I was trying to find a way to measure the amount of gas our gas meter was using. I checked out several ways but they all involved using either a hall sensor or a reed switch or a IR sensor or a light sensor. But all of these would not work for my application for a number a reasons. First my meter is outside, second there is no magnet in my meter, third the utility company will not allow us to attach any device to the dials or the electronics of the meter (US smart meter). By the way my meter is a Rockwell 250 (Siemens). So after much researching I'm using a HMC5883L magnetometer. It measures very low magnetic fields.
Please forgive my lack of pictures and links but when I was assembling it I never thought about it. I can get some pictures of the finished sensor if needed.
I found the sweet spot on my gas meter using an Android app on my phone called Sensors Box, which allows one to access the magnetometer inside of the phone. While the gas was flowing I just moved it around over the meter until I found a fluctuation that coincided with the gas flow. This is what I call the "sweet spot". I then built a sensor using the HMC5883L per (https://www.sparkfun.com/tutorials/301). But as of this writing I found that they are no longer making it but do have a replacement (https://www.sparkfun.com/products/retired/10530). I have it successfully connected to my serial gateway and am using Domoticz as a controller.
The initial problem I found was trying to convert the output a the magnetometer to something useful. The data that comes out is stream of numbers from three vectors that goes up and down. After looking at them in the serial plotter of the Arduino IDE I found one vector (y in my case) that looked like a sine wave. Then with a lot of help from my son, who wrote most of the code for the Arduino, it seems to be putting out decent data. However it does need to be fine tuned.
What we ended up doing is auto detecting the top an bottom of the sine wave, then dividing it up into 10 pieces to get useful pulses.
I'm working on getting the Metric and English units out put correct but for now the metric units work OK. Any input is welcome:
UPDATE: 3/12/17 - we have been using the most recent sketch (v.6) and it has been running for two weeks now without a problem. I do plan some updates to the code that I hope will include an interactive serial monitor to set up the sensor for the first use. Also if you have looked at the picture of the sensor it is quite large and I would like to make it a bit smaller.
Does anyone have any idea how to make it smaller yet water proof?
/*
*
*
*
*
* Currently the autoDetectMaxMin in set to true which will find the TOP and BOTTOM of the wave, however if you want
* to use it the gas must be flowing.
*/
#define MY_DEBUG
#define MY_RADIO_NRF24
#include <MySensors.h>
#include <Wire.h> //I2C Arduino Library
#define CHILD_ID 1 //ID of the sensor child
#define SLEEP_MODE false //prevent sensor from sleeping
#define address 0x1E //0011110b, I2C 7bit address of HMC5883
int TOP = 0; //highest magnetic field registered from meter (Ga)Initialize low if using AutoDetectMaxMin
int BOTTOM = 10000; //lowest magnetic field registered from meter (Ga) Initialize high if using AutoDetectMaxMin
int tol = 50;
unsigned long SEND_FREQUENCY = 30000; // Minimum time between send (in milliseconds). We don't want to spam the gateway.
bool metric = true; //sets units to Metric or English
bool autoDetectMaxMin = true; //lets Arduino decide the values for TOP and BOTTOM
bool pcReceived = false; //whether or not the gw has sent us a pulse count
bool rising = true; //whether or not a pulse has been triggered
bool inside = true; //whether the magnetic field is within TOP and BOTTOM limits
unsigned long pulsecount = 0; //total number of pulses measured ever
unsigned long oldPulseCount = 0; //old total
double vpp = metric ? 0.17698 : 0.00625;//Volume of gas per pulse (Rockwell gas meter 250)
unsigned long lastSend = 0; //time since last transmission - msec
double volume = 0; //Cumulative amount of gas measured
const int len = 3; //number of flow rate measurements to save
double flow [len]; //array of previous gas flow rate measurements
double avgFlow = 0; //average of all elements in flow array
double oldAvgFlow = 0; //previous average flow
int divider = 1; //Current divider
int totDividers = 10; //Number of dividers
int increment = (TOP - BOTTOM) / totDividers; //space b/w dividers
MyMessage flowMsg(CHILD_ID,V_FLOW);
MyMessage volumeMsg(CHILD_ID,V_VOLUME);
MyMessage lastCounterMsg(CHILD_ID,V_VAR1);
void setup(){
//Initialize Serial and I2C communications
Serial.begin(9600);
Wire.begin();
// Fetch last known pulse count value from gw
request(CHILD_ID, V_VAR1);
//Put the HMC5883 IC into the correct operating mode
Wire.beginTransmission(address); //open communication with HMC5883
Wire.write(0x02); //select mode register
Wire.write(0x00); //continuous measurement mode
Wire.endTransmission();
int y = 0;
int oldy = 0;
//WARNING: MAKE SURE GAS IS RUNNING IF USING THIS OPTION!!!
