I’d thought I’d share these cool retro 7 segment displays I obtained from an old aircraft radio. They are Wamco KW-104S direct view incandescent filament displays which are compatible with LED display driver code – just treat them like common anode 7 segment LED displays. Easy! You just have to bear in mind that they need an operating voltage of 4 volts and they draw around 15mA per segment. Due to their self current limiting nature, they do not need current limiting resistors between the driver chip and the display. Note I said driver chip as with the current drawn from these displays you are best using a power shift register such as the TPIC6B595 or a transistor array rather than driving them from the microcontroller or shift register pins directly.
A datasheet can be found here https://www.wamcoinc.com/assets/pdf/Display%20Catalog.pdf
Some images and a video
I know this is an older post, but I’ve recently come into a couple of KW-104S filament displays. You’re saying to treat them as common anode 7 segment LED displays. When I use the cathode on the common, the displays also work. Is there a reason you did common anode rather than common cathode? Do you have a circuit diagram/wiring plan for your KW-104s, I’m trying to use ESPHome to drive them. I’ve tried using a max7219, but can’t get it to work.
In theory they are not diodes so it does not matter if used as common Anode or Common Cathode, it’s just that Common Anode works best with sink driver chips (such as the TPIC6B595) and their higher operating voltage.
As for the MAX7219 not working I suspect it’s to do with the higher operating voltage that these displays need. The MAX7219 is designed for driving single LED chip per segment displays with a forward voltage of 1.8-2.2V. Also it has multiplexed drive with an average segment current of 5mA so likely this is the issue.
Code wise, they behave like 7 segment LED displays but need a driver circuit either discrete or power logic chips that can handle the total current if all segments are lit. Typically such drivers tend to be Common Anode.
Do you happen to have the schematics for such a circuit? Did you have to write custom code to drive the TPIC6B595 or is there a library?
Yes, if you look at my other posts, the most recent is a driver board for large 7 segment displays. I’ve also made some LED clocks and large 6 digit display boards. These could be adapted for use with the incandescent displays.
No libraries used, I used custom code. The projects include schematics and example code for an Arduino
Just to add, that 6 digit display should work as is but the 12v supply would have to be 4V and bypass the current limiting resistors. Off the top of my head I’d choose the TPIC6B595 as it can easily drive the wamco displays and has a standard SPI interface.
Thanks a lot for getting back to me on this! Much appreciated!