Battery powered PIR and temp/humid sensor

  • I have built a battery powered PIR temp/humidity and light sensor. I based the sketch on the Sensebender sketch which allows to control how long the sensor sleeps and how often to report measurements back. I changed the sketch now so that when the PIR is triggered an interrupt wakes up the sensor.


    This is all working well. However, now I lost total control over measurement intervals and send intervals. If I get it right retrieving millis will not work since they are not counted while the sensor sleeps.
    Any ideas how to solve that.

  • Hardware Contributor

    There is another sleep method which also takes a time in millis and wakes on both, intervall and interrupt. That might be a solution?!

  • @LastSamurai: I am using that method. My problem is that due to the fact that motion will trigger the interrupt and hence the sleep time in between measurements vary depending on movements. So when there is a lot of motion the send and measurement frequency will be much shorter and thus draining the battery faster.

  • Admin

    The return value from gw.sleep tells you if it woke up on timer or pin.

    So just send motions status when pin triggered. If timer triggered wakeup send temp.

  • @hek This will definitely help but it still means that there is no real means to control the time between temp/humid measurements. In the worst case the PIR triggers over a longer time always the interrupt and thus temp is never send. Even if I introduce some counter which when reached will trigger a temp measurement I have no glue what the interval length in between is. Or do I miss something?

  • Admin


    I don't understand.. the timer option will wake your board at the specified time even if no motion was detected.

  • @hek

    Sorry, I didn't express it well enough.
    Let's say my sketch would sleep between two measurements 60 sec and send every 30 measurements its value, which means every 30 minutes (which are the defaults of the sensebender sketch). I can increase or reduce the frequency by adjusting the sleep times and send intervals easily.

    By introducing the interrupt - which I think there is no way around -, the sleep time can be interrupted somewhere between 1 second and 60 seconds. And I don't know how long my sketch has slept. If I cannot determine the time how long my sketch was sleeping I cannot determine when I should take the next temp/humid measurement. Although I can still use the loop counter, I have no control over the elapsed time between two temp/humid measurements.

  • Admin

    True, if you wake up from pin change you haven't the exact knowledge of elapsed time (< MAX-SLEEP-TIME though).

    But in most applications I doubt it would super exact temp-send-interval would matter much... It will only diff when pin change wake-up interfere.

  • @hek

    Thanks! That confirms my understanding.

  • @tomkxy: Have you gathered some experiences with this setup over time? And would you mind sharing the Arduino sketch you are using?

    I am hoping to do more or less the same with Sensebenders and PIRs, and I am new to electronics of this sort.

  • @Haakon I have one of these sensor in place since about half a year and it is working well. Last battery change is about 4 month ago.

    Please find the sketch below which requires some cleanup.

