Re: [ATM] Electronics help needed - temperature control

["Don Clement" <clement.focuser@verizon.net>]

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/