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 community.

I wanted my design to be relatively easy to solder, even with a basic soldering iron. Cause that is what i had at that moment After researching options, I discovered the HT16K33 LED driver. It turned out to be the a god fit it supports 8x16 mode, with counting of the decimal dot on the LTP305 displays i needed 18x7 which i achieved by rewiring cathodes and some anodes of the displays and later deal with this in software, also HT16k33 is capable of supporting button (keys) 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!

First trials:

Next revision:

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 I2c 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

An entirely separate and interesting part of this project was discovering compatible LED displays for the design. While researching, I stumbled upon some displays that are essentially replicas of replicas of replicas of the original models. Despite this, they retain their retro charm and work perfectly with the project. During my search, I also came across this page on Industrial Alchemy, which was an interesting find related to these displays.

LTP-305R on Raspberry Pi 3A+

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 was born from my love of retro tech and the drive to learn. Designing my first PCB and improving it along the way was both challenging and rewarding. If you love retro displays or want to dive into PCB design, I hope this project inspires your own maker journey!

Inspiration and beginnings