
*/
void setup()
{
  pinMode(AC_LOAD, OUTPUT);// Set AC Load pin as output
  attachInterrupt(0, zero_crosss_int, RISING);  
// Chooses '0' as interrupt for the zero-crossing
}
// the interrupt function must take no parameters and return nothing
void zero_crosss_int()  
// function to be fired at the zero crossing to dim the light
{
  // Firing angle calculation : 1 full 50Hz wave =1/50=20ms  
  // Every zerocrossing thus: (50Hz)-> 10ms (1/2 Cycle) For 60Hz => 8.33ms

  // 10ms=10000us
  // (10000us - 10us) / 128 = 75 (Approx) For 60Hz =>65
  int dimtime = (75*dimming);    // For 60Hz =>65     
  delayMicroseconds(dimtime);    // Off cycle
  digitalWrite(AC_LOAD, HIGH);   // triac firing
  delayMicroseconds(10);         // triac On propogation delay
                                 //(for 60Hz use 8.33)
  digitalWrite(AC_LOAD, LOW);    // triac Off
}
void loop()  {
 for (int i=5; i <= 128; i++)
{
 dimming=i;
 delay(10);
 }
 }

Any ideas about how can i expand the code and circuit to work with 8 channels that can be INDEPENDENTLY controlled ?

Best Answer

Without doing an in-depth code review the problem is likely to be here:

delayMicroseconds(dimtime);    // Off cycle
digitalWrite(AC_LOAD, HIGH);   // triac firing
delayMicroseconds(10);         // triac On propogation delay

The delay functions cause the CPU to loop and no other processing can be done.

A better way would be to create a timer routine and call it for each channel. This would need a variable assigned for

  • the preset value (the value at which the timer output turns on),
  • the actual value (the current time value) and
  • the output state (timer done or not).

An easier method might be:

  • Divide your half-cycle into a discrete number of steps of, say, 50 μs.
  • In your main loop add a counter which is reset at zero-cross and increments every 50 μs.
  • In the loop compare the dimmer level for each channel with the timer and turn on that channel if dimmer level exceeded.

enter image description here

Figure 1. Relationship between current and trigger angle.

Note that the current produced does not vary linearly with the trigger angle due to the sinusoidal mains voltage waveform. Small changes around the peak voltage will have more significant effect than closer to the zero-cross. You may want to address this in your code if the visual effect does not match your dimmer setting.