OT:Switching line voltages

[KA4HJH]

>ONLY FOR PEOPLE WHO KNOW WHAT THEY ARE DOING!
>
>(Last time somebody fried his multimeter when misinterpreting some advise).

Lucky he didn't fry himself.  X(


>Bipolar transistors and mosfet can do this today, but it requires
>engineering skill to prevent the circuit from blowing up. I wouldn't
>claim that I would get such a circuit running in the first try. SCR/Triac
>circuits are quite robust, why not use such a device? I guess these
>timers use a SCR, because of simplicity and low losses / heat.
>There are semiconductor "relais" on the market, GTOs I guess.

I built a MCU controlled light dimmer system with triacs. SCR's only 
conduct half the cycle.


>Anyway:
>
>BE CAREFULL TO ISOLATE THE SIGNAL PATH FROM MAINS.  OTHERWISE IT MIGHT
>KILL YOU OR SOMEBODY ELSE. TRANSFORMERS, OPTOCOUPLERS.

I used the MOC3010 opto isolator. It's an LED photo-coupled to a 
photo-DIAC. Perfect for triggering triacs. Simple and inexpensive. 
This completely isolates the low voltage control circuit from the 
mains. Note that controlling inductive and non-inductive loads 
requires small circuit changes. What are you controlling?

Which reminds me. If you're just switching things on and off you 
should use an optocoupler with a zero-crossing detector built in, 
like the MOC3011. This cuts way down on the RFI.


>You see, a safe circuit isn't that easy, a mechanical relay with 5V
>or 12V DC steering coil seems the easiest and safest to me...

Probably always will be.

Terry Bowman, KA4HJH
"The Mac Doctor"

ICQ: 45652354