On Tuesday 01 July 2003 17:57, Jinx scribbled:
> A gated CMOS oscillator would be a low-power alternative to
> the 555 modulator - you didn't say if the transmitter will have an
> off switch. Appliance remotes use nA when sleeping, and your
> best chance of getting close to that would be a slow PIC at low
> voltage. Having a slow PIC means that you'll need to modulate
> externally because you won't be able to generate a 38kHz carrier
> with a 32kHz clock (well, I suppose you could with multipliers). The
> modulator could be powered from the PIC, which makes the
> choice a little irrelevant if it's using no power during down time
> anyway. And one thing that really helps transmission, especially
> on a lowV battery supply, is a reservoir cap (eg 100uF) close to
> the LEDs


I was thinking of a key-fob type transmitter (so would be on all the time=
). =20
My initial was thought was a PIC12F629 with internal oscillator, but that=
 was=20
when I was thinking of photo-diode/transistor, so I was not forced to use=
=20
38kHz or thereabouts.  I was not even thinking power consumption since th=
is=20
was another one of my spur-of-the-moment ideas that I just want to experi=
ment=20
with for now.  But I now would like to properly think this thru...

First, let's stick with the 12F629, since it'll allow me to code in my ow=
n=20
protocol quite easily.  With this, I'll also probably implement say 4 or =
5=20
different signals so I can use it for other projects in the future.

Now, power-wise, I'd need to stay in LP mode, so perhaps...

(1) A 131khz crystal would do the trick?  If I use PWM for 4 different=20
signals, this may be a bit unrealistic still.

(2) How about sleep and let it use 4Mhz very briefly on each wake-up?

(3) But I have a new idea .... hang on for a few minutes while I think ..=
=2E
=2E..
=2E..
=2E.. thanks for waiting so long ...

Here's something I just came up with on the whiteboard...


                                   ,-------------
              -^-                  |
          ,---o o---o--|>|-------->| RA0
          |         |              |
          |         '--|>|---.     |     =20
(Bat)     |                  |     |       PIC
+3V >-----o                  o---->| Vdd
          |                  |     |      12F629
          |         ,--|>|---'     |    =20
          |   -^-   |              |
          '---o o---o--|>|-------->| RA1
                                   |
                                   '-------------

Diodes above should be schottkies, and also with an LF PIC.
When a (momentary) switch is pressed, the PIC will start up,
and read the ports to see which switch it was, and perform the
appropriate action.  I can't see this solution drawing so much
power, especially for the project I'm now seeing this used for,
the buttons are really just for periodic setup/config.

Cheers,
-Neil.

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