Electronics Experiments with PSLab

Numerous college level electronics experiments can be performed using Pocket Science Lab (PSLab). The Android app and the Desktop app have all the essential features needed to perform these experiments and both these apps have quite a large number of experiments built-in. Some of the common experiments involve the use of BJT (Bipolar Junction Transistor), Zener Diode, FET (Field Effect Transistor), Op-Amp ( Operational Amplifier) etc. This blog walks through the details of performing some experiments using the above commonly used elements.  

The materials required for all the experiments are minimal and includes a few things like PSLab hardware device, components like Diodes, Transistors, Op-Amps etc., connecting wires/jumpers and secondary components like resistors, capacitors etc. Most of these elements would be a part of the PSLab Accessory Kit.

It is recommended to read this blog here, go through the resources mentioned at the end and also get acquainted with construction of circuits before advancing with the experiments mentioned in this blog.

Half Wave and Full Wave Rectifiers

The Bipolar Junction Transistor (BJT) can be used as a rectifier. Rectifiers are needed in circuits to obtain a nearly constant and stable output voltage and prevent any ripples in the circuit. The rectifier can be half wave or full wave depending on whether it rectifies one or both cycles of Alternating Voltage.

The circuit for the Half and Full Wave rectifier is given as follows:

  • Construct the above circuits on a breadboard.
  • For the half wave rectifier, connect the terminals of CH1 and GND of PSLab on the input side and the terminals of CH2 and GND on the output side.
  • The terminals of W1 and GND are also connected on the input side and they are used to generate a sine wave.
  • Use the PSLab Desktop App and open the Waveform Generator in Control. Set the wave type of W1 to Sine and set the frequency at 100 Hz and magnitude to 10mV. Then go ahead and open the Oscilloscope.
  • CH1 would display the input waveform and CH2 will display the output waveform and the plots can be observed.
  • The plot obtained will have rectification in only half of the cycle. In order to obtain rectification in the complete cycle, the full wave rectifier is needed.
  • For the full wave rectifier, the procedure is the same but an additional diode is used. Use an additional channel CH3 to plot the extra input.

  • The plot obtained from the above steps would still have ripples and so a capacitor is placed in parallel to cancel this effect.
  • Place a 100uF/330uF capacitor in parallel to the resistor RL and an additional 1 ohm resistor in the circuit.

BJT Inverter

  • Transistor has a lot of functions. The most common of them is its use as an amplifier. However, transistor can be used as a switch in a circuit i.e. as an inverter.
  • The circuit for this experiment is shown below. For this experiment, it is recommended to use an external 5V DC supply like a battery. Connect the transistor and the diode initially and then connect the resistors accordingly. (Connect the terminals of diode and transistor carefully else they will be damaged).
  • When the circuit is constructed completely, connect CH1 to Vi and CH2 to Vo. Vi and Vo are input and outputs respectively and are marked in the figure.
  • The terminals of W1 and GND are also connected on the input side and they are used to generate a sine wave.
  • Use the PSLab Desktop App and open the Waveform Generator in Control. Set the wave type of W1 to Sine and set the frequency at 200 Hz and magnitude to 10mV.
  • Then go ahead and open the Oscilloscope. Use the X-Y mode of the oscilloscope to obtain the plot between Vi and Vo which should look like the graph shown below.

Common Mode Gain and Differential Mode Gain in Op-Amps

Gain of any amplifier can be calculated by calculating the ratio of the output and input voltage. On plotting the graph in X-Y mode, a Vo vs Vi graph is obtained. The slope of that graph gives us the gain at any particular input voltage.

  • For finding the Differential Mode gain of an Op-Amp, construct the circuit as shown below.
  • When the circuit is constructed completely, connect CH1 to Vi and CH2 to Vo. Vi and Vo are input and outputs respectively and are marked in the figure. The terminals of W1 and GND are also connected on the input side and they are used to generate a sine wave.
  • The power supply provided to the Op-Amp are set to + 12V. (If faced with any confusion, please refer to the resources mentioned at the end of the blog to learn more about Op-Amps before proceeding ahead.)
  • Use the PSLab Desktop App and open the Waveform Generator in Control. Set the wave type of W1 to Sine and set the frequency at 1000 Hz and magnitude to 0.5V. Then go ahead and open the Oscilloscope. Use the X-Y mode of the oscilloscope to obtain the plot between Vi and Vo.
  • For finding the Common Mode gain of the Op-Amp, remove the waveform generator input i.e W1 from R3 and attach it to R2. The rest of the steps remain the same.

Schmitt Trigger

In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input signal to a digital output signal.

  • Construct the circuit as shown below. Although the diagram shows a variable resistor be used, a constant value resistor would also work fine.
  • When the circuit is constructed completely, connect CH1 to Vi and CH2 to Vo. Vi and Vo are input and outputs respectively and are marked in the figure. The terminals of W1 and GND are also connected on the input side and they are used to generate a sine wave.
  • The power supply provided to the Op-Amp are set to + 12V. (If faced with any confusion, please refer to the resources mentioned at the end of the blog to learn more about Op-Amps before proceeding ahead. If done incorrectly, Op-Amps will be damaged)
  • Use the PSLab Desktop App and open the Waveform Generator in Control. Set the wave type of W1 to Sine and set the frequency at 1000 Hz and magnitude to 0.5V. Then go ahead and open the Oscilloscope. Use the X-Y mode of the oscilloscope to obtain the plot between Vi and Vo which should look like the graph shown below.

Resources:

  1. Read more about Half wave and Full wave rectifier and their applications – https://en.wikipedia.org/wiki/Rectifier
  2. Read more about the Bipolar Junction Transistor and its use as a switch – http://www.electronicshub.org/transistor-as-switch/
  3. Understand the common mode and differential mode of Op-Amp – https://www.allaboutcircuits.com/video-lectures/op-amps-common-differential/
  4. Find more about Schmitt Trigger and its uses – https://en.wikipedia.org/wiki/Schmitt_trigger

Continue Reading Electronics Experiments with PSLab

SPI Communication in PSLab

PSLab supports communication using the Serial Peripheral Interface (SPI) protocol. The Desktop App as well as the Android App have the framework set-up to use this feature. SPI protocol is mainly used by a few sensors which can be connected to PSLab. For supporting SPI communication, the PSLab Communication library has a dedicated class defined for SPI. A brief overview of how SPI communication works and its advantages & limitations can be found here.

