Temperature and Pressure Control using the

AT90S8535

Louis Mo

Stephen Yu

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

 

Functionality:

1. Display Pressure or Temperature

20° C and 30° C.

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

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:

Temperature^2 VS Resistance

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.