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Project Notes

#111 NOR Gate with Resistor-Transistor Logic

Test the basic resistor-transistor logic NOR gate.

Notes

Resistor–transistor logic (RTL) is a class of digital circuits built using resistors as the input network and bipolar junction transistors (BJTs) as switching devices. RTL is the earliest class of transistorized digital logic circuit and is largely obsolete now.

It is interesting to see how various logic gate may be realised with BJTs and resistors alone. Here is the basic NOR gate.

This is a “classic” two-transistor NOR gate, often used when describing the fundamentals of digital logic. Given two ideal transistors (NPN) with common collector, we treat them as switches: when either is on, the output should be low:

A B OUT
0 0 1
0 1 0
1 0 0
1 1 0

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

Construction

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).

Breadboard

The Schematic

The Build

Credits and References

About LEAP#111 BJTRTLDigital Logic
Project Source on GitHub Project Gallery Return to the LEAP Catalog

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LEAP is just my personal collection of 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!).

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