The class dedicated for SPI communication with numerous methods defined in them. The methods required for a particular SPI sensor may differ slightly, however, in general most sensors utilise a certain common set of methods. The set of methods that are commonly used are listed below with their functions.

In the setParameters method, the SPI parameters like Clock Polarity (CKP/CPOL), Clock Edge (CKE/CPHA), SPI modes (SMP) and other parameters like primary and secondary prescalar which are specific to the device used.

Primary Prescaler (0,1,2,3) for 64MHz clock->(64:1,16:1,4:1,1:1)

Secondary prescaler (0,1,..7)->(8:1,7:1,..1:1)

The values of CKP/CPOL and CKE/CPHA needs to set using the following convention and according to our requirements.

  • At CPOL=0 the base value of the clock is zero, i.e. the idle state is 0 and active state is 1.
    • For CPHA=0, data is captured on the clock’s rising edge (low→high transition) and data is changed at the falling edge (high→low transition).
    • For CPHA=1, data is captured on the clock’s falling edge (high→low transition) and data is changed at the rising edge (low→high transition).
  • At CPOL=1 the base value of the clock is one (inversion of CPOL=0), i.e. the idle state is 1 and active state is 0.
    • For CPHA=0, data is captured on the clock’s falling edge (high→low transition) and data is changed at the rising edge (low→high transition).
    • For CPHA=1, data is captured on the clock’s rising edge (low→high transition) and data is changed at the falling edge (high→low transition).

public void setParameters(int primaryPreScalar, int secondaryPreScalar, Integer CKE, Integer CKP, Integer SMP) throws IOException {
        if (CKE != null) this.CKE = CKE;
        if (CKP != null) this.CKP = CKP;
        if (SMP != null) this.SMP = SMP;

        packetHandler.sendByte(commandsProto.SPI_HEADER);
        packetHandler.sendByte(commandsProto.SET_SPI_PARAMETERS);
        packetHandler.sendByte(secondaryPreScalar | (primaryPreScalar << 3) | (this.CKE << 5) | (this.CKP << 6) | (this.SMP << 7));
        packetHandler.getAcknowledgement();
    }

 

The start method is responsible for sending the instruction to initiate the SPI communication and it takes the channel which will be used for communication as input.

public void start(int channel) throws IOException {
        packetHandler.sendByte(commandsProto.SPI_HEADER);
        packetHandler.sendByte(commandsProto.START_SPI);
        packetHandler.sendByte(channel);
    }

 

The setCS method is responsible for selecting the slave with which the SPI communication has to be done. This feature of SPI communication is known as Chip Select (CS) or Slave Select (SS). A master can use multiple Chip/Slave Select pins for communication whereas a slave utilises just one pin as SPI is based on single master multiple slaves principle. The capacity of PSLab is limited to two slave devices at a time.

public void setCS(String channel, int state) throws IOException {
        String[] chipSelect = new String[]{"CS1", "CS2"};
        channel = channel.toUpperCase();
        if (Arrays.asList(chipSelect).contains(channel)) {
            int csNum = Arrays.asList(chipSelect).indexOf(channel) + 9;
            packetHandler.sendByte(commandsProto.SPI_HEADER);
            if (state == 1)
                packetHandler.sendByte(commandsProto.STOP_SPI);
            else
                packetHandler.sendByte(commandsProto.START_SPI);
            packetHandler.sendByte(csNum);
        } else {
            Log.d(TAG, "Channel does not exist");
        }
    }

 

The stop method is responsible for sending the instruction to the stop the communication with the slave.

public void stop(int channel) throws IOException {
        packetHandler.sendByte(commandsProto.SPI_HEADER);
        packetHandler.sendByte(commandsProto.STOP_SPI);
        packetHandler.sendByte(channel);
    }

 

PSLab SPI class has methods defined for sending either 8-bit or 16-bit data over SPI which are further classified on whether they request the acknowledgement byte (it helps to know whether the communication was successful or unsuccessful) or not.

The methods are so named send8, send16, send8_burst and send16_burst . The burst methods do not request any acknowledgement value and as a result work faster than the normal methods.

public int send16(int value) throws IOException {
        packetHandler.sendByte(commandsProto.SPI_HEADER);
        packetHandler.sendByte(commandsProto.SEND_SPI16);
        packetHandler.sendInt(value);
        int retValue = packetHandler.getInt();
        packetHandler.getAcknowledgement();
        return retValue;
    }

 

Resources:

Continue Reading SPI Communication in PSLab

I2C Communication in PSLab

PSLab supports communication using the I2C protocol and both the Desktop App and the Android App have the framework set-up to use the I2C protocol. I2C protocol is mainly used by sensors which can be connected to PSLab. For supporting I2C communication, PSLab board has a separate block for I2C communication and has pins named 3.3V, GND, SCL and SDA. A brief overview of how I2C communication works and its advantages & limitations compared to SPI communication can be found here.

The PSLab Python and Java communication libraries have a class dedicated for I2C communication with numerous methods defined in them. The methods required for a particular I2C sensor may differ, however, in general most sensors utilise a certain common set of methods. The set of methods that are commonly used are listed below with their functions. For utilising the methods, the I2C bus is first notified using the HEADER byte (it is common to all the methods) and then a byte to uniquely determine the method in use.

