Tag Archives: BMP180

Arduino Ethernet — This circuit contains an Arduino Nano and Pressure Sensor Communicating over Ethernet

In LESSON 16 we showed a simple Client Server model that allows us to send strings between Python running on a PC and the arduino over Ethernet. That lesson simply passed strings back and forth to show a very basic Server on Arduino, and Python acting as the Client. In this lesson we show a more practical example, with the Arduino connected to an Adafruit BMP180 Pressure Sensor. In order to complete this lesson, you will need an Arduino, an Ethernet Shield, and the Pressure Sensor. If you do not have this particular pressure sensor, you can probably follow along in the lesson using whatever sensor you have that is of interest. The video will take you through the tutorial step-by-step, and then the code we developed is shown below.

The key issue in getting this project to work is to get your mac address and IP address from your router or network. If you are at school, simply speak to your network administrator, and he will help you get an IP address for your arduino. If you are at home, you will need to connect to your router from a browser, and configure it to assign an IP address and agree on a mac address for your arduino. Some arduino Ethernet shields have a sticker with a mac address. If your Ethernet shield has a sticker with mac address, use that one. If it does not, you will need to come up with a unique mac address. There are thousands of possible routers and networks out there, so I can not help you with that part. But if you look in the router documentation, you should be able to get the IP address and mac address worked out. The arduino itself does not have a hard wired mac address, but you set the mac address in the arduino software, and the IP address as well. The key thing is that the mac address is unique on your network, and the router and arduino agree on the IP address and mac address. If you have a clearer way to explain this, please leave a comment below.

This is the server side software to run on the arduino. Again, you should use a suitable IP address and mac address for your network. Do not think you can just copy the ones I use in the code below.

#include <Ethernet.h> //Load Ethernet Library
#include <EthernetUdp.h> //Load the Udp Library
#include <SPI.h> //Load SPI Library

#include "Wire.h" //imports the wire library
#include "Adafruit_BMP085.h" // import the Pressure/Temperature sensor library
Adafruit_BMP085 mySensor; //Create a sensor object

float tempC; //Declare variable for Temp in C
float tempF; //Declare variable for Temp in F
float Pressure; //Declare a variable for Pressure

byte mac[] ={ 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEE}; //Assign mac address
IPAddress ip(10, 1, 15, 243); //Assign the IP Adress
unsigned int localPort = 5000; // Assign a port to talk over
char packetBuffer[UDP_TX_PACKET_MAX_SIZE]; //dimensian a char array to hold our data packet
String datReq; //String for our data
int packetSize; //Size of the packet
EthernetUDP Udp; // Create a UDP Object

void setup() {
  
  Serial.begin(9600); //Initialize Serial Port 
  Ethernet.begin( mac, ip); //Inialize the Ethernet
  Udp.begin(localPort); //Initialize Udp
  delay(1500); //delay
  mySensor.begin(); //initialize pressure-temp sensor
  

}

void loop() {
  
  packetSize =Udp.parsePacket(); //Reads the packet size
  
  if(packetSize>0) { //if packetSize is >0, that means someone has sent a request
    
    Udp.read(packetBuffer, UDP_TX_PACKET_MAX_SIZE); //Read the data request
    String datReq(packetBuffer); //Convert char array packetBuffer into a string called datReq
    
    if (datReq =="Temperature") { //Do the following if Temperature is requested
    
      tempC = mySensor.readTemperature(); //Read the temperature
      tempF = tempC*1.8 + 32; //Convert temp to F
      
      Udp.beginPacket(Udp.remoteIP(), Udp.remotePort()); //Initialize packet send
      Udp.print(tempF); //Send the temperature data
      Udp.endPacket(); //End the packet
      
    }
    
    if (datReq== "Pressure") { //Do the following if Pressure is requested
    
      Pressure=mySensor.readPressure(); //read the pressure
      
        Udp.beginPacket(Udp.remoteIP(), Udp.remotePort()); //Initialize packet send
        Udp.print(Pressure); //Send the Pressure data
        Udp.endPacket(); //End the packet
        
    }
      
  }
  memset(packetBuffer, 0, UDP_TX_PACKET_MAX_SIZE); //clear out the packetBuffer array
}

