Performing Custom Experiments with PSLab
PSLab has the capability to perform a variety of experiments. The PSLab Android App and the PSLab Desktop App have built-in support for about 70 experiments. The experiments range from variety of trivial ones which are for school level to complicated ones which are meant for college students. However, it is nearly impossible to support a vast variety of experiments that can be performed using simple electronic circuits.
So, the blog intends to show how PSLab can be efficiently used for performing experiments which are otherwise not a part of the built-in experiments of PSLab. PSLab might have some limitations on its hardware, however in almost all types of experiments, it proves to be good enough.
Identifying the requirements for experiments
- The user needs to identify the tools which are necessary for analysing the circuit in a given experiment. Oscilloscope would be essential for most experiments. The voltage & current sources might be useful if the circuit requires DC sources and similarly, the waveform generator would be essential if AC sources are needed. If the circuit involves the use and analysis of data of sensor, the sensor analysis tools might prove to be essential.
- The circuit diagram of any given experiment gives a good idea of the requirements. In case, if the requirements are not satisfied due to the limitations of PSLab, then the user can try out alternate external features.
Using the features of PSLab
- Using the oscilloscope
- Oscilloscope can be used to visualise the voltage. The PSLab board has 3 channels marked CH1, CH2 and CH3. When connected to any point in the circuit, the voltages are displayed in the oscilloscope with respect to the corresponding channels.
- The MIC channel can be if the input is taken from a microphone. It is necessary to connect the GND of the channels to the common ground of the circuit otherwise some unnecessary voltage might be added to the channels.
- Using the voltage/current source
- The voltage and current sources on board can be used for requirements within the range of +5V. The sources are named PV1, PV2, PV3 and PCS with V1, V2 and V3 standing for voltage sources and CS for current source. Each of the sources have their own dedicated ranges.
- While using the sources, keep in mind that the power drawn from the PSLab board should be quite less than the power drawn by the board from the USB bus.
- USB 3.0 – 4.5W roughly
- USB 2.0 – 2.5W roughly
- Micro USB (in phones) – 2W roughly
- PSLab board draws a current of 140 mA when no other components are connected. So, it is advisable to limit the current drawn to less than 200 mA to ensure the safety of the device.
- It is better to do a rough calculation of the power requirements in mind before utilising the sources otherwise attempting to draw excess power will damage the device.
- Using the Waveform Generator
- The waveform generator in PSLab is limited to 5 – 5000 Hz. This range is usually sufficient for most experiments. If the requirements are beyond this range, it is better to use an external function generator.
- Both sine and square waves can be produced using the device. In addition, there is a feature to set the duty cycle in case of square waves.
- Sensor Quick View and Sensor Data Logger
- PSLab comes with the built in support for several plug and play sensors. The support for more sensors will be added in the future. If an experiment requires real time visualisation of sensor data, the Sensor Quick View option can be used whereas for recording the data for sensors for a period of time, the Sensor Data Logger can be used.
Analysing the Experiment
- The oscilloscope is the most common tool for circuit analysis. The oscilloscope can sample data at very high frequencies (~250 kHz). The waveform at any point can be observed by connecting the channels of the oscilloscope in the manner mentioned above.
- The oscilloscope has some features which will be essential like Trigger to stabilise the waveforms, XY Plot to plot characteristics graph of some devices, Fourier Transform of the Waveforms etc. The tools mentioned here are simple but highly useful.
- For analysing the sensor data, the Sensor Quick View can be paused at any instant to get the data at any instant. Also, the logged data in Sensor Data Logger can be exported as a TXT/CSV file to keep a record of the data.
- The PSLab desktop app comes with the built-in support for the ipython console.
- The desired quantities like voltages, currents, resistance, capacitance etc. can also be measured by using simple python commands through the ipython console.
- A simple python script can be written to satisfy all the data requirements for the experiment. An example for the same is shown below.
This is script to produce two sine waves of 1 kHz and capturing & plotting the data.
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 #Connect W1 to CH1, and W2 to CH2. W1 can be attenuated using the manual amplitude knob on the PSlab 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()
- Read more about how to perform experiments using PSLab – https://blog.fossasia.org/electrical-experiments-with-pslab/, https://blog.fossasia.org/fascinating-experiments-with-pslab/
- Examples of writing python scripts for the desktop app to perform experiments – https://github.com/fossasia/pslab-desktop-apps
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