The send method is used to send the data over the I2C bus. First the I2C bus is initialised and set to the correct slave address using I2C.start(address) followed by this method. The method takes the data to be sent as the argument.

def send(self, data):
    try:
        self.H.__sendByte__(CP.I2C_HEADER)
        self.H.__sendByte__(CP.I2C_SEND)
        self.H.__sendByte__(data)  # data byte
        return self.H.__get_ack__() >> 4
    except Exception as ex:
        self.raiseException(ex, "Communication Error , Function : " + inspect.currentframe().f_code.co_name)

 

The read method reads a fixed number of bytes from the I2C slave. One can also use I2C.simpleRead(address,  numbytes) instead to read from the I2C slave. This method takes the length of the data to be read as argument.  It fetches length-1 bytes with acknowledge bits for each.

def read(self, length):
     data = []
     try:
        for a in range(length - 1):
             self.H.__sendByte__(CP.I2C_HEADER)
             self.H.__sendByte__(CP.I2C_READ_MORE)
             data.append(self.H.__getByte__())
             self.H.__get_ack__()
       self.H.__sendByte__(CP.I2C_HEADER)
       self.H.__sendByte__(CP.I2C_READ_END)
       data.append(self.H.__getByte__())
       self.H.__get_ack__()
    except Exception as ex:
       self.raiseException(ex, "Communication Error , Function : " + inspect.currentframe().f_code.co_name)
   return data

 

The readBulk method reads the data from the I2C slave. This takes the I2C slave device address, the address of the device from which the data is to be read and the length of the data to be read as argument and the returns the bytes read in the form of a list.

def readBulk(self, device_address, register_address, bytes_to_read):
        try:
            self.H.__sendByte__(CP.I2C_HEADER)
            self.H.__sendByte__(CP.I2C_READ_BULK)
            self.H.__sendByte__(device_address)
            self.H.__sendByte__(register_address)
            self.H.__sendByte__(bytes_to_read)
            data = self.H.fd.read(bytes_to_read)
            self.H.__get_ack__()
            try:
                return [ord(a) for a in data]
            except:
                print('Transaction failed')
                return False
        except Exception as ex:
           self.raiseException(ex, "Communication Error , Function : " + inspect.currentframe().f_code.co_name)

 

The writeBulk method writes the data to the I2C slave. It takes address of the particular I2C slave for which the data is to be written and the data to be written as arguments.

def writeBulk(self, device_address, bytestream):
        try:
            self.H.__sendByte__(CP.I2C_HEADER)
            self.H.__sendByte__(CP.I2C_WRITE_BULK)
            self.H.__sendByte__(device_address)
            self.H.__sendByte__(len(bytestream))
            for a in bytestream:
                self.H.__sendByte__(a)
            self.H.__get_ack__()
        except Exception as ex:
  self.raiseException(ex, "Communication Error , Function : " + inspect.currentframe().f_code.co_name)

 

The scan method scans the I2C port for connected devices which utilise I2C as a communication mode. It takes frequency as an argument to set the frequency of the communication and is by default set to 100000. An array containing the addresses of the connected devices (which are integers) is returned.

def scan(self, frequency=100000, verbose=False):
        self.config(frequency, verbose)
        addrs = []
        n = 0
        if verbose:
            print('Scanning addresses 0-127...')
            print('Address', '\t', 'Possible Devices')
        for a in range(0, 128):
            x = self.start(a, 0)
            if x & 1 == 0:  # ACK received
                addrs.append(a)
                if verbose: print(hex(a), '\t\t', self.SENSORS.get(a, 'None'))
                n += 1
            self.stop()
       return addrs

 

Additional Sources

  1. Learn more about the principles behind i2c communication https://learn.sparkfun.com/tutorials/i2c
  2. A simple experiment to demonstrate use of i2c communication with Arduino http://howtomechatronics.com/tutorials/arduino/how-i2c-communication-works-and-how-to-use-it-with-arduino/
  3. Java counterpart of the PSLab I2C library https://github.com/fossasia/pslab-android/blob/master/app/src/main/java/org/fossasia/pslab/communication/peripherals/I2C.java

Continue Reading I2C Communication in PSLab

Real time Sensor Data Analysis on PSLab Android

PSLab device has the capacity to connect plug and play sensors through the I2C bus. The sensors are capable of providing data in real time. So, the PSLab Android App and the Desktop app need to have the feature to fetch real time sensor values and display the same in the user interface along with plotting the values on a simple graph.

The UI was made following the guidelines of Google’s Material Design and incorporating some ideas from the Science Journal app. Cards are used for making each section of the UI. There are segregated sections for real time updates and plotting where the real time data can be visualised. A methods for fetching the data are run continuously in the background which receive the data from the sensor and then update the screen.

The following section denotes a small portion of the UI responsible for displaying the data on the screen continuously and are quite simple enough. There are a number of TextViews which are being constantly updated on the screen. Their number depends on the type and volume of data sent by the sensor.

<TextView
       android:layout_width="wrap_content"
       android:layout_height="30dp"
       android:layout_gravity="start"
       android:text="@string/ax"
       android:textAlignment="textStart"
       android:textColor="@color/black"
       android:textSize="@dimen/textsize_edittext"
       android:textStyle="bold" />

<TextView
       android:id="@+id/tv_sensor_mpu6050_ax"
       android:layout_width="wrap_content"
       android:layout_height="30dp"
       android:layout_gravity="start"
       android:textAlignment="textStart"
       android:textColor="@color/black"
       android:textSize="@dimen/textsize_edittext"
       android:textStyle="bold" />

 

The section here represents the portion of the UI responsible for displaying the graph. Like all other parts of the UI of PSLab Android, MPAndroidChart is being used here for plotting the graph.

<LinearLayout
       android:layout_width="match_parent"
       android:layout_height="160dp"
       android:layout_marginTop="40dp">

       <com.github.mikephil.charting.charts.LineChart
               android:id="@+id/chart_sensor_mpu6050"
               android:layout_width="match_parent"
               android:layout_height="match_parent"
               android:background="#000" />
</LinearLayout>

 

Since the updates needs to continuous, a process should be continuously run for updating the display of the data and the graph. There are a variety of options available in Android in this regard like using a Timer on the UI thread and keep updating the data continuously, using ASyncTask to run a process in the background etc.

The issue with the former is that since all the processes i.e. fetching the data and updating the textviews & graph will run on the UI thread, the UI will become laggy. So, the developer team chose to use ASyncTask and make all the processes run in the background so that the UI thread functions smoothly.

A new class SensorDataFetch which extends AsyncTask is defined and its object is created in a runnable and the use of runnable ensures that the thread is run continuously till the time the fragment is used by the user.

scienceLab = ScienceLabCommon.scienceLab;
i2c = scienceLab.i2c;
try {
    MPU6050 = new MPU6050(i2c);
} catch (IOException e) {
    e.printStackTrace();
}
Runnable runnable = new Runnable() {
    @Override
    public void run() {
        while (true) {
            if (scienceLab.isConnected()) {
                try {
                    sensorDataFetch = new SensorDataFetch();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                sensorDataFetch.execute();
            }
        }
    }
};
new Thread(runnable).start();

 

The following is the code for the ASyncTask created. There are two methods defined here doInBackground and onPostExecute which are responsible for fetching the data and updating the display respectively.

