Capacitive touch sensor without microcontroller: how to change a 'active low' analog signal to 'active high'?


Hi all,

I’m currently working in a soft circuits project that involves a capacitive touch sensor, LED sequins and conductive yarns + thread - and I read that it was possible to use these without a microcontroller like adafruit’s Gemma or Flora.

The basic idea is that when you touch the conductive material (input for the sensor), the LED sequin (output) would turn on.

the output of the touch sensor I’m using [] gives an active low signal when it’s “on”, so when I’m touching the conductive material (that I’m using as the switch), the output signal is "low’, which turns the LED sequin off.

Is there a way to turn this “active low” into an “active high” signal without using a microcontroller?

some help would be hugely appreciated!!


ping @jennablz - check this


Hi @celine So, it sounds like you need to invert a digital signal. In digital logic this is also called a NOT gate. Luckily this is pretty straight-forward using transistor(s) and resistor(s).

For a quick review, check out this site, specifically the section on the “NOT” gate …

We have plenty of transistors that would work for this in the ATS shop in the basement of 112 Maclean. I’d try out a PN2222A transistor and a few resistors to start.

Check out this link and this link for more ideas.


Thanks so much for your help Chris! I just dropped by the basement but couldn’t find the transistors- are they in a certain room?


Check in the EK lab B1-07 – there should be someone in the office.


hey chris - so I tried putting in the pn2222a transistor with a 10k resistor coming out of the output pin thinking it would convert the low reading to high, but it didn’t work. Can you see if my circuiting makes sense?


Is your led in backwards?


the working circuit!! thanks so much chris!