Sensor input mode measurements, build 320, B2, user-space
quozl at us.netrek.org
Wed Mar 21 03:46:55 EDT 2007
Thanks to some hints from Jaya Kumar, I've been able to obtain data from
the analog sensor input.
The pretty sample graphs:
measurements through a voltage divider of my UPS battery voltage during
a five to ten second power down of the charger. This sudden jump in the
curve is due to my plotting the absolute value of the sample instead of
treating it as 16-bit signed integer.
UPS charger output voltage during normal operation, showing the combined
effects of the charger switching and the inverter switching at 50HZ,
this is 1000 samples at 8000 samples per second, therefore 1/8th second,
so 6.25 cycles should be visible, and they are.
How it was done:
0. assemble a voltage divider to bring 13.57V DC input down to 1.184V,
(though an instrumentation amp with an offset would have been better),
1. disconnect the B2 unit from any other devices on the bench, then
connect the output of the voltage divider to the MIC input,
2. use alsamixer to set Analog Input to "on",
3. use "arecord -t raw -f S16_LE -r 8000" to record samples,
4. post-process the samples to generate one line decimal value per
16-bit sample in the file, (used od(1) and awk(1)),
5. plot with gnuplot.
James Cameron mailto:quozl at us.netrek.org http://quozl.netrek.org/
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