ATtiny13 PWM with Potentiometer

Projects Programming
1

Hello,
I'm trying to get my ATtiny13 to do the following task: The trimmer of a 10K potentiometer on PB2 is registered as an input. PB0 is used as an output for a 109kHz PWM signal. Depending on the current value of my potentiometer the interval between 1 second long PWM signals. So for example im my potentiometer is at 5K, then theres a 1 second long PWM signal and then there's 20 seconds of no output. Also if the potentiometer is below 1K, then the PWM signal is there all the time. I've already written the code for this, but for some reason it doesn't work right, as it is permanently giving me the 109kHz. Below is the code and a cutout of the mentioned circuit. The ATtiny is supplied with 5V DC.
I'm thankfull for any help regarding hard- or software.

#define F_CPU 9600000UL
#include <avr/io.h>
#include <util/delay.h>

// Timer konfigurieren
void setupTimer() {
    OSCCAL += 2; // Feinjustierung des Oszillators
    TCCR0A = (1 << WGM01) | (1 << WGM00); // Fast PWM, Modus 3
    TCCR0B = (1 << WGM02) | (1 << CS00);  // Kein Prescaler, Modus 7
    OCR0A = 43;  // Feineinstellung für 108 kHz
}

// ADC konfigurieren
void setupADC() {
    ADMUX = (1 << MUX1); // PB2 (ADC1) auswählen
    ADCSRA = (1 << ADEN) | (1 << ADPS1) | (1 << ADPS0); // ADC aktivieren, Prescaler 8
}

// ADC-Wert auslesen
uint16_t readADC() {
    ADCSRA |= (1 << ADSC); // Start der Konvertierung
    while (ADCSRA & (1 << ADSC)); // Warten auf Abschluss
    return ADC;
}

// Intervall basierend auf ADC-Wert berechnen
uint8_t getInterval(uint16_t adcValue) {
    if (adcValue < 102) return 1;   // 0-1k Ohm -> 1 Sekunde
    else if (adcValue < 204) return 3;  // 1-2k Ohm -> 3 Sekunden
    else if (adcValue < 307) return 5;  // 2-3k Ohm -> 5 Sekunden
    else if (adcValue < 409) return 10; // 3-4k Ohm -> 10 Sekunden
    else if (adcValue < 512) return 20; // 4-5k Ohm -> 20 Sekunden
    else if (adcValue < 614) return 30; // 5-6k Ohm -> 30 Sekunden
    else if (adcValue < 716) return 40; // 6-7k Ohm -> 40 Sekunden
    else if (adcValue < 819) return 50; // 7-8k Ohm -> 50 Sekunden
    else if (adcValue < 921) return 60; // 8-9k Ohm -> 60 Sekunden
    return 0; // Immer an (9-10k Ohm)
}

// Variable Verzögerung
void delay_ms_variable(uint16_t delay_ms) {
    while (delay_ms--) {
        _delay_ms(1); // Kleinste Einheit: 1 ms
    }
}

int main() {
    DDRB |= (1 << PB0); // PB0 als Ausgang
    setupTimer();
    setupADC();

    while (1) {
        uint16_t adcValue = readADC();
        uint8_t interval = getInterval(adcValue);

        if (interval == 0) {
            // Immer an
            TCCR0A |= (1 << COM0A0); // PWM aktivieren
        } else {
            // Intervallmodus
            TCCR0A |= (1 << COM0A0); // PWM aktivieren
            delay_ms_variable(1000); // 1 Sekunde an
            TCCR0A &= ~((1 << COM0A0) | (1 << COM0A1)); // PWM deaktivieren
            PORTB &= ~(1 << PB0);    // Ausgang auf Low setzen
            delay_ms_variable(interval * 1000 - 1000); // Pause
        }
    }
}

Screenshot 2025-01-12 213905
Screenshot 2025-01-12 213905882×696 14.6 KB

2

Compliments on your first forum post! A properly described and formatted question with all the relevant information attached. Well done.

Shouldn't that be:

ADMUX = (1 << MUX0);

image
image778×295 33.5 KB

You have to set bit 0 and you are setting bit 1

3

Thank you very much!
That apparently was the problem.

Now i just have one more problem: When I put the Poti at 9-10K the PWM signal should be on all the time but it only switches after around half a minute and when i have it at 0-1K there's no signal at all.

Best regards!

4

On some of my pots the slider apparently loses contact near its min or max points. Or give other erratic readings. However, they are rather ancient!

5

I don't understand the "-1000"

At 0-1K it would make (1 *1000 - 1000) is delay(0) where you want a one second delay, so use:

 delay_ms_variable(interval * 1000); // Pause

The slow response is caused by the long delays. It will take that amount of time before the next ADC read cycle. If you want a snappier response you will need to rethink you program logic.

6

I don't know what happenend there, but it's fixed now. Thank you for your help!