Temperature and Pressure Control using the AT90S8535

Temperature and Pressure Control using the

AT90S8535

Overview:

This project involves the implementation of control and monitor for dual processes. The variables monitored are pressure and temperature. The input control is a 16 button keypad and the output is monitored in a 16 character LCD The device can be widely deployed as a cheap solution to room and automobile climate control automation.

Assembly code for device
unctionality:


1. Display Pressure or Temperature

• Pressure will be displayed when button A is pressed.

• Temperature will be displayed when button B is pressed.

• Temperature is displayed in intervals of five Celsius from �20° C to 20° C and 30° C to 80° C.

• Displays the closest to 20° C, 23° C, 25° C, 28° C when in the range between

20° C and 30° C.

• Pressure will be displayed in lb/inch² from 0 to 30 PSI in intervals of one PSI.

2. Temperature can be controlled to any of the displayable threshold with approximately +/- 2° C control range.

• When Button D is pressed, user will be prompted to enter the temperature range desired.
• There are 24 temperature ranges available as shown in table 1. These ranges are selected by punching the range number in the keyboard.

• Temperature control has a three stage differential sensing scheme. When temperature is within approximately 2° C within desired temperature range, then a lower intensity fan is deployed. When temperature is approximately between 2° C to 4° C within the desired range, a higher intensity fan is deployed. When the temperature discrepancy from the desired temp is more than 4° C then the highest fan intensity is selected.

3. When Pressure is selected as LCD output, temperature is monitored every 20 read cycles or approximately 70035 m secs.
4. Pressure change alarm LED is flashed when the increase in pressure is past 5 PSI within five read cycles or approximately 35 m secs.
Implementation:
Hardware: 1 AT90S8535, 1 STK200, 1 RCM2034R LCD,

1 16 button keypad, Lucas NovaSensor NPC 410 pressure sensor,
1 NTC GE 76 thermistor
Wiring Scheme:

Circuit Specification:
Clock rate 4Mhz AREF 4.096 Volts
The following graph depicts the linearization relationship for the GE 76 thermistor:

Voltage step per PSI increase for the Lucas Novasensor:
4.1667mv per PSI
DC offset from output of NPC-410
7mv
Table of temperature with respective voltage.