LED Driver

A project log for Hex Display Module

Hex character module made from 3mm USSR 7-segment displays

robertRobert 09/24/2023 at 01:520 Comments

For a 4 character module I'll need to drive up to 32 LEDs with a common cathode configuration. Each character in the display will be a hexadecimal character of a 4-bit binary number. Additionally, the module must have a have a single latch line to latch data from a bus.

The MC14495 "Hexadecimal-to-Seven Segment Latch/Decoder LED Driver" is a common suggestion. It is designed for common cathode, it has a character ROM for 7-segment hexadecimal characters, it has built-in 290Ω current-limiting resistors and it has a latch. Unfortunately, to keep it simple, it requires 1 chip per character. And, they are not as common and cheap as they used to be.

For I/O, the MC14495 has a 4-bit data input (A, B, C, D) along with a latch enable (LE) input. For outputs, it has one for each segment in a 7-segment display (a, b, c, d, e, f, g), and a line that is low for characters 0 thru 9 and goes high when the character is A thru F (h + i). Finally, it has a line that is normally high-impedance but goes low when the character is F (j). I don't have a use for the (h+i) and (j) outputs, so I'll tie them to ground. 

The MC14495 is larger than the L104V, which  presents a challenge in keeping the finished project small enough and nice to look at.