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Maxim > Design Support > Technical Documents > Application Notes > Automotive > APP 5291
Maxim > Design Support > Technical Documents > Application Notes > Wireless and RF > APP 5291
Keywords: automotive, car, antitheft, ISM, wireless, transmitter, receiver, RSSI, ASK transmitter, ISM
band
APPLICATION NOTE 5291
ASK Transmitter/Receiver Pair Serves as an
Automotive Antitheft Alert System
By: Tom Au-Yeung, Director of Customer Applications
Wilson Tang, Member of Technical Staff
Apr 03, 2012
Abstract: After you park your car and go into your house, probably the last thing that you want to think
about is someone stealing your vehicle. This design idea presents a simple circuit that consists of a
transmitter/receiver pair and functions as an automobile antitheft alert system.
A similar version of this article appeared in the March 8, 2012 issue
of EE Times magazine.
This simple circuit consists of a transmitter/receiver pair and
functions as an automobile antitheft alert system. The premise for
the design is straightforward. You place the transmitter in a vehicle
parked outside your home and leave the receiver in your house.
When the vehicle leaves the area, this circuit sounds an alarm
because the distance between the transmitter and receiver
increases and the received power level falls below a predetermined
level (threshold). The circuit is, in effect, warning of a potential auto theft. This circuit can also be applied
to other applications for security purposes, such as securing USB flash drives or monitoring a child's
presence.
Figure 1 shows the ASK transmitter system with a carrier frequency of 315MHz. IC1 is the ICM7555, a
555-based timer that provides a bilevel oscillation signal. IC2, the MAX1472 ASK transmitter, has an
adjustable output power level of up to +10dBm. This circuit is placed in the owner's car.
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