[Autopilot-announce] Rev 2.4 board design available

[Trammell H. <hu...@ro...>]

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I've reworked the 2.3 board to be more modular based on the comments of
several folks on the list, as well as smaller overall and with the third
axis, too.  Some changes:

The inertial sensors are on their own boards, separate from the servo
controller / radio interface.  This gives smaller helicopters a means to
position the IMU at the center of gravity and the servo controller where
it is convienent.

The controller portion of the board is exactly 1/2 the size as before.
It is now 48 mm x 63 mm rather than 96 mm x 63 mm.  If you do not want
to use the inertial sensors but only want a servo interface, you can use
this by itself.

All three boards have full ground planes to help avoid the analog noise
that was causing jitter in the sensor readings.

There is no provision for an ADXL202-EB.  You have to surface mount the
two of them.

There is no ISP header.  You have to use the serial boot loader to
reflash the MCU.  I have never had any problems with this, even after
crashing one of the boards.  Still, I would recommend using a socket for
the MCU just in case it gets fried.

There is no DB9.  Very few people were using it, so I've switched to the
three pin header only.  The pinout has changed as well to make it
reverse TX/RX by plugging the header in backwards.  This lets you make a
nullmodem for different equipment.

There are only 10 regular servo drivers and 1 high-speed digital servo
interface.

The engine tach feeds into a LM2907 frequency to voltage converter so
that we do not spend any interrupt overhead tracking the engine speed.

There are three user headers if you want to use them.  On the Mega163,
two are interrupts and one is polled.  On the Mega16 or Mega32, all
three can be interrupts.

We have schematics this time!  ExpressPCB's software now includes a
schematic layout program.

Schematics and images of the layout are online here:

	http://autopilot.sf.net/rev2.4/

I'll be ordering three prototype Miniboards for testing tomorrow.  If
all goes well with them, Dennis will be organizing the group order for
the parts and silkscreened boards.

Trammell
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