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The firefly conductor is a vacuum fluorescent display (VFD) driver/controller.
Main parts:
The SER6500 VFD comes with 3 Supertex HV518 VFD drivers (2 are hidden behind the display).
They each can driver 32 channels (up to 90V). The VFD segments start already to be visible at 5V, but to get them bright you need higher voltages (I use 60V). This is particularly important because you have to drive the digits and matrix one after each other. If you do it fast enough, thanks to the persistence of vision they will not appear as flickering. But because the segments are not on all the time, you need to drive them with higher voltage so on average they appear bright enough. I drive the VFD with 60V and use a 100 Hz refresh rate.
The VFD has 10 digits (7+3 segments) and 12 dot matrix (7×5 segments). You would need 10*(7+3)+12*(5*7)=520 pins to drive each segment individuals. That's far too many. This is why they are multiplexed. One pin drives the same segment across all digits (or matrix). And you can select which digits/matrix you want to drive individuals. Thus is you want to display different text on the digits/matrix, you first drive the grid for this digits/matrix (and only this), drive the segment for this character, and then you do the same for all others (one after each other). That leaves us with 10+(7+3)+12+(5*5)=57 pins. And this is also why 3 VFD drivers are need, because each can only control up to 32 channels.
Controlling them is pretty easy. You just:
The drivers also provide a DOUT pin which will relay the serial data. This allows to chains them and shift the 3×32 data bits using a single line (the CLK pin is shared).
The CN2 connector at the bottom of the SER6500 has the following pinout:
The CN1 connector at the top of the SER6500 is used to forward the signals to the auxiliary VFD (to display the price for the customer). The second VFD has 10 digits, and is a copy of the 10 digits from the main VFD (minus comma and underline).
If you don't have the auxiliary VFD connected, the main VFD will not light up. To circumvent this protection just short the 3rd right-most to pin with the 2nd right-most bottom pin.
The three HV518 are chained. To control all the VFD segments you just have to shift 3×32 bits.
In the following tables the left-most 32-bit word is transmitted first, with least significant bit (right-most) shift first.
hex value (3×32 bits) | word | bit | display type | grid position |
---|---|---|---|---|
00000000 00000008 00000000 | 2 | 4 | matrix | 1 |
00000000 00000004 00000000 | 2 | 3 | matrix | 2 |
00000000 00000002 00000000 | 2 | 2 | matrix | 3 |
00000000 00000001 00000000 | 2 | 1 | matrix | 4 |
80000000 00000000 00000000 | 1 | 32 | matrix | 5 |
40000000 00000000 00000000 | 1 | 31 | matrix | 6 |
20000000 00000000 00000000 | 1 | 30 | matrix | 7 |
10000000 00000000 00000000 | 1 | 29 | matrix | 8 |
08000000 00000000 00000000 | 1 | 28 | matrix | 9 |
04000000 00000000 00000000 | 1 | 27 | matrix | 10 |
02000000 00000000 00000000 | 1 | 26 | matrix | 11 |
01000000 00000000 00000000 | 1 | 25 | matrix | 12 |
00000000 00002000 00000000 | 2 | 14 | digit | 1 |
00000000 00001000 00000000 | 2 | 13 | digit | 2 |
00000000 00000800 00000000 | 2 | 12 | digit | 3 |
00000000 00000400 00000000 | 2 | 11 | digit | 4 |
00000000 00000200 00000000 | 2 | 10 | digit | 5 |
00000000 00000100 00000000 | 2 | 8 | digit | 6 |
00000000 00000080 00000000 | 2 | 8 | digit | 7 |
00000000 00000040 00000000 | 2 | 7 | digit | 8 |
00000000 00000020 00000000 | 2 | 6 | digit | 9 |
00000000 00000010 00000000 | 2 | 5 | digit | 10 |