The raw data is fetched using the getRaw method of the MPU6050 object and stored in an ArrayList. The data type responsible for storing the data will depend on the return type of the getRaw method of each sensor class and might be different for other sensors. The data returned by getRaw is semi-processed and the data just needs to be split in sections before presenting it for display.

The PSLab Android app’s sensor files can be viewed here and they can give a better idea about how the sensors are calibrated, how the intrinsic nonlinearity is taken care of, how the communication actually works etc.

After the data is stored, the control moves to the onPostExecute method, here the textviews on the display and the chart are updated. The updation is slowed down a bit so that the user can visualize the data received.

private class SensorDataFetch extends AsyncTask<Void, Void, Void> {
   MPU6050 MPU6050 = new MPU6050(i2c);
   ArrayList<Double> dataMPU6050 = new ArrayList<Double>();

   private SensorDataFetch(MPU6050 MPU6050) throws IOException {
   }

   @Override
   protected Void doInBackground(Void... params) {
       try {
           if (MPU6050 != null) {
               dataMPU6050 = MPU6050.getRaw();
           }
       } catch (IOException e) {
           e.printStackTrace();
       }
           return null;
   }

   protected void onPostExecute(Void aVoid) {
       super.onPostExecute(aVoid);
       tvSensorMPU6050ax.setText(String.valueOf(dataMPU6050.get(0)));
       tvSensorMPU6050ay.setText(String.valueOf(dataMPU6050.get(1)));
       tvSensorMPU6050az.setText(String.valueOf(dataMPU6050.get(2)));
       tvSensorMPU6050gx.setText(String.valueOf(dataMPU6050.get(3)));
       tvSensorMPU6050gy.setText(String.valueOf(dataMPU6050.get(4)));
       tvSensorMPU6050gz.setText(String.valueOf(dataMPU6050.get(5)));
       tvSensorMPU6050temp.setText(String.valueOf(dataMPU6050.get(6)));
   }
}

The detailed implementation of the same can be found here.

Additional Resources

  1. Learn more about how real time sensor data analysis can be used in various fields like IOT http://ieeexplore.ieee.org/document/7248401/
  2. Google Fit guide on how to use native built-in sensors on phones, smart watches etc. https://developers.google.com/fit/android/sensors
  3. A simple starter guide to build an app capable of real time sensor data analysis http://developer.telerik.com/products/building-an-android-app-that-displays-live-accelerometer-data/
  4. Learn more about using AsyncTask https://developer.android.com/reference/android/os/AsyncTask.html

Continue Reading Real time Sensor Data Analysis on PSLab Android

Integrating Travis CI and Codacy in PSLab Repositories

Continuous Integration Testing and Automated Code Review tools are really useful for developing better software, improving code and overall quality of the project. Continuous integration can help catch bugs by running tests automatically and to merge your code with confidence.

While working on my GsoC-16 project, my mentors guided and helped me to integrate Travis CI and Codacy in PSLab github repositories. This blog post is all about integrating these tools in my github repos, problems faced, errors occurred and the test results.

travisTravis CI is a hosted continuous integration and deployment system. It is used to build and test software projects hosted on github. There are two versions of it, travis-ci.com for private repositories, and travis-ci.org for public repositories.

Read : Getting started with Travis CI

Travis is configured with the “.travis.yml” file in your repository to tell Travis CI what to build. Following is the code from ‘.travis.yml‘ file in our PSLab repository. This repo contains python communication library for PSLab.

language: python
python:
  - "2.6"
  - "2.7"
  - "3.2"
  - "3.3"
  - "3.4"
# - "3.5"
# command to install dependencies
# install: "pip install -r requirements.txt"
# command to run tests
script: nosetests

With this code everything worked out of the box (except few initial builds which errored because of missing ‘requirements.txt‘ file) and build passed successfuly 🙂 🙂

Later Mario Behling added integration to FOSSASIA Slack Channel.

Slack notifications

Travis CI supports notifying  Slack channels about build results. On Slack, set up a new Travis CI integration. Select a channel, and you’ll find the details to paste into your ‘.travis.yml’. Just copy and paste the settings, which already include the proper token and you’re done.

The simplest configuration requires your account name and the token.

notifications:
  slack: '<account>:<token>'     
notifications:
  slack: fossasia:***tokenishidden****

Import errors in Travis builds of PSLab-apps Repository

PSLab-apps repository contains PyQt bases apps for various experiments. The ‘.travis.yml‘ file mentioned above gave several module import errors.

$ python --version
Python 3.2.5
$ pip --version
pip 6.0.7 from /home/travis/virtualenv/python3.2.5/lib/python3.2/site-packages (python 3.2)
Could not locate requirements.txt. Override the install: key in your .travis.yml to install dependencies.
0.33s$ nosetests
E
======================================================================
ERROR: Failure: ImportError (No module named sip)

The repo is installable and PSLab was working fine on popular linux distributions without any errors. I was not able to find the reason for build errors. Even after adding proper ‘requirements.txt‘ file,  travis builds errored.

On exploring the documentation I could figure out the problem.

Travis CI Environment uses separate virtualenv instances for each Python version. System Python is not used and should not be relied on. If you need to install Python packages, do it via pip and not apt. If you decide to use apt anyway, note that Python system packages only include Python 2.7 libraries (default python version). This means that the packages installed from the repositories are not available in other virtualenvs even if you use the –system-site-packages option. Therefore I was getting Import module errors.

