[email protected] said: > Does any one have a circuit (tested - operational) for monitoring line > frequency? I'd like something that checks zero crossing so that it is > relatively insensitive to line voltage variations.
I'm assuming you are starting with an AC wall wart and 2 resistors to divide the voltage down to something within range. The easy to understand way is to use 2 more resistors to bias your input pin at the switching threshold and a cap to connect the middle of both pairs. The circuit would look like a H with 4 resistors on the vertical bars of the H and a cap on the horizontal bar. Top left of H connected to AC in, top right to +V, bottom left and bottom right to ground, and center right to input pin. You can do it with 3 resistors. Replace the lower of the 2 resistor setup with a pair, one to ground and the other to +V. Adjust the size of those resistors so the parallel resistance is the same as the one you are replacing and the middle voltage is the switching point. Mumble. There is a word for this that I can't remember. It's used for things like terminating ECL input signals. If you are going in to a RS-232 port, you can probably get a useful +V from one of the modem control signals. I forget the polarity. You may have to hack your software to set it to the right polarity. -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
