ELEC 332

Design Challenge

The structured lab portion of this exercise looked at a couple of piezoelectric sensors. Now it's time to get some experience with a resistive sensor.

The Sensor

The resistive sensor of choice is a MEMS (Micro Electro Mechanical System, not Mechanical Engineering and Materials Science) absolute pressure sensor. It consists of a thin diaphram with a sealed, evacuated chamber on one side and ambient atmospheric pressure on the other. Attached to the diaphram are four strain gages whose resistance changes as the diaphram flexes in response to changes in pressure. The gages are connected in a bridge configuration, as described in the Background section.

The Plan

Since this sensor measures absolute pressure, it can be used as a barometer. The design (and programming) challenge is to do precisely that, i.e. build an electronic barometer.

The Details

Your design should use the MPXM2102A Pressure Sensor as the pressure sensor. We have these in the M-Pac package.
Since the time frame for this exercise is shorter than that of Exercise 6, you should use components that already in stock. The following active components are available and should be adequate for your design:
- INA126 Instrumentation Amplifier (in MSOP-8 packages)
- LMV358: Dual Low-voltage, Rail-to-rail Output Op Amp (in SOIC-8 packages)
Your circuit should operate from a single +5 V supply.
Your circuit should produce an analog output voltage which optimally maps the expected range of atmospheric pressure into the range of the MSP430 A/D converter. You should also provide a scaled version of the bridge excitation voltage, V_ref.
Since we will be panelizing for commercial fabrication, your circuit must fit on a 1.5 x 1.5 inch breadboard module (BRD1x1).
Your module should connect to the CPU module using the standard 10-pin interface connector, i.e. the same as you used on the H-Bridge module in Exercise 4. You may utilize whichever pins are most convenient for your layout.
Your program should read the sensor output and the reference voltage, perform the necessary calculations to convert to pressure, and send the result to the PC via the serial port. You can report the pressure in any appropriate units (e.g. millibars, inches of Hg, etc.) but the resolution should be comparable to that given in a weather report.

The Schedule

In Exercises 3 and 4, your PCB layouts were fabricated by the instructor on a fixed schedule. In future exercises, it is expected that you will be able to fabricate your own boards within your own schedule. However, before you are able to do that, you must demonstrate proficiency with the T-Tech machine. This leaves the boards for exercises 7 and 8 as the perfect vehicle for this demonstration.

You will have to schedule your test drive(s) at a mutually convenient time, will may result in a few days delay between finishing your layout and being able to complete your fabrication. To account for this, the due date for this exercise has been extended for an additional week, until March 22.