Re: Comfort / Analogue Input / Op-amp ?

[Ake Hedman <akhe@xxxxxxxxxxxxx>]

Hi Nick,

I can't view the schematic and I don't know Comfort but if this is an=20
analog input connecting the opamp output to it should not be a problem.=20
Low impedance into a high impedance will be alright.  And if its an A/D=20
input nothing should come out of it.

The op amps also don't like going negative in respect to V- but feeding=20
it with +5V as you do would make sure that its not. Do you still have=20
+5V on the faulty board?

Also try to replace the opamp and check if it gets hot. If so something=20
in the circuit mite be wrong.

Do you have a schematic for the Comfort A/D input?

Cheers
/Ake



Nick wrote:

>
> 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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>
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Ake Hedman (YAP - Yet Another Programmer)
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