So basically, I'm trying to make a digital wall clock and using digital numbers, I have 7 sections of LED's per number, 4 numbers and one section for the colon in between them. A total of 30 sections. The colon will toggle every second so the the most possible simultaneously glowing sections is 27. That's because of the time 08:08. Is there any way to make this work with an arduino? Possibly by Charlieplexing the arduino into 30 sections, using 6 pins. Or is there something out there that has 30 pins!?

The problem of course with charlieplexing, is that you need it to become rapid pulses. I'm sure I'm going to need some help with this, and also with laying out a schematic.

To be clear, this is how the led sections are going to be laid out. I also know I'm going to need an npn transistor for every single one of them. the biggest section uses 20 LEDs. enter image description here


1 Answer 1


I would consider 74HC595N's. These are shift registers, which can control 8 'outputs' using less pins on your Arduino.

These are very cheap (buy them per 10) and you can daisy chain 4 of them, having 32 outputs, using only 5 pins of your Arduino. This would fit perfectly with your 30 sections.

Each of the 30 outputs can be used to control a transistors to control one LED sections.

See for an example for using shift registers with the Arduino: ShiftOut

Also you might need this: ULN2803 darlington drivers for each output (4 total).

  • 1
    Jij bent Nederlands of niet?
    – Hendriks3D
    Commented Aug 11, 2017 at 14:53
  • @Hendriks3D True (but it's better to write everything in English here). Commented Aug 11, 2017 at 14:58
  • Indeed.........
    – Hendriks3D
    Commented Aug 11, 2017 at 19:43

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