Vermes
Advanced Member level 4
A common problem in astrophotography is deposition of steam on the telescope optics/lens, when humidity is high.
The solution is to heat optics above the so-called dew point temperature. Initially, heaters were connected shortly to the battery, then a simple PWM controller for NE555. But now there is a dedicated system for this application, so that the telescope does not heat too much, what would degrade the image quality, as well as unnecessary increase of energy consumption.
Presented project is a PID controller equipped with humidity sensor and two temperature sensors. Dew point temperature (at which there is a vapour deposition) is calculated based on measurements of humidity and ambient temperature. The controller task is to keep the telescope temperature by a specific amount above the dew point.
Ordinary 680ohm resistors connected in parallel so that the emitted power on them was about 25W, placed in heat shrink tubing are formed near the lens of the telescope were used as an executive element.
Sensirion SHT21placed in a separate box was responsible for the temperature and humidity. The sensor is located on a DS1624 telescope. The whole is controlled by microcontroller PIC16F1827.
During testing, the driver proved to be without problems, with minimal heating energy consumption. At an ambient temperature of -4 degrees Celsius and humidity about 88% the driver maintain the set temperature by more than 6 hours without any problems, here a sample photo:
Inside the housing:
Schematic diagram:
Link to original thread (useful attachment) – Sterownik grzałek do (astro)fotografii