#include <Ethernet.h> //Load Ethernet Library

#include <EthernetUdp.h> //Load the Udp Library

#include <SPI.h> //Load SPI Library

#include "Wire.h" //imports the wire library

#include "Adafruit_BMP085.h" // import the Pressure/Temperature sensor library

Adafruit_BMP085 mySensor; //Create a sensor object

float tempC; //Declare variable for Temp in C

float tempF; //Declare variable for Temp in F

float Pressure; //Declare a variable for Pressure

byte mac[] ={ 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEE}; //Assign mac address

IPAddress ip(10, 1, 15, 243); //Assign the IP Adress

unsigned int localPort = 5000; // Assign a port to talk over

char packetBuffer[UDP_TX_PACKET_MAX_SIZE]; //dimensian a char array to hold our data packet

String datReq; //String for our data

int packetSize; //Size of the packet

EthernetUDP Udp; // Create a UDP Object

void setup() {

Serial.begin(9600); //Initialize Serial Port

Ethernet.begin( mac, ip); //Inialize the Ethernet

Udp.begin(localPort); //Initialize Udp

delay(1500); //delay

mySensor.begin(); //initialize pressure-temp sensor

}

void loop() {

packetSize =Udp.parsePacket(); //Reads the packet size

if(packetSize>0) { //if packetSize is >0, that means someone has sent a request

Udp.read(packetBuffer, UDP_TX_PACKET_MAX_SIZE); //Read the data request

String datReq(packetBuffer); //Convert char array packetBuffer into a string called datReq

if (datReq =="Temperature") { //Do the following if Temperature is requested

tempC = mySensor.readTemperature(); //Read the temperature

tempF = tempC*1.8 + 32; //Convert temp to F

Udp.beginPacket(Udp.remoteIP(), Udp.remotePort()); //Initialize packet send

Udp.print(tempF); //Send the temperature data

Udp.endPacket(); //End the packet

}

if (datReq== "Pressure") { //Do the following if Pressure is requested

Pressure=mySensor.readPressure(); //read the pressure

Udp.beginPacket(Udp.remoteIP(), Udp.remotePort()); //Initialize packet send

Udp.print(Pressure); //Send the Pressure data

Udp.endPacket(); //End the packet

}

memset(packetBuffer, 0, UDP_TX_PACKET_MAX_SIZE); //clear out the packetBuffer array

}

Once you have this on your arduino, and the arduino connected to the internet via an Ethernet cable, you can test by opening a command line in Windows. Then ping the address you have assigned to the Arduino. If it pings correctly and you get a reply, you are ready to develop the Python code. The Python will be the client. It will send the requests to the Arduino, and the Arduino will respond with data. Since our circuit can measure pressure or temperature, you can request either of those. When the arduino receives a request for temperature, it will go out, make the temperature measurement and then return the data to Python. Similarly, if you request Pressure the arduino will read the request, will make the Pressure measurement, and then return pressure reading to the client (Python).

from socket import *
import time

address= ( '10.1.15.243', 5000) #define server IP and port
client_socket =socket(AF_INET, SOCK_DGRAM) #Set up the Socket
client_socket.settimeout(1) #Only wait 1 second for a response

while(1):

    data = "Temperature" #Set data request to Temperature

    client_socket.sendto( data, address) #Send the data request

    try:

        rec_data, addr = client_socket.recvfrom(2048) #Read response from arduino
        temp = float(rec_data) #Convert string rec_data to float temp
        print "The Measured Temperature is ", temp, " degrees F." # Print the result

    except:
        pass

    time.sleep(2) #delay before sending next command

    data = "Pressure" #Set data request to Pressure

    client_socket.sendto( data, address) #Send the data request

    try:

        rec_data, addr = client_socket.recvfrom(2048) #Read response from arduino
        Pressure = float(rec_data) #Convert string rec_data to float temp
        print "The Measured Pressure is ", Pressure, " Pa." # Print the result

    except:
        pass

    time.sleep(2) #delay before sending next command

    print ""

from socket import *

import time

address= ( '10.1.15.243', 5000) #define server IP and port

client_socket =socket(AF_INET, SOCK_DGRAM) #Set up the Socket

client_socket.settimeout(1) #Only wait 1 second for a response

while(1):

data = "Temperature" #Set data request to Temperature

client_socket.sendto( data, address) #Send the data request

try:

rec_data, addr = client_socket.recvfrom(2048) #Read response from arduino

temp = float(rec_data) #Convert string rec_data to float temp

print "The Measured Temperature is ", temp, " degrees F." # Print the result

except:

pass

time.sleep(2) #delay before sending next command

data = "Pressure" #Set data request to Pressure

client_socket.sendto( data, address) #Send the data request

try:

rec_data, addr = client_socket.recvfrom(2048) #Read response from arduino

Pressure = float(rec_data) #Convert string rec_data to float temp

print "The Measured Pressure is ", Pressure, " Pa." # Print the result

except:

pass

time.sleep(2) #delay before sending next command

print ""