if(autoDetectMaxMin){
//determine max and min magnetic field strength over a few minutes
lastSend = millis();
while(millis() - lastSend < 300000){
y = readMag();
if(y > TOP){
TOP = y; //update TOP if new max has been detected
}
else if(y < BOTTOM){
BOTTOM = y; //update BOTTOM if new min has been detected
}
}
TOP -= tol; //nudge TOP and BOTTOM so that they have a chance of being triggered
BOTTOM += tol;
increment = (TOP - BOTTOM) / totDividers; //recalculate increment to match new TOP and BOTTOM
autoDetectMaxMin = false; //finished determining TOP and BOTTOM
}
Serial.print("Increment = ");
Serial.println(increment);
y = readMag();
oldy = readMag();
while(abs(y - oldy) < increment / 2){ //wait until difference b/w y and oldy is greater than half an increment
y = readMag();
}
rising = (y > oldy);
Serial.println(rising ? "Magnetic field is rising" : "Magnetic field is falling");
}
void presentation()
{
// Send the sketch version information to the gateway and Controller
sendSketchInfo("Gas Meter", "0.4");
// Register this device as Gas sensor
present(CHILD_ID, S_GAS);
}
void loop(){
if (!pcReceived) {
//Last Pulsecount not yet received from controller, request it again
request(CHILD_ID, V_VAR1);
return;
}
//detecting magnetic pulses - Fractional Simple Method
while(millis() - lastSend < SEND_FREQUENCY){
int y = readMag();
if(inside && rising && y > BOTTOM + divider * increment){
divider++;
pulsecount++;
}
else if(inside && !rising && y < TOP - divider * increment){
divider++;
pulsecount++;
}
if(inside && (y > TOP || y < BOTTOM)){ //switch directions once TOP or BOTTOM divider has been reached
inside = false; //keep this from happening multiple times once signal exceeds TOP or BOTTOM
Serial.println("OUTSIDE");
}
else if(!inside && (y < TOP - increment / 2 && y > BOTTOM + increment / 2)){
rising = !rising;
divider = 1;
inside = true;
Serial.println("INSIDE");
}
}
//shift all flow array elements to the right by 1, ignore last element
for(int idx = len; idx > 0; idx--){
flow[idx] = flow[idx - 1];
}
//calculate newest flow reading and store it as first element in flow array
flow[0] = (double)(pulsecount - oldPulseCount) * (double)vpp * 60000.0 / (double)SEND_FREQUENCY;
//display flow array state
Serial.print("Flow Array State: [");
for(int idx = 0; idx < len - 1; idx++){
Serial.print(flow[idx]);
Serial.print("|");
}
Serial.print(flow[len]);
Serial.println("]");
//calculate average flow
avgFlow = 0; //reset avgFlow
for(int idx = 0; idx < len; idx++){ //calculate sum of all elements in flow array
avgFlow += flow[idx];
}
avgFlow /= len; //divide by number of elements to get average
Serial.print("Average flow: "); //display average flow
Serial.println(avgFlow);
//send flow message if avgFlow has changed
if(avgFlow != oldAvgFlow){
oldAvgFlow = avgFlow;
send(flowMsg.set(avgFlow, 2));
}
//send updated cumulative pulse count and volume data, if necessary
if(pulsecount != oldPulseCount){
oldPulseCount = pulsecount; //update old total
//calculate volume
volume = (double)oldPulseCount * (double)vpp / 1000.0;
//send pulse count and volume data to gw
send(lastCounterMsg.set(pulsecount));
send(volumeMsg.set(volume, 3));
}
lastSend = millis();
}
void receive(const MyMessage &message)
{
if (message.type==V_VAR1) {
unsigned long gwPulseCount=message.getULong();
pulsecount = gwPulseCount;
oldPulseCount = pulsecount;
Serial.print("Received last pulse count from gw:");
Serial.println(pulsecount);
pcReceived = true;
lastSend = millis();
}
}
int readMag(){
int x = 0, y = 0, z = 0;
//Tell the HMC5883 where to begin reading data
Wire.beginTransmission(address);
Wire.write(0x03); //select register 3, X MSB register - was called Wire.send but the compiler had an error and said to rename to to Wire.write
Wire.endTransmission();
//Read data from each axis, 2 registers per axis
Wire.requestFrom(address, 6);
if(6<=Wire.available()){
x = Wire.read()<<8; //X msb
x |= Wire.read(); //X lsb
z = Wire.read()<<8; //Z msb
z |= Wire.read(); //Z lsb
y = Wire.read()<<8; //Y msb
y |= Wire.read(); //Y lsb
}
if(!autoDetectMaxMin){
//show real-time magnetic field, pulse count, and pulse count total
Serial.print("y: ");
Serial.print(y);
Serial.print(rising ? " Rising, " : " Falling, ");
Serial.print("next pulse at: ");
Serial.print(rising ? BOTTOM + divider * increment : TOP - divider * increment);
Serial.print(" Current Number of Pulses: ");
Serial.print(pulsecount - oldPulseCount);
Serial.print(" Last Total Pulse Count Sent to GW: ");
Serial.println(oldPulseCount);
}
else{
//show real-time magnetic field, TOP, BOTTOM, and time left in auto-detect mode
Serial.print("y: ");
Serial.print(y);
Serial.print(" TOP: ");
Serial.print(TOP);
Serial.print(" BOTTOM: ");
Serial.print(BOTTOM);
unsigned long remainingTime = 300000 + lastSend - millis();
Serial.print(" Time remaining: ");
Serial.print(remainingTime / 60000);
Serial.print(":");
remainingTime = (remainingTime % 60000) / 1000;
if(remainingTime >= 10){
Serial.println(remainingTime);
}
else{
Serial.print("0");
Serial.println(remainingTime);
}
}
return y;
}
