Re: [ATM] Electronics help needed - temperature control

[Kevin MIchael Zabbo <chaosopher23@yahoo.com>]

I was thinking of an out-of-range detector running in
analog mode, no IC's, all 2N2222 transistors and an
SCR for the motor, that would activate when the
temperature swung too far from a central range, for
example, 5 degrees up or down and the fan would turn
on, slow at first.

Knowing the weather conditions here in Iowa (and many
areas of the US), however, the air temperature is more
unstable than Element 106, therefore the fan(s) could
end up running full blast at any moment.

The 555 is cheap, but I think transistors are more fun
to work with, though IMHO, I vastly prefer tubes, but
they are hard to get new and more difficult to carry
to a field location and run from a 12V system.  I'd
rather leave them at home in the amplifier where they
belong.

Kevin

--- Don Clement <clement.focuser@verizon.net> wrote:

> 
> Mark,
> 
> 
> 
> I think your idea of the shunt and swapping the
> sensors would work. I have a
> suggestion: Use a 555 timer IC between the output of
> the comparator and
> switch. Use the comparator to change the duty cycle
> of the 555 driving the
> switch.  A 50% duty cycle could have the fans
> running at half speed for
> example.  Then up the duty cycle to 100% and the
> fans would go full blast.
> This way energy isn't being wasted with a shunt and
> the switch could drive
> one fan or many fans without changing circuit
> components.
> 
> 
> 
> Don Clement
> 
> 
> 
> > Don,
> >
> > I have been looking at your dew heater circuit as
> shown at atmsite.org.
> >  It seems that to make it work for fan driving,
> one needs two changes
> >
> > 1. The response of the thing needs to be reversed,
> so that it comes on
> > when the temperature difference between air and
> mirror rises.  That is,
> > when (air - mirror) > threshold output curent
> turns on.
> >
> > 2. very likely, most people will want the circuit
> to run a two-speed
> > system rather than an on-off system.  Couldn't
> this be done by putting a
> > shunt resistor around the power transistor to
> carry the low speed
> > current?  The shunt resistor would probably have
> to be sized for a
> > particular fan, and would have to have enough
> power rating for the job.
> >
> > I don't have enough experience with op amp
> circuits to know how to do
> > the logic inversion while maintaining the Schmidt
> trigger feature.
> > Could it be as easy as just moving the temperature
> gain adjust pot over
> > to the other sensor?
> >
> > Mark Holm
> > mdholm@telerama.com
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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