I am a plant scientist that studies what happens to plants at different temperatures. I am doing some experiments where I need to measure the plants at 25 and 35 degrees C (77 and 95 degrees F) but don't have continual access to a temperature-controlled chamber. Major props go to James Bruce's project on makeuseof.com. This project builds on his work by showing how you can make a nice box for the temperature control part of it, add an LCD screen to report the temperature and use a hair dryer as a cheap way to heat the thing. And....since I am a scientist, I will even throw a chart in at the end so you can see how well the temperature control works! Yeah data!
Step 1: Make Your Box
I needed a moderately large box to fit my measurement equipment in, but you could do any size. I used 8 cm thick styrene sheets used for housing insulation from the local hardware store. I cut them to size using a razor blade to cut as far as I could from each side, then I broke through the remaining material by pressing it against a spare piece. I glued it all together using an all-purpose glue that works with styrene (In Germany the store recommended "UHU Montage-Kleber" and it worked well for me). I used several tie down straps as a make-shift strap clamp to hold it all square while it dried. After it dried I used more of the glue in the joints as a caulk to make it look a little nicer
Step 2: Make Your Controller and Prepare the Hairdryer
To make the controller I used an arduino after the work of James Bruce. My temperature sensor (LM35 Temperature sensor) required a little different wiring and I opted to use a high voltage relay (JQC-3F(T73)) instead of the remote control. You can see I placed it in a plastic insulator to keep curious fingers away. I also made sure that everything was secured to prevent things from moving into a position where they might be dangerous. The bottom plate and switch were added by Waldemar at our University's tech services. Looks great! I also added an LCD screen to report the temperatures. I got all the parts from a handy arduino kit that allnet makes (ArdDevKIT1 ATMega328).
For the hair dryer you can use pretty much any one. I used one with variable fan and temperature settings so that I could play with them to get the best temperature control for a given temperature. I used some metal tape for duct work to join it to some PVC tubing. It is good to confirm that the size of the hair dryer will give you a good fit to the tubing you have availible to you.
Step 3: The Code
Here is the code for the Arduino
Step 4: Performance Check
Now time to see how it works. I tested a range of temperatures from 12-50 degrees C. Some temperatures work better than others, but you could optimize it further by putting baffles on the hair dryer or experimenting with insertion depth. I just needed 35 and possibly 50 degrees C so this is perfect for me.