RPM sensor - first draft

main.c

#include <Arduino.h>
#include <U8x8lib.h>
#include <Wire.h>

U8X8_SSD1306_128X64_NONAME_HW_I2C u8x8(/* clock=*/PIN_WIRE_SCL, /* data=*/PIN_WIRE_SDA, /* reset=*/U8X8_PIN_NONE); // OLEDs without Reset of the Display
#define REED_SWITCH D10
unsigned long rpms = 0;
void tick()
{
  static uint64_t previousTick = 0;
  uint64_t currentTick = millis();
  // limit to 12K RPMs (just in case the IRQ handler takes more than 5 millis)
  if ((currentTick - previousTick) <5) return;
  // Compute RPMs in thousands of RPMs.
  rpms = 60 / (currentTick - previousTick);

  previousTick = currentTick;
}

void setup(void)
{
  attachInterrupt(digitalPinToInterrupt(REED_SWITCH), tick, RISING);
  pinMode(REED_SWITCH, INPUT_PULLDOWN_SENSE);
  u8x8.begin();
  u8x8.setFlipMode(1); // set number from 1 to 3, the screen word will rotary 180
  u8x8.setFont(u8x8_font_inb33_3x6_r);
}

void loop(void)
{
  static unsigned long prevRpms = 1;
  if (prevRpms == rpms) return;
  u8x8.clearDisplay();
  u8x8.setCursor(0, 0);
  u8x8.print(rpms, 10);
  prevRpms = rpms;
  // Convert in better delay form like in tick().
  delay(10);
}