# Running out of pins in a 4x7-segment display clock

I've been playing around with the 7-segment displays and so far I've only been able to make 1 working display hooked up to a potentiometer that changes the number on the display with a switch that turns it into a counting-up timer

My main goal is to make a Clock but that uses 4 7-segment displays and I've already used up 7 pins for 1 display so now I either need to make more pins (I'm using Arduino Uno which has 14 Digital pins + 6 if you use the Analog In pins) or use the 7-segment decoders

if I use the 7 segment decoder that will take up 4 per display which totals up to 16 which is well in range the required amount of Pins

so can someone teach me what is easier to do:

Making more pins using the 8-bit shift registers or Use the 7-segment decoders to make space

and if you think one is easier can you tell me how to use them because I have no idea and I've been tinkering with the decoder for the past hour or two (btw the 7-segment displays are all Common Anode)

• A 4-digit 7-segement display needs 4+7 (not 4×7) pins. May 18, 2017 at 8:55
• I don't have a 4-digit 7-segment display I only have the 4 individual 7-segment displays May 18, 2017 at 9:08
• You can wire them just like a 4-digit display is internally wired. May 18, 2017 at 9:12
• butt how tho... May 18, 2017 at 9:16
• See for example here and here, and read about using a driver circuit. May 18, 2017 at 9:41

The basic idea is this:

First, connect segment A of each display together, and all the segment Bs together, and all the segment Cs and so on. Each "group" is driven by one pin on the Arduino. For this you will need seven pins.

Your displays will have either a common anode or common cathode - perhaps you have that connected straight to +5v or straight to ground currently. Instead, you connect the "common" pin from each display to a spare pin on your Arduino - so using another four pins.

Remember the resistors too.

Now, you can light up any segment on any display, by setting the appropriate segment pin and the appropriate common pin to the right values.

Make sense?

• Thanks for giving out an Answer but I've already figured it out a while ago with Edgar Bonet's help :P thanks tho May 18, 2017 at 14:38