Electronic – Capacitive sensor as drop-in replacement for mechanical button


I have a device X (talking toy), which has a jack of two wires for an external button. That is, I can short the two wires and device X accepts it as a press of a button.

Now, I want to use device X for it's function, but replace mechanical button with a capacitive sensor. I have options, but lets assume it's a cheap TTP223 module, with GND, VCC and IO pins, operating at 2 to 5.5 V. When I checked with 3.3 V, it gave about 2.64 V logical "1" on IO pin when touched. At 5 V, gives 3.8 V for "1".

The device X's jack gives about 5 V on it's button jack and even 800 Ohm resistor seems to trigger it. About 210 uA current flows through the button when shorted.

As I see it, the sensor will have it's own power supply (voltage is part of the question).

The main question is, what is the best way to convert logical "1" into "press of the button"? Preferably, without the need for multiple voltage levels. What could be good "relay" for the task?

Best Answer


simulate this circuit – Schematic created using CircuitLab

Figure 1. An NPN transistor will invert the logic signal from the touch sensor to the toy.

With 210 µA on a short it implies a pull-up of about 12 kΩ assuming a 3 V supply. An NPN transistor will be able to pull that low.