Controlled Current Through Resistive Heater

Hello most excellent People of Pololu

Lets say I have a resistive heater which I want to digitally set how hot it is. It’s a simple constant resistance heater. What system does one employ to transform an integer in my Baby-O’s app into a variable voltage/current level being fed to a fixed resistive load? Lets say 4 bits and 16 heater levels.

Or, is the smarter path to always feed the resistive heater a constant voltage, but vary the temperature with PWM? This seems noisier with all the switching required.

In either case, I have to go from the low-power AVR port to something capable of some delivering some more substantial milliamps. Is a FET circuit the solid state answer to that?

Thanks for your insight

Hi, Mike.

If you want to do it at all efficiently, some kind of PWM is the way to go. If your heater does not need to respond really quickly, your frequency can be just a few Hz or less. What kind of current are you talking about?

- Jan

Hi Jan

I’ve got proper test eqpt coming in the next couple days that will let me answer that.

Of course! Yes I suppose it could be very slow and it would not affect the results.

Hey Jan, I’ve got a couple heaters. One is 8 ohms and the other, smaller unit, is 45 ohms.

At 12V, the 8 ohm would draw 1.5 amps when engaged. The smaller heater would draw ~270ma.

This may sound weird but… can I use the motor chip on a Baby-O to drive these with PWM at these current levels?

Mike in Alaska

Yeah, that should be fine, though the 1.5A might be pushing it.

- Jan

Do you sell a motor driver I carrier could easily use with my Baby O to reliably drive these heaters 12V, slow PWM (seconds on), 1.5A?


You don’t need bidirectional current, so a bidirectional motor drivers like the ones we sell would probably be overkill for your application. You could just use a MOSFET controlled by one of the Baby Orangutan’s hardware PWM lines (or even with a slow software PWM on an arbitrary I/O line).

- Ben