This problem was solved by making following changes in the ‘.travis.yml‘ file

language: python

python:
  #- "2.6"
  - "2.7"
  #- "2.7_with_system_site_packages"
  - "3.2"
  #- "3.2_with_system_site_packages"
  - "3.3"
  - "3.4"
before_install:
    - sudo mkdir -p /downloads
    - sudo chmod a+rw /downloads
    - curl -L http://sourceforge.net/projects/pyqt/files/sip/sip-4.16.5/sip-4.16.5.tar.gz -o /downloads/sip.tar.gz 
    - curl -L http://sourceforge.net/projects/pyqt/files/PyQt4/PyQt-4.11.3/PyQt-x11-gpl-4.11.3.tar.gz -o /downloads/pyqt4.tar.gz
    # Builds
    - sudo mkdir -p /builds
    - sudo chmod a+rw /builds

install:
    - export DISPLAY=:99.0
    - sh -e /etc/init.d/xvfb start
    - sudo apt-get install -y libqt4-dev
    - sudo apt-get install -y mesa-common-dev libgl1-mesa-dev libglu1-mesa-dev
#    - sudo apt-get install -y python3-sip python3-sip-dev python3-pyqt4 cmake
    # Qt4
    - pushd /builds
    # SIP
    - tar xzf /downloads/sip.tar.gz --keep-newer-files
    - pushd sip-4.16.5
    - python configure.py
    - make
    - sudo make install
    - popd
    # PyQt4
    - tar xzf /downloads/pyqt4.tar.gz --keep-newer-files
    - pushd PyQt-x11-gpl-4.11.3
    - python configure.py -c --confirm-license --no-designer-plugin -e QtCore -e QtGui -e QtTest
    - make
    - sudo make install
    - popd
 # - "3.5"
# command to install dependencies
#install: "pip install -r requirements.txt"
# command to run tests
script: nosetests

notifications:
  slack: fossasia:*****tokenishidden*******


codacy

Codacy is an automated code analysis and review tool that helps developers ship better software, faster. With Codacy integration one can get static analysis, code complexity, code duplication and code coverage changes in every commit and pull request.

Read : Integrating Codacy in github is here.

Codacy integration has really helped me to understand and enforce code quality standard. Codacy gives you impact of every pull request in terms of quality and errors directly into GitHub.

codacy check

Codacy also grades your project in different categories like Code Complexity, Compatibility, security, code style, error prone etc. to help you better understand the overall project quality and what are the areas you should improve.

Here is a screen-shot of Codacy review for PSLab-apps repository.

codacyreport

I am extremely happy to share that my learning adventure has got  Project Certification at ‘A’ grade. Project quality analysis shows that more than 90% of the work has A grade 🙂 🙂

Travis CI and Codacy Badges for my GSoC Repositories:

PSLab : Python Library for Communication with PSLab

Travis CI Badge         Codacy Badge

PSLab-apps : Qt based GUI applications for PSLab

Travis CI Badge         Codacy Badge

Pocket Science Lab : ExpEYES Programs, Sensor Plugins

Travis CI Badge         Codacy Badge

That’s all for now. Have a happy coding, testing and learning 🙂 🙂

Continue Reading Integrating Travis CI and Codacy in PSLab Repositories

Design Your Own Experiments With PSLab

PSLab, with its simple and open architecture allows programmers, hobbyists to use the tool for various measurements and to develop new experiments with simple python code.

One of the main target group, the PSLab is aimed at, is high-school science teachers and students, who may or may-not be familiar with the computer programming. For such users it is difficult to design or develop new experiments on their own. They may also find it difficult to fetch the data and plot required graphs, if a ready-made GUI is not available for that particular experiment.

To enable such users to quickly design a simple experiment for studying various phenomena, we have developed a simple Experiment Designer GUI. This incorporates few controls, read-back elements and easy functions to select parameters and plot graphs.

The screen shot of the ‘Design Your Own Experiment’ GUI along with the App-window is here..

experiment designer1

Experiment Designer allows the user to define the control and read-back sequences of parameters and execute them.

Features of “Design Your Own Experiment” GUI

  • Configure Experiment : Here user can select the required channels ( manual / sweep / read-back). One can also add a derived channel for measuring some physical quantity, for example ‘current’.
  • Make Measurements : Selected channels are displayed. User can make measurements individually for each step or  can sweep in auto mode.
  • Plot and View Plots: Enables user to plot selected parameters. Acquired plots can be selectively displayed or deleted.
  • Save Plots: Data acquired can be save in a spreadsheet.
  • Save Profile : Experiment profile can be saved for repeating the experiment in future. Saved profiles can be loaded from “Load Profile” tab.

Example : Diode IV Characteristics Experiment

For this experiment one needs the following…

  • A variable voltage source : Needs to be swept from Voltage A to  B (say from 0V to 5V)
  • Current Monitoring : Needs to be read for every value of Voltage
  • Plotting and analytics :  Tools to plot the parameters and save data

Schematic Circuit diagram:

diode IV

CH3 monitors the voltage drop across the diode. PV1 is varied in steps, and for each step the current is calculated from the difference between voltages at PV1 and CH3, and the known value of the resistor. For example for 1K resistor, current through the diode is given by

I = (PV1-CH3)/1K

Procedure :

Step 1. Connect Fossasia PSLab to the pc. Connect the components –  Diode from CH3 to Ground and  1k resistor from PV1 to CH3

Step 2. From the terminal Run

Experiments

The App-window will pop-up. Click on ‘Design your own Experiment’ button to get the experiment designer GUI.

experiment designer2

Step 3: Select channels

Sweep Channel PV1 – Sweep from 0.00V -5.00V in 200 steps

Read-back Channel CH3 – for monitoring voltage across the diode

Derived Channel – To measure Current. Type the equation to calculate the current,   (PV1()-CH3())/1000

Step 4. Click on Prepare Experiment‘ to get measurements screen. Click on ‘Evaluate All Rows‘ to make the measurements.

Experiment designer3

Step 5. Select the required columns and click on Plot Selected Columns‘, a message window will pop-up, here user can select the Axes for plotting the graph. On clicking  ‘Plot‘, view plots screen will be displayed.

plotsdiodeiv

One can repeat the experiment and plot multiple curves and save them in a spreadsheet. Acquired plots can be selectively displayed or deleted.

