NIMO CLOCK – RECREATING THE LOOK OF A 60’S CRT DISPLAY
This project was inspired by Fran Blanche’s NIMO Tube video. It’s a fascinating video and I recommend watching it for detailed information on NIMO tube operation and history. In short, the NIMO tube was a single digit CRT display manufactured for a brief period in the late 1960’s and early 1970’s. After watching Fran’s video I really wanted to build a NIMO tube clock. Unfortunately, NIMO tubes are practically unobtainium these days. Even if you could get ahold of some they required a complex high voltage power supply to operate. I quickly abandoned the idea of a vintage NIMO clock and started looking at replicating the NIMO look with modern parts.
My design uses six 1.44-inch TFT LCD displays to display NIMO-style digits. These small LCD displays are cheap (around $3.50 US each) and use the ST7735 chipset and SPI bus. To drive the displays I’m using the Adafruit Metro M4. I found that a traditional ATmega328 based board wasn’t fast enough to update the displays once per second and didn’t have enough memory to store all the digits. The Metro M4 is fast, has plenty of memory and is compatible with the Adafruit ST7735 library.
I wanted to try to replicated the phosphorus CRT glow so I replaced the fairly dim white LED backlights of the LCDs with 16 WS2812B (NeoPixel) RGB LEDs. The digits are displayed on the LCDs as white characters on a dark background. The color is provided by the NeoPixel backlights. Finally, I used plano-convex lenses (LED flashlight condenser lenses) placed directly in front of the LCDs to create a tube-like appearance.
Step 1 – Source the LCD Displays
There are several different versions of these 1.44” LCD displays available on eBay and AliExpress. I recommend using the photos above (Figs 1-3) to identify the correct version when shopping for displays. If you are unable to find the exact version you may need to modify the 3D-printed parts to fit your displays. More on this in Step 3.
The most important factor when choosing the displays is that they use the ST7735chipset. This project uses the Adafruit ST7735 library to write bitmap images to the displays. When ordering displays it is vital to confirm that they use the ST7735 chipset. It is possible to find displays that look identical but use a different chipset and are therefor not suitable for this project.
I recommend purchasing a few extra displays in case of damage or failure. I ordered ten from eBay and ended up with seven that were usable for this project. One was nonfunctional and two had the wrong chipset.