Frequency counter not working

[saraverbeecke]

I am trying to measure my test signal of 20 kHz but the capture always returns the same value. What could be wrong? (i am using a nucleo board of the stm32h743)

from pyb import Timer, Pin
import time
timer = Timer(8, freq=1_000_000, mode=Timer.UP)
p = Pin(Pin.cpu.I5, mode=Pin.IN, pull=Pin.PULL_DOWN)
ch = timer.channel(1, Timer.IC, pin=p, polarity=Timer.RISING)
print(f"Timer 8 Frequency: {timer.freq()} Hz") 

# My test signal (confirmed on scope that this is 20kHz 3.3V pulses 50% duty)
t = Timer(3, freq=20000)
c = t.channel(1, Timer.PWM, pin=Pin(Pin.cpu.C6))
c.pulse_width_percent(50)
print(f"Timer 3 Frequency: {t.freq()} Hz")

prev_capture = None 

def measure_frequency():
    global prev_capture
    capture = ch.capture()
 
    if prev_capture is not None:
        period = (capture - prev_capture) & 0xFFFF
        print(f"🔍 Prev: {prev_capture}, Current: {capture}, Period: {period}")  # Debug

        if period > 0:
            frequency = 1_000_000 / period  # 1 MHz clock = 1 μs per tick
            prev_capture = capture
            return frequency

    prev_capture = capture
    return 0

while True:
    freq = measure_frequency()
    if freq > 0:
        print(f"Frequency: {freq:.2f} Hz")
    time.sleep(0.1) 

I always get:
Prev: 129, Current: 129, Period: 0
Prev: 129, Current: 129, Period: 0
Prev: 129, Current: 129, Period: 0
Prev: 129, Current: 129, Period: 0

[peterhinch]

You might like to look at Dave Hylands examples notably freq_counter.py.

[saraverbeecke]

thanks for the link @peterhinch but he is using the .counter() value and calculates the difference. I would like to use the "input capture" capabilities of the stm32. It is listed in the Micropython docs but I cannot get it to work properly. Any experience with the Timer.IC mode on stm32 in Micropython?
(purpose: I need to be able to measure the frequency of an external signal betwen 16Hz and 18kHz with a 0.5 Hz resolution)

[peterhinch]

I haven't used it. The official doc is rather confusing. If I were you I'd study the STM docs to understand its purpose and use.