M5StickC制作简易自行车时速表
ESP32自带霍尔传感器，理论上也能实现该功能，可能是作者考虑到安装方式和内置磁铁的干扰，本项目使用干簧管开关+磁铁实现记录圆周，继而根据例程计算时速。其中变量circumference需要根据实际测量的车轮周长计算将干簧管接G26和GND，通过中断检测
磁铁安装在辐条上，保证能被感应到
#include <M5StickC.h>
int64_t circumference = 2096; // ADJUST: 700 x 23C tire typical value
int64_t circumference_hour = circumference * 60 * 60;
int64_t last_time;
volatile int speed;
hw_timer_t *tim0 = NULL;
enum {RUN, STOP};
volatile int state = STOP;
// Display speed
void dispSpeed(int s)
{
if (speed > 999) return;// Ignore over ranged speed
int i = s / 10; // Integral part
int d = s % 10; // Decimal part
M5.Lcd.setCursor(0, 0, 7);
M5.Lcd.printf("%02d", i);
M5.Lcd.setCursor(75, 0, 6);
M5.Lcd.printf("%d", d);
M5.Lcd.setCursor(105, 0, 2);
M5.Lcd.print("km/h");
}
// Monitor stop state
// If the status is stopped, clear the speed
void IRAM_ATTR checkStopState_Handler()
{
if (state == STOP) {
speed = 0;
}
state = STOP;
}
void setup() {
M5.begin();
// Set reed switch input
// Pull-up and set interrupt
// Reed switch is directly connected between G26 and GND
// Reed switch has no polarity
pinMode(GPIO_NUM_26, INPUT_PULLUP);
attachInterrupt(GPIO_NUM_26, magnetPassed_Handler, FALLING);
last_time = esp_timer_get_time();
// Init LCD display
M5.Lcd.setRotation(1);
dispSpeed(0);
// Timer setting
// Monitor stop state
tim0 = timerBegin(0, 80, true); // two second
timerAttachInterrupt(tim0, &checkStopState_Handler, true);
timerAlarmWrite(tim0, (1 * 1000000), true); // 1sec
timerAlarmEnable(tim0);
}
void magnetPassed_Handler()
{
// Stop GPIO interrupt tentatively to avoid re-entrant
// I'm not sure this code works well or not
// There may be a better way to do the same thing
detachInterrupt(GPIO_NUM_26);
int64_t cur_time = esp_timer_get_time();
int diff_time = cur_time - last_time;
if (diff_time > 70000) { // Ignore over ranged speed
// Update speed x 10
speed = (double)(circumference_hour * 10) / (double)diff_time;
last_time = cur_time;
state = RUN;
Serial.println(diff_time); // debug
}
// Wait chattering time
delay(100);
// Set and re-start GPIO interrupt
attachInterrupt(GPIO_NUM_26, magnetPassed_Handler, FALLING);
}
void loop() {
delay(200);
dispSpeed(speed);
}
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