This signal then can be used to trigger an interrupt in the Arduino. Because the sine wave first goes through double phased rectification, the zero-crossing signal is given regardless whether the sinus wave goes up through zero or down through zero. A circuit that can do this is easy to build: The zero crossing is directly derived from the rectified mains AC lines – via an optocoupler of course- and gives a signal every time the wave goes through zero. The difference between leading edge cutting and PSM is mainly in the software: in both cases one will need a circuit that detects the zero crossing and that can control a triac.
#Arduino led dimmen pwm full#
Though it might be tempting, in PSM one should always allow a full sinuswave to be passed to the load, not a half sinus as in that case the load will be fed factually from DC which is not a good thing for most AC loads. Though effective, it is not a good way to dim lights as there is a chance for flickering. With PSM, one or more full cycles (sinuswaves) are transferred to the load and then one or more cycles are not. Pulse Skip Modulation Another way of doing this is by Pulse Skip Modulation. Opening the Triac after a number of microseconds delay starting from the zero crossing therefore gives a predictable level of dimming. This is a circuit that tells the Arduino (or another micro controller) when the sinus-wave goes through zero and therefore gives a defined point on that sinus wave. For that a zero crossing detector is necessary. One needs a reference point in the sinus wave. One could let an Arduino just open the Triac for a number of microseconds, but that has the problem that it is unpredictable during what part of the sinus wave the triac opens and therefore the dimming level is unpredictable. Phase cutting One way of doing it is through phase control with a Triac: the Triac then is fully opened, but only during a part of the sinus AC wave. a transistor is not really possible due to the large power the transistor then will need to dissipate, resulting in much heat and it is also not efficient from an energy use point of view. It becomes a bit more tricky if one wants to dim a mains AC lamp with an arduino: just limiting the current through e.g.
(I say Arduino, but if you use an 8051 or PIC16F877A microcontroller, there is stuff for you too here.) Switching an AC load with an Arduino is rather simpel: either a mechanical relay or a solid state relay with an optically isolated Triac. This will only work with a random fire optocoupler: NOT igniting at zerocrossing is the principle of this dimmer. WARNING: Some people try to build this with an optocoupler with zerocrossing coz 'that is better' right? Some are even told in electronics shops it is better to use such an optocoupler. WAIT!! before you decide to build this, it is good to know that a similar dimmer is available at Aliexpress at cost that is hard to beat (currently 2.70 euro)
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