Thursday, October 13, 2011

Diy Portable video projector

My newest project is to build a pocket sized, battery powered portable video projector that accepts a standard composite input. It all started when I received an old jvc (circa 1998) vhs camcorder with a tiny color lcd viewfinder. I took it apart and started hacking it. I quickly found the composite input to the display driver but was unable to get the screen to accept input without tethering it to the camera's main board (which told me that the camera was somehow initializing the driver board for the display). I powered the screen with 12V and 5V but nothing happened without connecting three specific wires to the mainboard. Time went by and I decided to pick up the project again recently. I once again noticed the group of three wires that seemed fishy so the first thing I though was SPI. I looked up all the data sheets and traced these three to the Mitsubishi M62353FP which is a 8 channel DAC and confirmed that they were three wire SPI thanks to the datasheet. The outputs led to some inputs for the display driver (Sony CXA1854AR) which controlled color, contrast, etc. I tried sniffing the data that was coming from the camera's mainboard with my PICKIT2's logic tool, but it didn't make much sense. Instead I measured the analog voltages on each of the DAC's outputs, calculated the binary values using a formula from the datasheet and wrote up a driver for my PIC which sends a four bit address (for each of the 8 outputs) followed by the 8 bit output value. I wired everything up, plugged it in and everything worked like a charm (well colors are a bit washed out but that can be fixed by adjusting the software a little). So now onto making the optics for the projector.

 Here's a shot of the tiny LCD (Sony LCX005BK). Pretty low resolution but it was free so I wont complain.

Here is the backlight. High voltage and not so bright so it needs to go.

This is the other side of the backlight. Note the step up transformer and switching mosfet.

Finally here is where I am at right now. I am running it all off of a 12V wallwart, using a LM7805 linear regulator for the 5V line (when I go to make this battery powered I will use a lithium rechargeable battery and a TI step up converter module to get the 12V). My PIC is on the right (with a little development board I made to make things easier) with code to set display values. I plan on adding buttons to allow the user to change brightness, contrast, saturation, etc on the fly. On the left is the display driver. and I attached a 1W white led as a replacement for the original backlight.

Sorry about the blurry display shots, photographing a .5" lcd is a lot more difficult than it would seem.


Full set up with my ipod outputting video. More to come soon.
datasheets available below:
CXA1854AR
M62353FP

Update! Working on optical assembly and took some test photos of video projection.

Here's my test setup with the optical assembly and projection lens in the center.
Picture of projection (about 10" or so) onto a glossy white screen in my room with blinds shut but lots of light seeping in.
Had to drag the setup into my bathroom to get a completely dark background. Once again image is around 10". I noticed that I nicked the lcd's polarizing filter a bit and that there are some dead/stuck pixels in the screen which show up in the image. Oh well, I got all the parts for free and this is merely a proof of concept so I don't really care.

Update: Made tons of progress on this project. Demo video below and pictures and explanation to come.

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