This python code will request Temperature, will then read the response, and then will print the data. It then requests Pressure, reads the response, and then prints it. If you look at our earlier lessons you can see graphical techniques to visually present the data. The hard part is getting the data passed back and forth, which we show how to do in this lesson.

Arduino, Tutorial

Arduino LESSON 21: Log Sensor Data to an SD Card

July 29, 2014 admin

In most of our work so far, we have just watched our data go by on the Serial Monitor. In most cases, you will want to have some means to store your data. The easiest way to do this is to use a simple SD card reader. For this example, we use the Virtuabotix SD Card Reader.

Arduino connected to a BMP180 pressure sensor and an SD Card Reader

In this tutorial, we will need to have some sensor hooked up so we will have some data to store. We will be using the BMP 180 Pressuer and Temperature sensor from adafruit. We have a complete tutorial on this sensor HERE. You will need to go to that lesson and get the sensor hooked up, the library installed, and the software done. All this is explained step-by-step in the LESSON.

The BMP180 is connected to the arduino as follows:

Connecting Up the BMP180 Pressure and Temperature Sensor
BMP180 Pin	Arduino Pin
Vin	5V
GND	GND
SCL	A5
SDA	A4

Once you have the BMP180 connected, test and make sure your code is working, and you are getting good pressure and temperature readings. Once that is working, you are ready to connect your SD card Reader/Writer.

The SD card reader should be connected as follows:

Connecting the SD Card Reader
Sd Card Reader Pin	Arduino Pin	Details
GND	GND	Common Ground
3.3 V – (NOT USED)
+5	5V	Power
CS	4	Chip Select
MOSI	11	SPI Data
SCK	13	Clock
MISO	12	SPI Data
GND	GND	Common Ground

In the video we will show step-by-step how to develop the software. You should follow along in the video, and not copy and paste the code below. You will never learn to program if you do not write your own code. The code below is to help you in case you get stuck.

#include <SD.h> //Load SD card library
#include<SPI.h> //Load SPI Library


#include "Wire.h"    // imports the wire library for talking over I2C 
#include "Adafruit_BMP085.h"  // import the Pressure Sensor Library We are using Version one of Adafruit API for this sensor
Adafruit_BMP085 mySensor;  // create sensor object called mySensor


float tempC;  // Variable for holding temp in C
float tempF;  // Variable for holding temp in F
float pressure; //Variable for holding pressure reading

int chipSelect = 4; //chipSelect pin for the SD card Reader
File mySensorData; //Data object you will write your sesnor data to

void setup(){
Serial.begin(9600); //turn on serial monitor
mySensor.begin();   //initialize pressure sensor mySensor

pinMode(10, OUTPUT); //Must declare 10 an output and reserve it
SD.begin(4); //Initialize the SD card reader
}

void loop() {
tempC = mySensor.readTemperature(); //  Read Temperature from BMP180
tempF = tempC*1.8 + 32.; // Convert degrees C to F
pressure=mySensor.readPressure(); //Read Pressure

mySensorData = SD.open("PTData.txt", FILE_WRITE);
if (mySensorData) {
Serial.print("The Temp is: "); //Print Your results
Serial.print(tempF);
Serial.println(" degrees F");
Serial.print("The Pressure is: ");
Serial.print(pressure);
Serial.println(" Pa.");
Serial.println("");
delay(250); //Pause between readings.


mySensorData.print(tempF);                             //write temperature data to card
mySensorData.print(",");                               //write a commma
mySensorData.println(pressure);                        //write pressure and end the line (println)
mySensorData.close();                                  //close the file
}
}

#include <SD.h> //Load SD card library

#include<SPI.h> //Load SPI Library

#include "Wire.h" // imports the wire library for talking over I2C

#include "Adafruit_BMP085.h" // import the Pressure Sensor Library We are using Version one of Adafruit API for this sensor

