At 01:21 PM 3/14/2004 +0000, you wrote:
>Any comments on the circuit at http://www.nosreme.org/tmp/selfpwr.png?
>
>The intention is to run a PIC-based circuit (16F628) from a 9V battery,
>but reducing the power consumption to (virtually) zero when not in use.
>I also want to be able to read the status of the push-to-make switch
>while running.
>
>The switch turns on the MOSFET via NPN Q2, and the PIC can then keep the
>power on through Q1.  It can read the status of the switch on another
>pin through R6.

Put another 10K resistor from the base of Q2 to ground. Use a TTL-level
input on the PIC. Then it should work reliably.

The 7805 wastes 5mA typically just by itself, quite a bit
of drain for a 9V battery, you'd be better off with a lower-power regulator.
The 78L05 and 78M05 are not that much better. If you do get a lower
power regulator, you can save a bit of current by increasing R2 to 100K.

>This is a one-off hobby project, and I already have these parts around,
>which is why I haven't just got a regulator with shutdown option.
>
>I have seen Roman Black's circuit at
>http://centauri.ezy.net.au/~fastvid/self_swi.htm, but as this circuit is
>likely to be running for a couple of hours at a time, I'd rather not
>have to sink 5-10ma the whole time.
>
>Thanks,

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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