Edited by Leland Teschler
This makes them candidates for use where
power comes from batteries. One chip in
this category is the TI CC1000 which works
in the UHF range. It is often powered from a
3-V coin cell and uses less than 10 mA in receive
mode. Current consumption in transmit
mode depends on output power but is
less than 30 mA at 10 dBm. Typical applications
include home automation, wireless
security systems, meter reading, and toys.
The CC1000 is generally intended for use
over short ranges. It operates at 315, 433,
868, and 915 MHz but can be programmed
in steps of 250 Hz for operation at other frequencies
in the UHF range.
The chip operates as a conventional heterodyne
receiver. The RF input is converted
to an intermediate frequency, then gets filtered
and fed to a frequency shift-key demodulator.
Demodulated data is available
on pin DIO, a synchronized data clock signal
at DCLK.
Values for the antenna matching network
components C41, L41, and C42 shown here
are for operation at 315 MHz using a quarter-
wave whip antenna. Of course, antenna VSWR will affect these values, and they
must be recalculated when using the chip to
transmit and receive at other frequencies.
A voltage-controlled oscillator on the
chip uses an external inductor L101 to set
its frequency. Its PCB layout should be close
to pins L1 and L2 and symmetrical to minimize
affects of stray fields and component
variations.
The digital bit stream on DIO controls the
frequency shift-keyed output. In this case
a PIC16F62X processor generates the bit
stream and reads the demodulated output
through one of its bidirectional I/O ports.
Similarly, it handles chip configuration
through a three-wire digital serial interface
on PCLK, PDATA, and PALE pins.
This particular circuit
was battery powered. Circuits
powered from an ac
supply should incorporate
filtering and decoupling
to avoid problems
from harmonics fed in
through the supply.
Douglas Bahniuk
Adelsys Inc.
Cleveland Heights, Ohio.