Google Summer of Code

The developer's goal is that PSLab Android App as an app should run smoothly on all the variety of Android devices out in the market. There are two aspects of it - the app should be able to support maximum number of Android versions possible which is related to the core software part and the other being the app should be able to generate the same user experience on all sizes of screens. This post focuses on the later. There are a whole range of android devices available in the market right from 4 inch mobile phones to 12 inch tablets and the range in the screen sizes is quite large. So, the challenge in front of app designers is to make the app compatible with the maximum  number of devices without doing any specific tweaks related to a particular resolution range. Android has its mechanism of scaling the app as per the screen size and it does a good job almost all the time, however, still there are cases where android fails to scale up or scale down the app leading to distorted layout of the app. This blog discusses some of the tricks that needs to be kept in mind while designing layouts that work independent of screen sizes. Avoid using absolute dimensions It is one of the most common things to keep in mind before starting any UI design. Use of absolute dimensions like px, inch etc. must be avoided every time as they are fixed in size and don’t scale up or scale down while screen sizes are changed. Instead relative dimensions like dp should be used which depend on the resolution and scale up or scale down. ( It’s a fair assumption that bigger screens will have better resolution compared to the smaller ones although exceptions do exist) . Ensure the use of correct layout/View group Since, android provides a variety of layouts like Linearlayout, Constrainedlayout, Relativelayout, Tablelayout and view groups like ScrollView, RecyclerView, ListView etc. it is often confusing to know which layout/viewgroup should be used. The following list gives a rough idea of when to use a particular layout or view group. Linearlayout - Mostly used for simple designs when the elements are stacked in ordered horizontal/vertical fashion and it needs explicit declaration of orientation. Relativelayout - Mostly used when the elements need to defined relative to the parent or the neighbouring elements. Since, the elements are relative, there is no need to define the orientation. Constraintlayout - It has all the features of Relativelayout and in addition a feature of adding constraints to the child elements or neighbouring elements. Tablelayout - Tablelayout is helpful to when all the views/widgets are arranged in an ordered fashion. All the above layouts can be used interchangeably most of the times, however, certain cases make some more favourable than others like when than views/ widgets are not present in an organised manner, it is better to stick to Linearlayout or Relativelayout. ListView - Used when the…

The PSLab Android App as of now supports quite a few sensors. Sensors are an essential part of many science experiments and therefore PSLab has a feature to support plug & play sensors. The list of sensors supported by PSLab can be found here. AD7718 - 24-bit 10-channel Low voltage Low power Sigma Delta ADC AD9833 - Low Power Programmable Waveform generator ADS1115 - Low Power 16 bit ADC BH1750 - Light Intensity sensor BMP180 - Digital Pressure Sensor HMC5883L - 3-axis digital magnetometer MF522 - RFID Reader MLX90614 - Infrared thermometer MPU6050 - Accelerometer & gyroscope MPU925x - Accelerometer & gyroscope SHT21 - Humidity sensor SSD1306 - Control for LED matrix Sx1276 - Low Power Long range Transceiver TSL2561 - Digital Luminosity Sensor All the sensors except Sx1276 communicate using the I2C protocol whereas the Sx1276 uses the SPI protocol for communication. There is a dedicated set of ports on the PSLab board for the communication under the label I2C with the ports named 3.3V, GND, SCL & SDA. Fig; PSLab board sketch Any I2C sensor has ports named 3.3V/VCC, GND, SCL, SDA at least along with some other ports in some sensors. The connections are as follows: 3.3V on PSLab - 3.3V/VCC on sensor GND on PSLab - GND on sensor SCL on PSLab - SCL on sensor SDA on PSLab - SDA on sensor The diagram here shows the connections For using the sensors with the Android App, there is a dedicated I2C library written in communication in Java for the communication. Each sensor has its own specific set of functionalities and therefore has its own library file. However, all these sensors share some common features like each one of them has a getRaw method which fetches the raw sensor data. For getting the data from a sensor, the sensor is initially connected to the PSLab board. The following piece of code is responsible for detecting any devices that are connected to the PSLab board through the I2C bus. Each sensor has it’s own unique address and can be identified using it. So, the AutoScan function returns the addresses of all the connected sensors and the sensors can be uniquely identified using those addresses. public ArrayList<Integer> scan(Integer frequency) throws IOException { if (frequency == null) frequency = 100000; config(frequency); ArrayList<Integer> addresses = new ArrayList<>(); for (int i = 0; i < 128; i++) { int x = start(i, 0); if ((x & 1) == 0) { addresses.add(i); } stop(); } return addresses; }   As per the addresses fetched, the sensor library corresponding to that particular sensor can be imported and the getRaw method can be called. The getRaw method will return the raw sensor data. For example here is the getRaw method of ADS1115. public int[] getRaw() throws IOException, InterruptedException { String chan = typeSelection.get(channel); if (channel.contains("UNI")) return new int[]{(int) readADCSingleEnded(Integer.parseInt(chan))}; else if (channel.contains("DIF")) return new int[]{readADCDifferential(chan)}; return new int[0]; } Here the raw data is returned in the form of voltages in mV. Similarly, the…

