Over the last couple weeks I’ve been playing around with my newly designed Cold brew controller, and I have to say … I did a pretty good job with the initial design! Though, I’ve already been working on a revision to fix some minor issues that I had not foreseen (mostly due to with the intricacies of the ESP32 board).

Temperature Control fully programmed and tested!

So after some tweaking (not twerking), I can repeatedly control and measure the valve temperature from about 10°C less than ambient to about 20°C more than ambient. In my case since it’s currently a sweaty 30°C in the house, I can go from 20°C to 50°C as you can see on my nifty thermal Graph!

The little bumpy part on the left side is actually because the peltier plate was not perfectly touching the valve. I’m modifying the CAD file to add a little more pressure on this spot and carefully apply the thermal paste. This along with a few other minor tweaks on the CAD will be added to the next revision.

I’m trying to see if I can increase these limits (but I don’t want to compromise on formfactor or size). I’ve already tried increasing the voltage I actually added a 6 volt regulator and increased the peltier plate voltage to 10v but it kept itself at a cool 2.8v … so it looks like you can’t over volt this thing … This actually made it less efficient as it couldn’t dissipate the energy fast enough.

The next step that I will try is to increase the heat sink and fan by just a little. just going from the 7.5mm to 12.5mm decreases the thermal resistance from 19.7°C/W to 11.7°C/W and and increase in fan size from 30mm to 35mm increases my flow from 4.6CFM to 7CFM … so I think this will make the biggest difference with minimal size change.

The nice thing is, I already did most of the work upfront. I designed the temperature controller using Circuit Simulator and the results were pretty awesome. I created a short video below to show exactly what this control is doing. (techno garble: with my PWM control, basically digital on-off switching to fake a lower voltage, The in-line inductors and capacitors to ground, make the peltier plate see only a smoothed output).

The neat part is that If I don’t smooth it out, it’ll still work. But over time, it will probably kill my TEC (peltier plate).


So, now I have Temperature control & Servo control (from my last post) about 90% complete … I say 90% since there are a few small things that I want to try to improve. But they are functional … and nowadays, companies always release their products at 90% (sometime less). This I why I love open source. It’s one of the main benefits of having open source designs. Because they are “open” they will get better over time. Often improved by the community. Improvements will be made, and upgrades will come. Many closed source products don’t have this luxury.

I will be on holidays for the next 3 weeks, so I probably won’t be blogging during this time. But if you follow my social media, I’ll try to post a few cool pictures of my travels. So hopefully this tides you over during my absence. Otherwise, you can look forward to a functional prototype of this beefed up coffee maker control system sometime in July. My taste buds are already salivating just thinking of how delicious this cold brew is going to be!

Happy holidays

-DropBOB Designs