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

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:

 

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

  1. PortC0
  2. PortC1
  3. PortC2
  4. PortC3
  5. PortC4
  6. PortC5
  7. PortC6

8 PortC7

  1. NPC Pin Connection

  2. PortA0


    VCC (separate power source)

  3. STK200 GND
  4. no connection
  5. no connection

  6. no connection

  7. 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.