AVR® 8-Bit RISC - Applications - Remote Access Control

What is Remote Access Control?
Remote Access Control (also referred to as Remote Keyless Entry and Remote Wireless Entry) is remote control of applications like doors, alarms, blinds etc. The communication is usually done via radio and the transmission uses IDs and encryption to provide authentication and prevent unauthorized users from accessing the system.

A typical Remote Access Control (RAC) system consists of one receiver and one or more transmitters.

The transmitter is a small radio with one or more pushbuttons while the receiver is a control box also handling other parts of the application. A typical example is a garage door opener where the transmitter has a button to open and close the garage while the receiver also handles motor control and light in addition to the radio communication.

What are the challenges of a modern RAC design?
A RAC system often uses battery powered transmitters to control access to cars, garages etc. Thus the two most distinct challenges is often security and power consumption. A RAC system is pretty useless if it is easy to override, or need new batteries all the time. Security is achieved by encryption of both IDs and commands, and it is critical for the design that the encryption is sufficient. By using well known and proven secure encryption like the AES algorithm, running on a high performance, yet low power microcontroller, sufficient security can be achieved without compromising on power consumption.

While the transmitter in a RAC system often has a simple interface of one or more buttons, the receiver is a more complex application. A modern car alarm or garage door opener uses only one microcontroller for the whole application, thus more is required from the microcontroller than radio communication and encryption only. Remote access control, Motor control, light control as well as sensors and sirens must be handled by one microcontroller. By using an efficient and well equipped microcontroller with onboard EEPROM for encryption keys, functionality, flexibility, size and cost required for a successful design can be achieved.

Atmel - a complete RAC solution provider
Atmel provides a complete secure RAC solution using Atmel AVR microcontrollers, Atmel Smart RF radios, Atmel RAC development tool and RAC application note(s). The RAC application note(s) are available free of charge from Atmel. Application notes and development tools for unidirectional RAC is available now and bidirectional RAC will be available soon.

AVR Remote Access Control – Unidirectional Link
The unidirectional link uses the ATtiny45 microcontroller with the T5753 (315 MHz) or T5754 (434 MHz) RF transmitter and the ATmega88 microcontroller with the ATA5743 RF receiver. With AVR microcontrollers, the system provides superior performance and flexibility to meet the requirements for a modern RAC system. The RAC communication is only requiring parts of the AVR performance and a complete receiver application handling motor control, lights, relays etc. is easily achieved by only one AVR microcontroller.

Key features
- Operate in the license-free ISM (Industrial, Scientific, and Medical) frequency bands at 315 MHz and 434 MHz. The ISM band is available in most parts of the world.
- Transmitter IDs and encryption keys stored in receiver’s EEPROM makes it flexible and easy to maintain approved transmitter list
- Each RF transmission is unique and prevents message replay attacks
- Encrypted authentication for each message makes it virtually impossible to predict future messages
- Uses the AES (Rijndael) symmetric block cipher algorithm. AES is public domain – no licenses or patents
- Fully configurable message field lengths, cipher key strength etc.
- Quick response, typically 30 ms from button pressed
- Highly modular code makes it easy to use in existing applications
- Secure(AES encrypted) learning mechanism to assign new transmitters to a receiver
- Automotive qualified devices (microcontroller and radio)
- Low power consumption with average power consumption for transmitter less than 0.3µA

Document	Software	Description
		AVR411: Secure Rolling Code Algorithm for Wireless Link (22 pages, revision A, updated 04/06) - Firmware for transmitter using ATiny45 - Firmware for receiver using ATmega88 - AES encryption algorithms - Documentation and complete source code included - Firmware written for the ATAKSTK512 Smart RF starter kit

Development Tools
RAC dedicated tools: ATAKSTK512 Remote Access Control - Unidirectional Kit
This kit contains a functional standalone UHF radio system consisting of a Transmitter (ATtiny45 + T5753 or T5754) and Receiver (ATA5743), and Interface Board.

The Interface Board provides a quick, one-step programming tool to configure Atmel RF receivers OR doubles as an expansion card for the STK500 AVR starter kit (not included in kit) to allow development of software for receiver applications using any of the AVR microcontrollers supported by the STK500.

The STK512 Starter Kit is available in 2 different versions covering 315 MHz or 434 MHz as designated by the part number suffix –3 or -4 respectively.

Standard AVR tool used for RAC development
Standard AVR development tools are used for debugging, programming, code writing etc.

AVR Studio: one free front-end for all Atmel AVR tools, including free simulator and assembler.

JTAGICE mkII for OCD: one tool support On-Chip Debug on all new and most present devices.

Dedicated starter kit support: STK500 with top modules present starter kit for all AVRs
Broad C-compiler offering from third party vendors: from free GCC compilers to high end IAR Systems

Support
Technical questions can be sent to avr@atmel.com