My SCT fogs up most evenings. I’m a little reticent to use a hair dryer and not sufficiently rich to buy a proper dew heater, so I played around to make my own.
I dug out some nichrome wire, cut it to the length of the diameter of my scope (about 1m) and played around with voltages until I had a small increase in temperature (comfortably warm enough to hold onto with my fingers). It must only be a few degrees. Just be warned its VERY easy to fry you fingers so start with low voltages and work up.
I had a Jaycar kit MOSFET power supply hanging around, slight overkill I know. I dug up a relay I’d used for something else, added a DHT22, an LCD display along with an Arduino and behold!
The power supply is turned on by driving the relay. The Arduino code reads the DHT22 every 5 seconds, calculates the dew point temp, displays the current temp, the dew point temp and relative humidity. If the current temp is within 4 degrees of the dew point it turns on the power supply.
BTW the knob is only used to control the contrast on the LCD as it gets to bright when the scope is taking pictures.
Note the insulator on the nichrome as well. My scope conducts!
An now turned on