In the Raspberry Pi Lens Heater post, the motivation for heating the RPI camera lens when operating in cold temperatures was given. A prototype version of a heater system was also presented, it has worked very well since early January. The images were significantly sharper when the lens is heated to around 15-20°C. Even well before that, the effect is significant.
Temperatures in January have been rather mild, around 0°C (+/-5°C), but recently we had a day below -15°C and the camera board temp sensor showed only +4°C at the lowest. Still, the star images and other details verified the heating had a good effect.
A friend showed interest in setting up a similar camera with heater, so that provided a chance to improve on the design. Clearly, the original “birds nest” implementation did leave something to be desired. My friend also wanted to accommodate 3 temperature sensors, one for the camera board (“CMOS”), one for camera house (“BODY”) and one for the outside (“OUT”). That meant an even bigger nest or something slightly smarter would be required.
After buying some parts from China via Ebay I came up with the rather obvious idea of eliminating the “nest” by assembling the components on a single board that would attach directly to the GPIO pins of the Raspberry PI. An informal sketch of the design follows:
The overall idea is based on a 4×6 cm prototype PCB board and a 2×13 Pin header soldered together in such a way that the board becomes a suitable add-on to the Raspberry PI. The mini relay for switching the heater on/off is placed on the opposite end of the board relative to the pin header, along with its control circuitry. Between the two there is room for a “bus” for multiple DS18B20 temperature sensors. One is placed on the board, screw connectors are provided for the other sensors off the board. As the DS18B20 sensors are “1wire” devices, they can be identified in software via their unique serial numbers.
The board design thus allows both GPIO relay control + reading of 3 temperature sensors.
This looks like an improvement to me. As designed, the board simply connects to the 28 GPIO pins of the Raspberry PI model B using the 2×13 Pin header. My friend is getting the Model B+ with more GPIO pins, but luckily the common pins of the two RPI models are the same, so the board should fit the B+ just fine.
A couple of quick tests showed that both the relay control and the temperature sensor worked just fine, so the board is fully operational and awaiting the Mark2 camera board heater element to be completed.
After completing the Mark2 heater board, I received some PCB Pin connector kits. They are possibly better alternatives than the screw connectors, since you do not risk getting the polarity wrong once the board has been properly made. Still, I am quite happy with the current Mark2 board!