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Originally posted by SaltyDog
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Additionally, I've limited pot reading to 10 times / sec instead of 1000 times as per Gounghouk, which I believe isn't necessary.
Reading is now done at the end of the Tx/sample sequence (right after the EFE sample) to avoid old values mixed with new values, which can happen when the calculation is interrupted.
I invite you to try it out.
PI_SaltyDog.zip
PHP Code:
/** Arduino Pulse Induction Metal Detector mods to drive the Tx and mainSample signals by PWM
*
* Version 2.0.1
* Date: Feb 8 2024
* Author: Teleno (based on George's original sketch)
*
* This version drives the Tx and mainSample pins using two PWM outputs of Timer1
* rather than driving them "manually" with digitalWrite(). This way the duration of
* the corresponding pulses is jitter free and can be changed in exact increments
* of the system clock period (62.5 ns).
*
* Since TImer1 only has two separate PWM outputs, the driving of the efeSample pin
* is still done manually with digitalWrite(). Jitter in the efeSample is less critical
* because at this delay the input signal is almost constant.
*
* In the original version the mainSample pin is already assigned to a PWM output of Timer1,
* so this pin is left unchanged. On the other hand, the Tx pin is not PWM, so in order
* to use this sketch you must swap the Tx and efeSample pins (Tx -> pin 10; efeSample -> pin 8)
* so that TImer1 PWM output OC1B can drive the Tx signal
*
* The original contains variables that can be replaced by #define statements of the C
* preproessor, saving memory for further modifications (adding an I2C display, etc.). Other
* variables are no longer necessary as this version requires less calculations.
*
* Timer1 is configured as CTC (clear timer on compare), with the maximum count being stored in
* the ICR1 register. This would be the txPeriodCount. The Tx pulse starts at count 1 and ends
* at txOn + 1, according to the values stored in OCR1B and the set/clear flags in TCCR1A. The
* interrupts take care of dynamically changing the configuration between each edge of the pulses to
* prepare the next edge. The timing of the Tx and mainSamnple signals is done by hardware and
* do not depend on the latency of the interrupts (no offset values required).
*/
// One microsecond is 16 system clock cycles
#define US 16
// Interrupt state machine
#define MODE_SAMPLE_ON 0
#define MODE_SAMPLE_OFF 1
#define MODE_EF_ON 2
#define MODE_EF_OFF 3
// Pin assignments
#define txPin 10 // Assign pin 10 to TX output
#define mainSamplePin 9 // Assign pin 9 to main sample pulse
#define efeSamplePin 8 // Assign pin 8 to EFE sample pulse
#define audioPin 11 // Assign pin 11 to audio chopper
#define boostPin 12 // Assign pin 12 to boost switch
#define delayPin A0 // Assign delay pot to A0
// Program constants
#define normalPower 50 // Normal TX-on time (50us)
#define boostPower 100 // Boost TX-on time (100us)
#define readDelayLimit 100 // Wait 100 TX periods (100ms) before reading delay pot
#define syncDemodOn LOW // Sample gate turns on when input high
#define syncDemodOff HIGH // Sample gate turns off when input low
// Detector timings
word txOn = normalPower; // TX-on time using normal power mode
volatile word mainDelay = 10; // Main sample pulse delay
#define defMainDelay 10 // Default main sample delay (10us)
#define mainSample 50 // Main sample pulse width (50us) >= 3us
#define efeDelay 240 // EFE sample pulse delay (240us)
#define efeSample 50 // EFE sample pulse width (same as main sample) >= 3us
#define txPeriod 1000 // TX period (1ms)
// Timing offsets
#define efeDelayOffset 12 // EFE delay pulse offset (12us)
// Program variables
volatile word txOnCount; // TX pulse
volatile word mainDelayCount; // Main sample delay
volatile word mainSampleCount; // Main sample pulse
volatile word efeDelayCount; // EFE sample delay
volatile word efeSampleCount; // EFE sample pulse
volatile word txPeriodCount; // TX period
