|This is the idea I came up with a few weeks ago and just kept toying with|
The projector is a Mitsubishi PK10 and came out in 2006. By today's standards, it is practically a relic. But I have used the newer model of these a year ago for a few weeks and had a fun time writing in some code in my control software to trigger the Princess Leia video clip. I came upon this one on eBay for $53. No cords, no battery, just the projector itself. I couldn't resist and bought it.
The resolution and brightness aren't stunning by the standards we have now, but for what we want R2 to display, should be more than adequate, assuming I can overcome some obstacles.
Powering the projector
With no battery or ac adapter, I couldn't even test the projector when it arrived. The specs on the projector say the power supply converted AC power to 15 volt, 2amp. Knowing that, I was able to search around my favorite electronics sites for something that could do that.
The Slip Ring power system I have been working on for months wouldn't cut it. At 12 volts, 2amps, the conversion process to boost the voltage drops the amps. Meaning, I could generate 15 volts but with only 2 amps coming in, it would be way short. I would need a power source with more amps. I contacted Dimension Engineering about what I was trying to do and they suggested the AnyVolt3. At a max amp of 3amps, it could take 12 volts and push it to 15 volts (or higher). It has a tiny potentiometer you twist to crank up or down your desired target voltage. Simply attach the multimeter to the leads and tune accordingly. They also provide a graph to indicate what amount of amps each incoming /outgoing voltage will produce. For 15 volts, it will do 1.85 amps. So close....but, it turns out, its enough to power the device!
That said, the projector will have to have its own dedicated power source, so I am using a 12 volt 7amp battery.
Getting video from computer to projector
The slip ring already occupies the dome plate, providing the dome with power from the batteries in the body. The computer is also in the body. So, how do we manage to get R2's computer to see the projector as a second monitor?
After reading tons and tons of reviews on Amazon.Com and NewEgg.Com, I found a product Warpia makes for streaming video from your computer to your big screen TV. The range is about 30 feet max and the reviews I read indicated the device works extremely well. Their Wireless USB Audio/Video Adapter sells for about $115 at many online stores. I checked eBay but they were much more expensive there for some odd reason. Before purchasing, I emailed their technical support team to find out what the power requirements were for the base station that hooks up opposite the PC source. It turns out the device uses just 5 volts 1 amp. Having spent a lot of time playing with 12 volt to 5 volt converters for the dome lighting, I knew that would be pretty easy to do. That done, I ordered the device from Amazon.Com which had overnight shipping for $10. Hard to pass up a deal like that!
It turns out that for both this device and the projector, the biggest challenge was getting the right power plug type to plug into the device. The projector took a type "B" plug, available at any Radio Shack. You could buy the $3.99 pack of two and solder your own leads. I tried that but the connectors are so small and hard to get at, it was worth buying the next option up. Radio Shack sells a wire with open connectors on each end, which you then push in whichever plug type you are going to use. In my project, I just cut the wire in half and now had a power plug for each device with bare wires on the other.
I couldn't match up the power connector for the Warpia device with anything they had. One fit too loose, one so tight I thought it would break it. I wound up cutting the end off the included power cord and verified that the lead with white marks was indeed positive. (Always test, never assume!)
Embarrassing true story: Always label your power leads. The projector and Warpia device take extremely similar plug types. However, one is 15 volts, the other is 5 volts. I mixed those up and fried the first Warpia device I bought. Oh sure, it lit up VERY brightly for an impressive second or two. But, then came the wiff of electronics doom and a piffle of blue smoke.
How am I going to mount this in?
The very first concern I had all along was how to mate this to the back of the holoprojector (HP). There is very little surface area to mount this to that wouldn't compromise mobility. It has to be able to withstand all the bouncing around R2 does while rolling around, being loaded/unloaded and so on. It has to stay perfectly aligned with the opening of the HP in order for the image to pass thru. It also needs to be accessible should I need to manually adjust the focus, power the device on, etc.
For access I am going to hinge the dome panel on top of where it sits. More on that later.
The HP's are threaded on the backside so that builders can install a light source and close the threaded cap. The thing is, no one knows what the size and threading is. Its rather fine so anything you find at a plumbing store will not fit, it will be too coarse. Same with various home and industrial electrical fittings.
I managed to make some new friends in my many journeys over the past few months. Roger, who works at a local sheet metal facility mentioned a sign shop proprietor who does a lot of projects and CNC/engraving work for fun. I met Fred and explained what I was trying to do. He was able to determine that the threading was 20 and most likely metric. He asked if I could leave the HP with him so his friend, another CNC operator, could investigate this unique riddle further.
While they did that, I worked with Roger on making a simple L-shaped shelf that would house the projector. What would have taken me an hour and God knows how many Dremel cutting discs, his press and brake had done in 4 minutes.
A day later I heard back from Fred and we compared notes. Fred was just as smitten with this puzzle as I was. Together we cut the access holes for the projector lens and cooling fan. His friend was able to make the perfect male threading piece and weld it onto a small piece of aluminum. Fred trimmed it down to fit over the lens opening and suggested that instead of drill/tapping holes to secure it in place that it be welded.
The next day, Fred had finished the welding work and let me know the part was ready. Once there, we put all the pieces together to see how everything would fit. Fred added some support bolts to keep the projector in place.
TO BE CONTINUED!