SURVIVAL EQUIPMENTS

Years ago, I saved a car radio from a Chrysler that had a digital display. I estimate 20 years later, I've finally taken time to tear it apart and scrounge parts from it. Inside I found a Vacuum Fluorescent Display (VFD). I didn't realize it was in there and found its glass package an immediate draw.

This is an example picture - my display has less elements. :)

I wanted to do a little investigating about VFDs and found this website. Much to my surprise, there were a number of online examples of people using them to amplify audio signals since they have the basic structure of a Triode vacuum tube. Apart from the unique implementation of the device, I did find the theory information helpful at this site.

My plan is to use this display in conjunction with an Arduino. My first challenge was to figure out how to run the filament. I chose 12 volts as my available input voltage and have estimated that the required voltage is 2.5 volts. With that in mind, I needed to figure out exactly what resistor would be needed to provide that voltage.

Here are the only input parameters to my problem:
Input voltage: 12 VDC
Filament voltage: 2.5 VDC (this was determined through tests)
Filament current: 75 mA (this was determined through tests)

Here is what I want to figure out: Ohms of the resistor I need in series with the filament to achieve the 2.5 VDC across the filament. Here is a good source I used to figure out my series resistor values.

E = I * R

E = voltage (volts)
I = current (amps)
R = resistance (ohms)

We know that current is constant across the series circuit, so using this equation, we find that the resistance of the filament is .

3 = .075 * R
R = 40 ohms

Expanding our equation, we can say that:

E = I * (R1 + R2) where R2 is our filament resistance. Substituting what we know, our equation looks like this:

12 = .075 * (R1 + 40)

solving to: R1 = 120 ohms