Mpr121 filtered data reading wrong?

Hardware Development
1

I have the adafruit mpr121 breakout hooked up to a seed and I wanted to see the raw or filtered data stream from the mpr121 so that I could understand what to set the thresholds to. I’m using the libraries function as such:

uint16_t filtered_data = mpr121.FilteredData(0);
hardware.PrintLine("Filtered Data: %u", filtered_data);

But the debug output is only 1 or 0 depending on if I’ve touched the capacitive pin. This does not seem like the filtered data as that function returns a 10-bit unsigned value. So it seems it should be outputting larger numbers.

Is this to be expected? How can I properly see the filtered data stream? Thanks

2

I haven’t tried MPR121 with Daisy, but I’d suggest reading the source code to see what to expect.

Edit: I’ve looked at the code, and I’ve looked at the mpr121 datasheet, this has got me curious. I have a MPR121 around here somewhere, maybe I can find it.

3

I’ll be curious too! I also noticed that adafruit’s arduino library is quite similar to libDaisy (perhaps even ported) and when they call their filtered data function it returns a stream of differing values corresponding to minor fluctuations in capacitive sensing.

4

According to Amazon, I’ve got 5 MPR121 around here, somewhere. When I find one, I’ll investigate.

AHA - found one!

And, yes, I see the same thing, FilteredData() returns 0 or 1.

5

Thanks for verifying! Any thoughts on how to get more in-depth data? I’m a bit lost in the addresses and bits in the mpr121 driver class.

6

I haven’t figured out WHY, but FilteredData(i) is returning the same value as Touched(), for all values of i.

I suspect register addressing isn’t working (at least on reads), and it’s only reading register 0, which is MPR121_TOUCHSTATUS_L.
This suspicion is supported by the following comment in mpr121.h:

        // this doesn't work for some reason...
        // uint8_t c = ReadRegister8(MPR121_CONFIG2);

I can’t tell if addressing works on writes, so I can’t be certain configuration is working at all. I wish I had a good I2C analyzer (for example - Total Phase Beagle I2C), like I used to have when I was working. Cost $400, but saved a ton of time.

7

Thank you for your analysis. Very helpful to me to know there is an issue with the library/hardware. I wonder how adafruit got it to work. It can’t be the differences between the Seed and an Arduino, I would think, as it all seems to be about the MPR121 registers.

8

I suspect it might be a peculiarity in libDaisy I2CHandle .
It might be interesting to see if it works in DaisyDuino.

Edit: Yes, it works in DaisyDuino, using Adafruit MPR121test.ino. This uses Arduino Wire library for I2C.

9

Well we’ve got the issue cornered now! Its an ironic choice to have to go with a higher-level language to get lower-level features. I’ll open an issue on the repo and hopefully this gets fixed.

edit: here