Nipple drinker for rabbit with heater

Anyone who keeps rabbits, quickly discovers, that water bowls are not the solution. The water gets dirty really quickly. (Sometimes it takes only few seconds. 😁) Nipple drinker is a solution. However, it has one problem, it freezes easily in winter. That's why decided to make a heating. 

System consist of 3 main part. 

- Main unit

- Heated nipple drinker

- Air thermometer with radiation shield

 

Air thermometer with radiation shield

One of the requirements, was energy saving. The heating should only be switched on, if the temperature id low enough. Air thermometer is small board witch LDOs, CAN transceiver, STM32F302 and temperature sensor SI7051. Of course, there is a status LED next to RJ45 connector. I didn't draw the radiation shield, I downloaded it and printed it out. I just drew new sensor holder, to fit RJ45 connector with the board. 

During testing I found, that using LDO was a bad idea. LDO heating up the board and this resulted in wrong temperature. I have to add small switch, which connect air thermometer to power supply every 2 minutes only for 2,5 seconds. After this modification temperature was correct. 

Heated nipple drinker

Drinker is made from IKEA food box. There is a heating element with floating switch and thermometer at the bottom. There is, of course, electronic board at the top of box. heating element is made from aluminum heatsink to which is attached aluminum PCB with SMD resistor and reed switch. The board is covered with epoxy to ensure waterproofness. On heater element is attached with screws floater with magnet. If the water level drops, the floater with magnet approaches the reed switch and heating is turned off. 

Heater element is attached to the holder together with thermometer.

 Thermometer is simple thermistor, but board is ready for 3 types of temperature sensor: analog thermistor, I2C, and 1-wire senor (maybe there will be some upgrade in the future). Board has STM32F302 microcontroller and also uses CAN interface. Each board has a header to set the CAN ID with jumpers. 

Main unit

Main unit is plastic box with 24V power source, IO RJ45 connectors, main board, display and some relays for disconnecting drinkers. I used the old sensor board again as the main board. 

I use CAN for communication between main unit, heaters and air thermometer. If air temperature is fall below 0.4°C relay connect drinker to 24V and starts heating them to 5°C (with hysteresis +-1°C). If air temperature rise over 1°C, relay is turned off and display show message "VYHRIEVANIE VYPNUTÉ" (heating off). During heating, display shows the temperatures of individual drinker. If the drinker is currently heating, a big dot will appear on the display. Drinkers send temperature over CAN every 2 seconds. If some drinker does not send message within 30 seconds, display show "ODPOJENE" (disconnected). 

I also made a simple RJ45 HUB that connects the RJ45 connectors together. 

GitHub