On Wednesday, May 1, 2013 7:39:37 PM UTC+1, Man at B&Q wrote:
On 1 May, 17:10, whisky-dave wrote:
On Wednesday, May 1, 2013 4:26:14 PM UTC+1, John Williamson wrote:


Add an external circuit to flag zero crossings
of the mains waveform,

Quite a minor point, I'd include the whole lot on one chip. The only externals would then be the switching relay, and a resistor/cap/diodes to create an LV supply from the mains.

The less thinking the cpu does, the smaller and cheaper it can be. The big obstacle to such a system is cost, and if the government keep their foolish fingers out the cost issue gets solved. If the government mandates it there will be zero motivation to sort the cost out, and every motivation to keep it exorbitant. £40 for a little custom cpu and a 5 discretes is certainly exorbitant.


Good you know it's a sine wave which will change in amplitude as well as fequency which makes zero crossing more difficult and less useful.

A zero crossing is a zero crossing regardless of amplitude. The change
in frequency is what you are measuring.

quite. Pass the mains signal through RC to eliminate hf junk, and feed it to a comparator in the IC, then you have 1 or 0 for the cpu to enjoy.


NT