Here I’ve soldered together the microcontroller board and mounted it on the display. The board is a PIC18F2620 driven by a 20Mhz crystal. A 74HC164 shift register is used to drive the LED matrix anodes since the PIC didn’t have enough output pins to do everything by itself.
The only crystal, capacitors, and resistors I had lying around were the big bulky through hole variety. I’ll replace these with smaller versions if I need more room for batteries.