BMOW title
Floppy Emu banner

LCD Contrast Adjustment in Firmware

Floppy Emu uses a generic LCD that’s a clone of the display in the Nokia 5110 phone. It’s a nice little bitmapped display with a good range of configuration options, including the ability to set the display’s contrast level through software instead of with an external resistor. Unfortunately there’s a huge variability in contrast response from one LCD to the next, and even the same LCD can exhibit contrast changes from day to day. I’m not sure if it’s due to temperature, fluctuating voltages, bad solder joints, or something else, but it makes it virtually impossible to choose one contrast level in the Floppy Emu firmware that will work well for all LCDs. Until now, I’ve been making a custom firmware build for each Floppy Emu that I assemble, with a hand-tweaked contrast level, but that’s a huge pain in the butt. No more!

Firmware 1.0L F11 introduces the ability to adjust the contrast level and save it to EEPROM. Now you can tune the contrast exactly how you like it. To adjust the contrast, hold down the SELECT and NEXT buttons while Floppy Emu is initializing (after pressing the reset button, or when first powering it on). After a few seconds, the contrast adjustment screen will appear. Press PREV and NEXT to tune the contrast level, and SELECT to save the contrast setting to EEPROM. Easy peasy lemon squeezy.

To apply this firmware update to your Floppy Emu hardware, download the firmware files, and copy the file femu.bin to your SD card. Then hold down PREV and SELECT while the Floppy Emu is initializing. This update only changes the AVR software (from 1.0K to 1.0L), the CPLD is unchanged (it’s still F11).

Happy contrasting!

Read 3 comments and join the conversation 

3 Comments so far

  1. makerimages - January 10th, 2014 6:51 am


    You load the AVR soft from the SD card, but how does one do that? I began to wonder, as this could prove usefl for me in the futures. You should write a tutorial on AVR-SD Card interfacing.

  2. Steve Chamberlin - January 10th, 2014 9:42 am

    Check out the source code if you want to see how the SD card bootloader is implemented. It’s based on this example from Atmel:

  3. Jens - May 29th, 2023 12:24 am

    Thank you for ceeating this. The screen has stopped working after I tightened the plastic screws for the case. First the Mac wouldn’t boot and it turned out that the NEXT key had been depressed by the case. Loosened it and the Mac booted. However, the screen on the FloppyEMU no longer shows anything. The backlight is on and the emulation for the Mac works, but I cant change images or navigate without a screen. I have tried the method for adjusting contrast as described here but to no avail. I’m not sure what FW is on the emu. Any advice will be greatly appreciated! All the best. Jens, Denmark

Leave a reply. For customer support issues, please use the Customer Support link instead of writing comments.