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Build a one-direction, 10-LED running light with a 555 timer and a CD4017 decade counter—no programming required. This low-voltage breadboard project uses one resistor per LED and an adjustable clock so you can assemble the circuit, see how it works, and tune its speed.
What this LED chaser does
A light chaser makes the apparent illuminated position move from one LED to the next. It is also called a running light or sequential LED flasher. In this circuit, a 555 timer creates clock pulses and a CD4017 advances its active decoded output from Q0 through Q9, then loops back. The intended effect is one LED on at a time; the basic circuit moves in one direction and does not fade or sweep back and forth.
The 555-and-CD4017 arrangement is a common no-code way to make a sequential LED effect. DigiKey’s project overview describes the same two-stage principle.
Parts for the 10-LED version
| Quantity | Part | Suggested specification |
|---|---|---|
| 1 | Timer IC | NE555, DIP-8 |
| 1 | Decade counter | CD4017B, DIP-16 |
| 10 | LEDs | Standard through-hole indicator LEDs |
| 10 | LED resistors | 680 Ω to 1 kΩ; start with 1 kΩ |
| 1 | Fixed timing resistor, RA | 10 kΩ |
| 1 | Timing adjustment, RB | 100 kΩ linear potentiometer, with a 10 kΩ series resistor |
| 1 | Timing capacitor | 10 µF electrolytic |
| 1 | Control-pin capacitor | 10 nF |
| 2 | Supply-decoupling capacitors | 100 nF ceramic, one per IC |
| 1 | Prototyping setup | Breadboard and jumper wires |
| 1 | Power source | Regulated 5–9 V DC for this beginner build |
Use a regulated low-voltage DC supply and check the data sheet for the exact timer and counter you have: allowable supply voltage and output-current limits depend on the part variant. The TI NE555 data sheet documents its astable operation; TI’s CD4017B data sheet covers the counter. Do not connect this breadboard circuit directly to household AC mains.
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How the circuit works
- The 555’s timing resistor-and-capacitor network charges and discharges to make a repeating output signal.
- Each rising clock edge at the CD4017 clock input advances the counter by one decoded output.
- Each counter output drives one LED through its own current-limiting resistor.
- After Q9, the sequence returns to Q0 and repeats.
The 555 astable frequency is approximately f = 1.44 / ((RA + 2RB) × C), where resistance is in ohms, capacitance in farads, and frequency in hertz. The equation is nominal; component tolerance, capacitor leakage, and the specific IC affect the actual rate. TI provides the astable timing equations in its NE555 documentation.
With RA = 10 kΩ, RB adjustable from roughly 10 kΩ to 110 kΩ (including the series resistor), and C = 10 µF, the estimated clock range is about 4.8 Hz down to 0.63 Hz. Since ten clock pulses complete one full sweep, that corresponds to roughly 2 to 16 seconds per full cycle. These are calculated nominal values, not a guaranteed measured range.
Wire the circuit
NE555 pin connections
| Pin | Name | Connection |
|---|---|---|
| 1 | GND | Ground |
| 2 | TRIGGER | Tie to pin 6 and the timing-capacitor positive node |
| 3 | OUTPUT | CD4017 pin 14 (clock) |
| 4 | RESET | Positive supply |
| 5 | CONTROL | 10 nF capacitor to ground |
| 6 | THRESHOLD | Tie to pin 2 |
| 7 | DISCHARGE | Junction of RA and RB |
| 8 | VCC | Positive supply |
Connect RA between VCC and pin 7. Connect RB between pin 7 and the joined pins 2 and 6. Connect the 10 µF timing capacitor from the joined pins 2 and 6 to ground, with its positive terminal at pins 2/6. Put a 100 nF capacitor between pins 8 and 1, close to the IC.
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- Complete DIY kit with N-555 timer and CD4017 counter ICs, pre-printed PCB, and all resistors, capacitors, LEDs, and connectors for easy assembly.
- Produces alternating red and blue dual-color strobe effects, ideal for model cars, decorations, or learning sequential LED control circuits.
- Operates on 5V–12V DC input, making it compatible with common power adapters, battery packs, or breadboard power supplies for flexible testing.
- Clear silkscreen markings and through-hole components simplify soldering, perfect for beginners, students, or hobbyists practicing circuit assembly.
- Compact board design with mounting holes, suitable for enclosures, displays, or embedding into custom electronic projects without extra wiring hassle.
CD4017 pin connections
| Pin | Function | Connection |
|---|---|---|
| 16 | VDD | Positive supply |
| 8 | VSS | Ground |
| 14 | Clock | NE555 pin 3 |
| 13 | Clock inhibit | Ground for continuous counting |
| 15 | Reset | Ground for the ten-step sequence |
Fit a 100 nF capacitor between CD4017 pins 16 and 8, close to the IC. Keep the 555-to-counter clock wire short on the breadboard.
Connect the LEDs
| Counter output | DIP pin |
|---|---|
| Q0 | 3 |
| Q1 | 2 |
| Q2 | 4 |
| Q3 | 7 |
| Q4 | 10 |
| Q5 | 1 |
| Q6 | 5 |
| Q7 | 6 |
| Q8 | 9 |
| Q9 | 11 |
For each output, wire the counter pin through its own resistor to the LED anode; connect the LED cathode to ground. The longer lead is normally the anode and the flat package edge commonly marks the cathode, but check the part if its leads have been trimmed. Verify this pin mapping against the package drawing for your exact CD4017 variant before applying power.
Assemble and power up
- With power disconnected, place both ICs across the breadboard center gap. Identify pin 1 from each package’s notch or dot, then connect the positive and ground rails.
