MPXM2010GS datasheet(4/24 Pages) FREESCALE

4 / 24 page

AN1950

Sensors

Freescale Semiconductor

OTHER

This system is designed to run on a 9.0 V battery. It

contains a 5.0 V regulator to provide 5.0 V to the pressure

sensor, microcontroller, and LCD. The battery is mounted on

the back of the board using a space saving spring battery clip.

Smart Washer Software

This application note describes the first software version

available. However, updated software versions may be

available with further functionality and menu selections.

Software User Instructions

When the system is turned on or reset, the microcontroller

will flash the selected LED and display the program title on the

LCD for five seconds, or until the select (SEL) button is

pushed. Then the menu screen is displayed. Using the select

(SEL) pushbutton, it is easy to scroll through the menu options

for a software program. To run the water level program, use

the select button to highlight the Water Level option, then

press the enter (ENT) pushbutton. The Water Level program

will display current water level, the rate of flow, a message if

the container is Filling, Emptying, Full, or Empty, and a

scrolling graphical history displaying data points representing

the past forty level readings.

The Water Level is displayed by retrieving the digital

voltage from the internal A/D Converter. This voltage is

converted to pressure in millimeters of water and then

displayed on the LCD.

Calibration and Calibration Software

To calibrate the system, a two-point calibration is

performed. The sensor will take a calibration point at 0 mm

and at 40 mm of water. Depressing both the SEL and ENT

buttons on system power-up enters the calibration mode. At

this point, the calibration menu is displayed with the previously

sampled offset voltage. To recalibrate the system, expose the

sensor to atmospheric pressure and press the SEL button

(PB1). At this point, the zero offset voltage will be sampled and

saved to a location in the microcontroller memory. To obtain

the second calibration point, place the end of the plastic tube

from the pressure sensor to the bottom of a container holding

40 mm of water. Then press the ENT button (PB2). The

voltage output will be sampled, averaged and saved to a

location in memory. To exit the calibration mode, press the

SEL (PB1) button.

Figure 5. Water Level System Set-Up

for Demonstration

Table 2. Parts List

Ref.

Qty

Description

Value

Vendor

Part No.

Pressure Sensor

Freescale

MPXM2010GS

Vcc Cap

0.1µf

Generic

—

Op-Amp Cap

0.1µf

Generic

—

Shift Register Cap

0.1µf

Generic

—

Red LED

—

Generic

—

Green LED

—

Generic

—

S2, S3

Pushbuttons

—

Generic

—

Quad Op-Amp

—

ADI

AD8544

Voltage Regulator

5.0 V

Fairchild

LM78L05ACH

Microcontroller

8-pin

Freescale

MC68HC908QT4

¼ W Resistor

22 K

Generic

—

¼ W Resistor

2.4 K

Generic

—

R3, R6

¼ W Resistor

1.2 M

Generic

—

R4, R5

¼ W Resistor

1.5 K

Generic

—

R7, R8

¼ W Resistor

10 K

Generic

—

R9, R10

¼ W Resistor

1.0 K

Generic

—

LCD (Optional)

16 x 2

Seiko

L168200J000

Shift Registor

—

Texas Instruments

74HC164

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