However, this brought me to thinking of how to build a simple see-through HUD.
The most conventional way would be to place a monochrome LCD with positive exposure above the viewer and a good backlight. Problem is I'd like at LEAST 320x240 resolution (see above, just as hard to afford as their color cousins so far at small sizes). Not looking for raster images, just line/vector (think fighter sim HUD display).
Then I thought about the old Virtual Boy. It used (from research) a 224 LED line to display 324? x 224 images. Now, I remember the headaches (roomate in college had one), but with an infinite focus and a view on the outside world, this should work a lot better. Oh, and a rotating 8 sided mirror. 450rpm should provide about 60 FPS update rate.
So, unfortunately even with 1mm spacing, even 0.5mm spacing, I'm seeing 12 to 24cm needed for a linear array. Well, a bit more complex hardware and we have two to four ofset lines as need be. Now, we're also talking 240 LEDs. Beyond the SMT driving transitors, we also have to deal with the IO. I originally thought an FPGA to take care of the optical encoder from the mirror wheel and all this, but I'd either need two or a BGA. Ouch. So, another idea came out. 60fps x 320 lines = 19.2KHz. Even at 5x that, we're looking at something that can be PIC driven. Now, I'm going to need 4 80 pin TQFP's, but it might work. As long as I can live with pure black and white (although PWM might be an option), I can also frame buffer all this into data RAM. 320x240 is 76800. This breaks down at one bit per pixel to 2400 bytes of RAM. Given I'd have to use high end 18F's for that pinout, they also come with 3.5K ram, so that will work.
Now, a fifth PIC would be needed for motor control and for sending a vsync and newframe signal to the other PICs. I figure leaving this to a smaller PIC would let it be used as a master controller, I/O interface, etc. It'd also let the other PICs focus on being graphics chips, with possible graphics calculations onboard.
Yeah, it's going to be expensive. For one or two units, the LED's are $0.14 each. 4 high end 18F PICs (Actel's new FPGA's might actually be cheaper for two! And they could be easily reprogrammed to run PWM to provide grayscale), plus PCB, power, and the mechanics and optics.
Anyone else have any thoughts on this? Better, cheaper, some small and low cost LCD I missed somewhere? Although I might throw together my LCD display, the HUD is unfortunately WAY on my backburner. Work gives me lots of time to think, but I get very little time to DO.
Although I'm dreaming it up for lots of uses, here's one: data downlink from an RC aircraft/car's onboard GPS sensor. You have a GPS unit in a data backpack. Add a mag compass/IMU and you can have the unit provide speed, range, and even a location marker over your field of view. You could also get a live power/fuel feed or other diagnostics.
Strange ideas, rambling technical thoughts
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