Python with Arduino LESSON 9: Measuring Pressure and Temperature with the BMP180 Sensor

One of our goals with this series of lessons is to learn how to plot live data in Python. To do that, we need some interesting streaming data from the Arduino. In this lesson we will provide a live stream of temperature and pressure data. We will hook up the circuit, program the arduino, and stream the temperature and pressure data over the serial port. Then in the next lesson, we will read the data stream into Python, and provide a live plot of the incoming data. We will be using the Adafruit BMP180 Pressure Sensor.

BMP180
This is the most excellent BMP180 Pressure Sensor from adafruit.

This is a really simple sensor to get set up. To connect it up, use the following connections:

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

 

With the circuit hooked up, you are ready to start coding. The first thing you will need to do is to download and install the adafruit library for this component. I prefer the API V1 version of the library, so we will download that one. Do not worry that the documentation lists a different part number. This is an upgraded version of the sensor, and the documentation still references the old part number. You can download the library for this part here:

https://learn.adafruit.com/bmp085/using-the-bmp085

Click the “Download the Adafruit_BMP085 Arduino Library” large green box. This will download as a zip folder. Open the zip folder, and then drag and drop the contents on your desktop.  You want the contents of the zip folder, not the zip folder itself. Rename the folder you dropped to your desktop “adafruitBMP180”. Now you need to drag and drop this folder into your arduino library folder. To find your arduino library folder, in the arduino IDE window, look in file, preferences. A window should pop open, and it should show you where your arduino sketchbook folder is.  Drop your adafruitBMP180 folder into the Library folder of your arduino sketchbook folder. If this is not perfectly clear, watch the video above and you can watch me do it step-by-step. Once your adafruitBMP180 folder is in your arduino library folder, you are ready to start writing your code. You need to kill your arduino IDE window and reopen it for it to find your new library.

Now, to get this sensor to work, you just need a few lines of code. To begin with, you must load the Wire.h library and the Adafruit_BMP085.h library (again, do not worry that the library is named after an earlier model of this sensor).  After loading the libraries, you will need to create a sensor object. Then in void setup you will need to start the sensor, and then in void loop begin making measurements. The code below is a nice example of how to do this.

Now run the program and check your serial monitor and you should see measurements of temperature and pressure. Pressure in Pascals is a big number. To convert Pascals to inches of Mercury, or in Hg, which is what the weather sites usually report, take the Pascal reading, and divide by 3386.389. Then you should be in Inches of Mercury and you can check your reading against a weather report for your area. The numbers should be close.

Python with Arduino LESSON 8: Introduction to Graphing with Matplotlib

While it is cool to create 3D visuals using vPython to represent our data coming from arduino, sometimes we want to make more quantitative graphs and charts from the data. To do this, we need to learn how to create graphs in Python. We do this using the library Matplotlib. We learned how to install and download this library in Python with Arduino LESSON 7: If you have not installed the library yet, make sure to go back and do in as shown in LESSON 7.

With the library installed, we are ready to learn Matplotlib. The video takes you through an introductory tutorial with step-by-step instructions. The code below is a sample of how to plot a sin and cos wave. You can watch the video, and then play around with the parameters to become familiar with this library.

 

Python with Arduino LESSON 7: Installing Matplotlib for Graphing

In this video we provide step-by-step instructions on how to install Matplotlib. Hopefully you have been following our lessons, and have already installed Python 2.7, the 32 bit version. If you stay on the same path as me as far as libraries and software versions, all my tutorials should work easily for you. In order for matplotlib to work, you need to have the numpy library installed. In Python with Arduino LESSON 2 we installed the vPython library. If you installed the vPython library, you already have numpy, as that was part of the vPython installation. If you have not already installed vPython, you should review that lesson now and do that.

Now, to install matplotlib, go to this page:

https://github.com/matplotlib/matplotlib/downloads/

If you are following my lessons and software versions, you will want to install this version, which should be towards the top of the page:

matplotlib-1.2.0.win32-py2.7.exe — Binary installer for 32-bit Windows, built using python.org’s 2.7 and Numpy 1.6.2

When the file downloads, then click on it and then follow the simple installation instructions.

Once it is installed you can test things with this simple program, which should plot a sine wave.

 

Python with Arduino LESSON 6: Installing PIP on Windows

In this series of lessons you have learned to send data from Arduino to Python, and then do some pretty cool things in Python. We have created little virtual worlds, and have done neat dynamic graphics. Unfortunately not all Python libraries are as easy to install as vPython and pySerial. Some are next to impossible to install. The good news is that there is a free program called PIP that will install just about any Python library very easily. We need to pause and install PIP. Many of the future lessons will require you to have PIP installed on your machine. Please follow along with me on the video, which shows you how to install PIP on your windows machine. These links will be useful. You can download pip at this link:

https://pip.pypa.io/en/latest/installing.html

Go to the section on PIP install as seen here:

Install PIP

Right mouse click on get-pip.py and download to your desktop. You will then want to run the program in python. We show you how to do this in the video above. Then, you need to edit your system path file by going to the control panel, select system, select advanced settings, and under environmental parameters select the path. Update your path file to show your system where your python folder is and where your python script folder is. If you are unsure of this, watch the video where I show you exactly how to do it. If you are adept with computers, you can just do it from this description. Add the two elements to your path. Adjust the parameters to reflect where your python installation is and where your python script folder is. For me, these are the two things added to my path:

C:\Python27

and

C:\Python27\Scripts

If you do not know exactly what I am saying, then watch the video for more detail.

Once you have these in your system path, you can test your PIP as follows.

Open a CMD box.

Type:

pip install -U pip

This asks pip to update itself. You should see it come up and indicate it is either up to date or is updating. This will tell you that you have the PIP installed correctly.

Your life with Python will now be much easier because your system now knows the path to both your Python program and your PIP installer.

Python with Arduino LESSON 5: Finishing our Virtual Reality Example

This Lesson finishes the work that was begun in Python with Arduino LESSON 4. In that lesson we built the circuit and programmed the arduino to measure the distance to a target and the color of the target. The program then output that data to the serial port. In today’s lesson we will use python to read that data stream, and use the data to dynamically update a virtual world we create.

You will need to start with the work in LESSON 4 to get your circuit working, and your arduino programmed up. Once you have done that, you are ready to use Python to program up your virtual world. Remember you will need to have the pyserial and the vPython libraries loaded. We showed how to install the software in Python with Arduino LESSON 2.

In the video we will go through the process step-by-step to create a virtual world. The code we end up with is posted below. You should not copy and paste the code, but just glance at it if you get stuck. In the end, you should develop your own virtual world and just use mine as a guide if you need more help.

 The video explains each line of the code.  Play around and tweak the values and see the effect on your virtual scene. Now your assignment is to take what you have learned here, and continue to expand your virtual world. Add objects to your virtual scene. Perhaps build an object for the breadboard, color sensor and arduino. I will give you several days to do this, and then when I come around for a project grade, I will want to see who has built the most impressive virtual scene. You should go well beyond the simple demonstration I have done here.

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