// Piece of code for metal detector with adjustable TX frequency (6-18kHz, - lets make this more interesing !!!) and synchronized dual ADC
// Fast dual analog reading with DMA and continuous scan mode
// Hardware:
// - VREF (LM336-2.5) on PA0 (ADC1_IN0) // - VREF Out to PA0
// - RX processed baseband sampled signal 1 on PA1 (ADC1_IN1) - "X" derivative
// - RX processed baseband sampled signal 2 on PA2 (ADC1_IN2) - "R" derivative
// - TX output on PA8 (TIM1_CH1) - TX clock, goes to TX driver
// - VREF GND to Blue Pill GND
// - VREF VDD through current limiting 2.2kΩ resistor to Blue Pill 3.3V
// - 0.1µF bypass cap between positive and negative
#define ADC_BUFFER_SIZE 3
#define PWM_FREQ_MIN 6000 // 6kHz - lets make this more interesing !!!
#define PWM_FREQ_MAX 18000 // 18kHz - lets make this more interesing !!!
volatile uint16_t adc_values[ADC_BUFFER_SIZE];
volatile uint32_t current_freq = 10000; // Start at 10kHz
void timer_pwm_init(uint32_t frequency) {
// Enable TIM1 and GPIOA clocks
RCC->APB2ENR |= RCC_APB2ENR_TIM1EN | RCC_APB2ENR_IOPAEN;
// Configure PA8 as alternate function output (TIM1_CH1)
GPIOA->CRH &= ~(GPIO_CRH_MODE8 | GPIO_CRH_CNF8);
GPIOA->CRH |= GPIO_CRH_MODE8_1 | GPIO_CRH_MODE8_0 | GPIO_CRH_CNF8_1;
// Calculate PWM parameters for 72MHz clock
uint32_t period = (72000000 / frequency) - 1;
TIM1->PSC = 0; // No prescaler
TIM1->ARR = period; // Auto-reload value
TIM1->CCR1 = period / 2; // 50% duty cycle
// PWM mode 1, preload enable
TIM1->CCMR1 = TIM_CCMR1_OC1M_1 | TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1PE;
// Enable output compare
TIM1->CCER = TIM_CCER_CC1E;
// Enable counter and main output
TIM1->CR1 = TIM_CR1_CEN;
TIM1->BDTR = TIM_BDTR_MOE;
}
void adc_dma_init(void) {
// Enable clocks
RCC->APB2ENR |= RCC_APB2ENR_IOPAEN | RCC_APB2ENR_ADC1EN;
RCC->AHBENR |= RCC_AHBENR_DMA1EN;
// Configure analog pins
GPIOA->CRL &= ~(GPIO_CRL_MODE0 | GPIO_CRL_CNF0 |
GPIO_CRL_MODE1 | GPIO_CRL_CNF1 |
GPIO_CRL_MODE2 | GPIO_CRL_CNF2);
// DMA configuration
DMA1_Channel1->CCR = 0;
DMA1_Channel1->CPAR = (uint32_t)&ADC1->DR;
DMA1_Channel1->CMAR = (uint32_t)adc_values;
DMA1_Channel1->CNDTR = ADC_BUFFER_SIZE;
DMA1_Channel1->CCR |= DMA_CCR_CIRC | DMA_CCR_MINC |
DMA_CCR_PSIZE_0 | DMA_CCR_MSIZE_0;
// Enable DMA
DMA1_Channel1->CCR |= DMA_CCR_EN;
// ADC configuration
ADC1->CR1 = 0;
ADC1->CR2 = 0;
// Configure for external trigger from Timer1
ADC1->CR2 |= ADC_CR2_EXTTRIG | // External trigger enable
(4 << 17) | // Timer1 CC1 event as trigger
ADC_CR2_DMA | // Enable DMA
ADC_CR2_ADON; // Enable ADC
// Scan mode configuration
ADC1->CR1 |= ADC_CR1_SCAN;
ADC1->SQR1 = ((ADC_BUFFER_SIZE - 1) << 20);
ADC1->SQR3 = 0 | (1 << 5) | (2 << 10);
// Sample times
ADC1->SMPR2 = (7 << 0) | // VREF: 239.5 cycles
(4 << 3) | // AN1: 41.5 cycles
(4 << 6); // AN2: 41.5 cycles
// Calibrate
delay_ms(1);
ADC1->CR2 |= ADC_CR2_CAL;
while(ADC1->CR2 & ADC_CR2_CAL);
// Start ADC
ADC1->CR2 |= ADC_CR2_ADON;
}
typedef struct {
float voltage1;
float voltage2;
} analog_readings_t;
analog_readings_t get_latest_voltages(void) {
analog_readings_t results;
uint16_t vref = adc_values[0];
