RKE is a short abbreviation of Remote Keyless Entry. I was inspired by the RF microcontrollers from freescale semiconductors. It had an RF transmitter and receiver block for establishing RF communication. I thought of trying my hands at these little wonders and came up with this simple project. The devices are capable of transmitting and receiving data at any ISM carrier frequency - 315, 434, 928 MHz. The aim of the project is to show a demonstration of the RF capability of these microcontrollers. 

I got hold of the reference designs from freescale and started modifying it my way. Here is a block diagram of my design. 

The transmitter uses HC908RF2 microcontroller from freescale and runs out of a single CR2032 button cell. The picture below show the transmitter hardware that I made. Note that the CR2032 battery holder is not soldered in that picture. The antenna is a modified loop antenna and could be tuned to any of the ISM band frequencies (315,434,928 MHz) 

The receiver uses MC33591 chip for the RF processing and connects to a controller board through SPI interface. Below is the picture of receiver. Note that the antenna is a simple PCB serpentine with no particular design consideration. The RX chip draws power from the controller board.

Below is the picture of the Receiver controller board that controls the receiver chip (MC33591). The controller board uses MC68HC908GP32 microcontroller from freescale. I love this controller as it has a bulk load of capabilities and best of all its easy to program. The controller board uses its own power and it serves as a bridge between the PC and the receiver. You can set/reset the receiver parameters from the PC using hyperterminal software. Further, the controller board has an LCD which displays the status and the active parameters in use.

I do not have the firmware for the boards as it was accidentally lost in my last computer crash. The complete schematics and the layout files for the hardware is available though. May be sometime later, I should re-write the firmware from the scratch.. Darn!!

Download the complete schematics and layout of my design