Adafruit_BMP085 mySensor; // create sensor object called mySensor

float tempC; // Variable for holding temp in C

float tempF; // Variable for holding temp in F

float pressure; //Variable for holding pressure reading

int chipSelect = 4; //chipSelect pin for the SD card Reader

File mySensorData; //Data object you will write your sesnor data to

void setup(){

Serial.begin(9600); //turn on serial monitor

mySensor.begin(); //initialize pressure sensor mySensor

pinMode(10, OUTPUT); //Must declare 10 an output and reserve it

SD.begin(4); //Initialize the SD card reader

}

void loop() {

tempC = mySensor.readTemperature(); // Read Temperature from BMP180

tempF = tempC*1.8 + 32.; // Convert degrees C to F

pressure=mySensor.readPressure(); //Read Pressure

mySensorData = SD.open("PTData.txt", FILE_WRITE);

if (mySensorData) {

Serial.print("The Temp is: "); //Print Your results

Serial.print(tempF);

Serial.println(" degrees F");

Serial.print("The Pressure is: ");

Serial.print(pressure);

Serial.println(" Pa.");

Serial.println("");

delay(250); //Pause between readings.

mySensorData.print(tempF); //write temperature data to card

mySensorData.print(","); //write a commma

mySensorData.println(pressure); //write pressure and end the line (println)

mySensorData.close(); //close the file

}

If you have the BMP180 and the SD card connected correctly, this should create a file called PTData.txt on the card, and write comma delimited data to the file. Note that if the file does not exist on the card, the command:

mySensorData = SD.open("PTData.txt", FILE_WRITE);

1	mySensorData = SD.open("PTData.txt", FILE_WRITE);

will create the file. If the file already exists, this command will append data to the existing file. If you want to start with a clean new data set, erase the old PTData file.

When you run the program, you end up with a PTData.txt file on the SD card. When you have finished logging your data, you can pop the card out, put it into your PC, and then import the data into excel. You should now be able to plot, graph or analyze the data using all the powerful features of Excel.

Arduino with Python, Tutorial

Python with Arduino LESSON 13: Calculating Height from Pressure measurements from BMP180 Pressure Sensor.

July 25, 2014 admin

It is time to bring together a lot of things we have learned in our earlier lessons to create a Height-O-Meter, which will plot how high our BMP180 pressure sensor is above the floor. For this lesson we make simplifying assumption of constant temperature. When we use the sensor for our space probe or other high altitude experiments we will need to derive the equation again to take into account changing temperature. We went through the math of calculating height from changing pressure in LESSON 12.

In this lesson, we start with the software we developed in LESSON 11 for measuring, streaming, and plotting pressure and temperature data from the BMP180 sensor.

Remember, we connect the sensor to the Arduino as follows:

Connecting Up the BMP180 Pressure and Temperature Sensor
BMP180 Pin	Arduino Pin
Vin	5V
GND	GND
SCL	A5
SDA	A4

The software we are using on the arduino side is shown below, from LESSON 11.

#include "Wire.h"    // imports the wire library for talking over I2C 
#include "Adafruit_BMP085.h"  // import the Pressure Sensor Library
Adafruit_BMP085 mySensor;  // create sensor object called mySensor

float tempC;  // Variable for holding temp in C
float tempF;  // Variable for holding temp in F
float pressure; //Variable for holding pressure reading

void setup(){
Serial.begin(115200); //turn on serial monitor
mySensor.begin();   //initialize mySensor
}

void loop() {
tempC = mySensor.readTemperature(); //  Be sure to declare your variables
tempF = tempC*1.8 + 32.; // Convert degrees C to F
pressure=mySensor.readPressure(); //Read Pressure


Serial.print(tempF);
Serial.print(" , ");
Serial.println(pressure);
delay(250); //Pause between readings.
}

#include "Wire.h" // imports the wire library for talking over I2C

#include "Adafruit_BMP085.h" // import the Pressure Sensor Library

Adafruit_BMP085 mySensor; // create sensor object called mySensor

float tempC; // Variable for holding temp in C

float tempF; // Variable for holding temp in F

float pressure; //Variable for holding pressure reading

void setup(){

Serial.begin(115200); //turn on serial monitor

mySensor.begin(); //initialize mySensor

}

void loop() {

tempC = mySensor.readTemperature(); // Be sure to declare your variables

tempF = tempC*1.8 + 32.; // Convert degrees C to F

pressure=mySensor.readPressure(); //Read Pressure

Serial.print(tempF);

Serial.print(" , ");

Serial.println(pressure);

delay(250); //Pause between readings.

