This code samples an analog signal from a guitar, detects its frequency, and displays the results on an LCD. However, the LCD is displaying random stuff instead of printing frequency value despite correct wiring, as it works properly with simpler examples. The issue likely lies within the ADC configuration or interrupt handling affecting the LCD operation.
#include <LiquidCrystal.h>
// initialize the library by associating any needed LCD interface pin
// with the arduino pin number it is connected to
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
//clipping indicator variables
boolean clipping = 0;
//data storage variables
byte newData = 0;
byte prevData = 0;
unsigned int time = 0; //keeps time and sends vales to store in timer[] occasionally
int timer[10]; //sstorage for timing of events
int slope[10]; //storage for slope of events
unsigned int totalTimer; //used to calculate period
volatile unsigned int period; //storage for period of wave
byte index = 0; //current storage index
volatile float frequency; //storage for frequency calculations
int maxSlope = 0; //used to calculate max slope as trigger point
int newSlope; //storage for incoming slope data
//variables for decided whether you have a match
byte noMatch = 0; //counts how many non-matches you've received to reset variables if it's been too long
byte slopeTol = 3; //slope tolerance- adjust this if you need
int timerTol = 10; //timer tolerance- adjust this if you need
//variables for amp detection
unsigned int ampTimer = 0;
byte maxAmp = 0;
volatile byte checkMaxAmp;
byte ampThreshold = 30; //raise if you have a very noisy signal
void setup() {
lcd.begin(16, 2);
// Print a message to the LCD.
lcd.print("hello, world!");
Serial.begin(9600);
pinMode(13, OUTPUT); //led indicator pin
pinMode(12, OUTPUT); //output pin
cli(); //diable interrupts
//set up continuous sampling of analog pin 0 at 38.5kHz
//clear ADCSRA and ADCSRB registers
ADCSRA = 0;
ADCSRB = 0;
ADMUX |= (1 << REFS0); //set reference voltage
ADMUX |= (1 << ADLAR); //left align the ADC value- so we can read highest 8 bits from ADCH register only
ADCSRA |= (1 << ADPS2) | (1 << ADPS0); //set ADC clock with 32 prescaler- 16mHz/32=500kHz
ADCSRA |= (1 << ADATE); //enabble auto trigger
ADCSRA |= (1 << ADIE); //enable interrupts when measurement complete
ADCSRA |= (1 << ADEN); //enable ADC
ADCSRA |= (1 << ADSC); //start ADC measurements
sei(); //enable interrupts
}
ISR(ADC_vect) { //when new ADC value ready
PORTB &= B11101111; //set pin 12 low
prevData = newData; //store previous value
newData = ADCH; //get value from A0
if (prevData < 127 && newData >= 127) { //if increasing and crossing midpoint
newSlope = newData - prevData; //calculate slope
if (abs(newSlope - maxSlope) < slopeTol) { //if slopes are ==
//record new data and reset time
slope[index] = newSlope;
timer[index] = time;
time = 0;
if (index == 0) { //new max slope just reset
PORTB |= B00010000; //set pin 12 high
noMatch = 0;
index++; //increment index
} else if (abs(timer[0] - timer[index]) < timerTol && abs(slope[0] - newSlope) < slopeTol) { //if timer duration and slopes match
//sum timer values
totalTimer = 0;
for (byte i = 0; i < index; i++) {
totalTimer += timer[i];
}
period = totalTimer; //set period
//reset new zero index values to compare with
timer[0] = timer[index];
slope[0] = slope[index];
index = 1; //set index to 1
PORTB |= B00010000; //set pin 12 high
noMatch = 0;
} else { //crossing midpoint but not match
index++; //increment index
if (index > 9) {
reset();
}
}
} else if (newSlope > maxSlope) { //if new slope is much larger than max slope
maxSlope = newSlope;
time = 0; //reset clock
noMatch = 0;
index = 0; //reset index
} else { //slope not steep enough
noMatch++; //increment no match counter
if (noMatch > 9) {
reset();
}
}
}
if (newData == 0 || newData == 1023) { //if clipping
PORTB |= B00100000; //set pin 13 high- turn on clipping indicator led
clipping = 1; //currently clipping
}
time++; //increment timer at rate of 38.5kHz
ampTimer++; //increment amplitude timer
if (abs(127 - ADCH) > maxAmp) {
maxAmp = abs(127 - ADCH);
}
if (ampTimer == 1000) {
ampTimer = 0;
checkMaxAmp = maxAmp;
maxAmp = 0;
}
}
void reset() { //clea out some variables
index = 0; //reset index
noMatch = 0; //reset match couner
maxSlope = 0; //reset slope
}
void checkClipping() { //manage clipping indicator LED
if (clipping) { //if currently clipping
PORTB &= B11011111; //turn off clipping indicator led
clipping = 0;
}
}
void loop() {
checkClipping();
if (checkMaxAmp > ampThreshold) {
frequency = 38462 / float(period); //calculate frequency timer rate/period
lcd.setCursor(0, 1);
lcd.print(frequency, DEC); //print results to LCD
Serial.print(frequency);
Serial.println(" hz");
}
delay(100); //delete this if you want
//do other stuff here
}