Some of the major components are illustrated and listed here.1.PCB
. I pay by the square inch to have boards made so I try to keep them small. As such, this one is double-sided and uses plated-through holes. You're welcome to try to make one at home but I really recommend getting one professionally fabricated. I had mine made by BatchPCB, a division of SparkFun. You can buy a board at http://www.batchpcb.com/product_info.php?products_id=44036&check=c260fda1c9d3f5c8cb643726708f6a35
or download the Eagle files at the end of this Instructable and sort it out yourself.2.Picaxe 18X
. This has since been superceded by the Picaxe 18M2, which should be pin-for-pin compatible. (and slightly cheaper)3.Temp Sensor
. The picaxe can natively interface with a DS18B20 digital temperature sensor from Dallas/Maxim, which makes it super easy to write the code. I found this waterproof version on eBay, whick is far more suitable for immersion in an ethanol-water-sugar solution. Depending on what you're actually using you thermostat to control, you may be able to use the bare sensor, which looks like a TO-92 transistor. However the waterproof version should only set you back about $6. Note that the one I bought had the pins swapped, so that pin 1 of the molex plug was actually pin 3 of the sensor! It is possible to carefully remove the pins from the plug body and move them into their correct places, or you could attach the socket to the board the other way around. Whatever you choose to do, CHECK THE PINOUTS OF THE TEMP SENSOR! On the sensor I used, pin 1 [ground] was the bare shield wire, pin 2 [DQ] was white, and pin 3 [VDD] was red. I repeat, please check before you assemble the circuit!4.IC sockets and pin headers
. To raise the LCD module and the the up/down temperature switches off the board, so they poke out of the front panel. I used strips of header and pins, cut to size.5.Resistors
. I used high-brightness LEDs for the indicators, but used very high value resistors to keep the brightness down. If you want brighter LEDs you may need to use lower values for R8 and R9. Rememer that the green LED is driven from 5v from the picaxe, but the red LED gets 12v from the mosfet. Choose your resistors accordingly!