Arduino Project on Transistor Curve Tracer

Teaching becomes easy and effective if it becomes a practical realm. Showing something practically with in-hand practice and conceptual demonstrations always help remember the learned concepts over a long period of time than the simple theoretical lessons’ explanations. This could happen with transistor curve tracers to know the concept of how the transistor works. This is an easy, good and practical way to know the working of a transistor and to determine its parameters.

The curve tracer usage is expanding nowadays for laboratory usage and other quality analysis purpose. This concept of implementing curve tracer by using an Arduino board enables students become more graspable about the transistor and Arduino technology.

Curve Tracer

A Curve-tracer is test equipment that displays voltage to current relationship of the component. There are several application areas in which these I-V curve tracers provide visual representation of current and voltage waveforms with quantitative measurements. Curve tracing equipment consists of hardware circuitry to test various basic electronic components like transistors, diodes, and other semiconductor devices. These curve tracers enables us to analyze the waveforms for finding different parameters like gain, impedance, offset, etc.


The above circuit shows how a simple curve tracer works for a device under test (DUT). A Step-down transformer is connected to a bridge rectifier circuit that converts AC to pulsating DC supply. The device under test is connected through a series resistor to limit the current. Voltage and current waves in the Cathode Ray Oscilloscope (CRO) are varied by varying the input voltage applied by the variable transformer. In this way,one can analyze and observe the curves using curve tracer.

Transistor Curve Tracer

Transistor is a current controlled device wherein the collector to emitter voltage current is controlled by varying the base current applied to the base terminal of the transistor. A transistor curve tracer is an instrument that measures the transistor’s parameters like current gain, impedance and breakdown voltages. It generates and displays a set of curves of the collector current IC versus the collector to emitter voltage VCE for different values of the base current. From this curves, the transistor current gain can be determined.

Three major functional circuits that are used in this tracer include a sweep voltage generator to control the collector voltage; a base current step generator to control the base current with equal number of increments of voltage seep generator; and, a timing circuit to change the base current for every start of the voltage sweep.

Transistor Curve Tracer
Transistor Curve Tracer

The sweep voltage generator applies Vs with a time period repetitively to the transistor. This sweep voltage can be observed in oscilloscope.And, also the base current source increases the base current IB in equal incremental steps for each consecutive voltage sweep with the steps synchronized to the beginning of each collector voltage sweep. The base current repeats this step sequence and becomes stable for the last incremented period. Selector switches are provided for each circuit to vary the input conditions.

                 The transistor current gain is determined by:

                                                b = DIc/DIB

Where, the setting of the Step Selector switch is represented as DIB.

Therefore, from the above waveform in the oscilloscope, we can determine the current gain of the transistor. Thus, the transistor curve tracer enables to find different parameters of the transistor and also provides the analysis of it waveforms for different input varying conditions.

Arduino project on Transistor Curve Tracer

Arduino project on Transistor Curve Tracer
Arduino based Transistor Curve Tracer circuit

This circuit is implemented with the use of a potentiometer connected to a transistor base to vary the base current. Arduino uno board is used as a main data acquisition controller that acquires the analog parameters of the base, collector and source voltages. A transistor with two resistors and one potentiometer comes under the circuitry under the test with the use of Arduino development board.

By varying the potentiometer, the base current is varied, and the base voltage, collector and emitter voltage values are read by the Arduino with an internal analog to digital converter. The Arduino program code is programmed in such a way that the acquired signals of the ADC are processed further and the results are calculated. The digitized values processed by this controller finds the below parameters.

                      Ib is determined by (Vs – Vb ) / Rb
And Ic by (5V – Vc) / Rc

Arduino board
Arduino based BiCMOS Transistor Curve Tracer

These values of base and collector currents must be plotted to determine the transistor’s characteristics. To plot these values,USB serial link is connected between the Arduino controller and host computer.The host computer consists of a special type of application to process and plot the graphs.Software or programs like SciLab and Octave can read and plot the values from the serial cable.

Advancement to the above Arduino project is by connecting the Arduino to plot the graphs of BiCMOS transistor. These curves are obtained by dual rail-to-rail I/O Operational Amplifier, resistors, and capacitors and solderless bread board.

Bulk voltage is selected by using a selector switch to change the PNP/NPN polarity. This project is same as the above project, but the code is somewhat different from the first one. After compiling and uploading the code into the hardware development board, there is a requirement of voltages from the transistor with different values of the base currents, which can also be changed by the program code.

This Arduino board processes these values and sends it to the computer to process and plot the values via a serial communication cable. As similar to the above project, application software allows to process and plot the acquired data for finding parameters of particular transistors like PMOS, NMOS, NPN and PNP transistors.

This is a simple Arduino project with a few external circuitries for obtaining the transistor curves. Some of the applications of Arduino based projects are home automation systems, street light controls, underground cable fault detection systems, etc. If you want any kind of help regarding these Arduino-based projects for developing code, circuit diagrams, simulation software and other technical guidance, you can reach us by commenting below.

Photo credits:

  • Curve-tracer by dos4ever
  • Transistor Curve Tracerby upenn
  • Arduino based Transistor Curve Tracer circuitby blogspot
  • Arduino based BiCMOS Transistor Curve Tracerby instructables

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