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Comfort / Analogue Input / Op-amp ?
- Subject: Comfort / Analogue Input / Op-amp ?
- From: "Nick" <nick@xxxxxxxxxxxxxxx>
- Date: Sun, 10 Apr 2005 16:22:37 -0000
Nasty techie one this. Also posted to the Comfort group, but if
Ake's about on here......
My temperature sensor schematic is shown here
http://www.nicklocke.co.uk/Auto/Schematic.JPG.
I have built it up
on stripboard as shown here
http://www.nicklocke.co.uk/Auto/Layout.JPG.
The bit on the left of
the layout is a five volt regulator to reduce what comes in from
Comfort. The op-amp is happy with 12V, but I know Comfort only
expects 0-5V on the analogue inputs.
After attaching the power wires to Comfort, I tested the voltage at
the output - it varied with the temperature as expected. I then
connected the output to a Comfort zone input (on the main board).
The measured voltage then moved to a more or less constant 4.4V
(trust me, it's not 33 degrees in the UK today!).
I then removed Zone connection and the output still remained
constant. So, it looks as if joining the op-amp output up to
Comfort has blown the op-amp. On reflection, Comfort could quite
possibly be pushing a voltage greater than 5V into the output. Does
it? Would that possibly blow the op-amp? How do I fix it?
Sorry, a long post - hope it makes sense!
Nick
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