2025 One Hertz Challenge: RPI TinynumberHat9

July 27, 2025 by Matt Varian 2 Comments

This eye-catching entry to the One Hertz Challenge pairs vintage LED indicators with a modern RPi board to create a one-of-a-kind clock. The RPI TinynumberHat9 by [Andrew] brings back the beautiful interface from high end electronics of the past.

This project is centered around the red AL304 and green ALS314V 7-segment display chips. These 7-segment displays were produced in the 1970s and 1980s in the Soviet Union; you can still find them, but you’ll have to do some digging as they are only becoming more rare. [Andrew] included the data sheet for these which was a good find, it is written in Russian but doesn’t hold any surprises, these tiny LEDs typically forward current is 5mA at 2V. One of the things that jumps out about these LEDs is the gold leads, a sure sign of being a high-end component of their day.

When selecting a driving chip for the LEDs, [Andrew] looked at the MAX7219 and HT16K33; he settled on the HT16K33 as it supports I2C as well as allows the easy addition of buttons to the HAT. Due to being driven by I2C, he was also able to add a Qwiic/Stemma I2C connector, so while designed initially to be a HAT for a Raspberry Pi Zero 2 W board, it can be connected to other things in the Qwiic/Stemma ecosystem.

Thanks [Andrew] for submitting this beautiful entry into the One Hertz Challenge. We love unique 7-segment displays, and so it’s pretty awesome to see 40-year-old display tech brought into the present.

A Raspberry Pi HAT with retro LED displays and a buttons, sitting on the keys of a laptop.

Good-Looking HAT Does Retro Displays Right

February 5, 2025 by Kristina Panos 2 Comments

Mick Jagger famously said that you cain’t always get what you want. But this is Hackaday, and we make what we want or can’t get. Case in point: [Andrew Tudoroi] is drawn to retro LEDs and wanted one of Pimoroni’s micro-LED boards pretty badly, but couldn’t get his hands on one. You know how this ends — with [Andrew] designing his first PCB.

The Pitanga hat is equally inspired by additional fruit that [Andrew] had lying around in the form of an 8devices Rambutan board. (Trust us, it’s a fruit.) With some research, he discovered the HT16K33 LED driver, which checked all the boxen.

The first version worked, but needed what looks like a couple of bodge wires. No shame in that! For the next revision, [Andrew] added buttons and decided to make it into a Raspberry Pi HAT.

This HAT is essentially a simple display with a basic input device, and a beauty at that. You can see all the various cool displays that [Andrew] tried both here and in the project log. Although he included pads for an ARM M0 microcontroller, he never did populate it. Maybe in the future.

Of course, this project was not without its challenges. For one thing, there was power compatibility to wrestle with. The Pi can sometimes work with I²C devices at 5 V, but this isn’t ideal long-term. So [Andrew] put the LED driver on the 3.3 V I²C bus. Despite the data sheet calling for 4.5 to 5.5 V, the setup worked fine. But for better reliability, [Andrew] threw a dedicated I²C logic level converter chip into the mix.

Don’t forget, you can run a noble amassment of HATs with the PiSquare.