RF Remote Control

1. RF Remote Control Sham Bhat Piotr Lupa Senior Design Laboratory July 30, 1999

2. Motivation for our Project • Why a remote control thermostat? • Part of the House of the Future • Ability to control house temperature from your bed at 2 A.M • Impress your guests

3. Overview • Design Considerations • Parts/Components • Transmitter and receiver • User Interface • Additional Logic • Shortcomings and possible improvements • Cost Analysis

4. Design Issues • Achieving the simplicity of design • Software vs. hardware • Choice of transmission scheme • Number of bits to be transmitted at a time • Number of decoders used • What temperature range should be allowed? • Feedback to user

5. Transmitter and Receiver • Used transmitter/receiver chips from LINX Technologies • 315 MHz frequency • Attached to antenna through 50 Ohm coaxial cable • Chosen for good transmission over fair distances and ease to use • Transmits serial data

6. Encoder/Decoders • Used Motorola MC14502 series • Allows for conversion from serial to binary data and vice-versa • Includes five address bits and four data bits • Allows for simple error check, bits are sent twice. • Connects directly to and from T/R pair

7. User Interface: Input • Input consists of keypad, push two buttons for temperature • Does not allow for temperatures less than 40 degrees or greater than 99 • Red LED lights up if user intends to enter “out of range” temperature • Green LED lights up if user enters temperature in range

8. User Interface: Output • Seven segment display • Allows display of actual temperature • Driven by display driver which converts binary data into data displayable by 7 segment display • Must be connected to resistors to avoid burnout

9. Additional Logic • Keypad Encoder • Keypad outputs shorted when button is pressed • Keypad encoder converts keypad number into binary representation. • Transmitter Logic • Keeps track of the order of the numbers pressed by user • Logic to alert user for “out of range” temperature

10. Additional Logic cont’d • Use of two decoders • Allows for tens and ones digits to be separated • Last address line differs between the two decoders • Display Drivers • Converts bits from binary to bits in segment notation

11. Shortcomings and Problems • Lack of available parts • Hardware difficult to debug • Combination of wiring mistakes and bad equipment. • Many parts getting burned out • Too much current being drawn from chips/displays • Solved by adding resistors/capacitors

12. Improvements • Possible to remotely control other home devices • Examples include doorbell, lights, window curtains • Two way communication • Feedback to user from the receiver end

13. Cost Analysis • Keypad $ 5 • Encoder/Decoders $ 20 • Keypad Encoder $ 5 • Transmitter/Receiver $ 6 • Seven segment displays/LED's $ 10 • Other Logic Chips $ 20 • Circuit Boards $ 30 • Wires/Resistors/Capacitors $ 15 • Other Costs(Parts) $ 20 • Total $ 131

14. What We Learned • Challenge of completing a project from scratch • Researching part descriptions • “Continuously” making changes • Gained practical experience • Ideal vs reality • Implementation of a project in hardware • Improving logic design skills

15. What We Learned cont’d • First Non-structured class • Documenting work and preparing a presentation

16. Any Questions? Thank you for attending!