MPXM2102AS datasheet(543/670 Pages) MOTOROLA

543 / 670 page

AN1950

3–397

Motorola Sensor Device Data

www.motorola.com/semiconductors

–

Figure 2. Amplification Scheme

R11

R10

500K

R12

500K

V2sensor

V4sensor

Vout

Vcc

0.1

µF

Vcc

Microprocessor

To provide the signal processing for pressure values, a

microprocessor is needed.

The MCU chosen for this

application is the MC68HC908QT4. This MCU is perfect for

appliance applications due to its low cost, small 8–pin

package,

and

other

on–chip

resources.

The

MC68HC908QT4 provides: a 4 channel, 8–bit A/D, a 16–bit

timer, a trimmable internal timer, and in–system FLASH

programming.

The central processing unit is based on the high

performance M68HC08 CPU core and it can address 64

Kbytes of memory space. The MC68HC908QT4 provides

4096 bytes of user FLASH and 128 bytes of random access

memory (RAM) for ease of software development and

maintenance. There are 5 bi–directional input/output lines

and one input line that are shared with other pin features.

The MCU is available in 8–pin as well as 16–pin packages

in both PDIP and SOIC. For this application, the 8–pin PDIP

was selected.

The 8–pin PDIP was chosen for a small

package, eventually to be designed into applications as the

8–pin SOIC. The PDIP enables the customer to reprogram the

software on a programming board and retest.

DISPLAY

Depending on the quality of the display required, water level

and water flow can be shown with 2 LEDs. If a higher quality,

digital output is needed, an optional LCD interface is provided

on the reference board. Using a shift register to hold display

data, the LCD is driven with only 3 lines outputted from the

microcontroller: an enable line, a data line, and a clock signal.

The two LEDs are multiplexed with the data line and clock

signal.

Figure 3. Multiplexed LCD Circuit

HC908QT4

HC164

LCD

DB0

DB1

DB2

DB3

DB4

DB5

DB6

DB7

CLK

PTA4

PTA3

PTA5

Multiplexing of the microcontroller output pins allows

communication of the LCD to be accomplished with 3 pins

instead of 8 or 11 pins of I/O lines that are usually needed.

With an 8–bit shift register, we are able to manually clock in 8

bits of data. The enable line, EN, is manually enabled when

8 bytes have been shifted in, telling the LCD that the data on

the data bus is available to execute.

The LEDs are used to show pressure output data, by

displaying binary values that correspond to a pressure range.

Leak Detection or water–flow speed is displayed by blinking

a green LED at a speed relating to the speed of water flow. The

Red LED will display the direction of water flow. Turning the

Red LED off signifies water flowing into the tub. Turning the

Red LED on signifies water flowing out of the tub, or there is

a leak.

Digital values for water height, rate of water flow, and

calibration values are displayed if an LCD is connected to the

board.

OTHER

This system is designed to run on a 9V battery. It contains

a 5V Regulator to provide 5V to the pressure sensor,

microcontroller, and LCD. The battery is mounted on the back

of the board using a space saving spring battery clip.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MPXM2102AS Datasheet(PDF) 543 Page - Motorola, Inc

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