Writing your own Micropython library

[roaldarbol]

Hi Brian,
I figured you would possibly be the right person to ask about this. I have this optic flow sensor, ADNS-3080, that I can't find a Micropython library for. I know there are Arduino libraries out there, and that it uses SPI, but that's about it. I have no idea how to go about writing a library myself, but I figured you might know how to. ;-) (but now worries if not). I was thinking there might be a way using the SPI class from machine, but that's where my brain stops. (There's talk of 0x42 which I don't really know about).
So I was wondering if you have some suggestions on where to start, if it's worth the time, or some suggested materials.
Thanks!

[BrianPugh]

So first step: ask ChatGPT 😄. It responds with:

import time
from machine import Pin, SPI

class ADNS3080:
    def __init__(self, spi, cs_pin):
        self.spi = spi
        self.cs = Pin(cs_pin, Pin.OUT)
        self.cs.on()
        self.reset()
        
    def reset(self):
        self.cs.off()
        self.spi.write(b"\x3A")
        self.cs.on()
        time.sleep_ms(50)
        
    def read_register(self, addr):
        self.cs.off()
        self.spi.write(bytes([addr | 0x80]))
        value = self.spi.read(1)
        self.cs.on()
        return value[0]
    
    def write_register(self, addr, value):
        self.cs.off()
        self.spi.write(bytes([addr]))
        self.spi.write(bytes([value]))
        self.cs.on()
    
    def read_motion(self):
        self.write_register(0x02, 0x01) # take image
        while not (self.read_register(0x03) & 0x80): # wait for motion
            time.sleep_us(100)
        dx = self.read_register(0x04)
        dy = self.read_register(0x05)
        self.write_register(0x02, 0x00) # stop motion
        return (dx, dy)

# set up SPI interface
spi = SPI(1, baudrate=5000000, polarity=0, phase=0)
cs_pin = 0 # change to the appropriate pin for your setup
adns = ADNS3080(spi, cs_pin)

while True:
    dx, dy = adns.read_motion()
    print("dx = ", dx, "dy = ", dy)
    time.sleep(0.1)

Some corrections that I think need to be made to ChatGPT's (above) code:

• According to the datasheet, I think all of the specified registers are off by one:
  • Motion register should be 0x02, not 0x03
  • According to the datasheet, the address for Delta_X is 0x03, not 0x04.
  • According to the datasheet, the address for Delta_Y is 0x04, not 0x05.

It's probably wrong in several other ways, but its a pretty good starting point. I would start from the above code, and sort of compare it against an existing repo as well as the datasheet.

Side note: For my classes that take in an spi object, like the Max6675 driver I wrote, I like to set the baudrate before each command, then restore it after. This is so that a bunch of different devices can share the same SPI bus, even if they don't all operate at the same speed. The baudrate restore code is a bit jank since it's not explicitly exposed by micropython; it's also unnecessary if all device classes set their own desired baudrate.

[BrianPugh]

As for testing the code, probably the quickest way would be to run belay run <PORT> my_driver.py

[roaldarbol]

Dude, that's amazing - thanks a ton! I'll give it a shot and report back. ChatGPT is a f*ing gamechanger. :P