What Is the CD4017? Decade Counter: Pinout, Operation and Uses
The CD4017 is a 10-output decade counter/divider. On each clock pulse exactly one output goes high in sequence (0→9→0). It is used in LED running-light (chaser), sequential timing and frequency-division (÷10) circuits and is classically driven by an NE555 oscillator. The output pin order is scattered (Q0=pin 3).
The CD4017 is a 10-output decade counter / divider. On each clock pulse exactly one of its outputs goes "high" in sequence (0→1→2…→9→0). This makes it the classic part for LED running-light (chaser), sequential timing and frequency-division circuits. For the concept, see sequential logic (shift register).
What is the CD4017 used for?
Running lights (LED chaser/sequencer), step sequencing, frequency division (÷10), simple counters and timers. A classic application takes the clock from an NE555 oscillator and uses the CD4017 to light 10 LEDs in sequence.
CD4017 pinout (16 pins) — outputs are scattered
| Pin | Function | Pin | Function |
|---|---|---|---|
| 1 | Q5 | 16 | VCC |
| 2 | Q1 | 15 | Reset (MR) |
| 3 | Q0 | 14 | Clock (CLK) |
| 4 | Q2 | 13 | Clock Inhibit (CE) |
| 5 | Q6 | 12 | Carry Out (÷10) |
| 6 | Q7 | 11 | Q9 |
| 7 | Q3 | 10 | Q4 |
| 8 | GND | 9 | Q8 |
The output numbers are not laid out in pin order (Q0=pin 3, Q1=pin 2, Q2=pin 4…); watch the pinout when wiring LEDs.
Control pins
- CLK (pin 14): the counter advances one step on each rising edge.
- CE / Clock Inhibit (pin 13): set high to stop counting (usually tied to GND).
- MR / Reset (pin 15): set high to return the counter to Q0 (usually tied to GND).
- Carry (pin 12): gives one pulse every 10 counts → for chaining 4017s.
Limitations
- It is CMOS; unused inputs must not be left floating (tie to GND/VCC).
- Output current is limited; a strong load needs a driver.
CD4017 equivalents and alternatives
- CD4022: the 8-output (octal) sibling.
- 74HC4017: the faster HC-family version.
- 74HC595: when you need an arbitrary pattern (full control, not a counter).
Find it in our catalog
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