AVR-Chat

Manne Tallmarken wrote:
> Hello folks,
> 
> I have a 230 V AC power line that is connected to a light dimmer. I
> want to determine how much this signal is dimmed, e.g. what the duty
> cycle is (i guess the dimmer regulates the duty cycle?). 8-Bit
> precision is enough (or less as well)   
> 
> Any suggestions how to connect the power line to the microcontroller?
> 
> My first thought was to connect a resistor and zener diode in series
> and an optocoupler over the diode, thereby making it possible to read
> the value from the other side of the optocoupler, but all
> optocouplers seems to need at least 20 mA through the led which would
> make the resistor suffer 4.5 watts...    
> 

I have done this before and it doesn't work very well. Domestic-type
light dimmers give a very unpredictable and irregular output - it is
hard (sometimes impossible depending on what load is on the dimmer) to
extract any timing information out of it. You will need to do a lot of
work with an oscilloscope and different loads to get an output you can
do anything with.

My application was non-isolated so we just used some resistors but your
optocoupler idea should work (with a lot less than 20ma) - remember that
the line voltage is quite low at the start and end of the mains cycle.

-- 
Tim Mitchell
tim@sabretechnology.co.uk http://www.sabretechnology.co.uk
Sabre Technology (Hull) Ltd, 3a Newlands Science Park, Hull HU6 7TQ
Registered in England and Wales no.3131504
t:01482 801003 f:01482 801078