Help reverse engineering a VFD

[parts-man73]

I have a VFD (Vacuum Fluorescent Display) that I pulled from a car in a salvage yard. This was in a overhead console display. It shows information such as temp, compass heading, fuel economy, distance till empty gas tank, etc.

I thought this would be VERY handy for certain projects, so I grabbed it, it's still soldered to the circuit board. This thing has 36 pins, but more than 40 segments that could light up. Any ideas on how to figure out a pinout for this thing? And possibly what voltage to drive it at? I see a 78L05 voltage regulator on the circuit board, but that may be for the other chips, and not the display.

Any ideas would be appreiated!
Brian

 

[Michael 2727]

Those things need a voltage of 90V or there abouts
to light the display.
Many VCR video recorders use these for displays and some ancient calculators.

 

[parts-man73]

Here's what I figured out so far. I found another on board voltage regulator, a LM2940S This one is a 12 volt LDO. I followed the circuit traces back to the main connector to the vehicle, so now I know where to apply 12 VDC and ground. I did so, and it lit right up. Displaying 40 degrees F and West on the compass.

I started probing with my voltmeter on each leg of the display, and I found some readings of 12 volt, several at 5.5 volts, and some at approx 2 volts.

One of the functions of the display is "ET" or Elapsed time. I can reset that and it will count upward. I can see as some of the legs of the display toggle as the display counts. Now I just have to figure out which pins do which segments on the display.

I'll advise you all of my progress.

 

[ylp88]

oooh... Does the compass work? Have you tried rotating the circuit oard to see if the compass changes? What is it's refernce orientation?

VFDs usually have a small transformer on them to step up the voltages to that required to drive the segments.

A nifty toy you have there!

<b><i>ylp88 </b> </i>

 

[parts-man73]

I jumpered from the 5.5 volt to various pins on the display, and I watched as certain segments lit up as I probed. Odd though, some of those pins were showing 12 volts, but when I touched with 5 volts, a segment lit up. I think my next step is to de-solder it from the circuit board, and plug it into a solderless breadboard.

I've checked though, and I don't find any of these higher voltages that I've been warned about. Perhaps the newer VFD's require less voltage???

 

[hippy]

Take a look at ....

http://www.noritake-elec.com/vfd_technology.htm

The control signals may be low-voltage DC, but there may be other and AC voltages required. It is unlikley to be a simple case of connecting one pin to another to get a segment to illuminate.

 

[parts-man73]

Thank you for that link, it was very informative.

It did state that it's possible that &quot;it only requires 10 to 15 volts DC to illuminate the display and, in some cases, illumination is possible using standard 12 volts C-MOS logic.&quot; If it's a static drive type VFD.

But there's also a chance that it's a Multiplexed. That looks alot more complex to drive.

Not sure...but I did touch the legs of the display with 5 volts, and it did light up 1 segment each time I tried a different leg.

 

[Matthewriley]

Did the compass work???!

 

[parts-man73]

The compass doesn't seem to work. The display shows the compass heading and the temp for 15-20 seconds or so, then the screen goes blank and displays &quot;CCD&quot;

From my experience in the automotive field, that refers to the CCD bus, that chrysler uses for communication between the various modules in a vehicle. The unit displays &quot;west&quot; and &quot;40&quot; which I can assume was the direction the vehicle was pointed, and the temp the last time the unit was powered up in vehicle and connected to the CCD bus.