Please read the textbox/description first. In this video I show how you can find out the pin connections of a Green or Red LED Clock unit, salvaged out of an (old) LED Clock.
And re-use that display, of course it has only 4 digits, anyway, more info in the video.
The best thing is, of course, to go to the www or via Google to find out all the pin connections (!). So where the cathode is on pin (X) or where the anode is on pin (Y). And how all the electrodes have to be driven, by a positive or negative current, always a tiny current.
And test it and use it via the manufacturer instructions. But this video gives an experimental test setup that is safe and always works to figure out which LED-bar in the display lights up when voltage/current is supplied to that specific LED bar, green or red. And where the plus and minus are.
Feel free to swap the (-) and the (+) on whatever electrode during testing, going “all over” all electrodes. No problems (burn out or so) can occur when you use the method of 9 Volts and a 1 K series resistor during testing.
Even when the (+) and (-) are not properly connected (say reversed, a LED is a Diode), the LED units cannot be damaged. Important: a method not (!) usable to test liquid crystal display units (!) only usable for LED displays/units, because they are polarized.
So in fact almost nothing can go wrong with this way of testing a LED clock unit, finding out where the negative and the positive is and which bars in the 7 segment display will light up.
Please note, perhaps it could be that some separate LED bars in the figure sometimes are multiplexed via an “intelligent” Chip. It means that they can serve 2 or more positions, I have heard about that, though whatever, that is also physics.
That is not the aim of this video, it is a much more complicated situation, this video does not show multiplexed driving of figure/display bars. It only shows simple DC driving of a 7 segment display, perhaps a 8 segment display, when the dot is included.
The current (via the 1 K resistor) is so low that nothing can go wrong, even when you make bad or reversed connections to the unit to be tested, reason: a red or green LED (bar) is/acts as a diode.
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I keep all my YT videos constant actual, so the original video’s with the most recent information are always on YouTube. Search there, and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc. Some persons try to find gold via my circuits. I take distance from all these fake claims. I can not help that these things happen. Upload 24 May 2022.