Step 6. The entire design ( Experiment Profile)  of the experiment can be saved for repeating the experiment in future. Saved profiles can be loaded from “Load Profile” tab.

experiment designer profile
This is a very important value add to PSLab Apps. It has enabled PSLab to reach out and help users, who do not have any background in programming. Now ‘designing your own experiments’ has become super easy 🙂 🙂 🙂

Continue Reading Design Your Own Experiments With PSLab

PSLab Communication Function Calls

Prerequisite reading:

Interfacing with the hardware of PSLab, fetching the data and plotting it is very simple and straight forward. Various sensors can be connected to PSLab and data can be fetched with a simple python code as shown in the following example…

>>> from PSL import sciencelab
>>> I = sciencelab.connect()     # Initializing: Returns None if device isn't found. The initialization process connects to tty device and loads calibration values.
# An example function that measures voltage present at the specified analog input
>>> print I.get_average_voltage('CH1')
# An example to capture and plot data
>>> I.set_gain('CH1', 3) # set input CH1 to +/-4V range 
>>> I.set_sine1(1000) # generate 1kHz sine wave on output W1 
>>> x,y = I.capture1('CH1', 1000, 10) # digitize CH1 1000 times, with 10 usec interval 
>>> plot(x,y) 
>>> show()
# An example function to get data from magnetometer sensor connected to PSLab
>>> from PSL.SENSORS import HMC5883L #A 3-axis magnetometer >>> M = HMC5883L.connect() >>> Gx,Gy,Gz = M.getRaw() 

The module sciencelab.py contains all the functions required for communicating with PSLab hardware. It also contains some utility functions. The class ScienceLab() contains methods that can be used to interact with the PSLab.

After initiating this class, all the features built into the device can be accessed  using various function calls.


Capture1 : for capturing one trace

capture1(ch, ns, tg)

Arguments

  • ch  : Channel to select as input. [‘CH1′..’CH3′,’SEN’]
  • ns  :  Number of samples to fetch. Maximum 10000
  • tg   :  Time gap between samples in microseconds
#Example >>> x,y = I.capture1('CH1', 1000, 10) # digitize CH1 1000 times, with 10 usec interval

Returns : Arrays X(timestamps),Y(Corresponding Voltage values)


Capture2 : for capturing two traces

capture2(ns, tg, TraceOneRemap='CH1')

Arguments

  • ns :  Number of samples to fetch. Maximum 5000
  • tg  :  Time gap between samples in microseconds
  • TraceOneRemap :   Choose the analogue input for channel 1 (Like MIC OR SEN). It is connected to CH1 by default. Channel 2 always reads CH2.
#Example 
>>> x,y1,y2 = I.capture2(1600,1.75,'CH1') # digitize CH1 and CH2, 1600 times, with 1.75 usec interval

Returns: Arrays X(timestamps),Y1(Voltage at CH1),Y2(Voltage at CH2)


Capture4 : for capturing four taces

capture4(ns, tg, TraceOneRemap='CH1')

Arguments

  • ns:   Number of samples to fetch. Maximum 2500
  • tg :   Time gap between samples in microseconds. Minimum 1.75uS
  • TraceOneRemap :   Choose the analogue input for channel 1 (Like MIC OR SEN). It is connected to CH1 by default. Channel 2 always reads CH2, channel 3 always reads CH3 and MIC is channel 4 (CH4)
#Example
>>> x,y1,y2,y3,y4 = I.capture4(800,1.75) # digitize CH1-CH4, 800 times, with 1.75 usec interval

Returns: Arrays X(timestamps),Y1(Voltage at CH1),Y2(Voltage at CH2),Y3(Voltage at CH3),Y4(Voltage at CH4)


Capture_multiple : for capturing multiple traces

capture_multiple(samples, tg, *args)

Arguments

  • samples:   Number of samples to fetch. Maximum 10000/(total specified channels)
  • tg :   Time gap between samples in microseconds.
  • *args :   channel names
# Example 
>>> from pylab import * 
>>> I=interface.Interface() 
>>> x,y1,y2,y3,y4 = I.capture_multiple(800,1.75,'CH1','CH2','MIC','SEN') 
>>> plot(x,y1) 
>>> plot(x,y2) 
>>> plot(x,y3) 
>>> plot(x,y4) 
>>> show()

Returns: Arrays X(timestamps),Y1,Y2 …


Capture_fullspeed : fetches oscilloscope traces from a single oscilloscope channel at a maximum speed of 2MSPS

capture_fullspeed(chan, amples, tg, *args)

Arguments

  • chan:   channel name ‘CH1’ / ‘CH2’ … ‘SEN’
  • tg :   Time gap between samples in microseconds. minimum 0.5uS
  • *args :   specify if SQR1 must be toggled right before capturing. ‘SET_LOW’ will set it to 0V, ‘SET_HIGH’ will set it to 5V. if no arguments are specified, a regular capture will be executed.
# Example
>>> from pylab import *
>>> I=interface.Interface()
>>> x,y = I.capture_fullspeed('CH1',2000,1)
>>> plot(x,y)               
>>> show()

Returns: timestamp array ,voltage_value array


Set_gain : Set the gain of selected PGA

set_gain(channel, gain)

Arguments

  • channel:   ‘CH1’ , ‘CH2’
  • gain :   (0-7) -> (1x,2x,4x,5x,8x,10x,16x,32x)

Note: The gain value applied to a channel will result in better resolution for small amplitude signals.

# Example
>>> I.set_gain('CH1',7)  #gain set to 32x on CH1


Get_average_voltage : Return the voltage on the selected channel
get_average_voltage(channel_name, **kwargs)
Arguments

  • channel_name:    ‘CH1’,’CH2’,’CH3’, ‘MIC’,’IN1’,’SEN’
  • **kwargs :   Samples to average can be specified. eg. samples=100 will average a hundred readings
# Example 
>>> print I.get_average_voltage('CH4')
1.002

Get_freq : Frequency measurement on IDx. Measures time taken for 16 rising edges of input signal. returns the frequency in Hertz

get_average_voltage(channel='Fin', timeout=0.1)
Arguments

  • channel :    The input to measure frequency from. ‘ID1’ , ‘ID2’, ‘ID3’, ‘ID4’, ‘Fin’
  • timeout :   This is a blocking call which will wait for one full wavelength before returning the calculated frequency. Use the timeout option if you’re unsure of the input signal. returns 0 if timed out
# Example
>>> I.sqr1(4000,25)
>>> print I.get_freq('ID1')
4000.0

Return float: frequency


Get_states : Gets the state of the digital inputs. returns dictionary with keys ‘ID1’,’ID2’,’ID3’,’ID4’
get_states()
#Example
>>> print get_states()
{'ID1': True, 'ID2': True, 'ID3': True, 'ID4': False}

Get_state : Returns the logic level on the specified input (ID1,ID2,ID3, or ID4)
get_state(input_id)
Arguments

  • input_id :    The input channel ‘ID1’ -> state of ID1 ‘ID4’ -> state of ID4
#Example
>>> print I.get_state(I.ID1)
False

Set_state : Set the logic level on digital outputs SQR1,SQR2,SQR3,SQR4
set_state(**kwargs)
Arguments

  • **kwargs :    SQR1,SQR2,SQR3,SQR4 states(0 or 1)
#Example
>>> I.set_state(SQR1=1, SQR2=0) #sets SQR1 HIGH, SQR2 LOw, but leave SQR3,SQR4 untouched.


