Create a Distance Sensor using PSLab

PSLab device is a small lab which supports a ton of features. Among its many features, integrating a distance measuring sensor like HC SR04 sonar sensor into it is one of them. This blog post will bring out the basic concepts behind a sonar sensor available in the current market, how it measures distance and how it is implemented in the PSLab device.

A sonar sensor uses a sound wave with a very high frequency. These waves are called ultrasonic waves. They cannot be heard by the naked ear. Human ear can only hear frequencies from 20 Hz up to 20 kHz. Generally HC SR04 sensors use a wave with frequency as high as 40 kHz so this makes sense. The basic principal behind the sensor is the reflectance property of sound. Time is calculated from the transmission time up to the time receiving the reflected sound wave. Then using general moment equation S = ut; with the use of speed of sound, the distance can be measured.

The figure shows a HC SR04 ultrasound sensor. They are quiet famous in the electronic field; especially among hobbyists in making simple robots and DIY projects. They can be easily configured to measure distance from the sensor up to 400 cm with a measuring angle of 15 degrees. This angular measurement comes into action with the fact that sound travels through a medium in a spherical nature. This sensor will not give accurate measurements when used for scenarios like measuring distance to very thin objects as they reflect sound poorly or there will not be any reflectance at all.

There are four pins in the HC SR04 sonar sensor. Corner pins in the two sides are for powering up the Sonar sensor. The two pins named ECHO and TRIG pins are the important pins in this context. When the TRIG pin (Trigger for short) is excited with a set of 8 square pulses at a rate of 40 kHz, the ECHO pin will reach to logic HIGH state which is the supply voltage (+5 V). When the transmitted sound wave is reflected back to the sensor, this high state of the ECHO pin will shift to logic LOW state. If a timer is turned on when the ECHO pin goes to logic HIGH state, we can measure how long it was taken for the sound beam to return to the sensor by turning off the timer when the ECHO pin goes to logic LOW state.

Having described the general implementation of a sonar sensor; a similar implementation is available in PSLab device. As mentioned earlier, TRIG pin requires a triggering pulse of 8 set of square waves at 40 kHz. This is achieved in PSLab using SQR pulse generating pins. The time is measured from the transmitting point until the receiving point to evaluate the distance. The real distance to the obstacle in front of the sensor can be calculated using following steps;

  1. Measure total round trip time of the sound beam. Take it as t
  2. Calculate the time taken for the beam to travel from sensor to the obstacle. It will be t/2
  3. Use motion equation S = ut to calculate the actual distance taking u = speed of sound in air. Substituting the time value calculated in step 2 to t, S will produce the distance

Resources:

Continue ReadingCreate a Distance Sensor using PSLab

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