volatile word delayVal = 0; // Delay pot value
volatile boolean readDelayPot = false; // Delay pot read (true or false)
volatile byte readDelayCounter = 0; // Read delay pot counter
volatile byte mode = MODE_SAMPLE_ON; // initial state of Interrupt state machine
byte potRange = 1; // fine 0=63 uS,or coarse 1=126 uS additional main sample delay
void calcTimerValues() {
if (digitalRead(boostPin) == HIGH) { // Get boost switch position
txOn = normalPower; // Set TX-on to 50us if HIGH
} else {
txOn = boostPower; // Set TX-on to 100us if LOW
}
txOnCount = 1 + txOn * US; // TX-on count for Timer1
mainDelayCount = txOnCount + mainDelay * US; // Main sample delay count for Timer1
mainSampleCount = mainDelayCount + mainSample * US; // Main sample pulse count for Timer1
unsigned int temp = (efeDelay - efeDelayOffset) * US;
efeDelayCount = txOnCount + temp; // EFE sample delay count for Timer1
efeSampleCount = efeDelayCount + efeSample * US; // EFE sample pulse count for Timer 1
txPeriodCount = txPeriod * US; // TX period count for Timer1
}
void setup() {
pinMode(txPin, OUTPUT); // Set TX pin to output mode
pinMode(mainSamplePin, OUTPUT); // Set main sample pin to output mode
pinMode(efeSamplePin, OUTPUT); // Set EFE sample pin to output mode
pinMode(boostPin, INPUT_PULLUP); // Set Boost switch pin to input mode with pullup resistor
calcTimerValues(); // Calculate all timer values
/** TIMER1 ***
* URL: https://dbuezas.github.io/arduino-web-timers/#mcu=ATMEGA328P&timer=1&topValue=ICR1&ICR1=54661&CompareOutputModeA=set&timerMode=CTC&CompareOutputModeB=set&OCR1A=54613&OCR1B=27307&InterruptOnTimerOverflow=off&interruptA=on&interruptB=on&InterruptOnInputCapture=on
* Mode : CTC
* Period : 1 ms
* Frequency: 1KHz
* Outputs :
* - OC1A: pin 9
* - OC1B: pin 10
*/
noInterrupts();
TCNT1 = 0;
OCR1A = mainDelayCount;
OCR1B = 1;
ICR1 = txPeriodCount;
TCCR1A = 1 << COM1A1 | 1 << COM1B1;
TIMSK1 = 1 << OCIE1A |1 << OCIE1B;
interrupts();
TCCR1B = 1 << WGM13 | 1 << WGM12 | 1 << CS10;
analogWrite(audioPin, 127); // Set audioPin with 50% duty cycle PWM
}
ISR(TIMER1_COMPB_vect) {
/* on OCR0B match - the TX signal */
// This was the rising edge of the Tx signal, prepare the falling edge.
OCR1B = txOnCount;
TCCR1A &= ~(1 << COM1B0); // clear Tx pin on compare match
// Disable OCR1B interrupt
TIMSK1 &= ~(1 << OCIE1B);
mode = MODE_SAMPLE_ON;
}
ISR(TIMER1_COMPA_vect) {
/* on OCR0A match - sample signals */
switch (mode) {
case MODE_SAMPLE_ON:
// This was the falling edge of the mainSample signal.
//prepare the rising edge.
TCCR1A |= (1 << COM1A1) | (1 << COM1A0); // set mainSample pin on compare match
OCR1A = mainSampleCount;
mode = MODE_SAMPLE_OFF;
break;
case MODE_SAMPLE_OFF:
// This was the rising edge of the Tx signal, disconnect this PWM pin and set it HIGH
// prepare EF sample rising edge
OCR1A = efeDelayCount;
digitalWrite(mainSamplePin, syncDemodOff); // pull OC2B high
TCCR1A &= ~((1 << COM1A1) | (1 << COM1A0)); // disconnect OC2B from output
mode = MODE_EF_ON;
break;
case MODE_EF_ON:
//digitalWrite(efeSamplePin, syncDemodOn); // Turn on EFE sample gate
PORTB &= 0xFE;
OCR1A = efeSampleCount;
mode = MODE_EF_OFF;
break;
case MODE_EF_OFF:
//digitalWrite(efeSamplePin, syncDemodOff); // Turn off EFE sample gate
PORTB |= 0x01;
// Prepare falling edge of mainSample
OCR1A = mainDelayCount;
TCCR1A |= (1 << COM1A1); // clear mainSample pin on compare match
//Prepare the rising edge of the Tx signal
OCR1B = 1;
TCCR1A |= (1 << COM1B0); // set Tx pin on compare match
// Enable OCR1B interrupt
TIFR1 |= (1 << OCF1B); // clear flag;
TIMSK1 |= 1 << OCIE1B; // Enable interrupt
mode = MODE_SAMPLE_ON;
}
}
void loop() {
// Read potentiometer, mask out the bottom 3 jittery bits and double the range if selected
mainDelay = defMainDelay + (((analogRead(delayPin)) & 0x03F8)<<potRange)/US; // new delay value
// wait till the end of the cycle to reacalculate the values
while(mode != MODE_SAMPLE_ON);
calcTimerValues(); // Calculate new timer values
delay(100); // read pot 10 times per second
}
)
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