Car Immobiliser GCSE Project. Adam J Sher. Contents. Electronic Idea Generation Electronic Idea Analysis Electronic Development / Diary Electronic Idea Testing Final Electronic Decisions Final Prototyping Product Idea Generation Product Idea Analysis Product Development / Diary
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Adam J Sher
A major car manufacturer would like a new, state of the art security system for their new design that will incorporate key-less technology.
This is because research has shown that car immobilisers are most often compromised when the user’s car keys are stolen.
I am going to manufacture a car immobiliser that utilises an electronic combination lock for the Fiat Stilo that is easy to use and that looks good.
Upon entering the vehicle, the user is going to enter an access code and press enter. The control process of the immobiliser will then determine whether the correct code has been entered, and if so then the starter motor of the car will kick in, but if the incorrect code is entered, then because the wire has been cut between the started motor and the Solenoid Switch, the starter motor will not start, and therefore the car cannot move.
It will be a simple case of entering the combination and pressing the enter key that will disable the immobiliser, because if it were any more complicated it would put off some of the potential customers.
Environmental and Costing
The immobiliser will be situated somewhere on the dashboard, so the product must be the same colour as the car interior in order to blend in and look good.
For the same reason, there cannot be lots of wires trailing from the keypad, as this would compromise the aesthetics of the dashboard.
The cost of a security product is directly proportional to the security that it offers. This will be a high quality automobile immobiliser, and could therefore cost anything up to £500. I estimate that the cost of production of a single unit to be about £30 for the prototype. The final version would obviously cost more because it would have to be tamper-proof and made to a better quality.
A systems diagram allows us to display ideas for different components in the car immobiliser in an easy-to-read and aesthetically pleasing way. There are three blocks: input, process, (2nd process) and output. This is known as an “open loop system” as there is no feedback block.
Below are some examples of what could be used in each block.
There were a number of inputs that I could have used for this project. Here I have listed them and the reasons why they may or may not be suitable.
Fingerprint Scanner – the user would place their thumb over the scanner, which would then read the digital signature of that thumb print and send that data to the process stage, where the system would decide whether to grant access to this user.
There are some problems with this idea. Firstly, these units are very expensive (£99.99 each) which would increase the price of the final product. And secondly, the process stage involved with such an input would be very difficult to program, and too expensive to purchase. I have therefore decided not to use this input.
Microphone – the user could speak into the microphone, which would convert his voice to a digital signal and send it to the process. The process would then decide whether or not to allow the user access to the car.
The problems with such a device are that, although it can be easily concealed, a good quality microphone would be expensive and the process stage involved would be incredibly difficult to integrate. I have therefore decided not to use this input.
Iris Scanner – the user would look into the device, which would then proceed to scan their iris and send the information to the process stage. The main problems with this input are also cost (more than £100 per unit), and the immense difficulty of integrating something with this device that is not a computer.
Keypad – the user would enter either his/her own combination or the unique combination supplied to them upon purchase of this unit, the process stage would then decide whether the code entered was correct or not, and act accordingly.
These devices are cheap (£2.99 each), and it is easy to interface with the process stage using either a PIC, logic or even comparators. This would make the keypad a suitable input for my system, and is the input that I intend to use.
For the processes I have done the same as the inputs. I have listed all the possibilities and then explained whether or not they are suitable and why.
Logic – I could use a series of logic gates as the process. These would only supply power to the output if the correct code was entered. The benefits of logic include that I would be able to use a computer program such as Crocodile Clips to simulate logic gates until I had perfected my program. The disadvantages are that more chips would be required which means that the PCB would have to be larger, and that it would not be as secure as using a PIC. (The combination could be found if someone got hold of the schematics, whereas someone would need the actual PIC programme to find the code.
Operational Amplifiers / Logic Gate – I could theoretically use a series of OP-AMPs instead of logic or a PIC. This would include comparing each input to whether it should be on or off. If all the correct buttons are pressed, then the OP-AMPs would all supply current to the next part of the circuit, which could be a simple logic system that gives power to the output.
The problem with this idea is that it would be difficult to program the combination lock to be as secure as it would with a PIC, or with logic gates.
4511 BCD to 7-segment decoder – I would use this in conjunction with a 7-segment display to show the user the key that he is pressing.
I’m not going to need this chip though because I won’t be using a 7-segment display. Please see the output section for the reasons.
