Home » Electronics » Interface with the Lumex LCD-A401C71TR via shift registers and Arduino Pro Min

Interface with the Lumex LCD-A401C71TR via shift registers and Arduino Pro Min

In this post, we’ll write an interface between an Arduino Pro Mini and a Lumex LCD-A401C71TR.


What’s Required

For this project you’ll need the following:

  • Lumex LCD-A401C71TR – I purchased mine through DigiKey, but there are many sources so use your favorite.
  • Breadboard
  • Arduino Pro Mini or another flavor of Arduino.  None of the code in this post is reliant upon the Pro Mini.
  • FTDI Basic Breakout Board
  • 74HC595 shift registers which you’ll need three of them
  • Various lengths of breadboard connectors


The Arduino Pro Mini has 14 digital I/O pins.  As you can see from the diagram below of the Lumex LCD (copied from the Lumex data sheet), the LCD has 40 pins and pin 1 starts on the bottom left and the moves from left to right and then pin 21 starts at the top right and moves from right to left.


The following diagram, also from the Lumex data sheet, shows how the connects work.


Based on this diagram, we can see that 6 of the pins are not used so we actually only have 34 digital pins.  Additionally, 4 of the pins are setup to show either dots or column markers which we can choose to wire these directly to power if we need them.  That means we don’t have to dynamically control those 4 pins so we actually have 30 pins that we need to control dynamically.

Pin 1 is the ground pin which always needs to be connected.  Using the chart, we can see that if we apply voltage to pin 5 then segment 1E will light up.  The following images show what segment 1E actually is.

Digit “1” in the 1E naming is the first digit on the left.  Digit “2” is the second digit from the left and so on.  This is shown below.


The segments also have a pattern so that 1E is the bottom left segment in the number.  The following diagram shows the segment layout.


With this naming convention, we can easily read the chart above and we know exactly how to light up each digit, dot and column.

Now, we can move onto the programming of the shift registers.

Before continuing, consider reading the post about shift registers.

Shift Register

We decided above that we have 30 pins to control.  Each shift register has 8 digital outputs pins.  So, we’ll need 4 shift registers.  So that our math stays simple, we’ll use 7 pins from each shift register so that we know shift register (1) controls digit (1), shift register (2) controls digit (2) and so on.

Wire up the first shift register (digit 1) and we’ll write some code to verify it works.  Follow the Shift Register tutorial to learn how to wire a shift register to the Arduino.

TODO – show a picture of the wiring here.

Adruino Code To Control First Digit

TODO – place the code sample here.