- Wire the NE555 supply, reset, and control pins; add its 100 nF supply capacitor and 10 nF control-pin capacitor.
- Build the timing network between VCC, pin 7, the joined pins 2/6, and ground. Check the electrolytic capacitor polarity.
- Connect NE555 pin 3 to CD4017 pin 14. Add the counter’s supply, ground, clock-inhibit, and reset connections, then fit its 100 nF capacitor.
- Wire Q0 through Q9 to ten separate resistor-and-LED branches. Recheck IC orientation, LED polarity, and the shared ground.
- Apply regulated 5 V DC first. Turn the potentiometer slowly and look for the illuminated position to advance and repeat. If you change wiring, disconnect power first.
The counter should advance one output per clock pulse. The exact first LED at power-up is not guaranteed: the counter may not start in a defined state. A circuit that must always begin at Q0 needs an added power-on-reset arrangement.
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Set the chase speed
The potentiometer changes RB and therefore the 555 clock rate. Increase RB or the timing capacitance to slow the chase; reduce them to speed it up. A fixed 10 kΩ resistor in series with the 100 kΩ potentiometer prevents RB from falling to zero. A linear-taper potentiometer gives a straightforward adjustment.
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Choose LED resistors and output drivers safely
Each LED needs current limiting. Estimate its resistor with R = (Vsupply − Vf) / ILED. For example, with 9 V, a red LED with an approximate 2 V forward voltage, and a target of 7 mA, the result is 1 kΩ. That is a conservative starting point for an indicator LED; 680 Ω may be brighter, but confirm the current against the data sheet for the particular counter and LED. Hobby circuits use different resistor values because supply voltage, LED forward voltage, and device limits differ; values are not interchangeable without checking.
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One resistor per LED is the clearest arrangement and remains predictable if LEDs differ or the circuit is modified. A shared resistor may save parts in some versions, but can cause uneven behavior if more than one output conducts during transitions.
The CD4017 is a logic counter, not a power driver. Direct connection is for small indicator LEDs only and must remain within that exact device’s output limits. Use a suitable transistor, logic-level MOSFET, or LED driver for high-power LEDs, strips, multiple LEDs on one output, relays, or other heavier loads.
Troubleshoot by symptom
| Symptom | Checks and recovery |
|---|---|
| No LEDs light | Check supply polarity, both ICs’ power pins and orientation, common ground, LED polarity, and whether reset or clock inhibit is at the wrong logic level. Then check whether the 555 produces pulses at pin 3. |
| One LED stays on | Look for a missing clock at CD4017 pin 14, an active reset, clock inhibit held high, or a miswired 555 timing network. Check that pins 2 and 6 are joined and that pin 7 is connected to RA and RB as described. |
| LEDs skip positions | Suspect a noisy or ringing clock, long breadboard wires, poor contacts, or inadequate decoupling. Keep the clock wire short and the 100 nF capacitors close to each IC; inspect the clock with a logic probe or oscilloscope if available. |
| Several LEDs glow dimly | Check for floating control inputs, output overload, crossed LED wiring, poor breadboard contacts, supply noise, or transition ghosting. Confirm each LED branch and resistor is separate. |
| LEDs are too dim | Confirm resistor values and supply voltage, then check the counter’s source/sink limits. Do not remove the resistors; use a driver stage if more current is needed. |
| Speed is unstable or too fast | Check potentiometer wiring and capacitor polarity, try a fixed timing resistor, and increase RB or C to slow it. Electrolytic leakage and component tolerance can affect slow timing. |
| Works at 5 V but not 9 V | Check the exact IC supply specifications, output/input voltage compatibility, resistor and capacitor ratings, supply regulation, and LED current. Do not assume every 555 and 4017 variant has the same limits. |
A multimeter may show a changing average voltage on the 555 output, but a logic probe or oscilloscope is better for confirming clock pulses. If there is no pulse at pin 3, isolate the timer and inspect its supply and timing wiring before debugging the counter.
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- Power supply voltage: DC 12V, control panel: 60.7x37mm, LED light panel: 35x26mm.
- This kit consists of a control board A and three light boards Blight board colors are red, blue, white. After power on, the redand blue light boards flash twice each successively, and then thewhite light board flashes once, so alternating cycle. Mastery of the principles of this kit, you can make a running billboard or decorative ambient light.
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Adapt the design for other effects
Use fewer than ten LEDs
For a four-step sequence, use Q0 through Q3 and connect Q3 to the active-high reset input so counting restarts after that step. Confirm the reset behavior and wiring for the exact counter version.
Use more than ten LEDs
Multiple CD4017 counters can be cascaded; follow the device data sheet for carry-out and clock connections. A larger multi-counter example is documented at Hackaday.io. Higher LED counts or heavier loads may require transistor driver stages.
Make a reverse sweep, fade, or custom pattern
A single CD4017 sequence is one-way and changes abruptly between outputs. A back-and-forth Knight Rider effect needs added logic, diode steering, a shift register, or a microcontroller. Fading requires additional circuitry such as transistor stages with suitable control, PWM, or a dedicated LED driver. A microcontroller is the more flexible choice for RGB effects, sensor input, brightness control, or arbitrary patterns; the 555/4017 is simpler when the goal is a fixed sequence without firmware.
Quick Recap
Safety and build limits
- Use low-voltage DC only; never connect the breadboard circuit directly to mains.
- Disconnect power before changing wiring and observe electrolytic capacitor polarity.
- Keep a current-limiting resistor in series with every discrete LED.
- Check the data sheet for the exact IC manufacturer, suffix, package, voltage range, pinout, and output limits.
- Do not use the counter output to drive a high-current load directly.
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