AC line zero crossing
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I'm trying to find a way to send a regular, fast pulse to a stamp input that
is synchronized with the zero crossings on an AC power line.
They tell me this can be done by directly inputting the line voltage
(through a current limiter) to an input pin on a PIC12C508. The pic is
supposed to have protection diodes that will allow this.
I would rather input to a stamp and have some isolation. Any ideas will
help.
Of course there ar ways to accomplish this easily, but without the
isolation, the stamp is at risk...
is synchronized with the zero crossings on an AC power line.
They tell me this can be done by directly inputting the line voltage
(through a current limiter) to an input pin on a PIC12C508. The pic is
supposed to have protection diodes that will allow this.
I would rather input to a stamp and have some isolation. Any ideas will
help.
Of course there ar ways to accomplish this easily, but without the
isolation, the stamp is at risk...
Comments
The most common way to solve this problem is with an optical isolator. The
4N25 is one of many types that should be appropriate. You would connect the
collector to a weak pullup resistor (perhaps 22K to +5V) and to the Stamp
input pin. Emitter goes to ground. The LED is connected to the AC line
through a series current-setting resistor. Add a reverse-connected diode
(1N4148) in parallel with the LED to prevent reverse breakdown. Be sure to
size that AC line resistor for adequate power dissipation...
>I'm trying to find a way to send a regular, fast pulse to a stamp input that
>is synchronized with the zero crossings on an AC power line.
>They tell me this can be done by directly inputting the line voltage
>(through a current limiter) to an input pin on a PIC12C508. The pic is
>supposed to have protection diodes that will allow this.
>I would rather input to a stamp and have some isolation. Any ideas will
>help.
>Of course there ar ways to accomplish this easily, but without the
>isolation, the stamp is at risk...
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!