Initial Projector Requirements and Thoughts

Since I'm not done with the embedded OS yet, I'll touch on the projector system.  I've been thinking about this a lot recently as the design and implementation will dictate other aspects of the total system design.

If we refresh our memories on the Requirements Page, we can see that Tier 2 requirements have been defined for the projector system.

I'll copy them here:

1. The projector system shall receive video over an RCA Component signal.
2. The projector system shall be powered by 12V.
3. The projector system shall be able to control brightness.

Here's what I currently have, hardware wise, for my projector system:

3.5in LCD Monitor

Yep, just the monitor.  I think I paid $18.29 for mine from a different seller on eBay.  Cheap enough that if I break it, I'm not out of a lot of money.

Here is a nice picture.

This is my idea for the projector.

My plan all along was to disassemble the LCD monitor and cut the connection to the backlight.  I also am going to remove the metal backplate that evens the backlight out, leaving just the raw LCD panel and the control circuit board.

For my new backlight, I found these really cool 0.8in 8x8 LED matrices from Adafruit that have an i2c controller.  The i2c controllers allow for four of the devices to be hooked to the Raspberry Pi's i2c lines.  I think I only need two of them initially.  The LED's themselves have 16 levels of brightness, which meet my Tier 2 requirement of being able to change the projector brightness.  The brightness will be controlled by 3 buttons connected to open GPIO pins on the RPi, one for increase, one for decrease, and the other will be a mode button to cycle between all LEDs on, every other LED on, and every 2 LED on.

So what does this design mean for the rest of the system?

Well, I now have to get the schematic drawn up for the STN1110 OBD chip since that will hook to the RPI uart lines.  I need to get all the components and attempt to get my ideas prototyped out.

On another note, I'm probably going to be working on putting the OBD library and ELM-327 device code on github soon.  Need to get a setup.py file created that will install it properly.