Good day everyone,
I am facing a weird problem with my Pololu magnetic encoder.
The problem is that I am currently trying to read it on my Arduino UNO R4 Minima; however, the output stays stuck at 1 and does not want to toggle into the usual quadrature format.
Here is the code I am using:
// Quadrature (Pololu 4761) on A=D2, B=D3 → RPM + speed (m/s) + distance (m) + ESC ramp
// Serial Plotter columns: A, B, rpmQuad, speed_mps, dist_m, ESCuS
#include <Arduino.h>
#include <Servo.h>
#ifndef IRAM_ATTR
#define IRAM_ATTR
#endif
// -------- Pins --------
const uint8_t pinA = 2; // External interrupt pin
const uint8_t pinB = 3; // External interrupt pin
// -------- Your empirical calibration --------
const float COUNTS_PER_METER = 615.0f; // <-- your measured value
const float METERS_PER_COUNT = 1.0f / COUNTS_PER_METER;
// (Optional) keep RPM too. If unknown CPR, this is just "effective RPM" vs. your earlier assumption.
// If your encoder really is 12 counts/rev at 4x on the motor shaft and you're on the wheel, CPR_QUAD should be "wheel counts per wheel rev".
// You can ignore RPM if you only care about speed & distance.
const int CPR_QUAD = 12; // keep as-is if you want RPM; otherwise you can delete all rpm code
// -------- Quadrature state (ISR) --------
const int8_t qtab[16] = {
0, -1, +1, 0,
+1, 0, 0, -1,
-1, 0, 0, +1,
0, +1, -1, 0
};
volatile long q_count = 0; // signed tick count
volatile uint8_t q_prev = 0; // previous AB state
volatile uint32_t q_lastEdge_us = 0; // for minimal deadtime
const uint16_t q_dead_us = 10; // ignore transitions arriving <10us apart
// -------- Kinematics computation (loop) --------
float rpmQuad = 0.0f; // signed RPM (optional)
float speed_mps = 0.0f; // signed linear speed (m/s)
float distance_m = 0.0f; // signed odometer (m)
const float rpmAlpha = 0.9f; // EMA smoothing for RPM (responsive)
const float speedAlpha = 0.5f; // EMA smoothing for speed (moderate)
uint32_t sampLast_us = 0;
long sampLast_cnt = 0;
const uint32_t SAMPLE_US = 25000; // 25 ms window (~40 Hz updates)
// -------- Plot timing --------
const uint32_t PLOT_HZ = 100;
uint32_t lastPlot_us = 0;
// ==================== ISRs ====================
inline void quadStepFromAB(uint8_t A, uint8_t B, uint32_t now) {
if ((now - q_lastEdge_us) < q_dead_us) return; // deadtime
uint8_t curr = (A << 1) | B;
uint8_t idx = (q_prev << 2) | curr;
int8_t step = qtab[idx];
if (step) {
q_count += step;
q_lastEdge_us = now;
}
q_prev = curr; // keep state updated
}
void IRAM_ATTR isrA() {
uint32_t now = micros();
uint8_t A = digitalRead(pinA);
uint8_t B = digitalRead(pinB);
quadStepFromAB(A, B, now);
}
void IRAM_ATTR isrB() {
uint32_t now = micros();
uint8_t A = digitalRead(pinA);
uint8_t B = digitalRead(pinB);
quadStepFromAB(A, B, now);
}
// ==================== Helpers ====================
// Compute RPM (optional), speed (m/s), and distance (m) from delta counts over SAMPLE_US
void updateKinematics() {
uint32_t now = micros();
if ((now - sampLast_us) >= SAMPLE_US) {
noInterrupts();
long cnt = q_count;
interrupts();
long dcnt = cnt - sampLast_cnt; // signed counts in window
uint32_t dt_us = now - sampLast_us; // us
float dt_s = dt_us * 1e-6f;
// ---- speed (m/s) from your counts-per-meter ----
float inst_speed = (dcnt * METERS_PER_COUNT) / dt_s; // signed m/s
speed_mps = speedAlpha * inst_speed + (1.0f - speedAlpha) * speed_mps;
// ---- distance (m) integrate counts ----
distance_m += dcnt * METERS_PER_COUNT; // signed odometer
// ---- RPM (optional) if CPR_QUAD is set meaningfully ----
// RPM = (counts / CPR) * (60 / dt)
float inst_rpm = (float)dcnt * 60.0f / (float(CPR_QUAD) / dt_s); // same as 60e6 / (CPR * dt_us) * dcnt
rpmQuad = rpmAlpha * inst_rpm + (1.0f - rpmAlpha) * rpmQuad;
// advance window
sampLast_cnt = cnt;
sampLast_us = now;
}
}
void plotNow() {
const uint32_t now = micros();
const uint32_t interval = 1000000UL / PLOT_HZ;
if (now - lastPlot_us >= interval) {
lastPlot_us = now;
int A = digitalRead(pinA);
int B = digitalRead(pinB);
Serial.print(A); Serial.print('\t');
Serial.print(B); Serial.print('\t');
Serial.print(rpmQuad, 1); Serial.print('\t'); // optional
Serial.print(speed_mps, 3); Serial.print('\t');
// Changed to println() and removed the trailing tab
Serial.println(distance_m, 3);
}
}
void rampUpAndDown() {
updateKinematics();
plotNow();
if (Serial.available() && (Serial.read() == 'z')){Serial.print("Serial Problem");}
}
// ==================== Setup / Loop ====================
void setup() {
Serial.begin(115200);
pinMode(pinA, INPUT); // Pololu board has pull-ups to its VCC
pinMode(pinB, INPUT);
// Initialize previous state
q_prev = (digitalRead(pinA) << 1) | digitalRead(pinB);
// Attach CHANGE interrupts on both channels
attachInterrupt(digitalPinToInterrupt(pinA), isrA, CHANGE);
attachInterrupt(digitalPinToInterrupt(pinB), isrB, CHANGE);
// Initialize sampling
sampLast_us = micros();
sampLast_cnt = 0;
// Serial Plotter header
Serial.println("A\tB\trpmQuad\tspeed_mps\tdist_m\tESCuS");
}
void loop() {
rampUpAndDown();
}
And a quick image of my setup:
What’s weird is that this used to work before hand, but right now it is refusing to change.