results.voltage1 = (adc_values[1] * 2.5f) / vref;
results.voltage2 = (adc_values[2] * 2.5f) / vref;
return results;
}
void set_frequency(uint32_t new_freq) {
if(new_freq >= PWM_FREQ_MIN && new_freq <= PWM_FREQ_MAX) {
current_freq = new_freq;
timer_pwm_init(new_freq);
}
}
void main(void) {
analog_readings_t readings;
// Initialize systems
timer_pwm_init(current_freq);
adc_dma_init();
while(1) {
readings = get_latest_voltages();
// Process readings here
// They are automatically synchronized with the TX signal
// Example: Adjust frequency based on some condition
// set_frequency(new_frequency);
}
}
// Configure ADC to use external VREF with two analog inputs
// Hardware setup:
// - VREF chip (like LM336-2.5) output connected to PA0 (ADC1_IN0)
// - First analog input on PA1 (ADC1_IN1) - "X"
// - Second analog input on PA2 (ADC1_IN2) -"R"
// - VREF GND to Blue Pill GND
// - VREF VDD through current limiting 2.2kΩ resistor to Blue Pill 3.3V
// - VREF Out to PA0
// - 0.1µF bypass cap between positive and negative
void adc_init_external_vref(void) {
// Enable GPIOA and ADC1 clocks
RCC->APB2ENR |= RCC_APB2ENR_IOPAEN | RCC_APB2ENR_ADC1EN;
// Configure PA0 (VREF), PA1 (analog1), PA2 (analog2) as analog inputs
GPIOA->CRL &= ~(GPIO_CRL_MODE0 | GPIO_CRL_CNF0 |
GPIO_CRL_MODE1 | GPIO_CRL_CNF1 |
GPIO_CRL_MODE2 | GPIO_CRL_CNF2);
// ADC configuration
ADC1->CR2 = 0; // Reset CR2 register
ADC1->CR2 |= ADC_CR2_ADON; // Enable ADC
// Wait for ADC to stabilize
delay_ms(1);
// Calibrate ADC
ADC1->CR2 |= ADC_CR2_CAL; // Start calibration
while(ADC1->CR2 & ADC_CR2_CAL); // Wait for calibration
}
// Structure to hold both readings
typedef struct {
float voltage1;
float voltage2;
} analog_readings_t;
analog_readings_t read_dual_voltages(void) {
uint16_t vref_reading, signal1_reading, signal2_reading;
analog_readings_t results;
// Read VREF on PA0
ADC1->SQR3 = 0; // Select channel 0 (PA0)
ADC1->CR2 |= ADC_CR2_ADON; // Start conversion
while(!(ADC1->SR & ADC_SR_EOC)); // Wait for conversion
vref_reading = ADC1->DR;
// Read first analog input on PA1
ADC1->SQR3 = 1; // Select channel 1 (PA1)
ADC1->CR2 |= ADC_CR2_ADON; // Start conversion
while(!(ADC1->SR & ADC_SR_EOC)); // Wait for conversion
signal1_reading = ADC1->DR;
// Read second analog input on PA2
ADC1->SQR3 = 2; // Select channel 2 (PA2)
ADC1->CR2 |= ADC_CR2_ADON; // Start conversion
while(!(ADC1->SR & ADC_SR_EOC)); // Wait for conversion
signal2_reading = ADC1->DR;
// Calculate actual voltages using VREF reading
// Assuming VREF chip outputs 2.5V (for LM336-2.5)
results.voltage1 = (signal1_reading * 2.5f) / vref_reading;
results.voltage2 = (signal2_reading * 2.5f) / vref_reading;
return results;
}
// Example usage in main
void main(void) {
analog_readings_t readings;
// Initialize ADC with external reference
adc_init_external_vref();
while(1) {
readings = read_dual_voltages();
// Use the readings
printf("Voltage 1: %.3fV\n", readings.voltage1);
printf("Voltage 2: %.3fV\n", readings.voltage2);
delay_ms(1000); // Read every second
}
}
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