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Project Notes

#221 ResistorTransistorLogic/XOR

Test the basic resistor-transistor logic XOR gate.



Exclusive OR (XOR) operation is true only when inputs are different. Truth table:

0 0 0
0 1 1
1 0 1
1 1 0

An XOR may be constructed using combinatorial logic: an OR ANDed with a NAND.

This circuit uses a diode-bridge and a single transistor - quite neat. It does mean however that there is no output buffer, in fact the output is powered from the inputs.

Here’s a simulation of the circuit using Circuit Simulator by Paul Falstad.

Here’s a sample trace. The lower two traces are the signal inputs, and the upper trace is the output of the gate.

processing trace

The Arduino is not really a core part of the circuit. It only does the following:

  • provides +5V power supply (for convenience)
  • automates the toggling of the driving inputs
  • measures the input and output voltages for plotting


The circuit uses a digital output pins to sequence inputs to the gate. Three analog input pins are used to read the two input signals and the resuting output, with the values is echoed to the Arduino serial port for plotting with PlotNValues (a simple Processing sketch).


The Schematic

The Build

Credits and References

About LEAP#221 BJTRTLLogic Gates
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.