Stand-alone Engine Board Design

I've been working on hardware, trying to make it easier to put together a system. One of my goals was to either produce a shield for the arduino, or a more cost-effective stand-alone board. After some thought, I figured it would be better, especially from a cost perspective, to just work on a stand-alone board. I'd like to get your feedback, both on the concept of a stand-alone board and on the design.

It looks like the total cost of one of these boards, in low volume production is going to fall between $25 and $50 (big range, I know =). The design is based on the single-sided board variant of the freeduino (although it's no longer single-sided). Everything is through-hole, so it should be easy to solder. That also means no USB. It has a plain DB9 cable, but you can buy inexpensive USB to serial adapters.

Here's an image of the design I'm working on - it's still has more work to go, but I may be sending off for the first prototype boards in the next week or two:

Here're the specs on it:

• 6 2.5mm stereo jacks
  
  • 4x motor control
    
    • 2x step/dir control only
    • 2x step/dir OR pwm/dir control
  • 1x Camera (isolated focus/shutter)
  • 1x Motor Aux
    
    • Motor Driver Sleep Line
    • Limit switch input
• 1x Serial LCD hookup
• 5x Button/GND hookups
• 1x RJ-45 jack
  
  • SPI motor interface
  • Additional I/O lines
• 1x Female DB9 (serial port)
• 2x LEDs
  
  • Power
  • Camera exposure

The motor limit switch input can be used for all limit switches. The input is pulled high when not connected, and GND is supplied as the 3rd contact on the stereo jack. Bringing any switch on the line low will trigger the motor limits - which disengages all step/pwm lines connected via the stereo jacks. This is done using AND gates, and so it will kill all motors should any limit be reached - even if the firmware is unresponsive.

The RJ-45 provides an SPI or serial interface. This will be used to drive serial DC motor drivers like the Pololu JRK 21v3 (an excellent DC motor driver with a good range of power output and lots of awesome features: http://www.pololu.com/catalog/product/1392), or a quad 2A stepper driver board that's currently in development.

The idea for this board is that it can be just popped into an enclosure once soldered - and be ready to run.

!c