    Multisensor Sketch
    Author: Thomas Krebs,
    This sketch reads temperature, humidity, light and presence.
    It is based on the various examples sketches from SparkFun and MySensors 
    It uses the following sensors:
    Light           - TSL2561
    Temp&Humidity   - HTU21D
    HTU21D and TLS2561 need to connect the I2C pins (SCL and SDA) to your Arduino.
    The pins are different on different Arduinos:
                        SDA    SCL
    Any Arduino         "SDA"  "SCL"
    Uno, Redboard, Pro  A4     A5
    Mega2560, Due       20     21
    Leonardo            2      3
    #define MY_DEBUG_VERBOSE_SIGNING //!< Enable signing related debug prints to serial monitor
    #define MY_SIGNING_ATSHA204
    #define MY_DEBUG
    #define MY_NODE_ID              26
    #define MY_RADIO_NRF24
    #define BATT_SENSOR
    #include <MySensor.h>
    #include <TSL2561.h>
    #include <SparkFunHTU21D.h>
    #include <SPI.h>
    #include <Wire.h>
    #include <avr/power.h>
    #define VERSION           "1.4"
    #define SKETCH_NAME       "Multisensor A"
    #define TEMP_CHILD_ID   1
    #define HUM_CHILD_ID    2
    #define LIGHT_CHILD_ID  3
    #define MOTION_CHILD_ID 4
    // Uncomment the line below, to transmit battery voltage as a normal sensor value
    #define BATT_SENSOR    199
    #define MAX_VOLTAGE    1316
    #define MIN_VOLTAGE    890     // it seems that about 0.89 V the sensor stops working
    // How many milli seconds between each measurement
    #define MEASURE_INTERVAL 120000
    // FORCE_TRANSMIT_INTERVAL, this number of times of wakeup, the sensor is forced to report all values to the controller
    // When MEASURE_INTERVAL is 60000 and FORCE_TRANSMIT_INTERVAL is 30, we force a transmission every 30 minutes.
    // Between the forced transmissions a tranmission will only occur if the measured value differs from the previous measurement
    // HUMI_TRANSMIT_THRESHOLD tells how much the humidity should have changed since last time it was transmitted. Likewise with
    // TEMP_TRANSMIT_THRESHOLD for temperature threshold.
    #define LIGHT_TRANSMIT_THRESHOLD  0.3    // relative change
    // Pin definitions
    #define LED_PIN            13            // TODO: need to check that
    #define BATTERY_SENSE_PIN  A0            // select the input pin for the battery sense point
    #define MOTION_SENSOR      3             // The digital input you attached your motion sensor.  (Only 2 and 3 generates interrupt!)
    #define INTERRUPT          1             // Usually the interrupt = pin -2 (on uno/nano anyway)
    // Global settings
    int tempMeasureCount = 0;
    int lightMeasureCount = 0;
    int sendBattery = 0;
    boolean isMetric = true;
    boolean highfreq = true;
    boolean motionDetected = false;
    int repeats = 2;
    // Storage of old measurements
    float lastTemperature = -100;
    float lastHumidity = -100;
    long  lastBattery = -100;
    long  lastLight = -5000;
    int   lastTripped = -1; 
    int   motionTrips = 0;  // count the number of cont. motion trips
    HTU21D myHumidity;
    TSL2561 myLight(TSL2561_ADDR_FLOAT); 
    // Sensor messages
    MyMessage msgTemp(TEMP_CHILD_ID,V_TEMP);
    MyMessage msgHum(HUM_CHILD_ID,V_HUM);
    MyMessage msgLight(LIGHT_CHILD_ID,V_LEVEL);
    MyMessage msg(MOTION_CHILD_ID, V_TRIPPED);
    #ifdef BATT_SENSOR
    MyMessage msgBatt(BATT_SENSOR, V_VOLTAGE);
     * Setup code 
    void setup()  
      pinMode(LED_PIN, OUTPUT);
    #ifdef MY_SIGNING_ATSHA204_PIN
      // Make sure that ATSHA204 is not floating
      pinMode(MY_SIGNING_ATSHA204_PIN, INPUT);
      digitalWrite(MY_SIGNING_ATSHA204_PIN, HIGH);
      // use the 1.1 V internal reference
      // setup sensors
      // setup motion sensor 
      pinMode(MOTION_SENSOR, INPUT);    
      Serial.println(F("Setup complete..."));
    void presentation()  {
      // Send the sketch version information to the gateway and Controller
      sendSketchInfo(SKETCH_NAME, VERSION);
      // Present all sensors to controller
      present(TEMP_CHILD_ID, S_TEMP);
      present(HUM_CHILD_ID, S_HUM);
    //  present(LIGHT_CHILD_ID,S_LIGHT_LEVEL);
      present(MOTION_CHILD_ID, S_MOTION);
    #ifdef BATT_SENSOR
      present(BATT_SENSOR, S_POWER);
      isMetric = getConfig().isMetric;
    #ifdef MY_DEBUG
      Serial.print(F("isMetric: ")); Serial.println(isMetric);
      Serial.println(F(" - Online!"));
    /* Setup HTU21d
    void setup_htu21d() {
    #ifdef MY_DEBUG  
      Serial.println("Setup temp/humid sensor completed");
    /* Setup TLS2561
    void setup_tls2561() {
      if (myLight.begin()) {
        Serial.println(F("Found light sensor"));
      } else {
        Serial.println(F("Light Sensor not found - cont. anyway"));
      myLight.setGain(TSL2561_GAIN_0X);          // set 16x gain (for dim situations)
      // Changing the integration time gives you a longer time over which to sense light
      // longer timelines are slower, but are good in very low light situtations!
      //tsl.setTiming(TSL2561_INTEGRATIONTIME_13MS);  // shortest integration time (bright light)
      myLight.setTiming(TSL2561_INTEGRATIONTIME_101MS);  // medium integration time (medium light)
      //tsl.setTiming(TSL2561_INTEGRATIONTIME_402MS);  // longest integration time (dim light)
     *  Main loop function
    void loop()     
      bool forceTransmit = false;
      if (motionDetected) {
        sendMotion(false);  // do not force transmission unless motion status has changed
        motionDetected = false;
      // do not enter into sensor data gathering on each motion tripped
      if ((!motionDetected) || (motionTrips > 3)) {
        motionTrips = 0; // avoid starvation of temp measure in case we have a lot of motion
