The CD4026B is a useful CMOS counter IC for circuits that need to count pulses and show numbers on a 7-segment display. Instead of using a separate counter IC and a separate display decoder, the CD4026B combines both functions in one device. This article explains the CD4026B pinout, internal operation, electrical specifications, display connection, two-digit counter circuit, and more.

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CD4026B Overview

The CD4026B is a CMOS decade counter with a built-in 7-segment display decoder. It counts clock pulses from 0 to 9 and converts the internal Johnson counter output into signals that can drive one numeric display digit.

The IC includes common control pins such as CLOCK, RESET, and CLOCK INHIBIT. A high RESET signal clears the counter to zero, while the CLOCK INHIBIT pin can stop counting without clearing the current value. The CD4026B also provides CARRY OUT, seven decoded segment outputs a–g, DISPLAY ENABLE, and an ungated C-segment output. Its low power use and reduced external component count make it practical for simple numeric display circuits.

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CD4026B Pin Configuration and Pin Functions

CD4026B Internal Operation Diagram

CD4026B Functional Diagram

As shown in the functional diagram, the CD4026B combines a decade counter and a 7-segment display driver into a single integrated circuit. The CLOCK input receives pulses that advance the count from 0 to 9, while the RESET input returns the counter to zero whenever a logic HIGH signal is applied. The CLOCK INHIBIT input can temporarily stop counting without clearing the displayed number. After processing each clock pulse, the internal counter sends the count value to the decoder section, which activates the appropriate segment outputs (a–g) to display the corresponding digit on a common-cathode 7-segment display. The diagram also shows the CARRY OUT output, which generates a pulse after every ten counts and is used for cascading additional CD4026B devices in multi-digit display systems. Other control signals, including DISPLAY ENABLE IN, DISPLAY ENABLE OUT, and the UNGATED "C" SEGMENT output, provide additional display control functions.

CD4026B Logic Diagram

The logic diagram provides a detailed view of the internal circuitry that allows the CD4026B to perform counting and display decoding. As shown in the diagram, the device contains a five-stage Johnson counter formed by interconnected flip-flops that generate a sequence of ten unique count states. These count states are processed by a network of logic gates that decode the counter outputs into the correct segment control signals for the 7-segment display. The diagram also illustrates how the CLOCK, CLOCK INHIBIT, and RESET signals interact with the counter stages to control counting operation. The logic circuitry generates the seven decoded outputs (a–g) as well as the CARRY OUT signal used for cascading counters. This internal architecture eliminates the need for a separate BCD decoder, allowing the CD4026B to directly drive a display while maintaining a relatively simple external circuit.

CD4026B Timing Diagram

The timing diagram illustrates how the CD4026B responds to clock pulses and how its outputs change over time. As shown in the diagram, the counter advances one count on each positive transition of the CLOCK signal, causing the displayed value to progress from 0 through 9 before returning to 0. The waveform also demonstrates the effect of the RESET input, which immediately clears the counter and forces the display back to zero. When the CLOCK INHIBIT signal becomes active, incoming clock pulses are ignored and the displayed value remains unchanged. The timing diagram further shows the operation of DISPLAY ENABLE IN and DISPLAY ENABLE OUT, which control whether the decoded segment outputs are visible on the display. The segment output waveforms (a–g) change according to the current count value, producing the correct digit patterns on the 7-segment display. In addition, the CARRY OUT waveform generates one pulse for every complete counting cycle, allowing multiple CD4026B devices to be synchronized in multi-digit counter applications.

CD4026B Electrical Specifications

Connecting the CD4026B to a 7-Segment Display

The CD4026B is designed to directly drive a common-cathode 7-segment display, eliminating the need for a separate BCD-to-7-segment decoder. As shown in the circuit diagram, the segment outputs (A–G) of the CD4026B are connected directly to the corresponding display segments. When clock pulses are applied to the CLK input, the IC automatically counts from 0 to 9 and activates the correct segment combinations to display each digit.

In this example, the Clock Inhibit (INH) pin is connected to ground, allowing the counter to respond to incoming clock pulses. The Display Enable In (DEI) pin is connected to the positive supply voltage to keep the display active, while the Master Reset (MR) pin remains low during normal operation. The common cathode terminal of the display is connected to ground, enabling the CD4026B outputs to illuminate the required segments.

The CD4026B outputs are labeled A, B, C, D, E, F, and G, corresponding directly to the seven segments of the display. As the counter advances, the IC internally decodes the count value and drives the appropriate segments without requiring additional logic circuitry. This simplifies circuit design and makes the CD4026B a popular choice for digital counters, timers, event counters, and display projects.

