Reevaluating the Feasibility

Published on 2019-05-09 in Kubik M0.

I compiled a custom CircuitPython firmware with all the pins exposed, and ran a simple program looking for any combination of pins that would give me 12 PWM outputs:

for permutation in permutations(pins):
    pwms = []
    for pin in permutation:
        try:
            pwms.append(pulseio.PWMOut(pin, frequency=50))
        except (RuntimeError, ValueError):
            pass
    if len(pwms) > 10:
        print(pwms)
    for pwm in pwms:
        pwm.deinit()

Yes, I know, I could have checked the datasheet for timers instead, but this is easier and makes more more certain.

That’s a lot of permutations to check, so it took some time, but ultimately it came up empty. There is no permutation that would give me more than 10 PWM outputs on the  SAMD21E18A chip. So what other options do I have now?\

I could use a SAMD21G18A that has 38 GPIO pins — I’m sure they come with some extra timers that would enable a few extra PWMs. But the SAMD21E18A costs \(2.38 in singles, while SAMD21G18A costs \)3.47. That increase in price wouldn’t be that bad by itself, however, for $4.01 I can have a SAMD51G19A instead, and a PCA9685 costs a dollar.

So now I have several options:

• SAMD21E18A + PCA9685 — $3.38

• SAMD21G18A — $3.47

• SAMD51G19A — $4.01

But it’s not just about the price, is it? The SAMD51 is a massively more powerful microcontroller, with much more RAM, faster clock and more flash. Also hardware floating point operations and a bunch of other stuff. And that is for just $2 more. I really think that it’s the best option. Besides, I’ve been wanting to make a board with that microcontroller for a while, but since project-86818 is on hold, I didn’t really have a chance. On top of that, I have one already in my drawer, so no need to wait for parts (though I will still need to wait for the PCB).