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 FM Receiver De-modulator PIC 16F628A 7-segment Driver

Car Unit Block Diagram AM Receiver PIC 16C56 Decoder Car Ignition Relay PIC 16F628A Temp. Sensor FSK Modulator FM Transmitter Voltage Sensor across car Battery

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 7- segment 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.

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. 16F628A Microcontroller

Temperature Sensor The digital temperature sensor used is a DS1624. The sensor reads in increments of 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 Micro- Controller. 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 Micro- Processor.

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?