I am a beginner, and I have a school project that requires me to use Arduino or any other microcontroller to control an LED light.

After some research, I found out that not all LEDs support dimming, and I would need to buy LED and a LED driver that supports TRIAC in order to make dimming works.

I found a tutorial online that uses Adruino and TRIAC to dim the lights bulb, but I am told that it wouldn't work with AC LED as the circuit in the tutorial is deisgned for resistive loads only. Link to the tutorial: http://m.instructables.com/id/Arduino-controlled-light-dimmer-The-circuit/

Is there anyway that I can modify the circuit in the tutorial to make dimming works with an AC LED? Perhaps attach a LED driver that supports TRIAC to the PCB, then connect the LED to the driver? Or do you suggest me do it using another method?

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    \$\begingroup\$ If you are a beginner I'd advise against building anything that deals directly with mains voltage. Please consider using low voltage alternatives. \$\endgroup\$ – Wesley Lee Apr 2 '16 at 23:31
  • \$\begingroup\$ Yeah man, I am also consulting my teacher in school about this! Thanks! \$\endgroup\$ – Lewis Apr 4 '16 at 5:09

If you select a "dimmable" LED bulb, it should work with your TRIAC circuit. Standard dimmer switches are generally TRIAC-based. In fact, it should work better as many dimmer switches Require a minimum wattage as they pull power from the circuit. Your's should work with even a minimum wattage bulb.

  • \$\begingroup\$ Oh! It means I don't have to get an extra LED driver to dim the light if I just get a dimmable LED bulb? \$\endgroup\$ – Lewis Apr 4 '16 at 5:07
  • \$\begingroup\$ That's correct. It's possible that not all dimmable bulbs would work but most should. \$\endgroup\$ – DoxyLover Apr 4 '16 at 5:10
  • \$\begingroup\$ I am thinking of using another method to do the dimming. I would have an AC/DC adapter, then connect it to a circuit made following this tutorial,m.instructables.com/id/… then I'll attach an LED light bulb to it. Would using PWM and the DC power supply allow me more LED options? \$\endgroup\$ – Lewis Apr 12 '16 at 9:27

Triac dimmers are not PWM in the normal sense. When a new AC cycle starts, the dimmer delays turn on until the voltage has risen to the value that the dimmer is set for. It does it on both halves of the sine wave. In other words, it takes a chunk out of both halves of the sine wave. True PWM switches between a DC level and zero. The triac dimmer is still AC. The PWM is DC. The PWM dimmer is well illustrated below this post


I think the normal procedure to have a variable brightness LED is to use pulse width modulation, or PWM. This means you give the LED a signal that alternates between high and low voltages very quickly, so quickly that the human eye cannot see that the LED is going on and off repeatedly, but just sees a constant brightness LED.

For example, you give the LED one of the waveforms shown below.


For the first diagram the LED is always off, and for the last one it is always on at full brightness. However, for the ones in the middle, it will show at different brightnesses.

To make it brighter, you make it so the LED is on for longer in the cycle, and off for shorter, so the human eye will percieve it being brighter. To make it dimmer, you only have it on for a short amount of time, so it is mostly off, and the human eye will percieve it dimmer.

The amount of time the LED is on for (therefore how bright it will be), is called the duty cycle, or pulse width, hence the name pulse width modulation

Does this help?

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    \$\begingroup\$ I think the OP is talking about dimming an LED light bulb replacement, connected to AC mains, not a raw DC LED. In this case, PWM is not appropriate. \$\endgroup\$ – DoxyLover Apr 2 '16 at 18:32
  • \$\begingroup\$ @DoxyLover: Actually, PWM is exactly how AC dimmers work, but the PWM is synchronized to the zero-crossings of the line voltage, which this answer doesn't cover. \$\endgroup\$ – Dave Tweed Apr 2 '16 at 20:13
  • \$\begingroup\$ @DaveTweed - Conceded. But as you say, his answer doesn't really answer the OP's question. \$\endgroup\$ – DoxyLover Apr 2 '16 at 22:43

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