The 4026 is a chip that counts in binary from 0 to 9. This chip works in conjunction with a 7-segment LED display.
Observe pin 6-7, and 9 to 13. They consist of seven outputs. See what we are getting at? Each pin will control a LED segment (a little LED in itself) of the 7-segment display LED. By combining outputs together – some lighting ON, some staying OFF – we can display numbers on the LED display.
Let's get a quick overview of each pin:
(1) CLK [Clock] = Our counter needs a clock to drive the counting. The speed of the counting depends on the frequency of the clock.
(2) CE [Clock Inhibit] = Inhibit the clock. In other words, a high logic to this pin will pause the counting.
(3) DE [Enable Display] = Enables the 7-segment display outputs or, in other words, enables the 7-segment display to present our numbers. If we drive the pin low, we won't have any numbers displayed but the counting will still continue.
(4) DEO [Display Enable Out] = Used to connect other 4026s together.
(5) CO [/10 Output] = It divides the input clock of the 4026 counter (pin 1) by 10 and outputs the new clock frequency from this pin. It is usually to drive another 4026 to provide multi-digit counting. We won't be using this pin for now, so we'll just connect it to ground.
(6, 7 , 9, 10, 11, 12, 13) 7-Segment Display Output = This output will be the input of our 7-Segement Display. We'll have to match the outputs correctly to the input of the 7-segment display, otherwise our numbers won't be displayed correctly.
(14) UCS [Ungated C-Segment] = Serves the same purpose as pin 13 – it’s meant to be connected to the 7-segment display C pin. But, this pin is not affected by the disabled clock input unless the count is above 2. We won't be using this pin, so we will be connecting it to ground.
(15) RST [Reset] = Reset the counter