Not original topic.

Brent I would be interested to know what type of FM tx you used? Is there =
any info on the www.

Thanks
Jason

>>> brent.brown@CLEAR.NET.NZ 10/06/00 03:14pm >>>
Hi,

I have just done almost exactly what you want to do. I used a
PIC16F876 with a 32.768kHz crystal on TMR1 to wake it up from
sleep every 2,4,8 or 16 seconds. The main crystal is 1.8432MHz
which gives OK processing speed, correct baud rates and fairly low
power dissipation. I send the data over a FM transmitter every 15
minutes, 2400 baud, using a 16 bit checksum on each packet, and
the packet is repeated 4 times with a random time period betweeen
each packet.

There is nothing wrong about using two crystals. It's also OK
waking up for a few milliseconds every now and then and going
back to sleep if its not time for the next conversion/transmission.
Do the maths to find out the average power consumed. I know you
want to save space also, so as I see it the next best alternative is
to use just a 1.8432MHz main crystal. I think a 32kHz operaing
speed may be OK for your ADC and processing but would be too
restricting on your baud rate.

If anyone knows of a two speed crystal switchable by a port pin -
now is the time to speak up.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brown@clear.net.nz=20

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