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• Inspiration and beginnings

  Andrew Tudoroi • 1 天前 • 0 comments

  Inspiration and Beginnings

  I’ve always been drawn to retro LED displays. While exploring Raspberry Pi extension HATs, I came across Pimoroni’s micro-LED board. I was immediately hooked and decided I needed one. Unfortunately, I wasn’t able to get my hands on it. This setback inspired me to try my hand at PCB design, making this project my very first — from initial design all the way to ordering PCBs from well-known manufacturers.

  For this project, I chose KiCad as my design tool for several reasons:

  • It’s open-source.
  • Highly recommended across the internet and by electronics enthusiasts (I’ve spent countless hours watching related videos 😄).
  • It has a supportive and vibrant community.

  I wanted my design to be relatively easy to solder, even with a basic soldering iron. After researching options, I discovered the HT16K33 LED driver. It turned out to be the perfect fit — not only easy to work with but also capable of supporting buttons for input functionality.

  After some trial and error, I successfully produced Gerber files for my PCB design. Despite some beginner mistakes, the PCBs were manufacturable and functional!

  Key Features

  With this in mind, I designed the board to include four through-hole buttons and decided to make it a Raspberry Pi HAT. While brainstorming a name, I drew inspiration from fruits — particularly the 8devices Rambutan board sitting on my desk. Thus, the Pitanga Raspberry Pi HAT was born!

  This HAT functions as a simple display for user output and a basic input device — almost like a joystick. I also included pads for an STM 8-pin ARM M0 microcontroller, though I never ended up populating it on the board.

  Challenges and Improvements

  One challenge I encountered was power compatibility. While the Raspberry Pi can sometimes work with I2C devices at 5V logic levels, this isn’t ideal for long-term use. To address this, I connected the HT16K33 to the Raspberry Pi's 3.3V I2C bus. However, the HT16K33 datasheet specifies a voltage range of 4.5V to 5.5V for optimal operation. Despite this mismatch, my setup worked fine during testing.

  To ensure better reliability, I searched for a proper solution and found the PCA9306DP, a dedicated logic level converter chip. It converts the Raspberry Pi’s 3.3V logic levels to 5V for the LED driver.

  With this improvement in mind, I designed a new revision of the board. This version included an additional button, bringing the total to five, and incorporated I2C logic transceivers. After assembling the updated PCBs, the result was a polished Pitanga HAT :)

  Back side:

  Exploring Retro LED Display

  A completely separate and fascinating journey was finding compatible LED displays for this design. These displays are replicas of replicas of replicas of the original models, yet they retain their retro charm and work beautifully with the project. Here are some of the compatible models I discovered:

  LTP-305R on Raspberry Pi 3A+
  

  
  LTP-305G with Raspberry Pi 4
  

  
  ALS340A1
  
  

  • Monsanto MAN 2
  • IEE - LRT1704R
  • DIALCO 745-0005
  • Lite-On LTP-305
  • Texas Instruments TIL-305
  • ALS340A
  • ALS340A1
  • 3LS340
  • 3LS363
  • AL104

  Each of these displays carries its own unique story and nostalgic appeal, adding character to the project.

  Final Thoughts

  The Pitanga Raspberry Pi HAT is a project born out of passion for retro tech and a desire to learn. From designing my first PCB to iterating on improvements, this journey has been both challenging and rewarding. Whether you’re a fan of retro displays or looking to explore PCB design, I hope this inspires you to embark on your own maker adventure!

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