Air Conditioner Control Unit

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Air Conditioner Control Unit

• ECE 345 Senior Design
• Kseniya Britton
• TA Purvesh Thakker
• University of Illinois at Urbana-Champaign
• Spring 2003

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Presentation Overview

• Motivation and Objectives
• Original Design Review
• Final Design and Functional Testing
• Combined Module Testing
• Successes and Challenges
• Cost Analysis
• Future Enhancements
• Conclusion

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Motivation

• The motivation for this design project was to
  create a logical control for wall or window air
  conditioner units. This design could be used in
  building a device that would be an external
  thermostat for a manually controlled air
  conditioner.

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Objectives

• Benefits
• Automated control versus manual control
• Saves energy
• Economically efficient
• Features
• User-friendly interface
• Can be used as a thermometer
• Insensitive to minor temperature fluctuations
• Compact design software versus hardware

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Original Design Review
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Original Design Review

• Power Converter
• The component receives 120 or 220 AC volt signal
  from a wall outlet. Converts AC signal to stable
  DC voltage used to power digital circuitry.
• Digital Circuitry
• This component is the brain of the system. It
  receives inputs from the keypad and the sensor
  circuit and makes a decision whether to turn on
  or off an air conditioner. Output is provided at
  LCD.
• Switch
• Digital circuitry controls whether the switch
  passes AC current to an air conditioner.

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Original Plan

• Design of temperature sensor differential
  amplifier circuit
• Design of AC/DC power converter circuit
• Program BX-24 microcontroller to substitute
  digital circuit module
• Integrate all the modules into a working project
• Package

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Final Design
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Temperature Sensor MTS 102

• VBE(T) 0.595 - 0.002265(T - 25), Temperature
  in ºC
• R1 44kO, RMTS102 6kO gt IC 0.1 mA

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Differential Amplifier Circuit

• Vout -(R2/R1)(V2 V1), Gain R2/R1 22
• Gain was determined based on 0V lt Vout lt 5V for
  A/D
• input of BX-24

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Test of Differential Amplifier

• Deviation from theoretical curves is due to the
  error in Rs
• Sensor_Temperature (21.84 Vout 2) for AC
  Control task

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Keypad Circuit Design

• BitX CInt(GetPin())
• Value Bit38 Bit24 Bit12 Bit0
• DA determines when Value is ready for reading and
  when a key is released

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Error Checking and Debouncing

• User enters the desired temperature, followed by
  the key
• Numbers lt 50ºF or gt 90ºF are not allowed gt error
  message Too Low/Hi and previous value
• Keys A, B, C, D are not allowed
• gt error message Bad Char and previous value
• Capacitor 1µF is inserted into Keybounce Mask
• Testing was done by correcting error checking
  lines to make the interface more user-friendly

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LCD to BX-24

• Uses
• - LCD2x16API.bas
• - LCDSerialPort.bas
• Displays
• - Ambient temperature
• - User keypad input
• - Error alert
• - Message explaining error

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LCD Testing

• The program using a separate LCDTask never worked
• The most obvious explanation was that the LCD and
  serial communications with the computer both used
  COM1
• Changing LCD output to Com2 did not fix the
  problem
• SOLUTION Since LCD collects and outputs all the
  variables from other tasks, it was better to move
  LCD code into Main. Correct temperature, keypad
  entry, and error messages were displayed

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Air Conditioner Control
OFF
ON
Low Temp
High Temp
TK
TK 2
TK 2
(TS TK 2) AND (TSL TK 2)
(TS TK 2) AND (TSL TK 2)
NO CHANGE

• Read only every 60 seconds
• If (TS TK 2) AND (TSL TK 2) Then
• Call PutPin(OutputPin, 1)
• ElseIf (TS TK 2) AND (TSL TK 2) Then
• Call PutPin(OutputPin, 0)

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Air Conditioner Control Testing

• TK temperature entered with the keypad (in ºF)
• TS temperature read by the sensor (in ºF)
• TLS temp. read by the sensor 120 sec ago (in
  ºF)
• Test 1
• TK 75, TS 77, TSL 76 gt OutputPin 0
• Test 2
• TK 75, TS 78, TSL 77 gt OutputPin 1
• Test 3
• TK 75, TS 73, TSL 78 gt OutputPin 1
• Test 4
• TK 75, TS 72, TSL 73 gt OutputPin 0

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Combined Module Debugging

• During Mock-up Demo all 3 individual tasks were
  demonstrated separately and worked
• LCD task was moved to Main()
• The problem was integrating all the individual
  tasks to run together
• The main problem arose when trying to integrate
  GetSensor and GetKeypad tasks
• Two tasks worked individually however, when
  GetKeypad was introduced, the program failed

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Solutions

• Introduced Semaphores
• Difficult to implement
• Introduced Queues
• Advantages
• Easy to implement
• Ideal for transmitting data between tasks
  (unbreakable)
• Several Queues could be use for different tasks

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Final Result

• During the Demonstration Review my project worked
  and performed as expected
• Final Solutions
• Used Queues to manage data between tasks
• Due to unknown data sharing problem in
  multitasking GetSensor and GetKeypad tasks never
  worked together
• GetSensor task had to be moved to Main. This did
  not interrupt the design logic
• Queues were managed by checking StatusQueue

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Successes

• Designed a differential amplifier circuit that
  had a linear output that differed from the
  theoretical output only by the error in resistors
• Created a modular design and successfully
  integrated all four modules
• Solved a problem with multitasking using Queues
  and moving two tasks inside the Main
• Demonstrated that the design performed as expected

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Challenges

• Output of the differential circuit was too noisy
• Choice of an operational amplifier
• Debugging was difficult because it was impossible
  to output to the screen due to multitasking.
  Output was sent directly to LCD
• Integrating the four modules
• Data sharing problem with multitasking
• Communicating to the my partner

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Cost Analysis
Estimated Actual
Labor 2.5 40/hr 120 hrs 12,000 Parts Keypad/LED 15.00 Temp Sensor 2.00 Protoboard 15.00 Misc. Chips 20.00 Total ..................52.00 Labor 2.5 40/hr 150 hrs 15,000 Parts Keypad/LCD 52.82 Temp Sensor 0.50 Protoboard 15.00 Misc. Chips 13.00BasicX Chip 49.95 Total ....................131.27
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Future Enhancements

• Design AC/DC power converter and add a switch for
  a complete design of Air Conditioner Control
  Device
• Package to make the device marketable
• Revise optimization of cost and area, i.e.
  possibly use digital components instead of
  BasicX-24 chip
• Use more sophisticated temperature sensor
• Adapt the device for users of temperature in ºC
• Add programmable interface

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Conclusion

• Things I have learned in ECE345
• Creative thinking for design ideas
• Programming a microcontroller
• Testing to analyze the performance
• Debugging
• Creating new solutions
• Modular design is the key!!!

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Questions?