Flex - `flex-print-slider` doesn't work after power cycles.

leonidbelyaev

With the built-in Arduino sketch flex-print-slider, I no longer get serial output after a few power cycles. I make sure that I do not touch the sensor for several seconds while it is powering on.

I can restore functionality of flex-print-slider by flashing a different program, say, flex-print-raw, and then, flashing flex-print-slider again.

I am using a Teensy 4.0.

Does this have something to do with mode setting? What's going on?

giuliomoro

Nothing on Trill is persistent, so after each power cycle it should work just like after the previous power cycle. If Trill is powered from a different power supply than the one powering the Teensy, then make sure that one is also restarted.

What do you mean by "lack of serial output" ? If that's nothing at all gets printed to the serial port while the program is running, then I suspect it may not have anything to do with Trill, but something Teensy-related. Try placing a

Serial.println("setup");

at the top of setup() and a

Serial.println("loop");

at the top of loop(). Do those get printed? Does loop get printed only once or several times?

leonidbelyaev

I did as you asked, and those get printed both when the Trill Flex outputs touches, and when it does not.

I'm trying now with a different microcontroller (Feather 32u4) and can replicate the behavior.

giuliomoro

And is Trill power cycled at the same time as the microcontroller?

leonidbelyaev

The Trill is powered off of the 3.3v supply of my MCU board, so yes.

It may be relevant that I may get some serial output to start off with (after which point touches do not produce more output):

Begin trill sensor init.
0 0 0 0 0 0 0 0 0 0
0 0

i.e., when I first power on, I might get 5 "touches" of size and position 0, which is then finished. I am not touching the sensor, it's just laying flat on my desk here.

giuliomoro

try adding

delay(10);
trillSensor.setPrescaler(4);
delay(10);
trillSensor.updateBaseline();

at the bottom of your setup() ?

leonidbelyaev

Thank you! That fixed it. I now get serial output of touches, on a touch, after every power cycle.
Perhaps it might be worth updating the official example with this.

giuliomoro

done, thanks.

For clarity, what happened was that your Trill Flex was initialised to the correct prescaler value when running flex-print-raw and that value would persist if, without power cycling it, you ran the flex-print-slider example. If after power cycling you ran flex-print-slider, then the default prescaler value would have been used, which is unsuitable for the device when the sensor slider is connected.