CD4026B Two-Digit Counter Application Circuit

The circuit diagram shows a practical two-digit counter built using two CD4026B decade counter and 7-segment display driver ICs. The system is powered from a 6 V supply and uses two common-cathode 7-segment displays to show count values from 00 to 99. Each CD4026B combines a decade counter and a 7-segment decoder, allowing it to directly drive a display without requiring additional decoding circuitry. This simplifies the design and reduces the number of external components needed for multi-digit counting applications.

The lower CD4026B (IC1) functions as the units counter. Clock pulses generated by the sensor input circuit are applied to its CLK pin, causing the displayed value to increase by one for each detected event. Internally, the IC counts from 0 to 9 and automatically activates the appropriate segment outputs (a–g) to display the corresponding digit on the first 7-segment display. When the count reaches 9 and another pulse arrives, the counter returns to 0 and generates a carry-out pulse.

The carry-out output of IC1 is connected to the clock input of the upper CD4026B (IC2), creating a cascaded counter arrangement. Each time IC1 completes a full counting cycle from 0 to 9, the carry-out pulse increments IC2 by one count. IC2 drives the second 7-segment display, which represents the tens digit. Through this cascading method, the circuit can display numbers from 00 to 99 using only two CD4026B devices.

The input sensing section consists of an LDR (light-dependent resistor), a BC547 transistor, and associated resistors. Under normal conditions, the LDR receives light and maintains a specific resistance level. When an object interrupts the light path, the resistance of the LDR changes, causing the transistor to switch states and generate a clock pulse. This pulse is then applied to the counter, increasing the displayed count by one. Because of this arrangement, the circuit can be used as an object counter, people counter, production line counter, or event counter.

The RESET pushbutton (S1) is connected to the reset inputs of both CD4026B ICs. When pressed, it forces both counters back to zero simultaneously, causing the displays to show 00. This feature allows the user to clear the count and begin a new counting cycle without disconnecting power from the circuit.

The resistor network connected to the displays helps limit current and ensures proper segment operation. The common-cathode terminals of the displays are connected according to the requirements of the CD4026B, allowing the IC outputs to directly illuminate the necessary segments. Proper power supply connections to the VDD and VSS pins ensure stable operation of both counters and reliable display performance.

This circuit demonstrates one of the most common uses of the CD4026B: building a multi-digit event counter without a microcontroller. By combining the counter, decoder, and display driver functions into a single IC, the CD4026B provides a simple and cost-effective solution for counting applications that require a numeric visual display.

CD4026B Real-World Applications

Digital Event and Object Counters

The CD4026B is commonly used in circuits that count events, objects, or user actions. Each clock pulse increases the displayed number by one, making it useful for button counters, product counters, visitor counters, and sensor-based object detection systems. Sensors such as LDRs, infrared sensors, photodiodes, and proximity sensors can generate the pulses needed by the CD4026B.

Production and Process Monitoring

In industrial settings, the CD4026B can help monitor repeated machine actions, conveyor items, packaging cycles, motor rotations, and production output. Its carry-out function also allows multiple ICs to be cascaded, so the system can display larger values beyond a single digit.

Scoreboard and Game Displays

The CD4026B can be used in simple scoreboard circuits for games, sports, quizzes, and competitions. Push buttons or electronic switches can send clock pulses to the IC, allowing the score to increase each time an input is triggered. For higher scores, several CD4026B ICs can be connected together to create multi-digit displays.

Frequency and Timer Displays

The CD4026B can work with timing circuits, oscillators, or pulse generators to display counted pulses within a time period. This makes it useful in basic frequency counters, elapsed-time displays, and timer circuits where a numerical display is needed without using a microcontroller.

Educational Electronics Projects

The CD4026B is useful for learning digital electronics because it shows how clock pulses, counters, reset control, cascading, and 7-segment displays work together. Since it already includes the counter and display decoder, students can build practical circuits with fewer parts while still understanding important digital logic concepts.

Laboratory and Test Equipment

The CD4026B can be used in simple test instruments that need to display pulse counts during measurement or testing. Its low component count, direct display-driving ability, and easy cascading support make it suitable for compact counters, test benches, and basic electronic measurement setups.

Common CD4026B Circuit Problems and Troubleshooting

CD4026B vs 74LS90 with 7-Segment Decoder

CD4026B Mechanical Dimensions

Manufacturer

Texas Instruments manufactures the CD4026B using mature CMOS logic production processes designed for low power consumption, stable switching performance, and long-term reliability. Its manufacturing capabilities include semiconductor wafer fabrication, IC assembly, package testing, electrical verification, and quality control. TI supplies the CD4026B in several package types, including PDIP, SOIC, and TSSOP, making it suitable for both through-hole and surface-mount circuit designs. The device is produced to support a wide operating voltage range, industrial temperature performance, RoHS-compliant options, and consistent logic operation. Through its global semiconductor manufacturing and supply chain network, Texas Instruments can support high-volume production, long product availability, and reliable sourcing for customers.