[Ovmsdev] 12V A/D conversion

Michael Balzer dexter at expeedo.de
Sat Feb 23 18:07:04 HKT 2013


I got some 12V alerts during the last 3 days. Checking the 12V reading 
after the alerts showed normal level, so I'm trying to figure out if 
they were false alerts.

Last alert was about 2 hours ago, alerting about 11.0 V -- my check only 
a few minutes later showed 12.1 V again...

I've read into the PIC18 doc on the A/D conversion (chapter 19). AFAIS 
inputs_voltage() differs from the example in two ways:

1) the example does not turn off the converter after reading the result 
(but I understand the ADRES register should keep the result)

2) the example step 3 says "wait for acquisition time if required", it 
seems our function currently does not wait.

"To determine acquisition time, see Section 19.1 “A/D
Acquisition Requirements”. After this acquisition
time has elapsed, the A/D conversion can be started."

Section 19.1 contains an equation based on hardware parameters I don't 
know. Can you please have a look and tell if missing that wait time 
could lead to false measurements?


Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
Fon 0202 / 272 2201 * Handy 0176 / 206 989 26

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