Do you just need to detect AC power failure or are you wanting to monitor
the AC line voltage?

Power failure detection is pretty easy if you square up the AC (by
rectifying and clipping it), then use the resulting pulses to reset a timer.
The timer is set to about the AC period, so that a missing pulse will let it
run out, thus indicating loss of AC power.

Don't forget that your 125-126 is RMS, which means a peak voltage of 178,
and that the AC line is susceptible to huge spikes during a thunderstorm.

> -----Original Message-----
> From: Bill Bennett [SMTP:benettw@BELLSOUTH.NET]
> Sent: Tuesday, December 07, 1999 4:31 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [OT] 120 Volt ac detection
>
> I am need of someway detecting when AC line voltages drops. What I
> would like to do is be able to receive a low when voltage drops to 90
> volts and then as line voltage rises receive a high when it reaches
> 105 volts. Usually around here line voltage runs 125-126 volts would
> like something able to withstand 140 volts.
>
> Thanks,
>
> Bill