I´m quite new to Arduino but have had some success building a data-logger. Now I want to build a temperature control chamber to perform entomological experiments inside. Humidity control is not important as the insect chamber inside the temperature control chamber will have separate air circulation. So I will not call it a climate chamber. It should have temperature logging ability and maybe an lcd screen to display set-point temperature and actual chamber temperature. Set-point temperature adjustment button or knob would be really cool.
The chamber inside dimensions should be about 20 x 20 x 12 cm. The the temperature control range should be +5 *C to +40 *C if lower temperature can be achieved then it`s a bonus. +/- 1 *C accuracy over 1 minute and longer period. Ripple could be a bit higher but no more than 3 *C peak-to-peak. Avoiding ripple could be a challenge, as the chamber is small.
I try to keep it simple and low cost. My first idea is to use old computer PSU to provide low voltage DC; an TEC1-12706 thermoelectric element (for low cost and low noise), which should have about 60W of cooling power; an old AMD CPU active copper core aluminium cooler for outside heat exchange; copper heat plate, tubing and aluminium radiators for inside heat exchange; a smaller fan to mix air inside the chamber; plywood and styrofoam as chamber walls and insulation; Arduino UNO as cnotroller; relay module with two 10A relays to switch on and reverse polarity of TEC1-12706; SD card and RTC modules to log temperatures with timestamp; DALLAS DS18B20 sensors for temperature monitoring (one for ambient, and two for chamber); 16x2 LCD screen.
As high power current control electronics seems expensive, I plan just to use the 12V rail on PSU for TEC1-12706 and vary the ON and OFF times of the element by switching the relays. The DALLAS DS18B20 has accuracy of 0.5 *C so I might need to average values of two or more sensors to get a more accurate result. I have 5 of them to use.
I ask for design advice and useful comments. Maybe someone has experience with similar builds or climate chambers?
The ambient temperature is going to be 30 *C maximum so 25 to 30 *C max. temperature differential should be manageable.?
How to solve the temperature set-point input? Button or knob adjustement would be much more convenient than having to hook UNO to my PC in order to adjust it.
Also I have no clue about the temperature control algorithm. The easiest way, I guess, would be to run some sort of if statement to compare set-point temperature and chamber temperature and switch the TEC1-12706 on or off when difference exceeds some value. But my worry is that this creates too much ripple, as heat transfer from the element to the chamber takes time. Also the TEC1-12706 performance could be influenced by ambient temperature as the cooling by the CPU heatsink gets better when ambient temperature is lower. But this is just a theory at the moment and needs to be tested first.
If anybody had thoughts or suggestions then I would appreciate it.