Wiring up the MAX6954
I discovered the MAX6954 4-Wire Interfaced, 2.7V to 5.5V LED Display Driver with I/O Expander and Key Scan which I’ll call the MAX6954 from now on. This chip allows me to drive up to 8 16-segment LEDs using one chip and a minimum of discrete parts.
The only issue I had with it was that it used a common cathode multisegment LED and I was using a common anode part. I quickly ordered 10 Kingbright 16 segment single digit common cathode displays (PSC08-11SRWA) and two MAX6954 chips. After they arrived I connected a single digit display using the sample circuit shown on Application Note 3212 Quick-Start: Driving 16-Segment Displays with the MAX6954. I took a picture after I hooked it up and it looked like this after I wrote some code using the previous SPI driver code to put the chip into Display Test mode (0x0701).
Single Digit Demo
The MAX6954 contains a mapping of character codes to LED segments which roughly follows the ASCII standard. I wanted to write a demo program which would allow me to manipulate the display without too much trouble. Since I had the SPI code already written I just need to slap on a user interface and experiment once that was done. I wired up the hardware and wrote the software and tested the unit. Things looked good until I got to the letter “B”.
You can see that one of the legs isn’t correct. A quick wiring change later and everything works according to plan!
Now that I’ve got it working for a single digit I need to prototype the full eight 16 segment displays.