Motion Sensor Recycled based on minimalistic PCB arduino design

  • Hardware Contributor

    Take an old motion sensor:
    Remove existing PCB:
    Insert mysensors technology:
    With more skills, it would look nicer:


    #include <SPI.h>
    #include <MySensor.h>
    unsigned long SLEEP_TIME = 7200000; // Sleep time between reports (in milliseconds)
    unsigned long SLEEP_TIME_AFTER_MOTION = 30000; // Forced Sleep after motion report
    #define DIGITAL_INPUT_SENSOR 3   // The digital input you attached your motion sensor.  (Only 2 and 3 generates interrupt!)
    #define INTERRUPT DIGITAL_INPUT_SENSOR-2 // Usually the interrupt = pin -2 (on uno/nano anyway)
    #define CHILD_ID 1   // Id of the sensor child
    boolean interrupted = false;
    int batteryRound = 0;
    #define BATTERY_ROUNDS 20
    MySensor gw;
    // Initialize motion message
    MyMessage msg(CHILD_ID, V_TRIPPED);
    void setup()
      // Send the sketch version information to the gateway and Controller
      gw.sendSketchInfo("Motion Sensor VC Int", "1.2");
      pinMode(DIGITAL_INPUT_SENSOR, INPUT);      // sets the motion sensor digital pin as input
      // Register all sensors to gw (they will be created as child devices)
      gw.present(CHILD_ID, S_MOTION);
    void loop()
      // Read digital motion value
      boolean tripped = digitalRead(DIGITAL_INPUT_SENSOR) == HIGH;
      gw.send(msg.set(tripped ? "1" : "0")); // Send tripped value to gw
      if ((interrupted == false) || // wake up from timer?
          (batteryRound >= BATTERY_ROUNDS) )
        batteryRound = 0;
        // measure battery state
        long sensorValue = readVcc();
        // 100 -> 3000, 0 -> 2000
        if (sensorValue < 2000)
          sensorValue = 0;
          sensorValue -= 2000;
        int batteryPcnt = (int)((float)(sensorValue) / 10.0);
        if (batteryPcnt > 100) batteryPcnt = 100;
      if (tripped == true) {
        // take a brake and do not report motion for some time
        interrupted = true;  // don't send vcc after short sleep
      // Sleep until interrupt comes in on motion sensor
      else interrupted = gw.sleep(INTERRUPT, CHANGE, SLEEP_TIME);
    // see
    long readVcc() {
      // Read 1.1V reference against AVcc
      // set the reference to Vcc and the measurement to the internal 1.1V reference
    #if defined(__AVR_ATmega32U4__) || defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
      ADMUX = _BV(REFS0) | _BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
    #elif defined (__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
      ADMUX = _BV(MUX5) | _BV(MUX0);
    #elif defined (__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__)
      ADMUX = _BV(MUX3) | _BV(MUX2);
      ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
      delay(2); // Wait for Vref to settle
      ADCSRA |= _BV(ADSC); // Start conversion
      while (bit_is_set(ADCSRA, ADSC)); // measuring
      uint8_t low  = ADCL; // must read ADCL first - it then locks ADCH
      uint8_t high = ADCH; // unlocks both
      long result = (high << 8) | low;
      result = 1125300L / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
      return result; // Vcc in millivolts
    void switchClock(unsigned char clk)
      CLKPR = 1 << CLKPCE; // Set CLKPCE to enable clk switching
      CLKPR = clk;

    Minimalistic PCB (self designed with fritzing):

    The PCB has a flexible design (use jumpers):

    • use with battery (used here)
    • use with 5 volt (and LE33 for NRF24L01+)
    • use with voltage stabilazitaion to 3.3V (LE33) for ATMEGA328P and NRF24l01+

  • @FotoFieber
    I am curious why you cut through the existing lens of the old PIR? Could you have used that lens instead for your HC-SR501 and discarded the little dome lens?

    Nice hack! I have also seen many cheap PIR devices and am in the process of hacking mysensors into a PIR led nightlight but I am trying to cross utilize the existing PIR. Almost there...

  • Hardware Contributor

    With the next PIR device I will try to reuse the lens. Attaching the HC-SR501 is more difficult with such a setup.

    I just wanted to use a proofen design I use in other setups with my first proof of concept.

  • Nice... I'm about to mod my motion sensor flood lights in a similar manner, but will reuse the lens and also have a relay for the lighting. Then any motion sensor could trigger any number of relay-enabled lights, like if motion is detected by any sensor on the back of the house all lights on the back could power on instead of just the one that detected motion..

  • Hardware Contributor

    Second design with reusing the lens:

  • @FotoFieber

    Nice and compact! Is that your custom board?

  • Hardware Contributor

    Yes, this is a minimalistic NRF Arduion PCB:

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