Automotive Heavy Duty Relay – This is technically not a process on its own, but I am classing it as a process because I will be using it in conjunction with a PIC. It is basically a switch that uses a power supply to determine whether it should be on or off. If the correct code is keyed into the keypad, then power is allowed to flow through the relay, this in turn allows power to the start motor that allows the car to start.
This is a very useful process to have because this component is built specifically for this kind of purpose and many existing products on the market use these.
The downsides are the cost (£1.49 each) but the advantages easily outweigh the disadvantages on using such a device.
PIC- A PIC is a micro-controller and is very easy to integrate into a circuit. It would be able to decide whether to grant the user access to the car in a fraction of a second. The downside of PICs is that they are relatively expensive (£2 each) and that the programming has to be done on a computer and downloaded onto the PIC via a PIC programmer, which means that if there is a bug in the program, the program has to be edited and reloaded onto the PIC.
For these reasons, I have decided to use a PIC in my system.
The output of the system is possibly the most crucial part because it either allows the user access to the car or it blocks the user’s access to the car.
There are several possible outputs, but one essential output which is the engine cut out.
I am going to break the wire in the starter motor which will stop the motor from starting, and therefore stop the car moving.
My circuit will cut the wire here, which will disable the motor unless the immobiliser code is entered.
Bulb – I could use a bulb in a similar way as an L.E.D. They are easy to install into the circuit and they are easy to see, even in daylight. There is little point however because bulbs cost 50p each, so for every bulb I buy I could buy five L.E.D.s.
Buzzer – Instead of a visual output, I could use an audible one. If the correct code is entered then the buzzer could beep once, and if the incorrect code was entered then the buzzer could beep twice. Buzzers are relatively expensive at £1.99 each and can also sound quite annoying after a while, so I probably won’t use one for my final project.
7-segment display – A seven segment display could display the number that the user has just pressed, allowing the user to see the number on the screen, and realise if he has made a mistake.
7-segment displays are cheap (79p each) but require an extra process which is the decoder that would have to be connected to the PIC.
I probably won’t use one of these because a passer-by could see the user inputting the code, steal his/her keys and come back later and steal the car.
L.E.D. – I could use two L.E.D.s, one green, one red. If the correct code was entered then the green L.E.D. would show and it would be possible to drive the car away, if the incorrect code was entered then the red L.E.D. would show and the car would be unable to start.
The benefits of L.E.D.s are that they are very cheap (10p each) and are easy to connect in a circuit.
If we put all the inputs, processes and outputs into a table we can see that they could make a total of 96 circuits. We obviously only want to make one circuit, so I will now remove all the inputs, processes and outputs that are impractical or too expensive.
I have now managed to take the number of circuits down from 96 to 9. Simply by removing the inappropriate system blocks, but we still want to try and get down to one final circuit. This can be done by eliminating the blocks that I feel would be too time consuming to integrate or ones aren’t as useful as other components.
I finally have one circuit, which will be the circuit I will use for this project. If I were to now put these into the systems diagram they would look like this:
In this section of the research, I will show some existing products and analyse their features, as well as pointing out the differences between my design and the already existing product.
GT Auto Alarm GT636 – This alarm/immobiliser unit from GT offers a “Self Powered Battery Backup 120dB electronic siren” as an output, as well as a “Flashing dashboard LED when system is armed to show the vehicle is protected”. The system costs around £ 350 to be fully fitted, and is approved to Thatcham Category One, which is a security standard set by Thatcham, an independent, non-profit making research centre. One great feature about this design is that the wiring is “All black unidentified cabling to conceal circuits into vehicles loom”. This is a great idea that I had not thought of, because if my wires are easily noticeable, a thief could follow them to the starter motor and short circuit my system. I am going to stick different coloured tapes on them during the manufacture stage so that I can tell them apart. The downsides to this product are that it uses remote controls, whereas a combination lock is potentially more secure because of pickpockets etc.
I like: the all black wiring.
The Vecta New Cat 2 is an immobiliser system that comes fully fitted for £175. This system incorporates a “Three Circuit Electronic Engine Immobiliser System”, which means that the power to the engine has been cut in three separate places. This system has “Passive arming”, i.e. it arms automatically after 30 seconds, this is a useful feature which I may implement in my device, as it means that the user doesn’t have to remember to immobilise his/her car before exiting the vehicle. This device does use a PIN Code override, but for my project the keys would still be unsuitable.
I like: the passive arming system.
