PWM frequency tweak on Arduino Uno for sumo bot — register hacking?

[jm_robotics]

Bumubuo ng 1kg sumo bot for inter-college comp soon. Default Arduino

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analogWrite()

runs PWM at around 490Hz on most pins, kaya may audible whine yung motors namin. More importantly, hindi maganda ang ramp-up ng speed.

Alam ko kayang i-manipulate yung AVR timer registers directly,

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TCCR0B

,

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TCCR1B

,

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TCCR2B

, change yung prescaler, bump PWM up to 31kHz. Catch is each timer also drives

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delay()

and

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millis()

, so pag tinangal mo Timer 0, sira na yung timing functions mo.

Plan ko ngayon: gamitin yung Timer 1 (pins 9 + 10) for motor PWM, leave Timer 0 alone. Pero mawawala na yung

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analogWrite()

sa pins 9/10, kelangan i-write directly yung OCR values.

May nakapag-try na ba nito sa sumo or line-follower? Mainly:

• Did the higher PWM frequency actually improve motor smoothness, or placebo lang?
• Any L298N gotchas? Baka nga hindi ito tumatanggap ng PWM above 10kHz nang maayos.
• Mas okay ba mag-Mega na lang for the dedicated timer pins?

Posting late kasi night testing namin. Reply niyo whenever, basahin ko bukas.

[tito_elmer]

Dating embedded engineer dito. Ginawa ko ito noong AVR pa lang yung choice for hobbyists. Tama yung plan mo: Timer 1 for motor PWM, leave Timer 0 alone for delay/millis.

Things worth knowing:

• Timer 2 free din for 8-bit PWM (pins 3 and 11). Less granular than Timer 1's 16-bit, pero kung 0-255 duty lang kelangan mo, OK na. Mas madali pa, walang OCR1A/OCR1B juggling.
• Phase-correct vs Fast PWM mode, Phase-correct gives you ~half the frequency pero cleaner motor control (walang glitching at 0% and 100%). For motor control usually phase-correct yung gusto mo.
• Frequency that matters, for brushed DC motors, 8-20kHz yung sweet spot. Higher than that, lugi ka sa switching losses ng L298N (BJT-based, slow yung switching).

Yung guess mo re: L298N + high PWM, tama. Above ~20kHz, yung BJT switching transitions take a meaningful fraction ng period at bumababa yung efficiency. 16kHz yung sinettle ko dati for hobby motor control.

Re Mega, sure pero hindi yan yung problem ng Uno. Same timer constraints kahit Mega. Sa code yung fix, hindi sa chip.

[sam_python]

Sa C++/AVR register side, kabisado ni Tito. From the other side, kung gusto mong tuluyang umalis sa AVR timer Tetris, yung Pi Pico's PIO (Programmable I/O) lets you write hardware-level PWM at any frequency you want, walang timer manipulation kelangan.

Para sa sumo-bot context maybe overkill (invested ka na sa AVR for the comp). Pero next year's bot, worth a look. PIO is a tiny state machine na tumatakbo in parallel sa main cores, outputs precise PWM, reads encoders, drives WS2812 LEDs, walang CPU overhead.

Sa MicroPython, parang 4 lines yung syntax:

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from machine import Pin, PWM
pwm = PWM(Pin(15))
pwm.freq(20000)  # 20kHz, walang register hacking
pwm.duty_u16(32768)  # 50% duty

Yung native PWM API exposes lang what's possible. Worth knowing for your toolbox kahit hindi sa current bot.