Capacitive touch sensors
Capacitive touch sensors
Looking at the touch facilities that other microcontrollers provide I was wondering if someone has implemented a capacitive touch sensor (for one or more keys) with the XS1 ports. I know that maybe a small uC could provide many keys via I2C, for a 1 or 2 key solution direct connection would provide a simpler path.
Well ST i think makes 4 pin touch ICs that sense on one pin and give a TTL signal on the other so thats pretty simple. But doing it using a xmos would be pretty cool.
Only problem is that i think you can't turn off internal pull ups on xmos chips. Since the way i would try doing it is drive the touch pad high and low over a big resistor (like 1M) and then count clock ticks how long it takes for it to actually get between 1 and 0. But if the pull up is week enough you could try outputting a 0 on the pin and then quickly switching to input and see how long it takes the pull up to bring it up to logic 1.
Only problem is that i think you can't turn off internal pull ups on xmos chips. Since the way i would try doing it is drive the touch pad high and low over a big resistor (like 1M) and then count clock ticks how long it takes for it to actually get between 1 and 0. But if the pull up is week enough you could try outputting a 0 on the pin and then quickly switching to input and see how long it takes the pull up to bring it up to logic 1.
From what I read in the manual (port specification), pull-ups are optional (via the set_port_pull_up function)....
So we need a bidirectional pin, we have it at zero, then we pull it up for a little while and then switch to high-impedance input.
So we need a bidirectional pin, we have it at zero, then we pull it up for a little while and then switch to high-impedance input.
Yep, it has been done. See: https://github.com/xcore/sc_capacitive_sensingale500 wrote:Looking at the touch facilities that other microcontrollers provide I was wondering if someone has implemented a capacitive touch sensor (for one or more keys) with the XS1 ports. I know that maybe a small uC could provide many keys via I2C, for a 1 or 2 key solution direct connection would provide a simpler path.
This is fantastic !... time to design a new board !