Hello Folks,
I am working on a Timber Clock situation. Since our AC is 60 hz, I am wanting to use this as a timer. If this 60hz should fail, I would like to apply a nine volt battery for backup. What would be the best way to do this?
My idea was the following:
The AC is about 24 volts.
1. Put a bridge on the AC to make pulsating DC
2. Throw the DC through a 7805 to. "Capacitate" the pulsating DC from 120 pulses to straightline.
3. Somehow measure the pulses off the AC (before the 7805), and if they disappear, apply the 9 volt battery backup.
The Capacitor will have enough juice to keep the chip going to turn on the 9 volt battery.
My biggest problem lies in checking to see if the AC is present or not. What is the best way to do this kind of job, using just one pin and very few components?
Thank you very much in advance.
Dwayne
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