Re: Comfort / Analogue Input / Op-amp ?

["Frank Mc Alinden" <fmcalind@xxxxxxxxxxxxxx>]

Hi Nick
Not familiar with Comfort , but quite common for alarm systems
to have an internal resistor(s) conected to +v and the circuit connections
go to gnd via a resistor.....Do you have to tell comfort that its now an
analogue input ??

Also measure the voltage of the comfort analogue input with the temp sensor
disconnected and see what voltage if any is present.........

Frank


----- Original Message -----
From: "Nick" <nick@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Monday, April 11, 2005 2:22 AM
Subject: [ukha_d] Comfort / Analogue Input / Op-amp ?


>
>
> 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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