Continue Reading PSLab Communication Function Calls

Communicating with Pocket Science Lab via USB and capturing and plotting sine waves

Design of PSLab combines the flexibility of Python programming language and the real-time measurement capability of micro-controllers.

PSLab, with its simple and open architecture allows users to use the tool for various measurements and to develop new experiments with simple functions written in python.

PSLab is interfaced and powered by USB port of the computer. For connecting external signals it has several input/output terminals as shown in the figure.

pslabdesign

Interfacing with the real world

Connecting to PSLab is as simple and straight forward as this…

>>> from PSL import sciencelab
>>> I = sciencelab.connect()     #Returns None if device isn't found
# An example function that measures voltage present at the specified analog input
>>> print I.get_average_voltage('CH1')

Various sensors can be connected to PSLab and data can be fetched with a simple python code as shown below…

>>> from PSL.SENSORS import HMC5883L #A 3-axis magnetometer
>>> M = HMC5883L.connect()
>>> Gx,Gy,Gz = M.getRaw()

The module sciencelab.py contains all the functions required for communicating with PSLab hardware. It also contains some utility functions. The class ScienceLab() contains methods that can be used to interact with the PSLab. The connect() function returns an object of this class if PSLab hardware is detected.

The initialization process does the following

* connects to tty device

* loads calibration values.

>>> from PSL import sciencelab
>>> I = sciencelab.connect()
>>> print I
<PSL.sciencelab.ScienceLab instance at 0x7fe9a7bf0e18>

After initiating this class, its various function calls will allow access to all the features built into the device. Some examples showing the use of few function calls are given below…

Example 1: Capturing and plotting a sine wave

The function call used,

capture1(self,ch,ns,tg,*args,**kwargs)

Arguments

  • ch  : Channel to select as input. [‘CH1′..’CH3′,’SEN’]
  • ns  :  Number of samples to fetch. Maximum 10000
  • tg   :  Time gap between samples in microseconds

Example Program

Connect WG1 to CH1 and run the following code.

>>> from pylab import *
>>> from PSL import sciencelab
>>> I=sciencelab.connect()
>>> I.set_gain('CH1', 3) # set input CH1 to +/-4V range
>>> I.set_sine1(1000) # generate 1kHz sine wave on output W1
>>> x,y = I.capture1('CH1', 1000, 10) # digitize CH1 1000 times, with 10 usec interval
>>> plot(x,y)
>>> show()

For running the script in IDE, one should define source code encoding, add this to the top of your script:

# -*- coding: utf-8 -*-

The output of the program is here…

sine1

Example 2 : Capturing two sine waves and plotting

The function call used,

capture2(self,ns,tg,TraceOneRemap='CH1')

Arguments

  • ns :  Number of samples to fetch. Maximum 5000
  • tg  :  Time gap between samples in microseconds
  • TraceOneRemap :   Choose the analogue input for channel 1 (Like MIC OR SEN). It is connected to CH1 by default. Channel 2 always reads CH2.

Example Program

Connect WG1 to CH1, WG2 to CH2 and run the following code.

# -*- coding: utf-8 -*-

from pylab import *
from PSL import sciencelab
I=sciencelab.connect()
I.set_gain('CH1', 2) # set input CH1 to +/-4V range
I.set_gain('CH2', 3) # set input CH2 to +/-4V range
I.set_sine1(1000) # generate 1kHz sine wave on output W1
I.set_sine2(1000) # generate 1kHz sine wave on output W2

x,y1,y2 = I.capture2(1600,1.75,'CH1') 
plot(x,y1) #Plot of analog input CH1
plot(x,y2) #plot of analog input CH2
show()

The output of the program is here…sine2

Example 3 : Capturing four traces and plotting

The function call used,

capture4(self,ns,tg,TraceOneRemap='CH1')

Arguments

  • ns:   Number of samples to fetch. Maximum 2500
  • tg :   Time gap between samples in microseconds. Minimum 1.75uS
  • TraceOneRemap :   Choose the analogue input for channel 1 (Like MIC OR SEN). It is connected to CH1 by default. Channel 2 always reads CH2.

Example Program

Connect WG1 to CH1, WG2 to CH2, SQR1 to CH3 and transducer mic to MIC (CH4) and run the following code.

# -*- coding: utf-8 -*-

from pylab import *
from PSL import sciencelab
I=sciencelab.connect()
I.set_gain('CH1', 2) # set input CH1 to +/-4V range
I.set_gain('CH2', 3) # set input CH2 to +/-4V range
I.set_sine1(1000) # generate 1kHz sine wave on output W1
I.set_sine2(1000) # generate 1kHz sine wave on output W2
I.sqr1(2000,duty_cycle=50) # generate 1kHz square wave on output SQR1

x,y1,y2,y3,y4 = I.capture4(800,1.75)
plot(x,y1) #Plot of analog input CH1
plot(x,y2) #plot of analog input CH2
plot(x,y3) #plot of analog input CH3
plot(x,y4) #plot of analog input CH4 : MIC
show()

The output of the program is here…waves

Next To Do for GSoC-16

A detailed User manual and programmers manual with description of all function calls. ( Work in progress 🙂  )

Read:
  1. Post about installing PSLab
  2. PSLab and ExpEYES and GSoC-16 work
Continue Reading Communicating with Pocket Science Lab via USB and capturing and plotting sine waves

Features and Controls of Pocket Science Lab

Prerequisite reading:

PSLab is equipped with array of useful control and measurement tools. This tiny but powerful Pocket Science Lab enables you to perform various experiments and study a wide range of phenomena.

Some of the important applications of PSLab include a 4-channel oscilloscope, sine/triangle/square waveform generators, a frequency counter, a logic analyser and also several programmable current and voltage sources.