}

We modify the Python code from LESSON 11 as explained in the video above to get this code for the Python side.

import serial # import Serial Library
import numpy as np  # Import numpy
import matplotlib.pyplot as plt #import matplotlib library
from drawnow import *
import time

tempF= []   #Array for our Temperature dat
pressure=[] #Array for our Pressure Data
ht=[]       #Array for our calculated Heights
arduinoData = serial.Serial('com11', 115200) #Creating our serial object named arduinoData
plt.ion() #Tell matplotlib you want interactive mode to plot live data
cnt=0

def makeFig(): #Create a function that makes our desired plot
    plt.ylim(0,10)                                 #Set y min and max values
    plt.title('My SuperCool Height-O-Meter')      #Plot the title
    plt.grid(True)                                  #Turn the grid on
    plt.ylabel('Height in Feet')                            #Set ylabels
    plt.plot(ht, 'ro-', label='Height')       #plot the height array
    plt.legend(loc='upper left')                    #plot the legend
    plt2=plt.twinx()                                #Create a second y axis
    plt.ylim(75,85)                           #Set limits of second y axis- adjust to readings you are getting
    plt2.plot(tempF, 'b^-', label='tempF') #plot temperature array
    plt2.set_ylabel('temp F')                    #label second y axis
    plt2.ticklabel_format(useOffset=False)           #Force matplotlib to NOT autoscale y axis
    plt2.legend(loc='upper right')                  #plot the legend

tempBucket = 0  #Create bucket to hold sum of temperature readings
PBucket=0       #Create bucket to hold sum of pressure readings

print "PLease put Sensor Circuit on Ground for Calibration"  #Calibrate sensor for readings on floor, P0
print "5"           #Give user time to put sensor on floor
time.sleep(1)
print "4"
time.sleep(1)
print "3"
time.sleep(1)
print "2"
time.sleep(1)
print "1"
time.sleep(1)
print "Calibrating Sensor . . ."

for i in np.arange(1,11,1):  #Loop ten times to take ten measurements
    while (arduinoData.inWaiting()==0): #Wait here until there is data
        pass #do nothing
    arduinoString = arduinoData.readline() #read the line of text from the serial port
    dataArray = arduinoString.split(',')   #Split it into an array called dataArray
    temp = float( dataArray[0])            #Convert first element to floating number and put in temp
    P =    float( dataArray[1])            #Convert second element to floating number and put in P
    print "P = ",P, " , Temp= ", temp
    tempBucket=tempBucket + temp
    PBucket = PBucket + P
P0 = PBucket/10  #Calcualte average pressure on floor
tempK = ((tempBucket/10)-32)/1.8 +273.15  #Calculate average temperature on floor in K

print "Baseline Temp in K is: ", tempK #Print resulrs
print "Baseline Pressure inPa. : ", P0
    


while True: # While loop that loops forever
    while (arduinoData.inWaiting()==0): #Wait here until there is data
        pass #do nothing
    arduinoString = arduinoData.readline() #read the line of text from the serial port
    dataArray = arduinoString.split(',')   #Split it into an array called dataArray
    temp = float( dataArray[0])            #Convert first element to floating number and put in temp
    P =    float( dataArray[1])            #Convert second element to floating number and put in P
    h=98.57*tempK*np.log(P0/P)
    ht.append(h)
    tempF.append(temp)                     #Build our tempF array by appending temp readings
    pressure.append(P)                     #Building our pressure array by appending P readings
    drawnow(makeFig)                       #Call drawnow to update our live graph
    plt.pause(.000001)                     #Pause Briefly. Important to keep drawnow from crashing
    cnt=cnt+1
    if(cnt>50):                            #If you have 50 or more points, delete the first one from the array
        tempF.pop(0)                       #This allows us to just see the last 50 data points
        pressure.pop(0)
        ht.pop(0)

import serial # import Serial Library

import numpy as np # Import numpy

import matplotlib.pyplot as plt #import matplotlib library

from drawnow import *

import time

tempF= [] #Array for our Temperature dat

pressure=[] #Array for our Pressure Data

ht=[] #Array for our calculated Heights

arduinoData = serial.Serial('com11', 115200) #Creating our serial object named arduinoData

