At last, a DIY programable water bath
Unfortunately, I meant to post more updates about the development of this water bath, but instead I just kept working on it. The good news is that I think it’s pretty much done! At least, it’s done enough for me to start using it in the lab.
Overall, the setup is pretty simple. There is a bucket water heater, a small circulation pump, a digital temperature sensor, a coil of copper pipe for cooling that will eventually be submersed in ice, and an Arduino Micro controlling everything. To control the bucket water heater, I picked up a PowerSwitch Tail 2 to avoid dealing with 120v mains myself (I’m not actually an engineer…).
The Adafruit DIY sous vide guide was an excellent starting point for this project. They give a great deal of information about several of the components I used, so I’ll mostly just refer people to their site. I did end up getting rid of the PID controller, it was more complicated than it needed to be especially with both heating and cooling (with very different properties). Another plus of building this water bath was that I had a sous vide along the way. I made a few steaks, and they were excellent!
I also picked up a little PVC outlet box from the local hardware store for about 20 cents to enclose the controller. I figured with water and electricity, a few preventative measures couldn’t hurt. I used molex plugs to attach all the components making everything easy to transport and swap out parts.
Cooling is an important component for me, as one of my phage induction steps requires reducing the temperature from 42C to 37C relatively quickly. I played around with using Peltier elements to cool the water, but it would have required a large power supply (> 120 watts) and wasn’t much better than the coil alone. For smaller volumes, I’m sure the Peltier would be a great solution, but I have some other ideas for Peltiers in the future.
I’ve posted the code for the controller on GitHub. The values in the code are “tuned” empirically, and actually do matter quite a bit based on the volume of water you’re using. I’m hoping to add some interactive control to the water bath, along with a real-time visual interface. As soon as I figure out how to do it, I’ll upload the circuit diagrams. They are very simple, so I’m sure most of you could figure out how to put it together without a problem.
I’m interested in hearing what other people would do with a programable water bath, especially if it involves microbial evolution experiments! I built this to save time for myself, but I imagine there are many experiments that are now feasible with a cheap programable water bath. I did a few sample runs and graphed the temperatures over time (in milliseconds). I’m very happy with the results.