Dana Frank Raymond wrote:

>If anyone knows where to start in sourcing airbag accellerometers, please
>speak up!  :-)

Sorry to take so long with this ...

Other people have already suggested the Analog Devices accelerometer, and have
provided an overview to it.  I think Dana has already concluded that this
device is too expensive for the product he is working on.  I can't suggest a
cheaper accelerometer either.  None-the-less, I thought I should provide the
following information for completeness sake.

Motorola is also manufacturing some accelerometers (primarily driven, I think,
by the air bag market).  The data sheets I have on their products is marked
as preliminary, so I do not know if common mortals like ourselves can get any
of the product yet.  (I would imagine that one of the auto manufacturers
could.)

Motorola has data sheets for three different versions in their 1995 Sensor
Device Data book (DL200 Rev 2), the XMMAS40G10x, the XMMAS250G10x, and the
XMMAS500G10x.  The .....40G... is for the +/- 40g range, the .....250G...
is for the +/-250g range, and (you guessed it) the .....500G... is for the
500g range.

To provide an overview of these products, here is the summary quoted from the
.....40G... data sheet (typos are likely mine) ...

"The MMAS40G family of silicon capacitive, micro-machined accelerometers
features integral signal amplification, signal conditioning, a 4-pole low-pass
filter and temperature compensation.  Zero-G offset, full scale span and filter
roll-off are factory set and require no external passives.  A calibrated
self-test feature mechanically displaces the seismic mass with the application
of a digital self-test signal.  The device is offered in two plastic packages,
thereby accommodating various axis orientation requirements.

"The MMAS40G incorporates a single polysilicon seismic mass, suspended between
two fixed polysilicon plates (G-cell).  The forces of acceleration move the
seismic mass, thereby resulting in a change in capacitance.  The G-cell is
sealed at the die-level, creating a particle-free environment.  The G-cell
features built-in damping and over-range stops to protect it from mechanical
shock.

"MMAS40G accelerometers are ideally suited for automotive crash detection and
recording, vibration monitoring, automotive suspension control, appliance
control systems, etc."

The description of the other two versions are similar to the above.

Unlike the AD devices, the Motorola devices are (supposedly) available in a
DIP package and a SIP package.  I would find these packages to be more
convenient to implement than the AD version, and perhaps, they may be cheaper.
I don't think they could be purchased for $0.50 each though.

        -Kevin.