plt.ion() #Tell matplotlib you want interactive mode to plot live data

cnt=0

def makeFig(): #Create a function that makes our desired plot

plt.ylim(0,10) #Set y min and max values

plt.title('My SuperCool Height-O-Meter') #Plot the title

plt.grid(True) #Turn the grid on

plt.ylabel('Height in Feet') #Set ylabels

plt.plot(ht, 'ro-', label='Height') #plot the height array

plt.legend(loc='upper left') #plot the legend

plt2=plt.twinx() #Create a second y axis

plt.ylim(75,85) #Set limits of second y axis- adjust to readings you are getting

plt2.plot(tempF, 'b^-', label='tempF') #plot temperature array

plt2.set_ylabel('temp F') #label second y axis

plt2.ticklabel_format(useOffset=False) #Force matplotlib to NOT autoscale y axis

plt2.legend(loc='upper right') #plot the legend

tempBucket = 0 #Create bucket to hold sum of temperature readings

PBucket=0 #Create bucket to hold sum of pressure readings

print "PLease put Sensor Circuit on Ground for Calibration" #Calibrate sensor for readings on floor, P0

print "5" #Give user time to put sensor on floor

time.sleep(1)

print "4"

time.sleep(1)

print "3"

time.sleep(1)

print "2"

time.sleep(1)

print "1"

time.sleep(1)

print "Calibrating Sensor . . ."

for i in np.arange(1,11,1): #Loop ten times to take ten measurements

while (arduinoData.inWaiting()==0): #Wait here until there is data

pass #do nothing

arduinoString = arduinoData.readline() #read the line of text from the serial port

dataArray = arduinoString.split(',') #Split it into an array called dataArray

temp = float( dataArray[0]) #Convert first element to floating number and put in temp

P = float( dataArray[1]) #Convert second element to floating number and put in P

print "P = ",P, " , Temp= ", temp

tempBucket=tempBucket + temp

PBucket = PBucket + P

P0 = PBucket/10 #Calcualte average pressure on floor

tempK = ((tempBucket/10)-32)/1.8 +273.15 #Calculate average temperature on floor in K

print "Baseline Temp in K is: ", tempK #Print resulrs

print "Baseline Pressure inPa. : ", P0

while True: # While loop that loops forever

while (arduinoData.inWaiting()==0): #Wait here until there is data

pass #do nothing

arduinoString = arduinoData.readline() #read the line of text from the serial port

dataArray = arduinoString.split(',') #Split it into an array called dataArray

temp = float( dataArray[0]) #Convert first element to floating number and put in temp

P = float( dataArray[1]) #Convert second element to floating number and put in P

h=98.57*tempK*np.log(P0/P)

ht.append(h)

tempF.append(temp) #Build our tempF array by appending temp readings

pressure.append(P) #Building our pressure array by appending P readings

drawnow(makeFig) #Call drawnow to update our live graph

plt.pause(.000001) #Pause Briefly. Important to keep drawnow from crashing

cnt=cnt+1

if(cnt>50): #If you have 50 or more points, delete the first one from the array

tempF.pop(0) #This allows us to just see the last 50 data points

pressure.pop(0)

ht.pop(0)

Please go through video for complete description of this software. Remember this is only valid for small changes in height over which temperature is constant.

Arduino with Python

Python with Arduino LESSON 12: Approximating Changes in Height from Changes in Pressure

July 25, 2014 admin

In LESSON 9 we learned how to hook up a BMP180 Pressure Sensor and make pressure and temperature readings. Then in LESSON 11 we learned how to stream that data to Matplotlib and create live graphs and charts of our data that update in real time. We could see that as we moved the pressure sensor up and down, we could see the pressure change, as the pressure decreases with increasing elevation.

This leads to the interesting question of whether we can use our circuit developed in LESSON 9 to create a Height-O-Meter . . . a simple device that will measure the height above the floor.

