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derrabe

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I am trying to figure out an alternative to a household dimmer switch. I need to be able to electronically control the output voltage on a 120v circuit. Any suggestions? Currently I am using a manual light dimmer switch but I would like to be able to us an electronic signal from a computer to raise and lower the voltage output on the circuit. Cheaply and reliably would be ideal. I don't need minute adjustments just like 1 volt incriminates should be fine.
 
I don't need minute adjustments just like 1 volt incriminates should be fine.

That's greater than 1% accuracy - that's pretty complex! The usual design of modifying a dimmer switch using a photodiode and LED wouldn't be accurate enough for this case, I feel.
 
Over all what I am trying to construct is a temperature controlled heating pad that through a computer program will act like a volt variable thermostat instead of an on off thermostat.
 
Over all what I am trying to construct is a temperature controlled heating pad that through a computer program will act like a volt variable thermostat instead of an on off thermostat.

It would be a fairly poor way to do it - the ON/OFF of a thermostat type system is ideal for heating applications.
 
Make life easy and consider one of these units. Use your software to drive an amplified D/A. Do you plan to monitor the temperature and use feedback? How much resolution you can get will be a function of the D/A.

Ron
 
Will this dim ac current? Yes I plan on monitoring the temperature and using electronic sensors and another devise to adjust the dimmer if the temperature is outside of the allowed range.
 
It would be a fairly poor way to do it - the ON/OFF of a thermostat type system is ideal for heating applications.

For most application yes but this is a for a live animal that the temperatures have to remain at a constant and can not create hot spots/periods due to it may burn the animal.
 
For most application yes but this is a for a live animal that the temperatures have to remain at a constant and can not create hot spots/periods due to it may burn the animal.

Does the pad heat up instantly?, I wouldn't have thought so.

In which case burst fire control is still far better than linear control.
 
Will this dim ac current? Yes I plan on monitoring the temperature and using electronic sensors and another devise to adjust the dimmer if the temperature is outside of the allowed range.

Yes, the unit I linked to will do exactly what you asked. Look at the specifications.

However, I did not catch the part about the small critter. You may want to rethink this towards what Nigel is suggesting and use pulses to slowly bring up temperature so the pad remains uniform during heating. You don't want your critter running around looking for a cool spot during heating. :)

Now if you plan to computer control this then the device I linked to could be used but you would pulse it or write a good PID loop in your control code. Since you have a critter in there you also want a fail safe over temperature to prevent a crispy critter in case something fails.

Ron
 
Yeah after thinking about it, it does make more sense to do what Nigel suggested. Plus in the long run it would probably be a cheaper solution with less soldering involved. I need to keep the temperature within like a 4 degree range. Can you recommend a good digitally controlled relay, and should I go with a physical relay or an electronic relay for long term use 5-10 years of constant use.
 
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There are plenty of cheap electronic thermostats on ebay etc, for household temperature ranges.

As for the thermal cycling, I have made a lot of temperature controlled systems and just use thermal lag (averaging). So in your case you could put a thin sheet of a hard material over your heat pad like a piece of glass or ceramic tiles etc. Even though the heat pad may cycle a few degrees up and down the heat at the top of the tiles will remain extremely constant.

If your critter is a reptile you can place 1/2" of sand over the pad and he will burrow down into the warmer sand or stay up on top of the cooler sand as he likes.
 
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