Hi
I'm using the touch sensor capacity of the teensy LC and also plan to use an adapted version of fasttouchRead for extra pins.
I have some questions about pulling the touchpads to ground and a ground pad to ground. All sensors have a plastic foil over them, no direct bare touch. Teensy is embedded in a plastic enclosure.
The system is connected by USB keyboard emulation and USB cable to a computer, which can be a battery powered laptop.
A) FastTouchRead uses :
pinMode(pin, OUTPUT_OPENDRAIN);
digitalWrite(pin, LOW);
--> I suppose that this gives a short peak current which is way above 5mA. Given the low capacity of the pads this doesn't seems to given problems. Works without resistor and I also tested it with a 100 Ohm resistor in series directly on the Teensy.
B) When using touchRead() I use :
pinMode(pin, INPUT_PULLDOWN);
delayMicroseconds(5); // Test gave about 5T= 3µsec for not touched sensor and about double for a touched one (2T is about 13% V)
Slower, but still very fast for a HMI device. (I want the not sensing pad to be pulled to ground instead of floating.)
C) I have also a ground "pad/surface" connected directly to ground.
My questions :
1) Is it safe -for the Teensy- to keep using the output open drain method without a resistor in series to limit the peak current? If not any suggestion about the size, 660Ohm seems a bit over secure?
2) after the initial pull down, which is safest : A) or B) and would adding a small resistor in series give significant extra protection?
3) Should I add a resistor in C) aka between the ground pad/surface and the Teensy ground pin?
I'm using the touch sensor capacity of the teensy LC and also plan to use an adapted version of fasttouchRead for extra pins.
I have some questions about pulling the touchpads to ground and a ground pad to ground. All sensors have a plastic foil over them, no direct bare touch. Teensy is embedded in a plastic enclosure.
The system is connected by USB keyboard emulation and USB cable to a computer, which can be a battery powered laptop.
A) FastTouchRead uses :
pinMode(pin, OUTPUT_OPENDRAIN);
digitalWrite(pin, LOW);
--> I suppose that this gives a short peak current which is way above 5mA. Given the low capacity of the pads this doesn't seems to given problems. Works without resistor and I also tested it with a 100 Ohm resistor in series directly on the Teensy.
B) When using touchRead() I use :
pinMode(pin, INPUT_PULLDOWN);
delayMicroseconds(5); // Test gave about 5T= 3µsec for not touched sensor and about double for a touched one (2T is about 13% V)
Slower, but still very fast for a HMI device. (I want the not sensing pad to be pulled to ground instead of floating.)
C) I have also a ground "pad/surface" connected directly to ground.
My questions :
1) Is it safe -for the Teensy- to keep using the output open drain method without a resistor in series to limit the peak current? If not any suggestion about the size, 660Ohm seems a bit over secure?
2) after the initial pull down, which is safest : A) or B) and would adding a small resistor in series give significant extra protection?
3) Should I add a resistor in C) aka between the ground pad/surface and the Teensy ground pin?