I am using a CTHSCIC06 capacitive touch button and have connected as per the datasheet (the motor side of the circuit is not needed) however I am still having trouble around the pnp side of the circuit. I am using the BC557C. The circuit is set up in the following configuration:
The idea with the button is that when the button is pushed the LED will turn on and will give a +5V logic signal to the MCU. When the button is not pushed the led is off and the logic signal is 0V.
I have this soldered onto prototype board and it works fine when the power supply is from the USB connection from the PC to the ardunio however when I connect a power supply with +5V even when the the pnp is suppose to be off, there is still a low to medium glow from the LED within the capacitive push button as if it is on. But from probing the MCU I/P when the low medium glow is present it is 0V going to the MCU. So it seems when the LED should be off, it is still on but not on fully.
Originally I thought maybe voltage ripple but the ripple on the power supply is no more that 15mV. I also thought maybe the pull up resistor isn't pulling the line high but this works when powered from from the PC usb.
If you guys have any suggestions or advice that would be great.
So I checked the voltage of the MCU O/P pin and found when powered from the USB V=4.8V but when powered from external power supply V=4.1V. Could this be a reason why the line is not going fully high?