ExpertTimers & Logic
Four-Bit Ripple Counter from D Flip-Flops
Use two SN74HC74s as toggle flip-flops to count 555 clock edges in binary and inspect ripple timing.
Parts from the database
Other supplies
- breadboardCommon build supply
- 5 V supplyCommon build supply
- four LEDsCommon build supply
- four 2.2 kΩ resistorsCommon build supply
- 10 kΩ and 68 kΩ clock resistorsCommon build supply
- 10 µF and 10 nF capacitorsCommon build supply
- reset button and 10 kΩ pull-upCommon build supply
- three 100 nF bypass capacitorsCommon build supply
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Connections
- 555 astable: pins 1/8 ground/+5 V, pin 4 high, pins 2/6 joined, 10 kΩ +5 V to pin 7, 68 kΩ pin 7 to pins 2/6, 10 µF node to ground (+ at node), 10 nF pin 5 to ground. Pin 3 is clock.
- Each HC74 flip-flop toggles by feeding D from its own /Q. Tie /PRE high. Tie all active-low /CLR pins high with 10 kΩ and use one button to pull all low for reset.
- Clock first stage from 555 pin 3; for an up-count, clock each next stage from preceding /Q so it sees a rising edge when Q falls. Verify DIP-14 pin mapping in TI's datasheet.
- Show each Q with LED/resistor; add 100 nF to every IC supply.
Build steps
- Verify the slow 555 output first.
- Build and test one toggle stage.
- Add counter stages one at a time and reset after power-up.
- Read LEDs as bit0–bit3; ripple stages do not switch simultaneously.
Software and firmware setup
This is a hardware-only circuit; no firmware is required.
Test your build
Counter advances 0000 through 1111 then wraps; higher bits toggle more slowly and with propagation delay.
Troubleshooting
- Random initial value: press the common active-low clear.
- Counts in reverse or skips: check next clock uses /Q and inspect 555 edge.
- Runs too fast: check 555 capacitor and resistor wiring.
Safety and limitations
Educational 5 V counter only, not a precision timer or safety controller.
Manufacturer and platform documentation
Community Notes for This Project
These are unverified visitor contributions, separate from the build guide and manufacturer specifications. Verify technical advice against the linked datasheets before relying on it.
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