Week 11
Output Devices

Seven-Segment Clock LED Array

For this week, I wanted to make the display for my final project alarm clock. I wanted it to be clearly visible, so I decided to use LEDs instead of an LCD. Also, in the spirit of making anything, I decided to try making the display out of charlieplexed LEDs instead of seven-segment displays.

First, I designed the LCD display board as well as a separate control board with the microcontroller. I separated these boards mostly for convenience. I wanted the display to be big, but didn't want to wait forever for the Modela to cut it out. Also, I needed to use the mega88, and in the past I had difficulting with the vinylcutter and the smaller pins. Below are schematics and layout for the two boards.









I cut the display board on the vinylcutter and the control board on the Modela. After a few hours of soldering, I had the completed boards:





Next, I programmed some test code onto the microcontroller. The expected LEDs lit up, but they were extremely faint. So, I decided to lower the resistor values. This worked for the single LEDs, but not for the set of 3 LEDs in parallel. The set of 3 is still very faint even when there is no resistance.