PARALYSER D3400 – this device utilises “hot wire warning lights” that make the indicators flash if someone tries to hotwire the car. It also uses “Fail safe immobilisation circuitry - if system looses +12 volts or one ground while driving, engine continues running.“ This is an issue that I need to look at in the “power” section of my research. I especially like the “Optional door, bonnet or boot protection” which I could easily implement in my design using a few push-to-make switches and some logic gates.
I like: Optional door, bonnet or boot protection and Fail safe immobilisation circuitry.
Many of these existing products have a lot in common. In most, all the wires are black so that they can’t be easily identified by a thief, the car wires are cut in at least two places inside the car engine, for example once at the fuel system and once at the starter engine. Most of them also use Automotive Relays to supply power to whatever circuit they cut.
All the existing products have a method of gaining entry to the car, whether it is a keypad or a remote control, and they also have a backup system for if something goes wrong.
From looking at these products, I have decided to make all my wires black and I will use a key switch as an emergency override in case the user forgets the code but still wants to get his/her car home.
There are several materials that I could use for the case that holds my system. Here I will list them and then explain why I have or have not chosen them.
Metal – I could make my case out of metal, the most likely would probably be steel. The benefits of such a material are that it will be very secure, it is hard for someone to break into a metal case unless they brought a screwdriver, and if I used tri-screws then the thief would need a special screwdriver to gain access to the case. The downsides to using metal are that it will short the system unless I use some sort of insulation around my circuit, and that metal is hard to mould into shape without using dangerous tools like welding torches. If my product was produced and sold, then this method may be used, but it is unsuitable for a prototype.
Thermosetting Plastic – This is plastic that can only be moulded into shape once, after this it stays in this shape, even when reheated. The benefits of using this kind of plastic are that it is stronger than Thermoplastic, because it undergoes a chemical change, and is therefore more secure for a security product. The downsides are that if I make a mistake when making my case, I will have to throw that sheet away and use a new sheet, which may make the process expensive in the prototype stage.
Thermoplastic – These can be heated and cooled as much as you like, and they will continue to change shape if used in a vacuum former several times, because they don’t undergo a chemical change whilst heating.
The benefits of Thermoplastics are that it would be cheaper and less wasteful because I could continue to use the same sheet of Thermoplastic, even if I make a mistake and need to remould it. The downsides to using this plastic are that it is soft, too soft to be used as a secure security device, and that it can easily be dented or fractured when installed in the front of a car, whereas Thermosetting plastic would not break at such treatment. If the product were to be mass produced, this material would be ideal because once the wooden block was made for the vacuum former the user would just keep putting more plastic in the vacuum former, and all the cases would be identical because the wooden block has been kept the same.
Wood – Wood is possibly the easiest material to work with, because the tools it requires are very simple to use, and wood is easily available for me to use. The downside to using wood for this project is that it would look out of place in the plastic/rubber interior of a Fiat Stilo. It could however be considered for cars with walnut dashboards, because it would blend in well with its surroundings.
Rubber – Rubber has advantages in that it is soft and can be cut into shape with a sharp craft knife, but I feel it is not suitable for my project because it would not look as good as some other substances, and that someone could break open the case with a knife and short out the entire input system, therefore gaining access to the car.
I could either use the interior or exterior colour scheme for my product, but the interior colour scheme would make the product look more professional because it would blend in with the rest of the buttons on the dashboard. Because this is a security device, I may only have the keypad and the LED display panel on show, and the rest of the system hidden away in the fuse box or under the seat. Whether I choose to leave the whole product on show or not, the best choice would be to use black or grey Thermoplastic, because it is cheap and easy to mould using a vacuum former. If the user wanted to specifically order a new colour for the box, Thermoplastic would be a good idea because a new colour Thermoplastic could be quickly moulded over the wooden block on the vacuum former.
If I were using Thermoplastics, then a whole range of colours would be available for the user to chose from, and it wouldn’t require as much work as it would have had I used wood and the user requested a different kind of wood.
Thermoplastics come in different colours, as shown by these plastic rods.
Because my system has to allow power to the engine, there are a limited number of power supplies that I could use that would be reliable enough to continuously supply power to the engine without suddenly shorting out.
