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'[PICLIST] Amplifying signal to drive PortB [EE]'
2000\12\15@062150 by Phil Tipping

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I need to amplify an intermittent high impedance square wave (100-
200Khz, 3V no load) to wake a 16F84 using the Port B wake on
change feature. The problem being that I need a low component
count (cheap) and very low quiescent current (uA's if poss with no
signal) as it is a battery powered device (3v ideally but could be 6v
with two lithium batts (for op-amp?)) .
Anybody got any good ideas/circuits/help?

Thanks

Phil

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2000\12\15@090751 by Thomas C. Sefranek

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Use an FET and the PORT B weak pullup.

Phil Tipping wrote:

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2000\12\15@094117 by Wynn Rostek

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> I need to amplify an intermittent high impedance square wave (100-
> 200Khz, 3V no load) to wake a 16F84 using the Port B wake on
> change feature

Phil,

What is the source impedance?

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2000\12\15@135734 by Robert Rolf

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Logic level MosFET biased off with high value R and parallel C to filter
out RF cycles.
Diode, coupling cap to your square wave input.
Drain connects to PortB pin with weak pullup's enabled.

If need be you can use two diodes and 2 caps to make a V doubler.
(clamp negative side to -.6  then use seriesed cap to add to input 3V
(about 4.8V drive in total).
You don't want to use Schottky diodes because they leak quite badly at
high temperature. Germanium would be nice, but who makes 1N34a's these
days?

Idle current is zero. Parts count is low.

Phil Tipping wrote:
>
> I need to amplify an intermittent high impedance square wave (100-
> 200Khz, 3V no load) to wake a 16F84 using the Port B wake on
> change feature. The problem being that I need a low component
> count (cheap) and very low quiescent current (uA's if poss with no
> signal) as it is a battery powered device (3v ideally but could be 6v
> with two lithium batts (for op-amp?)) .
> Anybody got any good ideas/circuits/help?

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2000\12\15@215403 by Dan Michaels

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At 10:49 AM 12/16/00 +1300, you wrote:
>> I need to amplify an intermittent high impedance square wave (100-
>> 200Khz, 3V no load) to wake a 16F84 using the Port B wake on
>> change feature. The problem being that I need a low component
>> count (cheap) and very low quiescent current (uA's if poss with no
>> signal) as it is a battery powered device (3v ideally but could be 6v
>> with two lithium batts (for op-amp?)) .
>> Anybody got any good ideas/circuits/help?
>


Maybe an old-fangled voltage doubler. 2 diodes and 2 caps.

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2000\12\15@231126 by Roman Black

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> Phil Tipping wrote:
> >
> > I need to amplify an intermittent high impedance square wave (100-
> > 200Khz, 3V no load) to wake a 16F84 using the Port B wake on
> > change feature. The problem being that I need a low component
> > count (cheap) and very low quiescent current (uA's if poss with no
> > signal) as it is a battery powered device (3v ideally but could be 6v
> > with two lithium batts (for op-amp?)) .
> > Anybody got any good ideas/circuits/help?


Try passing the signal through one diode into a small cap.
The cap will charge to the signal peak minus diode voltage.
Probably about 2.5v. Then connect this point to the PIC pin
with a high value resistor, should provide adequate voltage
to trigger a high level at the PIC pin. Choose the resistor
value so that the cap has time to discharge during the
"no signal" period into the PIC pin, or alternatively
add another high resistor across the cap to discharge.
3-4 parts, no current. :o)
-Roman
(who needs fets and op-amps??)

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