Continuing from this post, I’ve been working on a driver and control system for a couple of common-cathode LED bars. The driver circuitry (NPN transistors) was completed and detailed in the previous post. This post will take a closer look at the control board/layer that I had only started last time.

Here’s what I had at last post:

I finished wiring around the two sockets (destined to hold 74HC595 shift registers) and the result looks like this:

These shift registers are connected so the carry-output of the first feeds into the serial input of the next. This setup “cascades” the two registers so that they can operate as a single 16-output register, all controlled by a set of 3 wires. This concept is the basis of a huge multitude of projects in the hobby electronics world, since it allows the control of many outputs (16 in my case) through just a few wires. You can keep adding shift registers, with the only limit being how long it takes to shift out all the values.

Here’s the schematic for that board:

Each set of 4 output pins labeled “SIGNAL_OUT” is connected to pin headers that stick through the board to the one beneath. In this way, this board plugs into the board below it. The signals are then amplified by the transistors below to drive the LEDs.

Here’s the bottom of the board:

And viewing from the side, you can see the signal and power pins sticking up:

A view of the top (control) board partially inserted into the bottom (driver) board:

And here they are connected/stacked, and ready to hook up:

This module will control and power 16 channels of LEDs, and only needs 3 inputs (besides power/ground). I’ve done some preliminary testing, and it looks like it’s working great. I’ll work on getting some videos of the LEDs in action for a later post.