The Temperature Candle is a relatively simple design which essentially boils down to a microcontroller, a temperature sensor and an RGB (Red, Green, Blue) LED on a 1.5" diameter PCB - the same size as a standard votive candle. The microcontroller flickers the LED like a candle at a color determined by the ambient temperature. The color gives an indication of the room temperature in reference to the recommended sleep time temperature for babies to reduce the risk of SIDS (Sudden Infant Death Syndrome).
The actual temperature value, in degrees C, can be reported by pressing a reset button on the PCB or cycling power to the device. Upon power up or reset, the temperature is reported by blinking the LED blue for each ten degree increment followed by blinking the LED red for each single degree increment. For example, if the ambient temperature was 23 degrees C, the LED would blink blue twice and then blink red 3 times upon power up or reset. After this, the LED would go into candle mode and flicker the color orange, as dictate by the table below.
|< 16 DegC||Blue||Too Cold|
|> 16 DegC && < 20 DegC||Yellow/White||Just Right|
|> 20 DegC && < 24 DegC||Orange||Warm|
|> 24 DegC||Red||Too Warm|
The Temperature Candle was designed to be relatively cheap and easy to solder by using only through hole components that are readily available from common distributors, and also includes a jack for connection to a Microchip Pickit 3 programmer / debugger to allow for easy code modification and download.
Temperature Candle Design Documentation (PDF)
Schematic Image Ver 1.1
PCB Image Ver 1.1
PCB Fabrication Files (Zip)
Schematic and PCB Eage Design Files (Zip)
Bill of Materials (Open Office Calc file)
Software - Uses Free MPLAB IDE and HI-TECH Compiler (Zip)