Time to consider some sending units, first up will be boost, and it might as well include vacuum while I'm at it...  Something affordable and widely available to noodle with seems appropriate.

This 3-bar GM-style sensor seems to cross-reference with enough other OEMs that it will fit the "available" category, and with a range from 1 bar of vacuum to 2 bar of boost, it will more than cover the 20 inches of Hg (-10 psi) to 5 psi of boost I need.

It's listed by several vendors on eBay for less than $30 with free shipping and a 2 year warranty, and according to more than one of the listings it has the following specifications:

- Weatherpack connector and wiring - ground (brown), signal (orange), 5V power (yellow)
- Temperature operating range of -40 to 260 F
- Response time from 10% to 90% of range within .001 seconds
- Automatic temperature compensation
- Linear scaling at all boost and vacuum levels
- Minimum of 99% accurate over full scale
- Cross-referenced with OEM part codes as follows:
  - GM: 16040749, 12223861, 12223861K
  - AC DELCO: 2131562
  - STANDARD MOTOR: AS210
  - AIRTEX: 5S2556
  - WELLS: SU504

There's quite a bit of information on the web about these sensors, as they're available from Summit Racing and other sites.  There is a good cache of data at Robie the Robot specifically on the 3-bar sensor, including these data tables and drawings:

Formula for the GM 3 Bar MAP sensor is (V*8.94)-14.53, I have no idea why it's 14.53 and not 14.696, [rounds up to 14.7] but it works out on GM's chart every time. It is possible that Detroit is slightly above sea level, and you can use 12.11 in the formula for 1 mile above sea level.

A good full-size shot of this Delphi drawing and specs is available here.

The control board has been updated to take into account the internal switch layout, and the version number updated accordingly to 0.3x.

A slight improvement made to the power supply board today, to rotate the DC Out screw terminals (J3) to be accessible from the edge of the board, so the wires don't have to be threaded past the smoothing capacitor.

The version number is iterated to 0.31x and the silkscreen is updated accordingly.

During the next phase, when prototyping is happening on-car and on-bench in equal measures, it will be necessary to have an enclosure that makes things visible and easy to get in and out of a *lot*, while still being weatherproof.

To keep firewall-holes to a minimum, I'm thinking it makes sense to put the computing bits out under the hood, so this NEMA-rated, hinged clear-covered enclosure is hopefully just the right size for both the power supply and the Arduino together.  It is the WD-06-03 available at Polycase here.

And eventually, these waterproof power cables from AdaFruit should come in handy, along with the matching waterproof 4-way data cables.

Not forgetting that we need to put an enclosure *somewhere*, and that simplicity and protection are key design factors, it will be important to have more than one option.  There now exists a cover and extender for any combination of externally powered "innards", e.g. Arduino alone, power supply alone, or both together.  The Arduino connections come out through the case, and the main power supply line can be drilled and custom fit.

There's also an option for putting everything into one enclosure and keeping all but the most basic of wiring internal - a custom hole can be drilled for whatever power and data lines need to be run into the enclosure, then it can be sealed shut against the elements.