A year ago I picked up some new-old-stock "VQB 71" 7-segment displays — not for any particular project, but simply because they looked fantastic. These gorgeous, vintage common-anode digits have distinctive segments with six tiny LEDs each, internally connected with bond-wires and encapsulated in transparent red epoxy/resin:
This batch was manufactured in 1989* by WF Berlin (Werk für Fernsehelektronik), a division of the East German state-owned company VEB Kombinat Mikroelektronik Erfurt. The packaging is titled "lichtemitteranzeige" which is literally "light emitting display": an odd name by modern standards according to a German colleague of mine, who said this would simply be labelled "sieben segmentanzeige" today.
A few partial scans of datasheets for the VQB 71 are available online, with the one below from tu-chemnitz.de being the most complete copy I've found. A datasheet isn't strictly necessary here, but it's useful to have dimensions provided for the footprint, and I wanted to know the maximum current per segment specified by the manufacturer. After all, These parts haven't been made for nearly 30 years, so it would be a shame to destroy one accidentally.
It's easy enough to figure out the specs without knowing any German, but Google Translate makes quick work of the dry/technical language. Here's the English translation of this datasheet:
VQB 71 Not for new designs
Light emitting display made of red-beam GaAsP diodes in a segment design to display the digits 0...9 and a decimal point (DP). The wavelength of their max emission is 630...690 nm. The half width is 40 nm.
Forward direct current / segment or DP at θa -25...25 °C
max 15 mA
DC blocking voltage at θa -25...+70 °C
max 4 V
θa -25...+70 °C
Storage temperature for storage up to 30 days
θstg -50...+70 °C
Characteristic values at θa = 25°C
Luminous intensity / segment at IF = 10 mA
typ 150 μcd
↳ Decimal point
typ 100 μcd
Forward DC voltage / segment at IF = 10 mA
max 3.6 V
↳ Decimal point
max 1.8 V
Note that unlike modern LED datasheets, this doesn't specify maximum pulsed currents. Pulsed currents with modern LEDs are typically 3-5x the max constant current rating (dependent on duty cycle and pulse duration), which can give some head-room for driving them harder in multiplexed configurations.
Driving these segments with a constant 10mA as the datasheet suggests gives a high-contrast image in vivid red. The VQB 71's are so intensely red that it's proved difficult to capture an accurate representation of one on camera. Modern LEDs like those in the GPS Wall Clock look almost orange by comparison.
Driving all segments at this power increases the surface temperature of the digit by around 10°C, but who needs efficiency when you have style, right?
I hear we're building another clock
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