Though the fundamental operating model of all automobiles have not changed to major degrees, the accessories incorporated have definitely seen huge technological advancements, especially the electronic commodities which today have become a part of all vehicle interiors.
As an example, we can see that today's cars are going keyless and are being replaced by sophisticated remote controlled devices which not only ensure easy operations of the various vehicle locking features through casual “clicks" of a handset control system, but also provides complete foolproof security to it by entire ignition disablement functions, whenever desired, again through a mere press of a button.
However, these devices are included under luxury items and therefore are never cheap. In India a remote controlled car immobilizer circuit may cost you as high as Rs. 2000 (around $40) with installations charges that may snatch another 500 bucks from your pockets.
With the development of new ICs and chips, today electronics has become much smarter and easier, as now even the most complex circuits do not ask for a high number of discrete components, rather the assemblies are concluded by fixing just a few chips and a couple of other associated passive integrations.
If we take the example of the present discussion, a car security system operating with RF signals can be easily made just by assembling a couple of chips and transistors.
If you are an electronic enthusiast and own an unequipped car, you would certainly love building and installing this project at a cost that might be far less than 50% of the market value. You can even think a step further and go for an all out manufacturing plant of it, if the conditions favor you.
The present article is all about making a simple RF remote controlled car immobilizer cum central locker circuit. The entire procedure is explained through neat schematics.
Let’s try to understand the circuit operating principle of the unit.
The proposed idea is specified with the following two main operations:
- Central Locking
- Ignition Locking
What’s Central Locking and Ignition Locking in Cars
Before we understand the actual circuit operations, it would be first interesting to know how central lock devices installed in car doors work.
The diagram shows a typical central lock instrument which are normally fitted in each door of a car and is responsible for the required security actions in response to the applied electrical signals.
The shaft at the front “shoots" in a to and fro motion, in response to every subsequent electrical impulse which must be reversed after each trigger.
The shaft may be attached with the preceding mechanism for the desired locking and unlocking conversions.
An internal scan (if you open its cover) shows that the “solenoid" action of the device is actually implemented using an ordinary motor that’s integrated with the shaft through gears.
Thus when the motor is powered through external triggers, it goes through subsequent clockwise and anticlockwise reciprocating movements, initiating the resultant “solenoid" action in the shaft. However, the external applied pulses must be momentary and not continuous voltages, which may result in heating of the motor and permanent damage.
The two wire connections coming out from each central lock motor installed in each door of the car are made parallel and are commonly terminated to the electrical network, so that all the doors can be locked or unlocked simultaneously through the applied trigger pulses.
Vehicle ignition system primarily is all about igniting the fuel mixture inside the combustion chamber for initiating and sustaining the required piston operations which ultimately drives the vehicle wheels.
Ignition processes are always constituted through high voltage arcing without which they can never be initiated, resulting in a complete “paralysis" of the vehicles.
This implies that if by some means the arcing process is inhibited, this can well keep the vehicle immobilized – that’s exactly what’s targeted through the present idea for keeping the vehicle armed until the owner wishes to disarm it.
The security system basically comprises a data transmitter and receiver circuits, through which the required signal exchanges are transacted wirelessly for implementing the tasks discussed in the previous section.
Referring to the diagram, we can see two configurations, one is the transmitter section and the other one is the receiver block.
The ICs always come in paired packages and must not be procured isolated as the the pairs are compatible only to each other. For further information please read its datasheet.
The use of high tech chips has made the operations rather straightforward and may be understood with the following points:
IC TWS 434 is basically responsible for “manufacturing" un-modulated RF signals, however these signals do not carry any information and therefore are useless; IC HT-12E renders it with the required data and modulates it so that it may be transmitted into the atmosphere with the encoded data. IC HT-12E is equipped with four discrete data input feature, which enables the transmitter to send four distinct numbers of commands which do not interfere with each other.
In the receiver section IC RWS 434 is responsible for “plucking" or capturing the tuned signals from the above system, again this chip cannot read what’s encrypted inside the signals and therefore passes it to the next decoding section comprising IC HT-12D, where the data is retrieved systematically, decoded and converted into external logic pulses which is interpreted into the necessary actions like ignition and central locking/unlocking etc.
Since the incorporated ICs are highly sophisticated are vulnerable to static electricity and must be handled only after wearing ESD gloves.
Also the entire assembly must be done over a well designed PCB using a temperature controlled soldering iron.
Once the assembly is completed, the whole circuit of this car immobilizer can be fixed inside a suitable ABS plastic enclosure with the necessary wire outlets for the specified integrations.
The installation procedure inside the car as per the specified wiring instructions in the article must be completed only under the guidance of an experienced car electrician.
Circuit Analysis and Explanation – By Swagatam.