PRESTO with IO Expander - PWM and ADC advice

Support
1

I’ve just added an Breakout IO Expander to the Qw/ST I2C connection of my PRESTO to provide extra Input and output… (Just change the setup line in the examples to

PINS_PRESTO = {“sda”: 40, “scl”: 41}

get the board running on a PRESTO)

I can read the value of a button and turn an LED ON/ OFF.

I can read a potentiometer but the example program IO_adc.py example only provides a voltage - a FP value between 0 and 3.3v… Is it possible to get a integer in the normal MicroPython range of 0 to 65535?

Could someone please show me how to set up basic PWM to control the full brightness range of an LED.on a pin on the IO Expander?

Is there a document which lists all the MicroPython instructions for this board?

2

I’ve sorted out the PWM to drive LED brightness. ADC so duty-cycle range
is 0 - 16383

# IO_PWM
# Tony Goodhew 15th Feb 2025
import time
from pimoroni_i2c import PimoroniI2C
from breakout_ioexpander import BreakoutIOExpander

PINS_BREAKOUT_GARDEN = {"sda": 4, "scl": 5}
PINS_PICO_EXPLORER = {"sda": 20, "scl": 21}
PINS_PRESTO  = {"sda": 40, "scl": 41}

ioe_servo_pin = 6

# Settings to produce a 50Hz output from the 24MHz clock.
# 24,000,000 Hz / 8 = 3,000,000 Hz
# 3,000,000 Hz / 60,000 Period = 50 Hz
divider = 8
period = 60000 

i2c = PimoroniI2C(**PINS_PRESTO)
ioe = BreakoutIOExpander(i2c, address=0x18)

ioe.set_pwm_period(period)
ioe.set_pwm_control(divider)

ioe.set_mode(ioe_servo_pin, BreakoutIOExpander.PIN_PWM)

for dc in range(0, 16384,127):
    print(dc)
    ioe.output(ioe_servo_pin, dc)
    time.sleep(0.02)

for dc in range(16383, -1,-127):
    print(dc)
    ioe.output(ioe_servo_pin, dc)
    time.sleep(0.02)
    
ioe.output(ioe_servo_pin, 0)

Just integers in the same range directly rather than a backwards calculation from voltage. Any ideas?

3

Is this the ADC example you were trying? pimoroni-pico/micropython/examples/breakout_ioexpander/adc.py at main · pimoroni/pimoroni-pico · GitHub

If so, then change .input_as_voltage to .input to give you the integer value.

For what it’s worth, you can see all the Micropython bindings for this breakout here: pimoroni-pico/micropython/modules/breakout_ioexpander/breakout_ioexpander.h at main · pimoroni/pimoroni-pico · GitHub
(and similarly for most of our other breakouts that use bindings rather than native python modules)

4

For your servo and LED control, it’s worth looking at the regular Python examples for this breakout too:

Servo: ioe-python/examples/servo.py at main · pimoroni/ioe-python · GitHub
RGBLED: ioe-python/examples/rgbled.py at main · pimoroni/ioe-python · GitHub (which uses: ioe-python/ioexpander/devices.py at main · pimoroni/ioe-python · GitHub)

5

@ ZodiusInfuser Thank you - Just what I was after. I can now do all things I was looking to do.

This board helps makes up for the lack of normal IO on the PRESTO. I think it would be a good idea to advertise it on the PRESTO page as many PRESTO users may not find it otherwise.

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