Digital touch sensor with an LM358, analog input seems to looses the signal

Other Hardware General Electronics
1

I'm trying to create a touch sensor using an LM358. The schematic is as follows:

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The Arduino itself is connected to power over USB. The "TOUCH" boxes are floating wires. The idea is that these will be connected to a piece of metal that can be used as a digital touch sensor. I got the design from https://www.instructables.com/Digital-Touch-Sensor-Using-LM358-1/.

I've tried this first connecting the output to a led. This works fine. If I set the POT just right, the led goes on and off depending on whether I touch the wire. However, if I connect it to an analog input of the Arduino Nano Every, it responds for a while, and then stops responding after a few attempts. Then after some time (a minute? a little bit less maybe), it starts responding again. It almost gives the impression the Arduino gets overloaded and protects itself, but I couldn't really find anything Google-ing for this.

I'm pretty new to electronics so I may just be missing some components. But I really don't know which ones. I'd be grateful for some help.

2

Unfortunately, most Instructables are written by people who have no idea what they are doing, and since the web site owners don't allow critical comments, beginners have no way of distinguishing the 95% that are crap from the 5% that are actually useful.

That circuit will work only if your body happens to pick up enough electrical signals from the environment, and unreliably at that.

A bare wire attached to an analog input will work just as well, or as unreliably.

For a reliable touch sensor, look for capacitive sensing modules or FSR sensors. Adafruit has some, and they work. Example

3

Thank you. I was hoping I could get this to work, but I would really like it if the circuit is stable. I've settled on the MPR121. I like the bare circuit and it has 12 inputs and an I2C interface.

4

Place a 10K resistor from the touch sensor to the OpAmp input to prevent it from faulting because of to large of voltage.