08M as fan speed control.

[bonaur]

Hi everybody.

I would like to hear your opinion.
I would like to use a 08M to do a Zero-Cross-detection wait for some time, and fire up a TRIAC. At next zero-cross the TRIAC turns off (by itself) and one again after some time fired up.
(More or less replicate the attached schematic)

However the PAUSE command 'only' goes in steps of 1ms (0.5ms @8MHz) thus giving a maximum of resolution of 20 (10ms for each half sinewave(50Hz) @ 0.5ms intervals)

The next alternative is the 28X1 chip which has the PAUSEUS command, but that chip is overkill.

Is the resolution of 20 sufficent for most applications, or ?
Any orther recommendations ?

-Best regards, Bo Andersen-

 

[BeanieBots]

From your other posts you reference 240v which makes me think you might be UK based. If yes, that circuit would be illegal to use.

A delay resolution of 1mS would be fine for fan speed control. However, you might have fun with detecting the zero point to an accuracy that would warrant anything better. Admittedly R4 can be used to 'trim' the detection point but with a typical command overhead of 250uS going beyond 1mS resolution would be of little benefit anyway.

 

[hippy]

There was some previous discussion on zero-crossover detection so a forum search may be in order.

It should be possible to do what you want, though that's not a recommendation to use that or any other particular circuit. Providing the crossover can be detected a PULSOUT to a dummy pin can give a delay to 10us accuracy for triggering.

 

[bonaur]

Hi.
Thanks for the reply.

I know the circuit creates too much noise, hence illegal. (I'm from Denmark, but still illegal)

I will still built the circuit, more to test the ZCD, and to check wheater the 10ms resolution is enough.

Thanks hippy for the work around , my 'final' circuit requires all pins, but for this test purpose, it's great.

-Bo Andersen-