I think at that point, the FB is the wrong device - there are various tacho/speedo circuits that can be used.
Multiplexing the FB will reduce the outputs to 10 (3 digits).
Otherwise for binary, do you mean BCD, byte/word conversion, or serial? But add one chip to that and you save the FB.
That's called a shift register. It has a sort of memory. A lot of the big matrix signs use them as 7-bit chained using the last bit to send data to the next. You can control a lot of LEDs with just a few lines.
If you want to rotate the display, yes - that's a shift register.
I was writing about full drivers....
You can look into demultiplexers if you want to save outputs. Change the outputs fast enough and nobody will know that only one segment is on at one time.
Yeah a SIPO would work fine. For ease of use you can use the 74LS series of chips.
On multiplexing and resistorless LEDs....
SiliconChip August 2010 features a 6 digit (remote controlled up/down) timer.
It uses a total of 10 lines for its 6 digits (including power).
10 ATINY ports multiplex the segment anodes & cathodes directly.
They do not use resistors. Despite exceeding the LED current, the duty cycle keeps it under their pulse current tolerance (something Curiosity and others are familiar with).
Cute eh? 3 more digits than the above, 6 less ports, and (probably) 8-16 less resistors.
Using this method they achieve a constant brightness across all digits.
Has anyone considered trying to use a Projector as a HUD?
Have considered it, using a pico-projector such as the Acer C120, Acer K11 or K130.
Probably not visible in broad daylight. (have tried with a 15 lumen projector - it might work at night with the headlights off, but that wouldn't be very useful, would it?)
The minimum focus distance for those projectors are 40-60 cm, so it would require some sort of mirror setup or mounting the projector somewhere near the seats.
The windscreen is usually not flat, so the display might look pretty distorted.
Even if the other issues are overcome, there is still the "double-reflection" to sort out.
A laser projector does not need focusing and might be an idea.
You could look at this : http://www.microvision.com/solutions..._displays.html - they have a dev. kit available for 1695 $
Youtube also has a lot of HUD videos - however, I haven't found any DIY solutions that looked acceptable in daylight.
Would a LCD monitor with a massively overclocked backlight work as a HUD?