Add-on boards, both wired as well as wireless(NRF+MCU), enable measurement of physical parameters ranging from acceleration and angular velocity, to luminous intensity and Passive Infra-red. (Work under progress…)

As a reference for digital instruments a 12-MHz Crystal is chosen and a 3.3V voltage regulator is chosen for the analogue instruments. The device is then calibrated against professional instruments in order to squeeze out maximum performance.

Python based communication library and experiment specific PyQt4 based GUI’s make PSLab a must have tool for programmers, hobbyists, science and engineering teachers and also students.

PSLab is interfaced and powered by USB port of the computer. For connecting external signals it has several input/output terminals as shown in the figure.

pslabdesign
New panel design for PSLab

psl2

Feature list for the acquisition and control :

  • The most important feature of PSLab is a 4-channel oscilloscope which can monitor analog inputs at maximum of 2 million samples per second. Includes the usual controls such as triggering, and gain selection. Uses Python-Scipy for curve fitting.
oscilloscope
PSLab Oscilloscope

 

 

Waveform Generators

  • W1 : 5Hz – 5KHz arbitrary waveform generator. Manual amplitude control up to +/-3Volts
  • W2 : 5Hz – 5KHz arbitrary waveform generator. Amplitude of +/-3Volts. Attenuable via software
  • PWM : There are four phase correlated PWM outputs with maximum frequency 32MHz, 15nano second duty cycle, and phase difference control.

Measurement Functions

  • Frequency counter tested up to 16 MHz.
  • Capacitance Measurement. pF to uF range
  • PSLab has several 12-bit Analog inputs (function as voltmeters) with programmable gains, and maximum ranges varying from +/-5mV to +/-16V.

Voltage and Current Sources

  • 12-bit Constant Current source. Maximum current 3.3mA [subject to load resistance].
  • PSLab has three 12-bit Programmable voltage sources/ +/-3.3V,+/-5V,0-3V . (PV1, PV2, PV3)
controls
Main Control Panel

Other useful tools

  • 4MHz, 4-channel Logic analyzer with 15nS resolution.Voltage and Current Sources
  • SPI,I2C,UART outputs that can be configured and controlled entirely through Python functions. (Work in progress…)
  • On-board 2.4GHz transceiver for wireless data acquisition. (Work in progress..)
  • Graphical Interfaces for Oscilloscope, Logic Analyser, streaming data, wireless acquisition, and several experiments developed that use a common framework which drastically reduces code required to incorporate control and plotting widgets.
  • PSLab also has space for an ESP-12 module for WiFi access with access point / station mode.

Screen-shots of GUI apps.

advanced-controls
Advanced Controls with Oscilloscope
wirelesssensordataloger
Wireless Sensors ( Work in progress…)
logicanalyzer
Logic Analyzer

With all these features PSLab is taking a good shape and I see it as a potential tool that can change the way we teach and learn science. 🙂 🙂

 

Continue Reading Features and Controls of Pocket Science Lab

A low-cost laboratory for everyone: Sensor Plug-ins for ExpEYES to measure temperature, pressure, humidity, wind speed, acceleration, tilt angle and magnetic field

Working on ExpEYES in the last few months has been an amazing journey and I am gratful of the support of Mario Behling, Hong Phuc Dang and Andre Rebentisch at FOSSASIA. I had a lot of learning adventures with experimenting and exploring with new ideas to build sensor plug-ins for ExpEYES. There were some moments which were disappointing and there were some other moments which brought the joy of creating sensor plug-ins, add-on devices and GUI improvements for ExpEYES.

My GSoC Gallery of Sensors and Devices: Here are all the sensors I played with for PSLab..

The complete list of sensor plug-ins developed is available at http://gnovi.edublogs.org/2015/08/21/gsoc-2015-with-fossasia-list-of-sensor-plug-ins-developed-for-expeyes/

Sensor Plugins for ExpEYES

The aim of my project is to develop new Sensor Plug-ins for ExpEYES to measure a variety of parameters like temperature, pressure, humidity, wind speed, acceleration, tilt angle, magnetic field etc. and to provide low-cost open source laboratory equipment for students and citizien scientists all over the world.

We are enhancing the scope of ExpEYES for using it to perform several new experiments. Developing a low-cost stand alone data acquisition system that can be used for weather monitoring or environmental studies is another objective of our project.

I am happy to see that the things have taken good shape with additional gas sensors added which were not included in the initial plan and we have almost achieved all the objectives of the project, except for some difficulties in calibrating sensor outputs and documentation. This issue will be solved in a couple of days.

Experimenting with different sensors in my kitchen laboratory

I started exploring and experimenting with different sensors. After doing preliminary studies I procured analog and a few digital sensors for measuring weather parameters like temperature, relative humidity and barometric pressure. A few other sensors like low cost piezoelectric sensor, accelerometer ADXL-335, Hall effect magnetic sensor, Gyro-module etc were also added to my kitchen laboratory. We then decided to add gas sensors for detecting Carbon Monoxide, LPG and Methane.

With this development ExpEYES can now be used for pollution monitoring and also in safety systems in Physics/chemistry laboratory. The work on the low-cost Dust Sensor is under progress.

Challenges, Data Sheet, GUI programs

I had to spend a lot of time in getting the sensor components, studying their data sheets, soldering and setting them up with ExpEYES. And then little time in writing GUI Programs. I started working almost 8 to 10 hours every evening after college hours (sometimes whole night) and now things have taken good shape.

Thanks to my mentor at FOSSASIA for pushing me, sometimes with strict words. I could add many new sensor plug-ins to ExpEYES and now I will also be working on Light sensors so that the Pocket Science Lab can be used in optics. With these new sensor plug-ins one can replace many costly devices from Physics, Chemistry, Biology and also Geology Lab.

What’s next? My Plan for next steps

  • Calibration of sensor data

  • Prototyping stand-alone weather station

  • Pushing data to Loklak server

  • Work on [email protected] website

  • Fossasia Live Cd based on Lubuntu with ExpEYES and other educational softwares

  • Set-up Documentation for possible science experiments with the sensor plug-ins and low-cost, open source apparatus

Continue Reading A low-cost laboratory for everyone: Sensor Plug-ins for ExpEYES to measure temperature, pressure, humidity, wind speed, acceleration, tilt angle and magnetic field