ADC to PWM functionality

Updating the PWM library

We need to add the a new prototype to the pwm.h and the body to the pwm.c files, that converts the ADC value to a the correct PWM duty cycle against the specified period.

1. Open the pwm.h file and modify to include the prototype below called map:

   Suppressed code here [7 lines]

   #ifndef PWM_H
   #define PWM_H
   
   ...
   
   unsigned int map(u_int16_t adc_value, unsigned int period_ns);
   
   #endif
   

2. Next we need to modify the pwm.c file to include the body of the previously defined prototype, place the function at the bottom of the file:

   Suppressed code here [14 lines]

   ... 
   
   // Map ADC value to PWM duty cycle with user-specified period
   unsigned int map(u_int16_t adc_value, unsigned int period_ns) {
   
       if (adc_value > 4095) {
           fprintf(stderr, "ADC value out of range\n");
           return 1;
       }
   
       // Map ADC value (0 to 4095) to PWM duty cycle (0 to period_ns)
       unsigned int duty_cycle_ns = (adc_value * period_ns) / 4095;
   
       return duty_cycle_ns;
   }
   

3. Now you need to remake the library:

   Terminal

   $ make clean
   $ make uninstall
   $ make install
   

Implementing an example

4. We are going to create a script that utlises what we did for adc_read.c and pwm_test.c, by utilising both libraries pwm.h and adc.h.

   Suppressed code here [61 lines]

   #include "pwm.h"
   #include "adc.h"
   #include <stdio.h>
   #include <unistd.h>
   #include <stdint.h>
   
   int main() {
       PWM pwm;
       unsigned int adc_reading = 0;
       unsigned int user_defined_period_ns = 100000; // User-defined period in nanoseconds (1 ms for 1 kHz)
       unsigned int duty_cycle = 0;
   
       // Initialize PWM on a specified pin, for example "P8_13"
       pwm_init(&pwm, "P8_13");
   
       // Set initial PWM period
       pwm_set_period(&pwm, user_defined_period_ns);
   
       // Enable PWM output
       pwm_enable(&pwm);
   
       qprintf("Phy: %s\nChannel: %s\nChip: %s\nPeriod path: %s\nDuty Cycle path: %s\nEnable path: %s\nPin Mode Path: %s\nPin Mode Sate: %s\n",pwm.phy_pin,pwm.channel,pwm.chip,pwm.period_path,pwm.duty_cycle_path,pwm.enable_path,pwm.pin_mode_path, pwm.pin_mode_state);
   
       // Loop to read ADC values and update PWM duty cycle
       for (int i = 0; i < 30; i++) {
           adc_get_value(0, &adc_reading); // Read ADC value from channel 0
           printf("ADC Reading: %u\n", adc_reading);
   
           // Map the ADC reading to the PWM duty cycle and update it
           duty_cycle = map(adc_reading, user_defined_period_ns);
   
           pwm_set_duty_cycle(&pwm, duty_cycle);
   
           sleep(1); // Update every 1 second
       }
   
       // Disable PWM and clean up
       pwm_disable(&pwm);
       pwm_cleanup(&pwm);
   
       return 0;
   }
   

5. Remember to create a Makefile file:

   Suppressed code here [25 lines]

   # Compiler and flags
   CC = gcc
   CFLAGS = -Wall -Werror
   
   # Target executable name
   TARGET = adc2pwm
   
   # Source files
   SRC = adc2pwm.c
   
   # Library to link against
   LIBS = -lioctrl
   
   # Default target: build the executable
   all: $(TARGET)
   
   # Build the executable
   $(TARGET): $(SRC)
           $(CC) $(CFLAGS) $(SRC) $(LIBS) -o $(TARGET)
   
   # Clean up build artifacts
   clean:
           rm -f $(TARGET)
   
   # Phony targets to avoid conflicts with files of the same name
   .PHONY: all clean
   

6. If all is well, and you have connected up your circuity correctly, the LED should change it's brightness based on the resistance from the potentiometer, for example you may see this terminal output:

   Output

   PWM initialized with:
   Physical Pin: P8_13
   Channel: 7
   Chip: 1
   Period path: /sys/class/pwm/pwm-7:1/period
   Duty Cycle path: /sys/class/pwm/pwm-7:1/duty_cycle
   Enable path: /sys/class/pwm/pwm-7:1/enable
   ADC Reading: 0
   ADC Reading: 0
   ADC Reading: 283
   ADC Reading: 697
   ADC Reading: 1313
   ADC Reading: 1674
   ADC Reading: 1907
   ADC Reading: 2454
   ADC Reading: 2968
   ADC Reading: 3367
   ADC Reading: 3687
   ADC Reading: 3989
   ADC Reading: 3920
   ADC Reading: 4001
   ADC Reading: 3932
   ADC Reading: 3985
   ADC Reading: 4002
   ADC Reading: 4002
   ADC Reading: 4001
   ...