Download 2 Way FM Car Starter (TA: Saurav K

2 Way FM Car Starter
Dan Owens
April 12, 2005
Instructor: Dr. Pao-Lo Liu
Department of Electrical Engineering
University at Buffalo
Course Requirement for EE 413/513
Communication Electronics
OUTLINE
Introduction
Block Diagram
Procedure
AM Transmission
Micro-Controller
Temperature Sensor
FM Transmission
FM Receiver
7-Segment Driver
INTRODUCTION
 The Goal of this project is to design a car starter
with 2 way communication.
 Original concept included only FM transmission.
 Discovery of rolling code security through AM
transmission.
 key ring transmitter is pressed, AM Transmission
gets Decoded and the Micro-Controller takes
necessary action.
 Micro-Controller sends requested information
back to key ring.
INTRODUCTION
 key ring receives and decodes tranmission,
Micro-Controller processes signal, and displays
proper information.
key ring Transmitter Block Diagram
User Buttons/
LED’s &
7-segment
Display
PIC 12C508
Encoder
AM
Transmission
7-segment
Driver
PIC
16F628A
De-modulator
FM
Receiver
Car Unit Block Diagram
AM
Receiver
PIC
16C56
Decoder
Car
Ignition
Relay
FSK
Modulator
PIC
16F628A
Temp.
Sensor
FM
Transmitter
Voltage
Sensor
across car
Battery
PROCEDURE
 Start researching FM and AM transmitters and receivers.
 Order Pre-Programmed AM transmission IC chips.
 Design and construct FM transmitter circuit modulated
with a square wave.
 Design and construct FM receiver to retrieve the
information from the transmitted signal.
 Design and construct a FSK Modulator and Demodulator
for converting the digital signal to an analog signal.
 Write Program for the Serial communication between the
16F628A Micro-Controller and the Temperature Sensor
PROCEDURE
 Write program for key ring PIC 16F628A to receive
demodded signal and light proper LED or number on 7segment display
 Introduce a seven-segment LED driver that accepts the
binary value from Micro-Controller.
AM Transmission Circuit
 Research revealed original concept of FM
transmission was not secure.
 Found Preprogrammed 4 button Key ring
transmitter and receiver/decoder IC combo.
 Combo is programmed together with a secure
encoding/ decoding system called rolling or
“hopping” code.
 Single password systems are unsafe do to “code
grabbing” technology.
 Rolling code changes the password with each
press of the button.
16F628A Microcontroller
 Receives High signal from AM receiver circuit or Voltage
sensor.
 Depending upon witch I/O port goes high, the PIC:
 Sends “Light LED” code to Key ring
or
 Calls for temperature from temperature sensor, encodes the
information, and than sends it to the Key ring
 Programming the PIC must be done before any of this
happens.
 The information being sent back to the Key ring is sent
by simple FM circuit since no need for security.
Temperature Sensor
The digital temperature sensor used is a
DS1624.
The sensor reads in increments of
0.03125 degrees Celsius.
The sensor communicates with the PIC
through a two wire serial connection and
transfers the temperature in 13 bit word.
DS1624
Pin 7 an 8 (RX & TX) of the PIC become the serial lines
FM Transmission
A Digital Signal is received from the MicroController.
The Signal is digitally Modulated using a
FSK (Frequency Shift Key) modulator.
The now analog signal is then put through
the FM transmitter.
The FM Transmitter Modulates the digitally
modulated signal to a carrier frequency of
87.9 MHz and transmitted.
FSK Modulation
FM Transmitter Circuit
FM Receiver
 The FM Receiver tuned to 87.9 MHz picks up
the signal and demods it from the carrier
frequency.
 The design is a simple one transistor FM
receiver.
 Due to the complications in receiving the signal,
I ended up using a self modified, low cost,
handheld radio to pick up the signal.\
 The signal Is then digitally Demodulated using
the FSK demod IC and then fed to the MicroProcessor.
Key Ring PIC 16F628A
 The Micro-Controller receives the Demodulated signal.
 Depending upon the 8 bit word either lights an LED or
sends the word to a BCD to seven segment display
driver.
Questions?