VFD Extension Board
This board is a new version of the calculator extension board. The difference
is that it uses a 12 character wide vacuum tube display instead of the
8 digit 7-segment display.
VFD tubes have long been used in consumer electronics for displays.
They are vacuum tubes that can be seen as a kind of cross between a triode and
a low-voltage CRT. Unlike a CRT tube, it operates at very low voltages around 25V,
and there are no magnets to deflect the electron beam. Instead, the electrons
which are emitted from a heated wire and accelerated through a control grid,
are directed to an actively switched anode. This anode is coated with phosphor,
which emits light when the electrons hit it. The control grid can be used to switch
an entire segment on or off, so that the display segments can be easily multiplexed.
The display that I use for MyNOR comes from Samsung and has the part number
"HCS-12SS59T". This VFD can can be obtained from various places on the internet.
The advantage of this display over the 7-segment display is that it can display
not only numbers, but also the uppercase letters A to Z and some special characters.
This means that this board can also be used for many other applications than
just the calculator app.
More information and a detailed description of the circuit can be found in the
construction manual for this board.
Schematics and BOM
Click on the schematics to see it in full resolution (PDF).
You can get the design files in the download section.
All components can be sourced from
A great PCB manufacturer is JLCPCB (China).
All you have to do is upload the zip-file that contains the Gerber data to JLCPCB.
is selling a complete kit with all required components and the PCB.
You need additional software to be able to use the display. This board is not
supported by the operating system in the EPROM, because there is no more space
in the EPROM for the required drivers. Nevertheless you need ROM version 1.2 to
be able to use my provided application software (especially the calculator app).
Software for this board can be found in the software section.
|C1 C2||10 nF|
|C3||100 µF / 16V|
|C4 C5||100 nF|
|C7||2.2 µF / 16V|
|C8 C10||10 µF / 50V|
|D1 D3 D4 D5 D6||BAT41|
|J1 J2||Header 2x10 pin, 2.54mm|
|J3||Header 1x4 pin, 2.54mm, right angle|
|Q1 Q2 Q7 Q8||BC327|
|Q3 Q4 Q9||BC546B|
|R2 R5||22 kOhm|
|R3 R4 R6 R7||1 kOhm|
|R11 R16||470 Ohm|
|R12 R15||100 kOhm|
|SW1 - SW20 (20 pcs)||push button 6x4.3mm|