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OR gate from diodes

Logic Gates from Components · free online experiment, runs in your browser with no install or sign-up.

Open this experiment in the circuit simulator

Objective

Build an OR gate from two diodes and a pull-down resistor and check its truth table.

Procedure

Use the Controls tab (or the batteries' Properties) to set each input to 0 V or 5 V and press Start Simulation; turn Live on and drag an input slider to watch the output.

Theory

The higher input forward-biases its diode and pulls the output up to Vin − 0.7 V (4.3 V); the 10 kΩ resistor pulls it to 0 V when both inputs are low. The 0.7 V loss is why diode logic cannot be cascaded many times.

Questions to answer

Why is the high level only 4.3 V?

Components used

3 × Battery / DC source, 2 × Diode 1N4007, Panel voltmeter, Resistor 220 ohm 1/4W

About the model

Ideal wires; component models as listed in the catalogue (no parasitics, no temperature drift). Built without a breadboard so the schematic stays readable.