RF PC Light Control

1. RF PC Light Control Vladimir Peck Todd Wilson

2. Introduction Living in an age where almost every homeowner has a desktop PC, the computer is being used for daily tasks more now than ever before. The computer offers flexibility to perform many tasks. Now, using RF PC Light Control, the public can use desktop PCs to control the lights in their houses.

3. Objective • To design and implement a wireless system which uses a personal computer to control the lighting in a house or apartment

4. Original Design • Controlled only one light • We initially were going to develop our own transmitter/receiver • Original design also included a software timer function for the lights

5. Final Design • Controls up to 15 lights • Uses Linx transmitter and receiver modules • Uses much more receiver-side logic than original design (for decoding)

6. Final Design: Block Diagram

7. PC Application Goals • Needed to send pulses from the serial port • Needed the number of pulses sent to be equal to the light identification number • Needed to be easy to use • Needed to be available on a widely used platform

8. PC Application Implementation • Used Visual Basic 6.0 • For each pulse, used character of 240 in decimal because it translates to 11110000 in binary (50% duty cycle) • Could use any transmission speed as long as it was not greater than 5000 bytes/second (4800 bps seemed to work best…19200 also worked well)

9. Application Screen Shots

10. Transmitter-side Logic Goals • Needed to convert RS-232 signal to TTL signal • Needed to change -12V(RS-232 high) to 5V(TTL high) and 12V(RS-232 low) to 0V(TTL low)

11. Transmitter-side Logic Implementation • Used MC1489 converter to scale the RS-232 voltages to TTL voltages • Used inverter to change RS-232 logic states to TTL logic states

12. Receiver-side Logic Goals • Needed to count number of pulses received in a certain amount of time • Needed to compare number of pulses received to dip switch settings • Needed to emit a pulse to the power switch if those were equal

13. Receiver-side Logic Implementation • Used a 2 MHz clock/14-bit counter/4-bit counter to bring clock frequency down to 15 Hz (this created a 1/15 second window to receive pulses) • The first pulse received started the timer • While the timer is going, pulses are counted

14. Receiver-side Logic Implementation Cont’d • When timer runs out, a compare is enabled • If pulses received is equal to the dip switch value, a pulse is emitted to the power switch • All counters are cleared

15. Power Switch Goals • Needed to use a TTL signal to operate a 120VAC lamp • Wanted to protect receiver-side logic from AC power

16. Power Switch Implementation • Used J/K flip flop to take on/off signal from receiver-side logic • Used J/K output to control optical triac driver • Used optical triac driver to control triac • Used triac to turn light on and off

17. Project Build • Built and tested each module individually • After debugging each individual module, each interface was established and tested before another interface was added • Final debugging was done with all interfaces in tact

18. Functional Tests Performed • Software reliability • Transmission reliability • Decoding reliability • Triac maximum power

19. Functional Test Results • Software reliability • Never crashed through all uses of software on Windows 98 platform • Transmission reliability • Number of pulses requested through software was always equal to number of pulses outputted from serial port

20. Functional Test Results Cont’d • Decoding Reliability • Out of 100 transmissions, 99 were received and counted correctly • One was received correctly, but counted as one less than it actually was

21. Functional Test Results Cont’d • Triac maximum power control • Triac is rated at 4A@200V (800W) w/ peak surge current of 30A@200V • Tested triac with 4 100W lamps connected through a power strip with no problems • 800W should be enough for almost any single lighting ensemble

22. Challenges • Learning Visual Basic • Finding a part or circuit to convert RS-232 to TTL • Finding a way to turn on more than one light • Finding a way to use TTL to control a 120VAC device

23. Problems • Timing issues • Making sure counters was resetting at the correct times • Making sure clock edge was sharp enough to count correctly • Transmitted pulses act as clock edges for one counter • Faulty clock for demo

24. Development Costs • Labor • $15,000 (using $/hr x 2.5 x hours spent x 2) • Development Tools • Free of charge (used lab equipment) • Parts • Transmitter Parts = $7.81 • Receiver Parts = $17.46

25. Product Cost • Transmitter • $7.81(transmitter parts) + $3(housing) + $8(AC adapter) = approximately $20 • Receiver • $17.46(receiver parts) + $6(AC adapter w/o housing) + $3(housing) = approximately $27 • Software • Downloadable free of charge w/ purchase of transmitter

26. Recommendations • Have separate signals to turn lights either on or off instead of a toggle • Have software keep track of the state of each light and write that information to a file • Reasonably small package instead of protoboard (4” x 3” x 3”)

27. Recommendations Cont’d • Instead of using many different chips at the receiver end, manufacture all logic on one chip to reduce costs • Package transmitter-side logic and Linx transmitter into a serial connector (which includes input for 5VDC from wall adapter)

28. Conclusion • Currently the cost of the product is too high to be marketable • If recommendations mentioned are met, then the product would be more marketable

29. GROUP 35 T.A. Lee Rumsey Vladimir Peck Todd Wilson