Any ideas on this...controller?

[goodpickles]

Here is what I want to do. I am making a ventilation system: controlled by temperature a window will open and close. I will use a linear actuator to open it. Sounds simple?...OK here is catch 22:
I want 4 different stages (closed, 1/3 open, 2/3 open, and full-it would open further as the heat increases) I have thought of using 6- 4PDT relays...but it seems there should be a better way.
I know very little about micro controllers, however I was wondering if this would be the way to go.

Also does anyone know where I can get a 4 stage thermostat? Or should I make one?

I’d appreciate any help that you can give me.

 

[ljcox]

I suggest you use a thermistor and a 4 level threshold detector.

AS the temp rises, the actuator would be activated when the temp reaches the second level (the first level is where the window is closed as the temp falls). If the temp continues the rise, the activator would be activated again when the third threshold is reached, etc.

When the temp falls, the reverse process would occur. I would also include some hysterisis in order to prevent the possibility of oscillation.

Len

 

[goodpickles]

Where can I get more info on the 4 level threshold detector...Digkey search does not bring any results...is there another name?

 

[Sebi]

You can build it with comparators.

 

[ljcox]

The Sebi circuit looks good, but you don't need the rresistors in series with the + inputs to the comparitors. Also, I would include some hystersis.

Also, Sebi's circuit will probably need some logic at the output to drive the actuator. I can't suggest how to do it without knowing more about the actuator.

Len