In the final product, I would probably use the car’s battery to power the system, because this is about the most reliable power supply that I could effectively use. Cars usually use a 12 volt Lead-acid battery, which is recharged by the alternator when the car is in use. When the car is not in use, the battery is being used by certain systems such as the car alarm, or the computer clock, battery power lost this way is called parasitic drain. When the parasitic load is greater than 120 milliamps the battery can be drained overnight. If I use a resistor and a DPDT relay then I can get the parasitic drain down to only 40 milliamps, this means that the system can be left on overnight without draining the battery. This is the best power supply that could be used because it recharges itself so there is no need to buy replacement batteries apart from when replacing the car battery, and the power output is reliable. If the battery goes dead, my system will not work, but that won’t matter because a thief can’t steal a car with a flat battery. When making my prototype, I can connect eight AA batteries together in series to simulate a 12v car battery.
I had to do some research in order to find out how I can interface a PIC with a keypad. I went to Maplin Electronics to look at the keypads, and I noticed that they had only seven output pins for twelve inputs. I asked the store attendant if I would need some sort of decoder, but he assured me that I would not, and that I could find out how to interface the PIC using the internet.
I did some research and found out that because the keys are arranged in a 4x3 matrix, I have to provide power to one column of the keypad, whilst scanning the rows to see if a key has been pressed. I then move onto the next column and so on until I register a hit. Because I am using a PIC I will be able to scan these columns and rows so fast that the user wouldn’t notice that his key isn’t registered the moment he presses it.
For example, if I supply power to column 2, and scan the rows, I find that row 3 is high, meaning someone has pressed key 8.
I have researched existed car immobilisers that have made it onto the market in order to see what features the public seem to want. I have also researched all possible inputs, processes and outputs to decide which components would work best for my system. I have decided which materials and colours my product will be made out of, and I already have a rough idea of the circuit that I will need to build. I have also learnt a great deal about how immobilisers work and how I could make my own.
I think that my research has been very effective because I have learnt a lot about how I could make an immobiliser and what it would need to do. I also learnt little things like make all the wires black to make them less obvious in the car’s loom, which would make my product more secure.
I have found that the safest products cut the car’s wiring in more than one place to avoid a thief shorting the immobiliser circuit, and I am confident that I can produce a circuit that could not be bypassed unless someone had access to the car’s bonnet, some spare wire, wire cutters and a torch, which I feel makes my security system from being compromised by anyone but the most determined car thief.
Electronic idea generation means generating a number of different circuit diagrams and flowcharts that could potentially be used for my project. Analysis involves looking critically at my designs and explaining the flaws and/or benefits of each design.
As I have decided that the only processes I will use are the PIC and the Automotive Relay, my circuit designs will all look similar, and I will go into more detail about the programming of the PIC.
This is the basic design of my circuit, as designed by the ‘Crocodile Technology’ software. On the left we see the keypad, in the middle the PIC, and on the right a green LED that signifies our automotive relay.
This is the first flowchart that I made on Crocodile Technology. There are 3 subroutines, that all require the correct button to be pressed and then un-pressed before the subroutine will advance. The code is 1571, so the subroutine to enter the number 1 is used twice, this saves space on the chip. The subroutines work by powering a row of buttons, and then waiting for the correct input in order to proceed. If all four buttons are correctly pressed, then the LED which is supposed to resemble the automotive relay will come on.
In my first design, the program would ‘latch’ once the correct code was given and the engine turned on, this would mean that the power to my circuit would have turned off in order to reset the immobiliser. Now the immobiliser is reset using the code #1#. If a user presses #1# then the immobiliser turns off power to the automotive relay, preventing the engine from running. I have used a 3 digit reset code because if the code was shorter then the user may accidentally brush past the buttons and cut power to the starter motor, this means that the next time the user starts the car they’d have to put the code in, even if they hadn’t meant to immobilise the car. For example, while the car was being serviced the user may not wish to immobilise the car so that the person servicing the car didn’t need to know the code.
This is the most complex system that I have produced. On the next page is a detailed description of how everything in the side works.
This system still uses the code 1571, but I have greatly improved the security of the device, as well as adding two LEDs to indicate whether the car is immobilised or not.
As the unit is installed for the first time, the power flows to the PIC, and the user must press * and then enter the code 1571 to enable the car to start. The new security steps that I have taken mean that a thief has a harder time of cracking the code, because when entering the numbers 5 and 7, the programme resets back to the beginning of the code entry if the wrong key is pressed.
When the code has been correctly entered, a green LED comes on to show that the immobiliser is on, and the automotive relay is powered.
After the user has finished driving, he/she enters #1# which will immobilise the car by cutting power to the automotive relay and therefore the starter motor. A red LED also comes on to show that you are unable to start the car in it’s current condition.