The math to calculate altitude vs. pressure turns out to be very complex. Particularly, if we wanted something for our high altitude balloon flights, or for model rocketry. It turns out that for the case of measuring height inside and for relatively small changes in height we can make simplifying assumptions that make things much easier. The assumption we will make is that temperature does not change much over the range of our experiment. With this assumption, we can create our own Height-O-Meter. To do this though, we do need to to through some math. I show my math below, and go through it step-by-step in the video. Remember, this simplified approach is only valid for playing around with small changes in height. We will have to do the more complicated math when we make our high altitude balloon probe. For now though, this math will work pretty well.

Height and Pressure — Calculate Changes in Height from Changes in Pressure

We can rearrange the equation to solve for height as a function of pressure.

Height Pressure — Calculating Height from Pressure Changes

Arduino with Python, Tutorial

Python with Arduino LESSON 11: Plotting and Graphing Live Data from Arduino with Matplotlib

July 24, 2014 admin

We now have all the pieces put together to allow us to plot live data from the Arduino. If you have kept up with the earlier lessons, you will now have everything you need. If you have not done the earlier lessons, make sure you have python 2.7, vPython and pySerial installed from Python with Arduino LESSON 2. Make sure you have installed matplotlib (Python with Arduino LESSON 7), and install drawnow (Python with Arduino LESSON 10). Also, you need to build the BMP180 circuit and get the arduino programmed up as explained in Python with Arduino LESSON 9. With this business taken care of, you are now ready to start plotting live data.

Pressure Data — This chart shows live pressure and temperature data being plotted in real time

We are using the Adafruit BMP180 pressure sensor. We showed how to hook it up and program it in LESSON 9. As a reminder, we are using this code for the arduino. LESSON 9 explained in detail how the code works.

#include "Wire.h"    // imports the wire library for talking over I2C 
#include "Adafruit_BMP085.h"  // import the Pressure Sensor Library
Adafruit_BMP085 mySensor;  // create sensor object called mySensor

float tempC;  // Variable for holding temp in C
float tempF;  // Variable for holding temp in F
float pressure; //Variable for holding pressure reading

void setup(){
Serial.begin(115200); //turn on serial monitor
mySensor.begin();   //initialize mySensor
}

void loop() {
tempC = mySensor.readTemperature(); //  Be sure to declare your variables
tempF = tempC*1.8 + 32.; // Convert degrees C to F
pressure=mySensor.readPressure(); //Read Pressure


Serial.print(tempF);
Serial.print(" , ");
Serial.println(pressure);
delay(250); //Pause between readings.
}

#include "Wire.h" // imports the wire library for talking over I2C

#include "Adafruit_BMP085.h" // import the Pressure Sensor Library

Adafruit_BMP085 mySensor; // create sensor object called mySensor

float tempC; // Variable for holding temp in C

float tempF; // Variable for holding temp in F

float pressure; //Variable for holding pressure reading

void setup(){

Serial.begin(115200); //turn on serial monitor

mySensor.begin(); //initialize mySensor

}

void loop() {

tempC = mySensor.readTemperature(); // Be sure to declare your variables

tempF = tempC*1.8 + 32.; // Convert degrees C to F

pressure=mySensor.readPressure(); //Read Pressure

Serial.print(tempF);

Serial.print(" , ");

Serial.println(pressure);

delay(250); //Pause between readings.

}

The video in this lesson above explains step-by-step how to develop the code on the Python side, and how matplotlib and drawnow work together to make live graphs and plots of data streaming from the arduino in real time. The code below is what we developed in the video. Do not simply cut and paste this code, but make sure that you understand it so you are able to create your own live graphing programs from scratch. If you are in my class, you will be required to be able to develop live graphing code like this from scratch, so don’t take a shortcut and copy and paste.

import serial # import Serial Library
import numpy  # Import numpy
import matplotlib.pyplot as plt #import matplotlib library
from drawnow import *

tempF= []
pressure=[]
arduinoData = serial.Serial('com11', 115200) #Creating our serial object named arduinoData
plt.ion() #Tell matplotlib you want interactive mode to plot live data
cnt=0

def makeFig(): #Create a function that makes our desired plot
    plt.ylim(80,90)                                 #Set y min and max values
    plt.title('My Live Streaming Sensor Data')      #Plot the title
    plt.grid(True)                                  #Turn the grid on
    plt.ylabel('Temp F')                            #Set ylabels
    plt.plot(tempF, 'ro-', label='Degrees F')       #plot the temperature
    plt.legend(loc='upper left')                    #plot the legend
    plt2=plt.twinx()                                #Create a second y axis
    plt.ylim(93450,93525)                           #Set limits of second y axis- adjust to readings you are getting
    plt2.plot(pressure, 'b^-', label='Pressure (Pa)') #plot pressure data
    plt2.set_ylabel('Pressrue (Pa)')                    #label second y axis
    plt2.ticklabel_format(useOffset=False)           #Force matplotlib to NOT autoscale y axis
    plt2.legend(loc='upper right')                  #plot the legend
    

