Need help building a thermostat

[moomate]

I want to build a thermostat (proportional i think?) that can maintain a specified temperature within about 1 degree F. It will be set at probably 88F but I will need to be able to adjust between around 70F-100F. I need it to act as a rheostat, not On/Off. I want it to have a display panel that will display the temp that it is set to and also the temp that it is at. I will be using flexwatt heating tape as the heatsource, which is pretty much just like a heating pad with standard wall outlet plugs. I would like it to be able to hold up to around 600 watts and i would also like some type of security so that if it gets too hot it will shut off completely. The temperature probe needs to be able to withstand humid climates and sealed incase of contact with liquids. Can anyone give me some helpful tips on where to start? I'd like to build these relatively cheap. Under $50 bucks if possible..

 

[rjvh]

that's a lot of

I need
I want
I would like (that's the best one to start with)

What is your idea about it how to aproach, as you ask for a complete sophisticated design

there are a lot of shematics already posted on the net

you have the intention to build it your self and if so what is your experiance level yet in electronics

Robert-Jan

 

[Hero999]

Using it as a rheostat is a very bad idea.

Supose it operates the heater at 150W, it will be dissipating 150W so the total heating power will be 300W - double what you'd expect!

You're better off geting it to turn the heater off when the temperature is 0.5°F> required temperature and on when the temperature is 0.5°F< required temperature.

 

[Diver300]

If there is any delay in the heating, it is very difficult to get good temperature control. You need something much more sophisticated than a simple temperature switch or you will get bad hunting.

You would need a microcontroller or similar and it is a lot of work when it has already been done and is available off the shelf.

https://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4683766

or

https://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6119879

 

[Boncuk]

You would need a microcontroller or similar and it is a lot of work when it has already been done and is available off the shelf.

I agree.

My primary job was pilot in the GAF (German Air Force) and I've learned a lot about avionics. An auto-pilot e.g. has to have a tendency recognition circuit. For the ease of the pilot they are programmable for certain things to control, like heading and altitude changes.

Assuming I program the desired altitude for a descent rate at initially 4,000ft/min the aircraft would considerably undershoot the desired altitude (with a tolerance of +/-300 ft allowed by air traffic control since air traffic density makes it necessary to stack the traffic vertically 500ft apart in opposite directions) which could cost a pilot's license or lifes in the worst case. The tendency recognition circuit calculates the value differences between desired and actual values continuously. Depending on aircraft aerodynamic parameters the autopilot decreases descend rate at a certain point (e.g. 1,000ft above the desired altitude) to easily make a smooth roundout to level the aircraft at the programmed altitude. The elevator will be set for slightly inverse function 100ft above the programmed altitude. The same applies to heading changes using the autopilot.

Everybody can purchase such an autopilot for his Piper or Cessna, however they cost a few Cents.

Transfering this to electronics that's about the same way. A good SMD solder oven has to have that kind of circuit, too.

Boncuk