I2C sensor with WiPy2

  • Hi!
    I'm trying to read a VL6180x distance sensor with my WiPy2.
    The WiPy detects the sensor and can read stuff from it, but the results doesn't really make sense.
    According to the datasheet, register 0 should contain a model ID = 0xB4. The first time I read it I get the correct value, but if I keep reading it after that I get random values. If I reboot the sensor, I can read the correct value again one time. The same thing goes for all other registers I've tried to read.
    The code I use to read:

    from machine import I2C
    i2c = I2C(0, I2C.MASTER)
    i2c.readfrom_mem(0x29, 0, 1)

    The sensor is on a breakout board with a voltage regulator, and there's nothing wrong with it, because if I connect it to an Arduino and do the same thing, it works perfectly. I've tried both to have the sensor connected directly to the WiPy, running it on 3.3V, and via a levelshifter, running it on 5V.
    I have also tried different baudrates, but with no change.
    What am I doing wrong?

  • @iotmaker Hello , can u tell me please what is maximum distance range?

  • Great! Now I'm starting to understand this a bit!
    I can read and write stuff using @robert-hh's suggestions, and the sensor seem to output correct data. Now I just have to modify my library with new read/write methods.

    Thanks a lot for the help!

  • @SesamProductions I'm afraid I don't have any more information on that library. But smbus is just the I2C library for whatever hardware platform it was written for. You should be able to substitute pycom's I2C functions readfrom_mem and writeto_mem for b.read_byte_data and b.write_byte_data, respectively. But note, I've never actually tried to access 16-bit addresses using pycom's I2C functions. If they don't work, please do submit a bug report, and in that case, you should be able to accomplish the same thing using the writeto and readfrom method that @robert-hh suggested earlier.

  • @SesamProductions For writing to a register, just append the data for the register to the address in a single write.
    About @iotmaker's comment. The VL53L0X device he uses requires just an 1 byte address just like the memory devices.

  • Thanks for the suggestions!

    YES! That is working! Thank you! I can now read data from registers in a controller way.
    Unfortunately I'm now very confused about this. If the writeto function is used to tell the device what register I want to read, how do I write things to the registers? For instance to tell the device I want it to start measuring range.

    To me it looks like you're doing the exakt same thing I'm doing, and according to the short datasheet I found for your sensor, it should work similar to mine.
    So why yours is working and mine is not is definitely beyond me.

    When I've tried the sensor on the Arduino I've used the Adafruit library your linked code seem to be a python port of. I had myself not found that python version, so what I've done is my own python port of the Adafruit Arduino library. The problem is that in order to deal with all the complexities of the sensor and initialize it, I need to be able to read and write to registers, which is the part that isn't working.
    The python-version you're linking to is using a module called smbus to deal with everything I'm having problems with. Where do I get that from? I didn't find any links for that on the github page, and import smbus is not working on my WiPy. Where you using it on a WiPy, or some other Pycom device?
    I had not heard about smbus before and a quick google for it seem to indicate it's a different, but fairly similar, protocol than i2c. Was there a reason for using smbus instead of the builtin i2c?

  • I have it working like this

    sensor= 0x29#I2C Address
    print("Revision ID ")
    print("Device ID ")
    print("Pre Range config Period")
    print("Final  Period")
    #To read first check the status
    #if val is equal to 64 then it read the distance 
    #read the value
     datasensor=i2c.readfrom_mem(sensor,0x14,12)#Read sensor data
        distance=datasensor[10]*256+datasensor[11]#combine integers

    I have it working on the VL53L0X hope it helps

  • @SesamProductions From the spec, I assume that the sequence should be:

    i2c.writeto(0x29, b'\x00\x00')
    i2c.readfrom(0x29, 1)

    The address for a read is a two byte value.

  • @SesamProductions said in I2C sensor with WiPy2:


    Yes, this is a fairly complex device that requires a lot of initialization (although I would think reading back the model ID could be done without init, but who knows). We used this driver: https://github.com/luciengaitskell/python-adafruit-vl6180x/blob/master/i2c/vl6180x.py

    We've since moved on from using this sensor (it's a very interesting device, but it did not work well in our particular application), but I had no problem communicating with it. In fact, the only problems I've ever had with I2C on any pycom device was with the lack of clock stretching support on the software-based I2C (and now that hardware-based I2C is supported, that's no longer a problem).

  • @SesamProductions
    If you look at C library
    you must do much more work to work with this sensor

  • @robert-hh Thanks for that insight, that turned out to be exactly what's happening! And after doing a closer inspection in the datasheet I found this sentence:
    "After the first data byte has been transferred, the index is automatically incremented by 1."
    Now on to learning how to use that feature.

    Regarding i2c.readfrom_mem()
    I might have missunderstood how it works, but how can I read a specific device register without it?
    The machine-module documentation says in connection to readfrom_mem:
    "Some I2C devices act as a memory device (or set of registers)", and I interpreted that to mean that it's the function to use when targeting a specific register.
    Is that instead referring to devices with some other register functionality?

    I just now tried doing i2c.writeto(0x29, 0), which returned 1, and then i2c.readfrom(0x29, 1), but it didn't return any useful values, mostly zeroes but sometimes other values. If I understood your suggestion correct that should have given me the 'b4' I want.

  • @SesamProductions So it looks as if instead just the first byte all registers of the first group are transferred. I wonder why you use i2c.readfrom_mem(), since this is not a memory device. I would expect that you first have to send the register address with i2c.writeto() and then read back the intended number of bytes with i2c.readfrom().

  • @livius Thanks for the tip, I had not noticed that there were new firmwares out. Unfortunately it didn't help.
    Do I have to make any changes to my code with this?

    I have now tried this with two different WIPy2 borads with the most recent firmware. I have also tried with two different identical sensor boards, as well as three other i2c-devices, none gives any sensible output to the WiPy, but all work well with Arduinos.

    I did notice one thing that could possibly be relevant, although I have no idea how.
    This is a readout made just after reboot:

    >>> os.uname()
    (sysname='WiPy', nodename='WiPy', release='1.7.6.b1', version='v1.8.6-703-g5e80328a on 2017-07-05', machine='WiPy with ESP32')
    >>> from machine import I2C
    >>> i = I2C(0, I2C.MASTER)
    >>> i.scan()
    [41, 57, 87, 104]
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)
    >>> i.readfrom_mem(0x29, 0, 1)

    The first response, b'\xb4', is the correct one, but should not change. The commands are sent about one second apart.
    The interesting thing is that the response sequence is always identical, with both sensors and both boards, it's always:
    and so on.

    I have absolutely no idea what's wrong or what to try next and will appreciate any help!

  • @SesamProductions
    try upgrade to recent firmware because now i2c is hardware implementation not software as was previously

  • (sysname='WiPy', nodename='WiPy', release='1.7.2.b1', version='v1.8.6-650-g9bacbbd4 on 2017-06-09', machine='WiPy with ESP32')

  • @SesamProductions
    which firmware


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