I have a seven segment display with 14 pins on each side and three digits. The display include a decimal point. However, I'm struggling to figure out the function of each pin. This item is described as a "3-digit Common-Cathode Display". enter image description here

I'm struggling to find the purpose of each pin. 28/3 is not an even number, so I assume all the pins......share the cathode. However, each segment has 8 L.E.D.s on it, so I don't know why I would has 4 extra pins or how to determine which ones are shared.

Can anyone help me with this? Also, not sure how to check what kind of voltage/resistors it needs, I can't find a data sheet. It's old.

  • 3
    \$\begingroup\$ how about checking with a multimeter in diode test mode? \$\endgroup\$
    – FrancoVS
    Commented Oct 27, 2021 at 17:58
  • 1
    \$\begingroup\$ Here are a pair of datasheets for 28-pin 3-digit displays: #1, #2 and this seems to be a common pinout. (7 pins for display segments, 1 pin for the dot 1 pin for common-cathode) x 3 digits == 27 pins. So only 1 'spare'. \$\endgroup\$
    – brhans
    Commented Oct 27, 2021 at 18:05

1 Answer 1


You can use a DMM in Diode mode to find which segment is connected where.

Or, you can check the datasheet. It is a generic part from multiple vendors. Here is one option.


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