Archive of the former Yahoo!Groups mailing list: MOTM

----- Original Message -----
From: Simon <simon@...>
...Battery, rechargeable or not, is a workable solution, not ideal though.

OK, if you are bound and determined to do it without bringing the AC to the
front panel, then see how you like this idea

A largish electroyltic capacitor can store plenty enough energy to energize
the coil of a relay for a short time. There are plenty of ways to make a
circuit like this as I see it.

I would look to a connection to charge the capacitor through a diode from
the power supply with a small amount of resistance to soften the charging a
little. The diode would assure no discharging through anything except the
relay coil. So, the capacitor picks up the relay coil (probably a 12 volt
relay with a resistor in series). You have to watch the wattage on the
resistors (not something we normally do). Use T=R∗C to size stuff. Time the
discharge curve and the charge curve (allowing for time for the PS to power
up) so the level that the cap discharges to during relay pick up never drops
below the drop out voltage on the coil. Use the -15 rail since you will be
adding load to the P.S.

We do this on portable substations to trip a 10 amp circuit breaker coil
even if the AC supply to the charging circuit is suppressed (long boring
explanation about AC circuit behaviour during short circuit conditions
omitted). In permanent installations we use batteries constantly under
charge.

Having said all that, I'd still just switch the AC with a front panel
switch.
A big one like this:
http://www.wiseguysynth.com/larry/misc/switch3.jpg

LEDs....Sure. But, analog meters are more cool.
http://www.wiseguysynth.com/larry/misc/meters.jpg

Larry (just a Stooge)