I'm trying to use TTP223 touch buttons touch button.
I placed them (3) on a PCF8574 inputs.
They work fine on the breakout board but don't work on the PCB, because the signal voltage doesn't drop low enough (about 2.5 to 3v instead of ~0). Then it doesn't trigger the I2C controller.
I'm running out of ideas to diagnose this case. Can someone help ?
Here is what I did already.
#1 Isolate from electric, magnetic and electrostatic field
I put the touch button at the end of dupont wires to make sure nothing interferes with the button.
=> No luck
#2 give a power boost
I added a big enough capacitor on the power, next to the button, to make sure anything else doesn't requires too much power.
=> No luck
#3 Checked the program to make sure software is right.
I removed the touch button and played with dupont wires to send LOW or HIGH signal to the I2C controller (PCF8574)
=> Works well
#4 Checked the power
Powered in 5v
#5 remove power noise
I added a tiny capacitor next to the buttons to make sure power is cleaner.