MULTIPURPOSE DIGITAL CDMA FM REMOTE CONTROLLER FIRDOUS KAMAL MIZAN MIAH EE – 513 4/19/2005 COMMUNICATION ELECTRONICS

OVERVIEW Project description - Goals and objectives Functional units - Transmitter and Receiver Circuit description - FSK: Modulation, Demodulation; Filters and Amplifiers DATA encoding - PIC 16F767 mcu data processing Time management and costs Performance

PROJECT DESCRIPTION House appliances such as heater, lights, oven, electrical outlets, security gates etc. do not have standard remote controllers. Common consumer remote controllers have distance and directional limitations. RF implementation is difficult due to noise issues and because RF bandwidth is expensive. Security issues and cross connection between users are other concerns. Our goal - hardware implementation of CDMA FM remote controller for household appliances.

OBJECTIVES One transmitter and two receiver units. Each receiver has one switch and two BCD digits. Inputs are entered using a (4x4) keypad. CDMA encoding is implemented for the two receivers. FSK transmission and reception of data – Pulse length variation for high and low bit. 8 – bit PIC16F767 microprocessor used for data encoding and decoding.

FUNCTIONAL UNITS

CIRCUIT DESCRIPTION: TRANSMITTER FSK MODULATOR – VCO OSCILLATORNJM 2211D – MONOLITHIC PLL CHIP The VCO unit of the PLL can be used to generate a square wave of a desired frequency. The lock detector filter is then internally grounded with ref. V out f 0 = 1 / (R 0 C 0 ) Operating f 0 designed around 100kHz Tracking bandwidth is given by:  f / f 0 = R0 / R1 Designed for 10% bandwidth

CIRCUIT DESCRIPTION: RECEIVER PLL FSK DEMODULATOR 2 nd ORDER ACTIVE FILTER (LOW PASS) NON-INV AMPLIFIER (HIGH Z IN ) RF and CF provides a low pass data filter network. C1 and R1 provides feedback and loop damping. For the low-pass filter: 3dB point = 1/ 2  RC = 160kHz Non-inverting amplifier provides high input impedance and a closed loop gain of around 2.

DATA ENCODING Pulse Width variation is used to determine a binary 1 or 0. Binary 1 is a high of 5ms followed by a low of 3ms. Binary 0 is a high of 3ms followed by a low of 3ms. Only 8 bits were retrieved by the receiver following the channel code. Thus if a bit was missed, the error could be corrected by implementing a code correcting algorithm. Furthermore, the data can be sent multiple times to reduce chances of error. 7ms5ms6ms 2ms Start Sequence Channel A ms5ms 3ms 5ms6ms 2ms f1f1 f2f2 f2f2 f1f1 f1f1

TIME MANAGEMENT TasksFebruaryMarchApril Research and Background Study Dividing Project into Modules Determine and Order Components Needed Perform Simulations Hardware Design and Constraints Design RF Transmitter and Receiver Program Microcontroller Output Configuration Testing Controller Documentation

Cost estimates Transmitter unit:$ 25 Receiver units:$ 20 each Total project cost:$ 85 including solder boards Hours spent:170 hrs (aprx) by each group member Estimated manufacturing cost for each unit with a 20 x 4 line LCD display will be under $10 if smt or soic components are used with blow soldering on pre-printed circuit boards. Sold for $25 will beat any commercially available unit currently on the market by more than $30 accounting for design costs by engineers. We have assumed around 10,000 units for mass production. PROJECT COST

PERFORMANCE All of our units were tested and demonstrated functional within the allocated time period. We have constructed and implemented our own FSK receiver and transmitter and completed the system integration by the project demonstration date. The units are powered by 9V batteries. Wireless transmission is achieved for a distance of 10cm. During testing we successfully transmitted a distance of 20mm through a partex board. On a testing trial of 50 times no errors (cross connection) between the two receiving units are observed. The total project cost is within the proposed budget.

FURTHER IMPROVEMENTS We down-shifted our carrier frequency from about a MHz to 100kHz to implement a frequency upconverter. The 1MHz FSK generator implemented with a 555 timer was tested functional. However, most high frequency components are surface mount and lacking the facilities and time, we were unable to utilize a better frequency range. As further improvements, a higher frequency carrier will improve range (up to 50 yards with at 100MHz) with no significant increase in power. Multiple users (receiver units) can be implemented to the current system by simply changing the channel code for each unit for the PIC mcu. Some error bits were noticed during testing (within the same channel). This can be corrected by implementing Hamming or similar error detection/correction procedures.

QUESTIONS & COMMENTS ?