Homebrew PCBs

--- Len Warner <yahoo@...> wrote:

> 
> That would be a good idea, except that the 7106
> circuit chosen
> uses it in its 9V battery "inputs floating w.r.t.
> supplies" mode.
> 

Yes, it's a hassle I've run up against myself. A DC/DC
converter would do it but it's kind of overkill.

> There is adequate information in the datasheet to
> allow a
> redesign of the input bias and reference circuit so
> that it
> is all ground-referenced, which would then allow a
> simpler
> parallel control circuit to be used, but consider
> further...

It's tricky, I'm still studying the best way to get
around it.
> 
> The control circuit will need an input for set-point
> and, hopefully,
> some kind of output of the setting. How will this be
> done?
> 
> Will it be an analogue input such as a
> potentiometer,
> which also gives mechanical display of its setting?
> If so, you will have a thermostat with a digital
> temperature
> display giving an impression of precision but an
> analogue
> setting which will seem unattractively vague in
> comparison.
> 

A potentiometer and push-button for switching between
set-point and measurement is the common solution. Even
without that you can always tweak it until the
reading's on the dot. Turn the set-point way up and
keep an eye on the reading. When it's right turn it
down until the relay or whatever turns off.

- YD.


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