Acknowledgment: Thanks to Peter Balch for publishing this project on Instructables. All credits for designing this nice tool. https://www.instructables.com/member/Peter+Balch/

What is it?

A transistor curve tracer is a tool that displays the current curve at different voltages. it is a very useful tool to :

match transistors

measure the gain of bipolar transistors

measuring the threshold of MOSFETs

measuring the cutoff of JFETs

measuring the forward voltage of diodes

measuring the breakdown voltage of Zeners

When you switch on the curve tracer, the main menu screen is displayed.

Select the kind of device by touching one of "PNP NPN", "MOSFET" or "JFET". You can test diodes in the "PNP NPN" mode.

Put the Device Under Test (DUT) into the ZIF socket. The menu screen shows you which pins to use. PNPs, p-channel MOSFETS and n-channel JFETS go in the left side of the socket. NPNs, n-channel MOSFETS and p-channel JFETS go in the right side of the socket. Close the ZIF socket.

After a second or so, the tester will realise that it has a component and will start to draw the curves.

For a PNP or NPN transistor it plots Vce (the voltage between the collector and emitter) versus the current flowing into the collector. A line is drawn for each different base current - e.g. 0uA, 50uA, 100uA, etc. The gain of the transistor is shown at the top of the screen.

For a MOSFET it plots Vds (the voltage between the drain and source) versus the current flowing into the drain. A line is drawn for each different gate voltage - 0V, 1V, 2V, etc. The turn-on threshold of the FET is shown at the top of the screen.

For a JFET it plots Vds (the voltage between the drain and source) versus the current flowing into the drain. A line is drawn for each different gate voltage - 0V, 1V, 2V, etc. With depletion JFETs, current flows when the gate voltage is equal to the source voltage. As the gate voltage is changed to be further from the drain voltage, the JFET turns off. The cut-off threshold of the FET is shown at the top of the screen.

The most interesting part of a MOSFET or JFET curve is around the turn-on or cut-off voltage plus or minus a few hundred mV. In the main menu, touch the Setup button and the Setup screen will be shown. You can select the minimum and maximum gate voltage: more curves will be drawn in that region.

For a PNP or NPN transistor, the Setup screen allows you to select the minimum and maximum base current

With diodes, you can see the forward voltage and with Zener's, the reverse breakdown voltage. In the image above, I've combined the curves of several diodes.

The curve tracer can communicate with a PC via a serial link (9600bps, 8-bit, no parity).