Question 3 Hothouse Temperature Control

You are to draw a structure diagram and from this write the C program that controls the temperature inside a hothouse. The hothouse temperature is controlled by two methods: a) to increase the temperature, a heater controlled by a PWM signal is used, and b) to decrease the temperature, windows connected to a servo motor can be adusted.

The operation is as follows

Window

• At night time the window should be closed (A light level below ADCW = 250 )
• Daytime the window is:
  • closed if temperature is below 10⁰
  • quarter open if temperature is between 10⁰ and 15⁰
  • half open if temperature is between 15⁰ and 20⁰,
  • three quarters open if temperature is between 20⁰ and 25⁰
  • fully open if temperature is above 25⁰

Heater

• At daytime the heater should be off. (A light level above ADCW = 750 )
• Night time the heater is
  • fully on if the temperature is below 10⁰
  • three quarter on if temperature is between 10⁰ and 15⁰
  • half on if temperature is between 15⁰ and 20⁰,
  • quarter on if temperature is between 20⁰ and 25⁰
  • off if if temperature is above 25⁰

Servo Motor Characteristics

The period of the pulse used to conrol the servo motor should be 30ms

The mark should be

• 2ms for window closed
• 2.5ms for window quarter open
• 3ms for window half open

Temperature Characteristic

The temperature range is the ADCW reading times by 10, e.g 10⁰ will have a ADCW reading of 100, e.g 15⁰ will have a ADCW reading of 150 etc

ADC

The ADC should be set to 10 bits, and should run using ADC interrupts.

Inputs	Outputs
Temperature sensor ADC7	Servo Motor Timer1A (PB5)
Light Sensor ADC6	Heater Timer0A (PB7)