MULTIPURPOSE DIGITAL CDMA FM

REMOTE CONTROLLER

FIRDOUS KAMALMIZAN MIAHEE – 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

+R

+

C

+

-

V+

V-

MAX427

VDD

CIRCUIT DESCRIPTION: TRANSMITTER

+

Rin220k

1

Q2Q2N2222

6

+

CX15pF

12

8

+R122k

13

+

C1330pF

RX10K

14

10

4

+

CVDD0.1uF

FSK out

Q1Q2N2222

11

15

VDD

3

VDD

2

+

Rout56k

Switching in

7

9 +

RC1k

FSK MODULATOR – VCO OSCILLATOR

NJM 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. Vout

f0 = 1 / (R0 C0)Operating f0 designed around 100kHz

Tracking bandwidth is given by:f / f0 = R0 / R1Designed for 10% bandwidth

CIRCUIT DESCRIPTION: RECEIVER

+

C10.1nF

RX10K

+

C0330pF

+

R022k

+

C11nF

1

2

3

+Rs470k

+RF100k

+Cin0.1uF

Switching out

+

CVDD0.1uF

+CGND0.1uF

FSK in

1

14

10

12

11

9

4 +R1220k

VDD

6

5

7 8

13

PLL FSK DEMODULATOR

VDD

+

R0

10k

Signal in

Signal out+

-

V+

V-

MAX427

+

C10.1n

+

R1

10k

+

C00.1n

2nd ORDER ACTIVE FILTER (LOW PASS)

Signal outR110K

+

-

V+

V-

MAX427

+RF4.7k

Signal inVDD

NON-INV AMPLIFIER (HIGH ZIN)

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.

7ms 5ms 6ms

2ms

Start Sequence Channel A - 011100

3ms 5ms

3ms

5ms 6ms

2ms 2ms 2ms

f1

f2 f2

f1 f1

TIME MANAGEMENTTasks February March April

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 ?