New Schematic with Software Friendly Column Assignments

A project log for 16 Digit LED Display Board

An I2C Interfaced simple LED board.

bharbourBharbour 04/16/2024 at 15:050 Comments

A lot of the noodling projects that I do wind up being used in a real project later. In order to make it easier to re-use this idea later, I did the corrections while it was fresh in my mind. Here is the updated schematic.

Updated Schematic Drawing
Updated Schematic Drawing

 The major changes are:

1) Assign the row drive signals to the LED segments, and the column drive signals to select the display to light. Inside the driver chip, there are two groups of 8 bit column control registers and in this configuration, all of the segments and the decimal point for one display are controlled from one column control register.

2) Re-arrange the LEDs on the schematic so that matrix 1 is in the top row and the most significant digit is at the left end. Less obvious in this change is that the column select 1 signal is now selecting the leftmost digits in each group of 8 displays.

3) Add a 470uF electrolytic cap on the power supply to help supply the current spikes that the IS31FL3730 chips generate. The scanning frequency on these chips is high enough that the electrolytic caps are not a great choice, but 470uF of ceramic caps would be large and expensive. The cap was installed on the back side of the PCB and did not require increasing the size of the board.

Throughout this writeup, I have been using the term matrix in multiple ways. The first way is to describe the intended use for these drivers, driving an 8x8 or similar LED device which resemble a matrix. The second usage is to describe the group of column registers in the IS31FL3730 chip that control the on/off for each LED. The manufacturer data sheet for the chip refers to the group of common cathode LEDs as matrix 1 and the group of common anode LEDs as matrix 2.