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.

Functionality:

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:

LCDpin 	Connection
1	gnd - Port A			
2	+5 volts - PortA7
3 	trimpot wiper
4	PortD6
5	PortD5
6	PortD4
7-10	no connection
11	PortD0
12	PortD1
13	PortD2
14	PortD3

Keypad pin Connection

PortC0
PortC1
PortC2
PortC3
PortC4
PortC5
PortC6

8 PortC7

NPC Pin Connection

PortA0

STK200 GND
no connection
no connection

no connection

GND(separate source A)

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.