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VFD Extension

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 extension board

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 Reichelt, Mouser or Digikey.

A great PCB manufacturer is JLCPCB (China). All you have to do is upload the zip-file that contains the Gerber data to JLCPCB.

Note: BudgeTronics 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 C210 nF
C3100 µF / 16V
C4 C5100 nF
C682 pF
C72.2 µF / 16V
C8 C1010 µF / 50V
C9100 pF
D2Zener 27V
D1 D3 D4 D5 D6BAT41
J1 J2Header 2x10 pin, 2.54mm
J3Header 1x4 pin, 2.54mm, right angle
L1330 µH
Q1 Q2 Q7 Q8BC327
Q3 Q4 Q9BC546B
Q5 Q6BS170
R16.8 Ohm
R2 R522 kOhm
R3 R4 R6 R71 kOhm
R88.2 kOhm
R915 Ohm
R10220 Ohm
R11 R16470 Ohm
R12 R15100 kOhm
R1310 kOhm
R142.2 kOhm
SW1 - SW20 (20 pcs)push button 6x4.3mm
U1Samsung HCS-12SS59T