I started this idea because I thought it would be cool. Then I started searching... And searching... Found some ideas about back facing cameras and thoughts on a rangefinder but nothing that would actually work. I'm an electronics engineer/technician so I figured I had nothing to lose except some time. I started searching for parts. I have about 2 days of spare time in this design researching and making all the drawings. Note that I use free and open source software for online publishing as well as a lot of my own personal stuff so I can always share files or at least a semi compatible version of my originals.
Note: If electronics terms, electricity, and components you can fry by touching them bothers you, hit the back button now. I will be glossing over some things. This isn't for newbies. Just attempting this build will likely void any warranty there was on the parts. In all honesty, there are some fat fingered "technicians" I wouldn't give this build to.
Here is what I found:
Miniature (micro?) pinhole cameras with a microphone and composite video output $15-$20. The one I based this design off of has infrared LED's mounted around the camera. You can also use an alternate camera without the infrared "night vision" which may be smaller and give you a cleaner or easier install. Another alternative is to remove the infrared LED's and it may still have decent "night vision".
http://www.ebay.com/itm/Micro-Mini-Hidden-Color-Audio-Spy-CCTV-Camera-Pinhole-Night-Vision-/261913185215Miniature display with a composite video input $40.
https://www.adafruit.com/product/911What I didn't find is a similarly sized display in 16:9 format. In theory, this would fit better in the range finder and be closer to canon but then finding a 16:9 camera might also be a problem. I went with what I found that would work. We can search and wish more later.
The display works with 6-12V and the camera 5V so without much trouble, a simple 9V battery setup can be made to work. You can buy a 5V regulator in a TO-92 case or one can be custom made with a few parts for the camera supply. The TO-220 case regulator may work, but you might over heat your dremel carving out the space for it. I highly suggest the custom made regulator route because the typical 3 pin regulator has a somewhat high input to output loss which will cause you to use up 9V batteries before they are dead. An alternate battery system would be 6 or 8 AAA batteries in holders. The video is a direct hookup. Out of necessity, you'll have to chop and splice the wires to conserve the little space left in the range finder. There is going to be some really small wires to deal with. Optionally, the microphone can be connected to an amplifier such as an LM386 based board and small speakers. Almost everything is contained in the rangefinder body. Just 2 wires for power and an optional 3rd for an audio connection.
The next problem is what rangefinder and how big is it. The artist in me got stuck on Sabine Wren so I gathered lots of images and carefully measured and scaled. I'm still doing template art and drawings for Sabine. In any case, I have references on top of references. If I get the time and money, a male Sabine is possible. The rangefinder is the Sabine Wren scaled to match a helmet measuring about 10 inches wide (TMA). If it is scaled larger, it might fix a few problems. I have a detailed actual size DXF (Qcad) and SVG (Inkscape/Illustrator/Corel Draw) files. The PNG file is an export of the colorized SVG from Inkscape.
Before you look at that PNG file, you need to know some things. The colors are not canon and are only meant to highlight some of the details. Where possible, a 1/8 inch wall is left on all covers and surfaces. The only exception may be the side plates (shown in orange) and the display cover (shown in black). The side plates are actually over scale but probably not enough for anyone to notice. This should be easy to 3D print or even fabricate by hand. I had to make some educated guesses about the size of some things because I don't have the parts in hand. Lastly, this is a concept drawing. By adding a few cuts and ridges, this could easily be made to snap together. There is no hole for the microphone shown and needs to be added if desired. The only part you can't make is the rectangular tube for the stem. Wires will have to exit the tube near the pivot which may cause some problems for some. There are some special considerations for dealing with wires that move frequently. I have no idea if the image orientation will be correct. The camera housing may need adjustment or removed. The controller board for the display hides behind the display and needs a different cutout from the display section. Additionally there may be some modifications needed to the controller board and wires directly soldered.
To allow/help viewing the screen at such a close distance, get 2 pocket/wallet magnifiers and some thin clear or mostly transparent sheet. The magnifiers are thin fresnel lenses. Use the flat sheet to create some space between the lenses and the display. Be sure to use only the center part of the fresnel or you can get some weird optics. You can't cut out 2 lenses from one larger one. They just don't work that way. An alternative is to place a "reading" lens strategically on the helmet eye area. These instantly give you a bi-focal area though I don't know how well they work.
Additionally, if you use clear plexiglass and score it, just right, it should be possible to add actual range markings if it is side lit with some bright red LED's (red is canon for Sabine though I don't remember which episode). (Home brew might not be as effective as the various commercial side lit markings found in many products. I need to try this on some scrap plexiglass.) More electronics and more dremel work to add that feature.
The top view is to scale in the up position.
The middle view is the down position facing the camera. Camera is pink and black. Infrared LEDs in red but real is smoked.
The bottom view is the down position looking at the display from the back. Green is the display area.
All views are correctly oriented with the rangefinder on the user's right.
Could I build one? I've already made the CAD drawings. The above PNG file is directly from colorizing the DXF files. So I am pretty sure things will fit as drawn. The first step would be to get all the hardware. I need real measurements and to actually see it work to finalize the clearances and the electronics. The next step would be dealing with a 3D printer and likely adding much more detail for the 2 covers. I would make both covers snap in place, slots to hold the boards, hollow out the range finder shape for easy wiring, add in holes for various options like the side lit range marks, and a hidden screw to hold the stem. There would be no visible fasteners but you have to allow the option to take it apart. So I need 3 new drawings to define the main body and the 2 covers. There is a good chance the display cover needs to be metal anyway.
Could it work for other rangefinders? Maybe. Scale, surface angles and sizes have to be right or at least something that can be made to work. The Sabine range finder has mostly flat surfaces. Some of the rangefinders seem to have no real thought as to being functional though a display similar to Google Glass might make it work with the odd shapes. There are also back lit projection LCD displays found in some camcorders. I would gladly rip just about anything apart if I knew it would work with the other hardware. Even the above build has to mess with the side scale so it would be nice to have a slightly smaller display.
Last is a comment on internal helmet displays. Obviously this build will work for a rear view camera and perhaps even a range finder mounted camera with an internal display. Optically, this range finder build is pushing limits. I've already done some testing with the fresnel system I suggested above and it may not be enough. An internal helmet mounted display will push those limits even more. The younger crowd and those without near vision problems may be able to focus that close. After age 40 or so, that near vision is going to go away whether or not it's good now. The next best thing would be mounting one of the several personal viewing systems either above or below the eye opening. The optics are there, the electronics would be compatible and the eye slot of most typical mando helmets is narrow enough that this can work. The question then becomes one of expense and mounting something in a way it was never designed to work.
If you have any electronics questions, ask, I can do everything all the way up to full multi-layer through-hole and surface mount PCB designs. Or in plain English, I can make some really small circuits or some not so small traditional stuff. One off designs can get expensive though.
