Controlling a heating coil 120v w/ 5v.

So what would be the best way of controlling a heating coil with the arduino? The HC runs off of 120 vac. I was thinking of a solid state relay, but as I've been reading it seems like they don't have very quick switching times. I don't need exact temp measurements, maybe 8 degrees F, maybe that would be a large enough range to let the relay keep up?

solid state relays have pretty quick switching times. Are you sure your not talking about mechanical relays? I think a solid state relay will more than suffice for your application. What siwtching times would you want?

If you're running the heating coil off an AC mains supply, then the supply switches on and off 100 or 120 times per second anyway. Relays of either mechanical or solid-state construction will be fine.

Driving the heating coil is the easy part and a SSR would be the simplest. Now you have to figure out how you are going to measure the temperature of whatever material you are heating and work out the control software. There is a PID control library available in the playground area.

Good luck

Lefty

Hmmm okay.

How about this relay?

http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtSzCF3XBhmWx3JwO0RjjQeWbUv0S9xVh8%3D
The data sheet says '1,800 operations / hr at rated load (electrical)', but I don't think I'll exceed that.

For the control I was anticipating using a thermistor, http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMv1TUPJeFpwbkR8Sw1NpNdxlW%252b2N3gTo4Y%3D

Although the data sheet for that one says 'accuracy 25* C', so I may have to find an alternative solution for the temp.

For this thermocouple amp, it states that the maximum temperature is 0-50c, but it shows the thermocouple temperature going as high as 500c. I'm slightly confused...

So an SSR lacks the moving magnetic field driven coil that a mechanical switch has?

Yes, and SSR is basically a semiconductor device (triac).
It lacks a coil (ugh, nasty back EMF) and contacts (ugh, nasty arc welding).
I think SSRs are simpler and more reliable than the mechanical one you've chosen.

What sort of temperature range are you looking at?
Have you looked at the LM34 (Farenheit) or LM35 (Celsius) sesnors?
Accurate and easy to interface.

I'm looking for temperatures between 300-400 degrees F (~150 - 205 centigrade).

I'll check those out though, thanks!

Thermocouples are cheap on ebay!

Thermocouples are cheap on ebay!

Yes, simple and reliable with wide temperature range. However complex to properly amplify, cold junction compensate and linearize.

Lefty

Oh, its not soo hard :wink:
I use the ATTiny85 to control a soldering iron. The thermocouple is directly connected to the differential inputs of the ADC. Gain set to 20 and ADC in differential mode. Its best to calibrate the ADC before the first measurement for offset and then plot a temperature/ADC value diagram once to get the characteristics of the thermocouple.

Btw, i control the iron through an opto-triac (MOC3043) which in turn drives the main triac. The advantage of this solution is the 'automatic' zero-cross switching.
Here's the details:
http://www.schoeldgen.de/avr/