Wireless Pressure Sensor – first results

JeeNode connected to XBee

JeeNode connected to XBee

Here you see my first setup of a JeeNode with pressure sensor connected to a XBee Series 2 module.  And it’s working! With Hyperterminal i captured the raw data coming in on my XStick:

XBee API mode packets with sensor data

XBee API mode packets with sensor data

The ‘experts’ will immediately recognize the first character (tilde, ~) as being the frame header of a XBee packet. The payload on the first line is ‘26311 39767’. All characters before that are XBee API frame related as well as the last character, which is the checksum. When you have a look at the code you can see what the payload is made of.

This is absolutely very cool; it think in total it has cost me an evening to put this all together; something i would have never dared dreaming about a year ago!

But there’s still a lot to do:

There seems to be a timing issue in the code, cause i saw the XBee having a bit of trouble joining the PAN. Maybe give it some more time in the setup routine, or give some more time during powering up the XBee to send a new sample… we’ll see.

I need to write some software on PC-side to test reliability of it all.

How long will the batteries survive? I haven’t got a clue… and how am i going to test this? For example, i can’t switch off my PC now, cause the XStick is powered by it; XStick not powered means no PAN means the XBee will keep on searching for the PAN and will use much much more power…

To make the whole package smaller, i need to stop using the pin headers on the JeeNode and just solder the wires right onto the board.

A big step ahead, but still a lot of questions to be answered…

Here’s the code that is currently running on the JeeNode:

#include <Ports.h>
#include <RF12.h>
#include "PortsBMP085.h"
#include <avr/sleep.h>
#include <NewSoftSerial.h>

NewSoftSerial XBSerial = NewSoftSerial(2, 3);
PortI2C two (2);
BMP085 psensor (two);

int pinXBee=7;                        // to Control XBee on/off
int pinCTS=6;                         // to monitor CTS

static int SampleInterval = 1000;     // 60000;
static int HeartBeatInterval = 10000; // 300000;
static int CTS=0;                     // value of XBee CTS pin

struct {
    int16_t temp;
    int32_t pres;
} payload;

static void lowPower (byte mode) {
    // prepare to go into power down mode
    // disable the ADC
    byte prrSave = PRR, adcsraSave = ADCSRA;
    ADCSRA &= ~ bit(ADEN);
    PRR &= ~ bit(PRADC);
    // zzzzz...
    // re-enable the ADC
    PRR = prrSave;
    ADCSRA = adcsraSave;

EMPTY_INTERRUPT(WDT_vect); // just wakes us up to resume

static void watchdogInterrupts (uint8_t mode) {
    MCUSR &= ~(1<<WDRF); // only generate interrupts, no reset
    WDTCSR |= (1<<WDCE) | (1<<WDE); // start timed sequence
    WDTCSR = bit(WDIE) | mode; // mode is a slightly quirky bit-pattern

static byte loseSomeTime (word msecs) {
    // only slow down for periods longer than twice the watchdog granularity
    if (msecs >= 32) {
        for (word ticks = msecs / 16; ticks > 0; --ticks) {
            lowPower(SLEEP_MODE_PWR_DOWN); // now completely power down
            // adjust the milli ticks, since we will have missed several
            extern volatile unsigned long timer0_millis;
            timer0_millis += 16L;
        return 1;
    return 0;

static MilliTimer SampleTimer;     // Interval for reading a sample from the BMP085
static MilliTimer HeartBeatTimer;  // forced maximum interval (Heartbeat)

static byte periodicSleep (word msecs) {
    // switch to idle mode while waiting for the next event
    return SampleTimer.poll(msecs);

static void Send (const void* ptr, byte len) {

  unsigned long tXB1;    // time XBee was woken up
  unsigned long tXB0;    // time XBee was put to sleep

  Serial.println("Sending payload");

  // wake up Xbee

  // wait for CTS to become LOW
  } while (CTS != LOW);

  // wait 2 msec otherwise data will be received all messed up

  // send dummy data
  XBSerial.print(" ");

  Serial.print(" ");

  // wait again for XBee to finish transmission

  // switch off XBee

static int16_t prevTemp;           // save previous temp value
static int32_t prevPres;           // save previous temp value

// this code is called once per second, but not all calls will be reported
int ReadSensor() {

    int16_t temp = psensor.measure(BMP085::TEMP);
    int32_t pres = psensor.measure(BMP085::PRES);

    Serial.print("Readings: ");
    Serial.print(' ');
    Serial.println(' ');

    int changed = (temp != prevTemp) || (pres != prevPres);
    prevTemp = temp;
    prevPres = pres;

    payload.temp = temp;
    payload.pres = pres;

    changed = 1;            // force sending always during testing
    return changed;


void setup() {

  // setup XBee
  digitalWrite(pinCTS,LOW);   // really necessary?

  // give XBee some time to join PAN

  // let the world know we're here

  watchdogInterrupts(0); // 16ms

void loop() {
    if (periodicSleep(SampleInterval)) {
      // sensor values changed or heartbeat interval elapsed?
      if (ReadSensor() || (HeartBeatTimer.poll(HeartBeatInterval)))
         Send(&payload, sizeof payload);


Making a Wireless Pressure Sensor

I don’t own a weather station, nor do i intend to buy one, but i always did like the idea of having a pressure sensor. Now i have 🙂

This BMP085 based pressure sensor doesn’t only do pressure, but can also measure the temperature. Time to hook it up to a JeeNode!

Due to the fact that our plans for today had to be canceled by the bad weather, i had some extra time to test this Pressure Sensor. First i had to solder the 2nd JeeNode i bought last week, cause it was still unassembled in it’s plastic bag. Soldering a JeeNode is quite easy to do; it’s really hard to do something wrong… This time i left the RF12 radio off because i wanted to use one of my XBee modules to send the raw measured values. And i attached a battery holder, cause eventually this is my goal: a battery powered pressure sensor.

I installed the Ports library, uploaded the BMP085 demo sketch from the Ports Library examples  to the JeeNode and everything ran fine:

BMP 26265 39759 225 99390
BMP 26260 39755 225 99372
BMP 26267 39761 226 99400
BMP 26263 39756 225 99378
BMP 26265 39759 225 99390
BMP 26263 39758 225 99384
BMP 26261 39757 225 99378

Next step will be adding code for the XBee and sleeping. To bad, time’s up for now… hopefully, later this evening i have some time left to finish this sensor.

JeeNodev4 with BMP085 Sensor

JeeNodev4 with BMP085 Sensor


They arrived last Tuesday. 2 JeeNodes, together with a JeeLink and a pressure sensor. And an additional Arduino for experimental stuff.



Although i had a lot of other things to do, i just couldn’t resist building at least one of the two i ordered. The JeePlug kit is easily soldered together so after half an hour i had my JeePlug and first JeeLink running. Next thing to do is get the Pressure Sensor working, receiving the data and processing it in my Domotica system.With all the information provided on Jean-Claude Wippler’s website that shouldn’t be a problem 🙂

So when you find a pressure chart on my website in the near future, you know where the data’s coming from…