Re: Re: Comfort / Analogue Input / Op-amp ?

[Ake Hedman <akhe@xxxxxxxxxxxxx>]

Nick,

Sorry I should have noted the dots... z-)   Looks good.

TL071 is fine. If you need more (other brand but anyway) go to Microchip=20
and sample ten or so for free (http://sample.microchip.com/)  You
will=20
have them delivered home in a couple of days. No questions asked. I=20
should have emailed on to you if I could.... ;-)

If you suspect there is something strange at the "input" put two
diodes=20
on the opamp output. One from ground to the opamp output and one from=20
the opamp output to vcc. This is often used to protect an input from a=20
negative signal and signal above VCC.

But its very strange if the A/D input behaves like this. Its should only=20
behave like a big resistance. If its a ground path you probably will=20
burn the opamp but it would survive being connected to another output if=20
within +5V.

Have you tried to connect a pot (or a variable power supply) to the=20
input and see if you get reasonable results?

/Ake
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
Nick wrote:

>
> > I can't view the schematic
>
> Damn Yahoo --- just lose the "." off the end of the URL,
that's
> supposed to be the end of the sentence, not part of the URL!
>
> > I don't know Comfort but
> > if this is an analog input
> > connecting the opamp output
> > to it should not be a problem.
> > Low impedance into a high
> > impedance will be alright.=20
> > And if it's an A/D input
> > nothing should come out of it.
>
> That might be the problem.  The Comfort zones work both as
"normal"
> zones to which you connect PIR contacts etc and as A/D inputs.  That
> is why I am suspicious that something will be coming out of the
> input!
>
> > The op amps also don't like going
> > negative in respect to V- but feeding
> > it with +5V as you do would make
> > sure that its not. Do you still have
> > +5V on the faulty board?
>
> Yes, the faulty board still has 5.03V exactly as before.
>
> > Also try to replace the opamp
> > and check if it gets hot.
> > If so something in the circuit
> > might be wrong.
>
> I was suspicious of my circuit at first, but as it worked properly
> until the output of the op-amp was connected to Comfort's input....
>
> I can try changing the op-amp (and would appreciate your advice on
> whether the TL071 is a good choice or not) but need to wait until I
> can get to the shops.
>
> > Do you have a schematic for the Comfort A/D input?
>
> Unfortunately not - it doesn't seem to be published and there is
> very little documentation apart from "0 - 5V input".
>
> As usual, many thanks for the prompt response and for trying to help.
>
> Nick
>
>
>
>
>
>
>
>
>
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--=20
---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergav=E4gen 17, 820 50 LOS, Sweden
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