Like this
https://www.iceinspace.com.au/forum/...d.php?t=144679
He said in a self aggrandising sort of way. Actually I must update it as it's changed a lot since then.
It's an Arduino pwm controlled heater. Measures ambient temp/humidity using one of several available sensors, heater temp using the ds18b20, and can use cheapo MOSFET modules as you don't need much power.
Can set power manually, variable according ambient temp relative to dew point, or feedback control of heater temp relative to dew point.
Chris