LED bright red/resistors req? (12-Key Cap Touch sensor MPR121, adafru.it/1982)

(Sorry if it's in the wrong subforum, I wasn't sure where to put it.)

I've got two hardware questions related to the Adafruit 12-Key Cap touch sensor breakout board.

1) I'm experimenting with the thresholds and noticed that sometimes the LED doesn't just light up a bit, it stays bright red - probably forever, I usually disconnect the whole setup once this happens. AFAIK, nothing I do in programming should affect the LED, that's the internal basic functioning of the device.

2) May be related, though I don't think so. In some of the descriptions I've read (usually talking generally about I2C or the MPR121), a need for pull-up resistors is mentioned. The Adafruit instructions I've seen don't say anything, but since I'm not using an arduino on the othe end (it's a Teensy 3.2), I'm not sure if they would be required or not. I'm assuming that if they're necessary, they're already included in the breakout board, but I want to make sure I'm not doing something wrong. (It does work, after all. Just not very reliable, but that may well be my programming or even soldering.)

Maybe there's a tutorial that'll explain this stuff - if so, please point me towards it. I'm (obviously, I guess) new at this.

AFAIK, nothing I do in programming should affect the LED, that's the internal basic functioning of the device.

That's not completely correct. If you connect the IRQ line to p.e. D2 and your program sets that pint as an output and LOW the red LED will be lighted constantly.

In some of the descriptions I've read (usually talking generally about I2C or the MPR121), a need for pull-up resistors is mentioned. The Adafruit instructions I've seen don't say anything, but since I'm not using an arduino on the othe end (it's a Teensy 3.2), I'm not sure if they would be required or not.

The pullups are on board, included in the level converter. You do need pullups for the I2C bus, exactly once per bus.

pylon: That's not completely correct. If you connect the IRQ line to p.e. D2 and your program sets that pint as an output and LOW the red LED will be lighted constantly.

Hm. That shouldn't be the issue, as the IRQ isn't connected to anything, the light only occassionally stays full red, so I assume it's a misreading of the sensor chip. Maybe my soldering, or the next part:

The pullups are on board, included in the level converter. You do need pullups for the I2C bus, exactly once per bus.

I see. I don't have that (yet) - I wasn't sure if they're needed, and it seems to work as well without, but probably not really just as well.

Thanks.

I don't have that (yet) - I wasn't sure if they're needed, and it seems to work as well without, but probably not really just as well.

Did you read what I wrote? The pullups are on the board as part of the level converter. So you don't need additional pullups as you have them already. But to your question if you need them: yes you need them but in your setup they are on the breakout board.

pylon: Did you read what I wrote? The pullups are on the board as part of the level converter. So you don't need additional pullups as you have them already. But to your question if you need them: yes you need them but in your setup they are on the breakout board.

D'oh, now I get it. Sorry, I misread what you wrote - not sure what I was thinking...