Hi there!
I want to build a musical keyboard with around 300 hundred keys using the touch pins. Obviously, I'm gonna need some multiplexer. I ran some tests on the classic 74HC4067, but the base level (value read when the key is not being pressed) goes up to 3000, and the reading take much longer. Now, I'm gonna guess the touch pins work by sending some voltage to the key (whatever is soldered to the pin) until it's capacitance is full, like measuring the time it takes for a capacitor to charge. The 74HC4067 has an internal resistance of around 250 Ohms in an open channel, which is probably what is slowing down so much the time the key takes to charge. Is this right?
Now, the question is:
a) can we somehow use a higher voltage on the touch pins so that the key charges up faster, despite the resistance?
b) is there any other multiplexer similar to the 74HC4067, but with a lower internal resistance? I found one, but it was too small to solder by hand.
c) can the circuit behind the touch pins be easily replicated?
I want to build a musical keyboard with around 300 hundred keys using the touch pins. Obviously, I'm gonna need some multiplexer. I ran some tests on the classic 74HC4067, but the base level (value read when the key is not being pressed) goes up to 3000, and the reading take much longer. Now, I'm gonna guess the touch pins work by sending some voltage to the key (whatever is soldered to the pin) until it's capacitance is full, like measuring the time it takes for a capacitor to charge. The 74HC4067 has an internal resistance of around 250 Ohms in an open channel, which is probably what is slowing down so much the time the key takes to charge. Is this right?
Now, the question is:
a) can we somehow use a higher voltage on the touch pins so that the key charges up faster, despite the resistance?
b) is there any other multiplexer similar to the 74HC4067, but with a lower internal resistance? I found one, but it was too small to solder by hand.
c) can the circuit behind the touch pins be easily replicated?