This is a project I did a couple of years back for a business friend of mine to automatically log all his phone calls into his computer. The hardware (pictured above) uses an microprocessor to monitor the phone calls (incoming and outgoing) and send the data out the serial port to be read by the computer.
The hardware is controlled by an Atmel AVR ATmega32 microprocessor. The processor uses optoisolators to see if the phone is off-hook and to check if the incoming line is ringing. If the phone is off-hook a DTMF decoding chip CM8870CP is used to decode the number that is dialed. If it is an incoming call an FSK decoding chip XR2211 is used to decode the Caller ID data.
Phone Call Logging Project - [Link]
Atmel’s ATA874x single-chip UHF ASK/FSK RF transmitter family targets a broad range of proprietary wireless industrial and consumer applications such as metering, alarm systems and home control applications. This new AVR® product family offers RF performance operating in the license-free ISM frequency bands (868 to 928 MHz, 433 MHz, and 315 MHz).
AVR mcu with integrated RF transmitter functionality - [Link]
Low Power Radio Solutions announces new wireless modules from Circuit Design Inc., the leading producer of narrowband radio modules. The CDP-TX-02E-R and CDP-RX-02E-R radio modules are intended for use in wireless industrial products.
The CDP-TX-02E-R and CDP-RX-02E-R are housed in small, robust shielded cases and require only a small number of additional components to make a working radio system. Thy use narrow-band FSK modulation for high noise immunity, and the high-sensitivity receiver ensures stable operation even in weak signal fields. The modules achieve a line-of-sight communication distance of more than 600 m with only 10 mW power output. They also combine a very small footprint with HF characteristics that guarantee high reliability and resistance to mechanical vibration and shock. [via]
Narrowband radio modules span 600 m with 10 mW - [Link]
RFID cards are commonly used in many areas like access control, security, and for other identification purposes. One of simplest cards to read are HID ISOProx that don’t use any encryption. Their carrier frequency is 125 kHz.
Hardest part in this reader project is the reader itself as it has to power the tag with magnetic field and sense the transmitted signal. For this series resonance of 150 kHz circuit – antenna is used. Signal from antenna is passed through low pass and band pass circuits and then to PIC comparator, where RFID FSK pulses are detected and decoded. Latest ASM source can be seen here. Probably RFID reader could use more advanced microcontroller than PIC16F628A for more efficient signal reading by using interrupt based compare capture module as this one already uses it for 150 kHz carrier signal generation. [via]
RFID reader based on PIC microcontroller - [Link]