I have an old Roland TR707 drum machine with a very faded LCD display, which seems to be a common problem per numerous threads on the internet.
I've tried to improve it (checking the voltages, cleaning the Zebra strips, replacing the polarising film, etc) but all to no avail - and given it's not backlit, I wondered if I could do better and replace it with something more modern.
It uses a HD61602 controller (service manual here:
https://www.synthxl.com/wp-content/uploads/2019/07/Roland-tr-707-service-notes.pdf), and taking advantage of the Xmas break, I broke out the logic analyzer to understand the protocol. Things are actually pretty simple - each LCD segment corresponds to a bit in the controller ram, and a two byte sequence selects the address then the value to write.
The interface itself is comprised of Reset, Write Enable, and Chip Select lines along with an 8-bit data bus. I originally wondered if I could prototype an MCU-based translation using an Arduino Micro, but the period of the lines toggling is ~1us - which I believe to be too fast to monitor by GPIO interrupts (at least with this board).
I'm much more acquainted with software than hardware, but I think my options are therefore:
- Move to a beefier MCU (STM32?), although I'm wary of spinning monitoring interrupts when the display needs attention, too
- Look at building something with an FPGA
- Build hardware that could buffer the bus values so an MCU could interpret it at a more leisurely rate
- Per one of Dave's videos, look at designing a custom replacement LCD that works with the original controller (even if I have to design a new PCB)
Can anyone suggest better options? Thanks in advance!