Vacuum Fluorescent Display Controller

A simple interface circuit to drive VFD displays. No fancy parts required, and runs on serial communication.

Feb 22, 2019

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Components and supplies

2

CD4017

1

VFD Display

2

BC547

1

PC817

1

470nF Capacitor

4

1N4007 – High Voltage, High Current Rated Diode

4

Electrolitic Capacitors

2

CD4094

1

Arduino UNO

17

BC557

1

Dupont Jumpers

1

Perfboard

24

1/4W Resistors

Tools and machines

1

Wire Clipper

1

Solder Wire

1

Wire

1

Soldering iron (generic)

Project description

Code

Arduino code with working routine

arduino

Downloadable files

General Schematic

I avoided drawing ALL the BC557 transistors because they are just there connected on all the CD4094 outputs, all the same. There's a jumper selector (running on the red line) you must configure on the 4017 chips, it resets the two 4017 at the completion of the grids scanning, you must connect (or solder) the flying jumper on the output pin AFTER the last grid, so if your display has 10 grids the jumper goes on the 11th output. The Arduino connections are outlined in red, you can use the USB power for it but it's strongly advised to use a regular old-style transformer for the remaining supplies if you already have a grounded power supply like your PC. These supplies must be all DC except maybe the filament supply, I added some diodes because it's likely you need a separate transformer with a low voltage secondary. The filament power usually ranges around 3V 150mA, a 5V AC transformer will suffice. The "ballast" thing will possibly be a wirevound power potentiometer of like 100ohms, or a fixed resistor, or also some 1N4007 diodes to reduce the voltage. The BC557 transistors pull the anodes up to anodic voltage and the 100kohm resistors will let the voltage drive fall when the segment is off, while the CD4094 remain at 5V normally. The CD4017s will be powered with grid voltage and don't require additional transistors. There's a "ghetto" reset circuit for the 4017 that lasts like one tenth of a second, you have to wait for it to settle before running the code. The "original" schematic for cascading some CD4017 required other logic gates chips, I used instead an NPN transistor and the optocoupler itself to replicate an AND gate, it's fast enough at closing so it's perfect for the task, at releasing it's instead a bit slower but we don't care, especially because the clock inputs on the 4017 are schmitt triggered and the required speed is not "scary" there. There are various grounds for the chips and stuff as you can see, take a good look.

General Schematic

General Schematic

I avoided drawing ALL the BC557 transistors because they are just there connected on all the CD4094 outputs, all the same. There's a jumper selector (running on the red line) you must configure on the 4017 chips, it resets the two 4017 at the completion of the grids scanning, you must connect (or solder) the flying jumper on the output pin AFTER the last grid, so if your display has 10 grids the jumper goes on the 11th output. The Arduino connections are outlined in red, you can use the USB power for it but it's strongly advised to use a regular old-style transformer for the remaining supplies if you already have a grounded power supply like your PC. These supplies must be all DC except maybe the filament supply, I added some diodes because it's likely you need a separate transformer with a low voltage secondary. The filament power usually ranges around 3V 150mA, a 5V AC transformer will suffice. The "ballast" thing will possibly be a wirevound power potentiometer of like 100ohms, or a fixed resistor, or also some 1N4007 diodes to reduce the voltage. The BC557 transistors pull the anodes up to anodic voltage and the 100kohm resistors will let the voltage drive fall when the segment is off, while the CD4094 remain at 5V normally. The CD4017s will be powered with grid voltage and don't require additional transistors. There's a "ghetto" reset circuit for the 4017 that lasts like one tenth of a second, you have to wait for it to settle before running the code. The "original" schematic for cascading some CD4017 required other logic gates chips, I used instead an NPN transistor and the optocoupler itself to replicate an AND gate, it's fast enough at closing so it's perfect for the task, at releasing it's instead a bit slower but we don't care, especially because the clock inputs on the 4017 are schmitt triggered and the required speed is not "scary" there. There are various grounds for the chips and stuff as you can see, take a good look.

General Schematic

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