4-bit Johnson counter: build and simulate it online
A shift register whose last inverted output feeds the first: 8 states from 4 flip-flops.
Build the 4-bit johnson counter in the free online simulator — it checks your circuit automatically.
What you need
- 1 logic switches labelled CLK
- 4 probes labelled Q0, Q1, Q2, Q3
- 4 D flip-flops
Step by step
- Inputs and outputs. From the Logic section of the library, drop digital inputs (0/1 boxes) or logic switches for the inputs, and digital outputs or probes for the outputs; give each its label in the inspector (the checker finds them by label). Switch CLK; Probes Q0, Q1, Q2, Q3
- Four D flip-flops in a ring. Q0 → D1, Q1 → D2, Q2 → D3, and Q̄3 (QN of the last) → D0.
- Prove it. It fills with 1s, then with 0s: 1000, 1100, 1110, 1111, 0111, 0011, 0001, 0000.
Expected sequence
| # | inputs | clock | Q0 | Q1 | Q2 | Q3 |
|---|---|---|---|---|---|---|
| 1 | — | ↑ | 1 | 0 | 0 | 0 |
| 2 | — | ↑ | 1 | 1 | 0 | 0 |
| 3 | — | ↑ | 1 | 1 | 1 | 0 |
| 4 | — | ↑ | 1 | 1 | 1 | 1 |
| 5 | — | ↑ | 0 | 1 | 1 | 1 |
| 6 | — | ↑ | 0 | 0 | 1 | 1 |
| 7 | — | ↑ | 0 | 0 | 0 | 1 |
| 8 | — | ↑ | 0 | 0 | 0 | 0 |
Frequently asked questions
How do you build a 4-bit johnson counter?
A shift register whose last inverted output feeds the first: 8 states from 4 flip-flops. In short: inputs and outputs, then four d flip-flops in a ring, then prove it.
How does a 4-bit johnson counter behave clock by clock?
It is checked over 8 steps: 1000, 1100, 1110, 1111, …. The table on this page shows the expected Q0, Q1, Q2, Q3 after each clock.
What parts do you need for a 4-bit johnson counter?
4 D flip-flops — plus logic switches for the inputs and probes for the outputs.
Can I simulate a 4-bit johnson counter online for free?
Yes. Open it in the BitForBytes Embedded Lab, a free browser-based circuit and logic simulator: drag in the gates, wire them, and press "Check my circuit" — every clock cycle is simulated and marked for you. No download or sign-up needed.
Part of DSD 37 · Ring and Johnson counters in the free BitForBytes digital system design course.