7 Segment Display


so I recently started to work with an arduino uno R3 and to date everything worked fine, but now I would be thankful for any tip or help for this:

I want to use something else than simple LEDs to display information, so I took an old clock and disassembled it for parts, most importantly the Display.

It’s a 4 digit (obviously) 7-Segment Display, with a double point in the middle and another light that was used to show if the alarm function was activated.

That thing has 24 pins (I don’t need to use all Digits, so thats ok) and all the logic was attached to a different board, so there is nothing “intelligent” left, other than the built in circuit that isn’t visible, which is the whole problem: I can’t figure out how to display certain patterns, especially decimals. All google finds me are 7 segment displays which use 7 pins per digit and a common cathode/anode, so this can’t be the case on my display.

So these things I already figured out:

There is one pin used to light up the double point and another for the alarm-mark.

There are four groundings pins, where two of them are connected to different halfs of the lights:
14 Pins are connected to the digits: 1 Pin powers up 2 lights, but each light of those two is connected to a different grounding pin, so I can light up the patterns you see in the attachments. (And I can disconnect one of the grounds, so one of those lights goes out)
First I thought the other 2 grounding pins would make the deal, but they show exactly the same behavior.

As you might have noticed there are 4 pins left: And hell: I don’t know what they are for. Neither 5V or 0V seem to have any influence on the lighting…

So could someone please (after reading through this wall :blush:) help me out? Do you know what I could try out next? Or have you already seen something like this?

Thanks in advance. :slight_smile:

Any other numbers on it besides the 6221xx?

On the left side it says SIO-10 and on the back SY-DDC6054G.

Welcome to the world of bedside clock displays! :smiley:

These are multiplexed as 2 by n, using alternate phases on the centre-tapped power transformer. Since the power transformer also is used as a timebase at the line frequency, the same signal to the clock chip is used to synchronise the multiplexing. You can observe the effect if you pick up the clock and wave it in the air in front of you.

So you need to identify the two principal commons, whether they are anode or cathode; once you do that the rest will rapidly become clear.


2-phase multiplex.

Have a look here:

// Per.

Wow, thank you guys a lot. My googling attempts failed at not knowing the right terms.

Going to look at the link at home again, now it all makes more sense to me.

Thank you! :slight_smile: