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Johnson (twisted-ring) counter
Digital Systems Lab · free online experiment, runs in your browser with no install or sign-up.
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Objective
Feed the inverted last stage back to the first: a 4-bit register gives an 8-state sequence with only one bit changing at a time.
Procedure
- Run and read Q3 Q2 Q1 Q0 after each edge.
Theory
D = NOT Q3. The register fills with 1s and then with 0s: 0000, 0001, 0011, 0111, 1111, 1110, 1100, 1000. n flip-flops give 2n states.
Questions to answer
- Why is a Johnson counter easy to decode?
Components used
4-bit shift register, Clock source, 4 × Logic probe / LED, NOT
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.
Open this experiment in the circuit simulator