Source: https://mokxi.com/parts/cd4017 Updated: 2026-11-10 Part # CD4017 decade counter Ten outputs, one high at a time, stepping along on every clock. See every part - 16 pins - 1 setting - In 1 project Drawn live by the editor's own code, at the size you see it. At a glance ## The CD4017 decade counter in brief What it is, and every setting the properties panel gives it. The CD4017 is the decade counter in LED chaser kits: ten decoded outputs, Q0 to Q9, exactly one of them high, and each rising edge on CLK moves the high one along. CO is high for counts 0 to 4, RST high sends the count to 0, and INH high freezes it. VDD takes 3 to 18 volts. A 555 astable usually supplies the clock, but any Arduino pin will do: CLK to a digital pin and one short HIGH pulse per step, from an Uno at 5 volts or from an ESP32 with VDD at 3.3. Mokxi models the weak metal-gate outputs as 2500 / VDD ohms, 500 at 5 volts, so an LED with no resistor gets a few milliamps and glows; the clock delays of 500 nanoseconds to an output and 400 to CO at 5 volts; and Q5 wired to RST counting to five. The model property offers the 74HC4017, whose strong outputs do need resistors. The classic mistakes are leaving RST or INH floating, which turns the whole count unknown, and wiring the LEDs in pin order when pin 1 is Q5. Minimum pulse widths and a real chip’s random power-up count are not modeled. Family Logic Pins 16 model CD4017B (or 74HC4017) Pins ## 16 pins Named as the editor names them, so a wire lands where you expect it. ### Output11 - Q5 - Q1 - Q0 - Q2 - Q6 - Q7 - Q3 - Q8 - Q4 - Q9 - CO ### Input or output2 - VSS - VDD ### Input3 - INH - CLK - RST How to use it ## How to use the CD4017 decade counter with an Arduino VDD to 5 V, VSS to ground, RST and INH to ground so it counts, and a clock on CLK: every rising edge moves the one high output along, Q0 to Q9 and around again. The chaser here takes its clock from a 555 at about 4 Hz with no code; from an Arduino, CLK goes to a digital pin and each short HIGH pulse is one step. The outputs are not in order around the chip: pin 1 is Q5 and pin 3 is Q0, which is why the wires to the LEDs cross. The LEDs need no resistors because a CD4017 output is a weak 500 ohm switch at 5 V. Leave RST or INH floating and the whole count goes unknown; wire Q5 to RST instead of ground and it counts to five. Part pin Board pin VDD 5 V VSS GND CLK 555 OUT (pin 3) RST, INH GND Q0 to Q9 LED anodes, cathodes to GND With VDD at 3.3 V an ESP32 pin can clock it; the outputs are weaker still at that supply. The 74HC4017 model has strong outputs that do need resistors. Click to open it in the editor This is the simulator itself, running here. Click anything to open it in the editor. Open this project in the editor Read the full tutorial How it is modeled ## What is true about the CD4017 decade counter, here In its help article’s own words: what the simulation gets right, and where it stops. ### Modeled The outputs are weak. A metal-gate CMOS output is a few hundred ohms. The model uses 2500 / VDD ohms, which is 500 ohms at 5 V and matches the MC14017B data sheet's typical drive currents at 5, 10 and 15 V to within a few percent. An LED with a 220 ohm resistor on an output gets about 4 to 5 mA at 5 V and glows rather than blazes, exactly as it does on a real breadboard, and the output voltage sags under that load. It is slow, and the delay depends on the supply. From the MC14017B data sheet's typical column at 50 pF: 500 ns from the clock to a decoded output and 400 ns to CO at 5 V, falling to 230 and 175 ns at 10 V and 175 and 125 ns at 15 V. Supplies in between are interpolated along those points. Resetting from an output works. Wire Q5 to RST and the counter runs 0, 1, 2, 3, 4 and starts again, because Q5 resets the chip the moment it goes high. Q5 is high for about half a microsecond each time, as on the real chip, which is too short to light an LED. ### Not modeled The Johnson counter inside a real 4017 is modeled as the count 0 to 9 it decodes to, which is all its pins ever show. It powers up at 0 rather than wherever it likes. There are no minimum clock pulse widths or reset removal times: a pulse of any length counts. Below 5 V the delays are held at the 5 V figures, where a real chip is slower still. Input thresholds are half the supply, where the data sheet only promises 30% and 70%. From CD4017 decade counter, in full. Projects ## See the CD4017 decade counter in a project One built-in project uses it. It opens in the editor, already wired. More parts ## The rest of the bench Every one of these is drawn and simulated the same way. Full-size breadboard A real 0.1 inch grid with the rails and the center channel, 63 columns wide. Jumper wires Drag from any pin or hole to any other. Corners snap, and you can drag them. Power A supply rail at the voltage you choose. Ground The other end of every circuit. LED Lights when current flows. Five colors, and the brightness is what your eye would see. Filament lamp A tungsten bulb in a holder: an inrush when it is switched on cold, tens of milliseconds to warm up, and dim on half its voltage. Resistor Any value you like, with the color bands drawn to match. ESP32-C3-DevKitM-1 A RISC-V board that runs your firmware at 160 MHz on the real memory map. Pushbutton A 12 mm tactile switch. Hold it while the simulation runs. Raspberry Pi Pico The RP2040 board on our own Cortex-M0+ core. Pick a program and press Run. Raspberry Pi Pico W Raspberry Pi Pico W (RP2040). The same board and the same pinout as a Pico, with the CYW43439 on it. The WiFi is simulated (no radio; real internet through the Cloud panel’s switch), and the on-board LED, which hangs off that chip rather than off GP25, is driven through the same path. Everything else is the Pico. Raspberry Pi 4 Model B Raspberry Pi 4 Model B: the 40-pin header, driven by main.py with RPi.GPIO or gpiozero. See every part ## Wire up the CD4017 decade counter Open the editor and push it into the breadboard. It is free, and it runs on your own machine. Start building free Open the editor