Annual Competition in 2025: RPI's TinyHat9 Strives for 1 Hz Performance
In an intriguing blend of old and new, a project by [Andrew] showcases the integration of Soviet-era 7-segment displays from the 1970s and 1980s with a modern Raspberry Pi board. Initially designed for a Raspberry Pi Zero 2 W board, the project can now be connected to other components in the Qwiic/Stemma ecosystem.
The displays, primarily vacuum fluorescent displays (VFDs) or neon counting tubes, were produced in the Soviet Union during the mentioned period. They are typically robust, with specifications that differ from modern LEDs but operate on relatively low voltages for VFDs.
[Andrew] chose the HT16K33 driving chip for the LEDs, as it supports I2C and allows for easy addition of buttons to the HAT. The HT16K33 driving chip also enables the addition of a Qwiic/Stemma I2C connector to the project, expanding its compatibility with other devices.
These vintage LED indicators, identifiable by their gold leads, are becoming increasingly rare. The typical forward current for these LEDs is 5mA at 2V.
The project, an entry to the One Hertz Challenge, uses the red AL304 and green ALS314V 7-segment display chips. [Andrew]'s decision to use the HT16K33 chip over the MAX7219 was due to its I2C compatibility.
Key points about these Soviet-era 7-segment displays and their specifications:
- Types:
- Vacuum Fluorescent Displays (VFDs) like the IV-12 (NB-12) were commonly produced in the Soviet Union. These have phosphor-coated anodes shaped as segments that glow when electrons from a heated cathode strike them.
- Neon-filled tubes like the ZM1070 (though German-made, similar Soviet tubes existed) were also used for numerical display, using neon glow for segments and decadic counting.
- Operating Characteristics:
- VFDs require a heated filament (cathode) to emit electrons, with typical filament voltages around a few volts (e.g., 1.2–3.3 V) and filament currents on the order of tens of milliamps to maintain electron emission.
- Segment voltages are generally in the tens of volts range (e.g., 30–50 V) to make phosphor glow.
- Forward segment currents for VFDs are typically low in terms of electron flow but result in visible bright segments.
- Neon-filled tubes require higher sustaining voltages (~60–180 V for Nixies, probably less for 7-segment neon tubes) but they are not forward biased like LEDs; instead, they ignite glow discharge in segments.
- Forward current and voltage:
- Unlike LEDs, which have a forward voltage of ~2 V and forward currents of 10–20 mA, Soviet-era VFD segments are driven by higher voltages (20–50 V) and lower currents due to phosphor glow.
- Exact values vary by model, but typical filament current can be about 10–50 mA; segment currents are lower since they are driven by electron flow, not direct conduction.
- For neon tubes, ignition voltages can be 60–90 V with currents in the microamp to milliamp range since neon glow discharge requires sustaining voltage rather than classical diode forward current.
- Where to find them today:
- Soviet vintage 7-segment VFDs and neon tubes like IV-12 can be found through online vintage electronics stores specializing in Soviet components, auction sites such as eBay, dedicated forums and collector communities for Soviet or retro electronics, and display tube collector websites such as display-tubes.org. Physical stores are rare; sourcing is mostly through used part dealers or remnants from old Soviet electronic equipment (e.g., calculators, clocks, measurement devices).
- Additional context:
- Soviet 7-segment VFDs differ from the LED 7-segment displays that became mainstream worldwide in the 1970s-80s, which had lower voltage (1.8–2.2 V) and controlled currents (around 10–20 mA).
- VFDs are brighter and more durable in harsh environments but require more complex driving circuitry (filament heater plus segment voltage supply).
- Neon and nixie tubes were largely replaced by VFDs and LEDs by the 1980s.
In summary, Soviet 7-segment displays from the 1970s-1980s are mostly vacuum fluorescent types that require low filament voltage/current and higher segment voltages, with specifications reflecting electron emission and phosphor excitation rather than LED diode conduction. They can be sourced today mainly from vintage electronics sellers and collector outlets. For precise specs on specific part numbers, further specialist research and datasheet hunting are needed. The project's versatility is enhanced by its compatibility with the Qwiic/Stemma ecosystem.
The project by Andrew, showcasing the integration of Soviet-era 7-segment displays with a modern Raspberry Pi board, utilizes electronics such as the HT16K33 driving chip, which is a key component in managing the LEDs and enabling I2C connectivity, expanding the project's compatibility with other technology components in the Qwiic/Stemma ecosystem. The vintage LED indicators, reminiscent of the 1970s and 1980s, are primarily vacuum fluorescent displays (VFDs) or neon counting tubes, and their specifications differ from modern LEDs, with specifications reflecting electron emission and phosphor excitation rather than LED diode conduction.
