Hacking A 4 Digit 7 Segment Display, Colon to Decimal Point

Thread Starter


Joined Jun 17, 2014
Hello there,

A friend of mine was nice enough to give me a 4 digit 7 segment display the other day. I hadnt used one in ages. It's pretty nice too, they are better than they used to be i think.
So i hooked it up to the microcontroller and got it running as a clock/timer with a colon in the middle as a clock normally has. The digits are 0.56 inch high so they are very visible and the LEDs are very bright, so bright in fact that you have to turn the brightness down by altering the signals going to the controller chip, which a little unfortunate, is on the board with the display.

Now at the same time i had been causally working on some wireless telemetry for the car out in the driveway and was thinking what a nice display for the data (such as the voltage) this would make. So i went to use the decimal point on the display and was very surprised to find that you can not use the four decimal LEDs even though they are physically in the display as well as the colon and the normal 7 segments for each digit. The reason being that the manufacturer of this type of display makes the LED part the same for all models, but before they pot it they hard wire up either the decimal point segment or the colon segment to one of the pins. All in all they only save 1 pin so that's a little strange, but that's how they do it.

I was thinking, the wiring to the dp segments is already inside the potted display along with the colon, so all i would have to do is dig into the potting with a dremel and hook a wire to the dp segment line. That would allow me to drive any of the decimal points through multiplexing.

So i was wondering if anyone here ever tried this. It's unfortunate that the display is soldered to the PC board, but the dp's are near the bottom so it could be possible to dig into the bottom side of the display to get to the dp segment wiring. It would be easier to do from the back, but the back is not accessible without unsoldering the display from the board so i was hoping to get into the bottom part. If anyone did anything like this before it would be great to hear about it, and even if it was from the back not the bottom.
I know i could get a better display, but i thought it would be interesting to mod this one, and cheaper too :)