PSLab Android App supports a lot of features and each of these features need components & views for their implementation. A typical UI of PSLab is shown in the figure below. Considering the number of views & components used in the figure, implementation of each view & component separately would lead to a huge volume of repetitive and inefficient code. As it is evident that the EditText and two buttons beside it keep repeating a lot, it is wiser to create a single custom component consisting of an EditText and two buttons. This not only leads to efficient code but also results in a drastic reduction of the volume of code. Android has a feature which allows creating components. For almost all the cases, the pre-defined views in Android serve our purpose of creating the UIs. However, sometimes there is a need to create custom components to reduce code volume and improve quality. Custom components are used when a particular set of component needed by us is not present in the Android view collection or when a pattern of components is frequently repeated or when we need to reduce the code complexity. The above set can be replaced by defining a custom component which includes an edittext and two buttons and then treating it like just any other component. To get started with creating a custom component, the steps are the following: Create a layout for the custom component to be designed <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="horizontal" android:layout_width="match_parent" android:layout_height="match_parent"> <Button android:id="@+id/button_control_plus" android:layout_width="0dp" android:layout_weight="0.5" android:layout_height="20dp" android:background="@drawable/button_minus" /> <EditText android:id="@+id/edittext_control" android:layout_width="0dp" android:layout_weight="2" android:layout_height="24dp" android:layout_marginTop="@dimen/control_margin_small" android:inputType="numberDecimal" android:padding="@dimen/control_edittext_padding" android:background="@drawable/control_edittext" /> <Button android:id="@+id/button_control_minus" android:layout_width="0dp" android:layout_weight="0.5" android:layout_height="20dp" android:background="@drawable/button_plus" /> </LinearLayout> The layout file edittext_control.xml is created with three views and each one of them has been assigned an ID along with all the other relevant parameters. Incorporate the newly created custom layout in the Activity/Fragment layout file <org.fossasia.pslab.others.Edittextwidget android:id="@+id/etwidget_control_advanced1" android:layout_height="wrap_content" android:layout_width="0dp" android:layout_weight="2" android:layout_marginLeft="@dimen/control_margin_small" android:layout_marginStart="@dimen/control_margin_small" /> The custom layout can be added the activity/fragment layout just like any other view and can be assigned properties similarly. Create the activity file for the custom layout public class Edittextwidget extends LinearLayout{ private EditText editText; private Button button1; private Button button2; private double leastCount; private double maxima; private double minima; public Edittextwidget(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); applyAttrs(attrs); } public Edittextwidget(Context context, AttributeSet attrs) { super(context, attrs); applyAttrs(attrs); } public Edittextwidget(Context context) { super(context); } public void init(Context context, final double leastCount, final double minima, final double maxima) { View.inflate(context, R.layout.edittext_control, this); editText = (EditText) findViewById(R.id.edittext_control); button1 = (Button) findViewById(R.id.button_control_plus); button2 = (Button) findViewById(R.id.button_control_minus); button1.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Double data = Double.valueOf(editText.getText().toString()); data = data - leastCount; data = data > maxima ? maxima : data; data = data < minima ? minima : data; editText.setText(String.valueOf(data)); } }); button2.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Double data = Double.valueOf(editText.getText().toString()); data = data + leastCount; data = data > maxima ? maxima : data; data = data < minima…