I have a TTP223 touch sensor, a BC347 Npn transistor and 10Kohm resistor. I want to make a touch button as substitution for my pwr physical button on the case of my pc.
On the motherboard I have 2 pin, PWR+ (5V) and PWR- (GND) and, if I short them, the Pc turn on: That’s the logic I have to replicate. Now, The problem is that the ttp223, when touched, apply a voltage (about 4.5V) to his output pin (I/O and GND). I don’t want this voltage because I only need to short the pin on the motherboard and not to apply any other voltage to them.
So, I used a transistor controlled by the touch sensor’s I/O pin on the base, the PWR+ connected to the collector and the PWR- to the emitter.. BUT IT DOESNT WORK .. whyyyy.. the logic is: the touch sensor apply a voltage to gate and source and this should close the interrupt between source and drain that is PWR- and PWR+ . So I don’t understand..
I measured with a tester and the voltage between source and drain is 5V (like it should be) when not touched and it drops to 4.8 when touched, BUT this is not enough to trigger the motherboard and turn on the PC. I think it should go really close to 0V.
So what I’m not considering? thanks for the help
Here the schematic
So, what i need is: on touch --> Voltage between base and emitter --> short between PWR+ and PWR-
I also noticed that i dont need to short the PWR+ with PWR- only. It works with every GND PIN even one of another ATX power supply. So probably, in order to work, it just need to pull to 0V the PWR+ (from 5V) I also thought about relay but I prefer a transistor which makes no noise and its significantly smaller.. Someone also said to me that one of my problem is that, between base and emitter, can be 0,7V max.. and I apply 4,3-4,5V .. could that be the reason why it doesnt work? how can i reduce the voltage with a resistor? (how many ohms?) I want to link another question on this forum which works for him.. and it s almost my same situation -->
[Similar Question] : https://electronics.stackexchange.com/questions/334362/capacitive-sensor-as-drop-in-replacement-for-mechanical-button