        // I do the battery check at the beginning
        if (sendBattery > 60) {
           sendBattLevel(forceTransmit); // Not needed to send battery info that often
           sendBattery = 0;
        if ((lightMeasureCount > FORCE_TRANSMIT_INTERVAL) || (tempMeasureCount > FORCE_TRANSMIT_INTERVAL) ) { // force a transmission
          forceTransmit = true; 
          tempMeasureCount = 0;
          lightMeasureCount = 0;
        // Get & send sensor data
      wait(100);  // I don't know whether that is really required; however I have the impression that shutting down the radio leads to
                     // problems in the communication when using signatures
      Serial.println("going to sleep");
        motionDetected = true;
      Serial.print("Motion detected="); Serial.println(motionDetected);
     * Sends state of motion sensor
     * Parameters
     * - force : Forces transmission of a value (even if it's the same as previous measurement)
    void sendMotion(bool force) {
      bool tx = force;
      // Read digital motion value
      bool tripped = digitalRead(MOTION_SENSOR) == HIGH; 
      Serial.print(F("Tripped: ")); Serial.println(tripped);
      if (lastTripped != tripped) tx = true;
      if (tx) {
        resend(msg.set(tripped?"1":"0"),repeats);  // Send tripped value to gw 
        lastTripped = tripped;
     * Sends temperature and humidity from HTU21D sensor
     * Parameters
     * - force : Forces transmission of a value (even if it's the same as previous measurement)
    void sendTempHumidityMeasurement(bool force) 
        bool tx = force;
        float hum = myHumidity.readHumidity();
        float temp = myHumidity.readTemperature();
        Serial.print(F("lastTemperature: ")); Serial.println(lastTemperature);
        Serial.print(F("lastHumidity: ")); Serial.println(lastHumidity);
        float diffTemp = abs(lastTemperature - temp);
        float diffHum = abs(lastHumidity - hum);
    #ifdef MY_DEBUG
        Serial.print(F("TempDiff :"));Serial.println(diffTemp);
        Serial.print(F("HumDiff  :"));Serial.println(diffHum); 
        if (isnan(diffHum)) tx = true; 
        if (diffTemp > TEMP_TRANSMIT_THRESHOLD) tx = true;
        if (diffHum >= HUMI_TRANSMIT_THRESHOLD) tx = true;
        if (tx) {
          tempMeasureCount = 0;
          lastTemperature = temp;
          lastHumidity = hum;   
     * Sends light level from TLS6512 sensor
     * Parameters
     * - force : Forces transmission of a value (even if it's the same as previous measurement)
    void sendLightLevelMeasurement(bool force) {
      bool tx = force;
      uint32_t lum = myLight.getFullLuminosity();
      uint16_t ir, full;
      ir = lum >> 16;
      full = lum & 0xFFFF;
      Serial.print(F("IR: ")); Serial.print(ir);   Serial.print(F("\t\t"));
      Serial.print(F("Full: ")); Serial.print(full);   Serial.print(F("\t"));
      Serial.print(F("Visible: ")); Serial.print(full - ir);   Serial.print(F("\t"));
      double lux = myLight.calculateLux(full, ir);
      Serial.print(F("Lux: ")); Serial.println(lux);
      float diffLux = abs(lastLight - lux);
    #ifdef MY_DEBUG
        Serial.print(F("Lux difference since last measurement: ")); Serial.println((float)diffLux/abs(lastLight));    
        if (isnan(diffLux)) tx = true; 
        if (diffLux/abs(lastLight)  >= LIGHT_TRANSMIT_THRESHOLD) tx = true;
        if (tx) {
          lightMeasureCount = 0;
          lastLight = lux;
     * Prints error on I2C comm bus
    void printError(byte error)
      // If there's an I2C error, this function will
      // print out an explanation.
      Serial.print(F("I2C error: "));
      Serial.print(F(", "));
        case 0:
        case 1:
          Serial.println(F("data too long for transmit buffer"));
        case 2:
          Serial.println(F("received NACK on address (disconnected?)"));
        case 3:
          Serial.println(F("received NACK on data"));
        case 4:
          Serial.println(F("other error"));
          Serial.println(F("unknown error"));
     * Sends battery information (battery percentage)
     * Parameters
     * - force : Forces transmission of a value
    void sendBattLevel(bool force)
      if (force) lastBattery = -1;
      long batteryV =  analogRead(BATTERY_SENSE_PIN);  
      for (int i = 1; i<5; i++) {
        long newSample = analogRead(BATTERY_SENSE_PIN); //readVcc();
        batteryV -= batteryV / (i+1);
        batteryV += newSample / (i+1);   
       // 10M, 2,86M divider across battery and using internal ADC ref of 1.1V
       // Sense point is bypassed with 0.1 uF cap to reduce noise at that point
       // ((10+4,7)/4,7)*1.1 = 3.4404255
       // 3.4404255/1023 = Volts per bit = 0.003630748
      long vcc  = batteryV * 3.3630748;
      if (vcc != lastBattery) {
        lastBattery = vcc;
    #ifdef BATT_SENSOR
        // Calculate on the fully charged cell. Since I have a step-up in place I go as low as possible no offset for minimum
       sendBatteryLevel(  ((vcc-MIN_VOLTAGE)*10.0)/((MAX_VOLTAGE-MIN_VOLTAGE)*10.0) *100.0);
     * Send message, resend on error
     * Parameters
     * - msg : message to send
     * - repeats: number of repetitions
    void resend(MyMessage &msg, int repeats)
      int repeat = 0;
      int repeatdelay = 0;
      boolean sendOK = false;
      while ((sendOK == false) and (repeat < repeats)) {
        if (send(msg)) {
          sendOK = true;
        } else {
          sendOK = false;
          Serial.print(F("Send ERROR "));
          repeatdelay += random(50,200);
     * Internal battery ADC measuring 
    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__)
        ADcdMUX = _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

