This particular 3 digit LED was salvaged from an old Kidde Nighthawk carbon monoxide alarm. Most of these carbon monoxide alarms start to signal “error” after about 3 or 4 years and need to be replaced, but IMO the LED readout is worth saving for various projects. I modified the following specification graphic to also show all the backside connections. You know how difficult it is to keep those pins organized if you ever tried to hand wire a digital readout. The process was less prone to error after printing this graphic. I also believe the 4.7K current limiting resistors that I used on each of the segments is greater than the multiple resistors IC that was originally on the Kidde board. Regardless, the segments are still plenty bright.
