Arduheater is a full open source intelligent heat strip controller for astronomy usage.
The source is still under heavy development so things move around a bit.
To access source code and detailed instructions visit the Github repository.
I hope someone may find this project useful.
I'll keep this thread updated as soon as I'm able to release the schematics and build instructions.
I didn't want to carry more death weight, so I decided to optimize the battery life by having a more energy efficient dew buster.
- Remotely controllable: This was a very important part of the design, most heat controllers, specially the DIY ones, rely on the PWM signal for each channel being manually adjusted by means of a potentiometer. This either requires the user to be near the device tweaking it or to set it to a temperature which is higher than the average needed temperature. Arduheater uses a serial connection so you can use any USB-Serial-TTL dongle to adjust it's settings either you're next to the thing or on the other side of the world.
- Efficient energy usage: Manually adjusted heaters will either require the user to be constantly tweaking it or they will "let it run" thus wasting energy due to the general tendency to use a higher setpoint than it's really required; this is valid for any PWM or bang-bang style controllers. Arduheater uses a temperature sensor (DHT22) to measure basic environmental properties such as temperature and humidity, by knowing them both, the calculation of the dew point is now possible. Arduheater also uses a temperature sensor (NTC) for each heating strip, allowing the micro-controller to have a rough estimation of the temperature the equipment is at; it will be a rough estimation because we are really interested on the lenses surface temperature but we are actually measuring the heat strip temperature, to mitigate this, Arduheater allows the user to set specific offsets per heating strip. Arduheater uses a PID controller to efficiently manage the energy so only the required amount of energy to maintain a temperature setpoint is delivered to the heating strip. This is possible due the usage of a PWM signal while driving the outputs; the delta between the environmental dew point (plus offset, i.e. setpoint) and the heating strip temperature will make the micro-controller output a PID-calculated PWM signal until this delta reaches zero. In practical terms if a 12V heating strip full on consumes 12W of power (1A) it may be possible for it to use only 1W or even less to keep the equipment above dewpoint and the power usage will be automatically updated during the night as conditions vary, so the system will be always using the least amount of power to keep the dew away.
- Builder friendly: Using off-the-shelf components such as the Arduino Nano and easily available parts Arduheater is aimed to be build by anyone with a soldering iron and some patience, no degree in electronics required.
- Multiple independent outputs: Each of the four outputs have independent controls such as offset, min and max output power and of course the three main properties of the PID controller (Kp, Ki and Kd).
 Dew point is that dreadful threshold at which water condensation starts to happen on the lenses/equipment.
 A proportional–integral–derivative controller (PID controller) is a control loop feedback mechanism (controller) commonly used in industrial control systems.
Here are some shots of the bench prototype using a power resistor as the heating element and it's serial configuration interface:
The "field" prototype on it's box:
The heating strips (more build info will be provided further ahead):
And of course all of this would not be possible without the usage of the force. ;-)
Edited by jbrazio, 03 August 2017 - 10:07 AM.