  • Thanks, @tomkxy, fantastic! I will be trying it our shortly, as soon as I got those PIRs working on 3V.

  • @Haakon Regarding the PIRs: There are a couple of postings in the Internet or I think even in this forum. For example, have a look here:

  • Hardware Contributor

    @tomkxy How did you power it though? I wanted to use a battery (or several ones) that might fall under 3.3V when used. So I decided to use a step-up converter but that seems to introduce too much noise, so I get false positives from the pir. From a stable 3.3V source it worked just fine.

  • @LastSamurai I powered it through 3.3v step up with one AA battery. I cannot confirm that I get false positives.

  • Plugin Developer


    What range on the PIR do you get on 3.3 V?

  • Around 4 meters. However, this puppy is sitting in my entrance which is rather narrow.

  • Hardware Contributor

    @tomkxy said:

    @LastSamurai I powered it through 3.3v step up with one AA battery. I cannot confirm that I get false positives.

    Nice, what PIR and what step up did you use? Hopefully I can get the same ones too 😉

  • I used this one one which is rather expensive. I do not remember, however whether I bought really at Sparkfun or some other place. That were one of my first purchases when I started with all that crazy stuff 🙂

  • Hi @tomkxy

    I'm going to add one of these sensors myself, looks like you've done the hard work...

    Could I ask what board you are using, perhaps a simple schematic too if you find a moment? I have a bunch of Nano's, some light sensors (BH1750) and temperature sensors (DS18B20's) - I presume I can swap over the code as required. Thankfully I also have a number of those exact step ups!

  • @Mark-Swift I used a ProMini 3.3v. Unfortunately, I have no schematic. Since I used breakout boards anyway this is not a big deal. You connect those boards to your power, ground and a digital pin or on SCA, SCL pins. I don't know what the power consumption of the Nano's is. So that is something you have to try out.

  • @tomkxy it is a few mA while sleeping. This means that it has to be modified (no VDO and no LED) - consumption drops to a reasonable 160uA or even below.