Popular in DVD/VCR players, as in Salvaging a Samsung DVD-M101 Player: the vacuum fluorescent display. A glorified vacuum tube, VFDs provide superior contrast and visibility compared to other display technologies like LCDs and LEDs (but OLEDs are giving them a run for their money).

I have acquired several VFDs, here is the Samsung HNV11SS27 you may recall was salvaged from a Samsung DVD-M101:

and another VFD salvaged long ago, a NEC FIP7FM7 (“FIP” is a trade name for Fluorescent Indicator Panel, a vacuum fluorescent display):

lastly, a newer VFD in a newer DVD player, labeled on the reverse side “Samsung HNV-08SS53”:

In this article, I’ll determine the pinout of each of these VFDs, so they can be used in another homemade circuit for some other purpose.

Theory of Operation

How to power these things? For background theory, A Guide to Fundamental VFD Operation is worth reading:

The electrons emitted from the cathode filaments are controlled by the grids. When the grid is supplied with a positive voltage, it attracts the negative electrons, diffuses them and, due to their acceleration, many flow through the grid mesh towards the anode (opposite charges attract). However, when the grid is supplied with a negative voltage, it repels the negative electrons and prevents them from reaching the anode (similar charges repel).

Here’s the HNV11SS27 pinout from the schematic in the service manual, as covered in Salvaging a Samsung DVD-M101 Player:

Knowing the theory of operation, the meaning of the labels are clear: F+/F- for the filament, G1-G11 for grid, and P1–18 for the phosphor. Measuring with a multimeter, there is a 3.344 V DC voltage across F+/F-, not too far from what we could expect with the 3.9 V zener diode (FD9) between VF+ and VF-, and the voltage drop across the FR17 and FR16 100 Ω 1/4 W resistors. Measured voltage across G1 and P#, about 10 V or 7 V, AC.

Desoldering & measuring the Samsung HNV11SS27

I left this VFD on the board it came with, so it can be powered up and actively used, instead of desoldering it immediately. This allows the VFD to be tested and probed to better understand how it works. But now comes the time to desolder it. All 33 of these pads:

Removed all the solder with a soldering wick (used MG Chemicals Desoldering Braid #4 Fine Braid Super Wick with RMA Flux, 25' Length x 0.1" Width, Blue):

and the VFD came out easily, very little force required to pull it out:

I then painstakingly soldered on wires and plugged into a breadboard:

Powering it up for the first time, we see the “LOAD” text as expected:

Reverse-engineering the segments

The “LOAD” text only illuminates four grids, determined by the process of elimination to correspond to G3, G4, G5, and G6. Unplugging those wires and inserting into the other inputs allows us to move the letters around:

and illuminate each of the grids anywhere:

Testing G1 through G11, the pinout becomes clear:

The letters are built from 42 individual visual segments, but not all can be lit individually since there are only 18 pins. This 16-segment display (plus other miscellaneous indicators) is quite an improvement over the 7-segment display seen in 4x7-segment LED display as a digital clock using two 74HCT595 8-bit shift registers, able to represent a larger number of characters, both numbers and letters, clearly distinguishable. Displays from Wikipedia:

This is a 16-segment display, although the diagonal segments are at less of an angle than shown above. Nonetheless, it can show all the same characters:

Testing each of the segments, the segment pinout can be deduced as follows:

This is the chapter grid (“CHP”, G8), representative of the others, except for G11 and G1.

We now have enough information to build a controller for this VFD, but first, lets take a look at another VFD device.

Reverse-engineering another VFD: NEC FIP7FM7

The same DVD player’s VFD driver can be used to power other VFDs, and reverse-engineer the pinout as well. The filaments are on the sides as usual, and the group/phosphors are together. For some reason, this VFD (a FIP7FM7 produced by NEC) has some “missing” pins:

but it works with the DVD player, for a first test, I lit up the “XPR” segment:

Probing around, here is how a upper horizontal segment is illuminated:

and from the other side:

When probing to determine the pinout, it is important to note that since the signal is AC, the polarity of the group/phosphor pins is irrelevant — that is, the two yellow wires above can be swapped and will light up the same segment. The polarity does not determine which pins are for groups and which are for phosphors within the group, you have to test them all. After painstakingly probing every combination, here is the result:

Curiously, the group pins are not all one one side as we saw with the Samsung HNV11SS27 VFD, but irregularly interspersed with the phosphor pins. The only way to tell for sure is to test each one. And here are segments:

I labeled the phosphor segments alphabetically, and after knowing the pinout it seems to make sense. The only oddity is that P13 (“g”) seems to be unused, neither a phosphor or group pin, so I arbitrarily labeled it P13/g.

Groups 7, 8, 12, and 14 (the digits) follow this pattern; others, the last:

and the first two, group 2 and 5:

The middle group, G9, only has two segments: “i” for TUE, and “b” for the colon. Unlike the segmented display shown in 4x7-segment LED display as a digital clock using two 74HCT595 8-bit shift registers, the dots of the colon cannot be set individually, only together.

Reverse-engineering the Samsung HNV-08SS53

The newest VFD I have, this one happens to be the brightest. Is it compatible with the signaling of the other two VFDs? Taking some measurements: the filament voltage (F+ on left, F- on right) is about 2.0 VDC, compared to 3.3 VDC for the HNV11SS27. Across some of the group/phosphor pins, measured 14.5 VAC or 8 VAC (compared to 10 or 7). Lower bias voltage, but higher phosphor voltage, hmm. If it works, I can salvage this board and use the other one for driving this VFD until I replicate the circuitry.

Unsoldering using solder wick, the VFD comes out no problem:

picture of the reverse side (TODO: are these traces useful for pinning out?):

And the relevant part of the circuit board, if it provides any clues (pins seem to be split into 12, 4, then 8):

First things first, I plugged the VFD into a breadboard. Or tried to. Unfortunately my breadboard has 0.1" spacing, as nearly all do, but this component has a tighter pitch. So I only plugged in the filament pins and bent the others outwards:

Testing driving it with the other DVD player’s circuit, it works:

This pinout is more straightforward than the NEC, matches what you would expect from looking at the PCB traces:

The middle 4 pins appear unused. Segment “a” (pin #13) is used for the colon and dash on G3, G4, G6; pins for the 10-segment display are:

This pinout was easy to quickly reverse-engineer on this VFD, after having experience with the first two. I would expect most (all?) other VFDs to operate similarly and their pinouts could be determined in a similar manner. All you need is an old VCR or DVD player, wire up the outer two pins to the filament DC bias voltage of a few volts (2–3 VDC), then apply ~10 VAC across each combination of all of the other pins, then the pinout falls out.

Conclusion

We have seen how to reverse-engineer pinouts of three vacuum-fluorescent display (VFD) devices:

• Samsung HNV11SS27, 9 x 14-segment display + SVCDVD etc.
• NEC FIP7FM7, 4 x 7-segment display + AM/PM etc.
• Samsung HNV-08SS53, 7 x 10-segment display + pause/play etc.

The next step to use these devices for a practical application would be to develop a controller circuit to supply the appropriate DC and AC voltage.