Barometric pressure measurement. The Motorola MPX4115A is a pressure sensor that can measure a pressure ranging from 15 to 115 kPa (2.2 to 16.7 psi) and has a corresponding voltage output from 0.2 to 4.8 V. The small outline package of this device has eight pins. Among these eight pins, only three pins carry useful signals:

This pressure sensor is often used in aviation altimeters, industrial controls, engine control, and weather stations and weather reporting devices.

Connect an MPX4115AC6U (or MPX4115A6U, case 482) device to your HCS12 demo board to measure the current ambient barometric pressure once every second and display the pressure on the LCD display. The data sheet of the MPX4115A can be found on the complementary CD. Since the barometric pressure is in a narrow range (use the range mentioned in Example 12.11), you may need to construct a signal-conditioning circuit to translate and scale the voltage output of the pressure sensor to the range of 0 to 5 V.

Example 12.11

Describe the circuit connection of the ASCX30AN and the voltage level shifting and scaling circuit, and write a program to measure and display the barometric pressure in units of mbar.