lis3dh_ad example broken

[jerryneedell]

There are a few problem with the lis3dh_adc example.
I get the same results on a CPX and CPB

The I2C initialization needs to be updated:
I changed it to use the same init as in the other examples:

# Hardware I2C setup. Use the CircuitPlayground built-in accelerometer if available;
# otherwise check I2C pins.
if hasattr(board, 'ACCELEROMETER_SCL'):
    i2c = busio.I2C(board.ACCELEROMETER_SCL, board.ACCELEROMETER_SDA)
    int1 = digitalio.DigitalInOut(board.ACCELEROMETER_INTERRUPT)
    lis3dh = adafruit_lis3dh.LIS3DH_I2C(i2c, address=0x19, int1=int1)
else:
    i2c = busio.I2C(board.SCL, board.SDA)
    int1 = digitalio.DigitalInOut(board.D6)  # Set to correct pin for interrupt!
    lis3dh = adafruit_lis3dh.LIS3DH_I2C(i2c, int1=int1)

and it seems happy, but then I get

Press any key to enter the REPL. Use CTRL-D to reload.
Adafruit CircuitPython 5.0.0-alpha.0-287-g7cbae3d20 on 2019-08-28; Adafruit CircuitPlayground Express with samd21g18
>>> 
>>> import lis3dh_adc
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "lis3dh_adc.py", line 39, in <module>
  File "adafruit_lis3dh.py", line 206, in read_adc_raw
RuntimeError: buffer size must match format
>>> 

the error appears to be here
https://github.com/adafruit/Adafruit_CircuitPython_LIS3DH/blob/master/adafruit_lis3dh.py#L206

[ladyada]

yeah we are much pickier now about the unpack format matching the size of the buffer. wanna try fixing? you just need to slice the array to the right size

[jerryneedell]

sure -- I'll give it a try

[jerryneedell]

OK -- I have it working now -- just cleaning up the example - will have PR later tonight or more likely tomorrow. All the boards with on-board LIS3DHs have the ADC inputs tied to Vdd the example is not very interesting ;-) -- I'll add some notes to the example that it is really only useful on the breakout.

[ladyada]

yeah - best not to have them floating if unused, the ADCs are kinda not great :)