while True: # While loop that loops forever
    while (arduinoData.inWaiting()==0): #Wait here until there is data
        pass #do nothing
    arduinoString = arduinoData.readline() #read the line of text from the serial port
    dataArray = arduinoString.split(',')   #Split it into an array called dataArray
    temp = float( dataArray[0])            #Convert first element to floating number and put in temp
    P =    float( dataArray[1])            #Convert second element to floating number and put in P
    tempF.append(temp)                     #Build our tempF array by appending temp readings
    pressure.append(P)                     #Building our pressure array by appending P readings
    drawnow(makeFig)                       #Call drawnow to update our live graph
    plt.pause(.000001)                     #Pause Briefly. Important to keep drawnow from crashing
    cnt=cnt+1
    if(cnt>50):                            #If you have 50 or more points, delete the first one from the array
        tempF.pop(0)                       #This allows us to just see the last 50 data points
        pressure.pop(0)

import serial # import Serial Library

import numpy # Import numpy

import matplotlib.pyplot as plt #import matplotlib library

from drawnow import *

tempF= []

pressure=[]

arduinoData = serial.Serial('com11', 115200) #Creating our serial object named arduinoData

plt.ion() #Tell matplotlib you want interactive mode to plot live data

cnt=0

def makeFig(): #Create a function that makes our desired plot

plt.ylim(80,90) #Set y min and max values

plt.title('My Live Streaming Sensor Data') #Plot the title

plt.grid(True) #Turn the grid on

plt.ylabel('Temp F') #Set ylabels

plt.plot(tempF, 'ro-', label='Degrees F') #plot the temperature

plt.legend(loc='upper left') #plot the legend

plt2=plt.twinx() #Create a second y axis

plt.ylim(93450,93525) #Set limits of second y axis- adjust to readings you are getting

plt2.plot(pressure, 'b^-', label='Pressure (Pa)') #plot pressure data

plt2.set_ylabel('Pressrue (Pa)') #label second y axis

plt2.ticklabel_format(useOffset=False) #Force matplotlib to NOT autoscale y axis

plt2.legend(loc='upper right') #plot the legend

while True: # While loop that loops forever

while (arduinoData.inWaiting()==0): #Wait here until there is data

pass #do nothing

arduinoString = arduinoData.readline() #read the line of text from the serial port

dataArray = arduinoString.split(',') #Split it into an array called dataArray

temp = float( dataArray[0]) #Convert first element to floating number and put in temp

P = float( dataArray[1]) #Convert second element to floating number and put in P

tempF.append(temp) #Build our tempF array by appending temp readings

pressure.append(P) #Building our pressure array by appending P readings

drawnow(makeFig) #Call drawnow to update our live graph

plt.pause(.000001) #Pause Briefly. Important to keep drawnow from crashing

cnt=cnt+1

if(cnt>50): #If you have 50 or more points, delete the first one from the array

tempF.pop(0) #This allows us to just see the last 50 data points

pressure.pop(0)

You should be seeing data like the graph on the top of this lesson. You will probably need to adjust your y-axis scale parameters in Python to ensure the scale is suitable for the data you are taking. If your chart is blank, likely your y-scales are not right for your data measurements.

Technology Tutorials

Tag Archives: BMP180

Python with Arduino LESSON 17: Sending and Receiving Data Over Ethernet

Arduino LESSON 21: Log Sensor Data to an SD Card

Connecting Up the BMP180 Pressure and Temperature Sensor

Connecting the SD Card Reader

Python with Arduino LESSON 13: Calculating Height from Pressure measurements from BMP180 Pressure Sensor.

Connecting Up the BMP180 Pressure and Temperature Sensor

Python with Arduino LESSON 12: Approximating Changes in Height from Changes in Pressure

Python with Arduino LESSON 11: Plotting and Graphing Live Data from Arduino with Matplotlib

Making The World a Better Place One High Tech Project at a Time. Enjoy!