[chbot] Circuit help please, low voltage cutout

Chris Hellyar chchrobotics@lists.linuxnut.co.nz
Mon, 23 Apr 2007 12:29:32 +1200 (NZST)

> b. Can Q2 be replaced by a normal transistor and a relay? is the choice
> of a mosfet because it will use less power than a relay?


last time I reply to this, promise... :-).

Yes, I imagine that is why they used a mosfet, if you just wanted to drive
a relay with the circuit you could use a Bipolar transistor on the output
of the opamp to save the cost of the mostfet.  Another BC548 or one of the
TIP darlingtons for a sledgehammer.

You could also use a resistor & cap in parallel on the relay coil to
reduce the current drawn by the circuit in operation if you wanted to use
a relay, but also were concious of current draw.

Cheers, Me.

> I know it was mooted that i could do it by using a voltage divider to
> one of the pics ADC pins etc, but i want it to cover all of the
> circuitry on the bot (even if the controller is disconnected).
> I will probably still monitor the voltage into the controller to
> determine bot behavior but thats a ways off yet.
> Thanks all,
> CR
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Cheers, Chris Hellyar
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