These are neat little touch buttons that are easy to add to any project. They usually come in packs of 10 for around 3 bucks shipped! I know that the ESP32 has built-in touch sensing capability, but using these boards makes things more simple and eliminates software configuration errors. The maximum standby current of the touch IC is only 7µA, so not much power is wasted adding this button.

Disable the LED

The output pin on the button goes high and a LED on the back lights up whenever your finger gets within a few mm of the touch surface. Removing the resistor to the LED disables it, reducing the power consumption. Creating a solder bridge across the A and/or B pads changes if the button toggles and if the output is high or low when active. In our case, we are going to leave these bridges open, which will make the button act as a momentary switch.

Cut Traces

The voltage input of the button lines up perfectly with the 3.3v output of the main board. Unfortunately, the signal and ground pins don't, so we will have to make some modifications. Using a hobby knife or other sharp blade, cut the reset trace on the back of the main board and the trace to pin 13 on the front. Inspect the cut with a magnifying glass to make sure there is no residual metal. These holes will now host the signal out and ground pins of the touch board, respectively.

Flush mount the Header

There isn't much spare room in this project, so any space saving tricks comes in handy. It's best to cut the pin header before soldering to reduce how high it protrudes from the touch board. Cutting the header after soldering makes it more difficult to get it flush as the base of the solder cone is very thick and not easy to cut. So, cut the header flush with the touch board and then solder it on. Place the board and header into the main circuit board and cut the other side of the header so it is also flush, then solder it on.

Wire it up

For small and low-power wiring, I like to use 26ga. magnet wire, as it's cheap and easy to work with, though any small wire can be used here. To make connections, the enamel on the wire can be scraped off with a knife or melted off by holding a soldering iron with a solder ball on the tip to the end of the wire. Do this to one side of the wire and then attach it to the ground pad. Measure and cut the wire so that it reaches the ground pin of the touch button. Then repeat the enamel removing process on the other side of the wire. Hold down the the wire with tweezers and solder it onto the touch ground pad. Repeat this process to connect pin 12 to the signal out pin of the button. Clean up any residual solder flux and the button is done!