Good day to all,

I know it’s been a long time since I posted stuff up here,been busy working.

So here’s the first of my recent projects to pop up soon enough.

It’s a Car Anti-Theft System based around an Arduino Nano,a Sparkfun common 12 buttons Keypad and some more circuitry.


Here’s how it work:

-Car won’t start unless you provide it with the correct password/keycode.

-Audible signals will alert you if password/keycode entered is Accepted or not ( in this case,some random for wrong and Super Mario Song for success) via a standard piezo speaker.

-A relay(or 2 since 1.1) will be activated for a definite period of time and thus enable you to start your car.

-Bypass hidden security switch provide a solution if you forget your password.

-Power is provided by a China-made USB Hub powered directly from 12V Accessory line of your car via a LM7805 circuit.

-A relay circuit is enclosed alone to allow placement anywhere you want it

-2 LEDs display states (keypressed,password good/wrong)

-A thief will find it really confusing to hijack your car with that amount of wires under the dashboard…

-Quick software update to the Arduino via the USB Hub which is easily accessible.

-Bonus: Start Engine switch to look cool =3

Before going on,here’s 2 important points:

1-I think that an Arduino Nano ain’t that overkill here as a car is a very sound application where stability is required.

2-The under-dashboard USB hub is perfect for future dev or embeded device like GPS or Bluetooth headset as this one has 7 ports on which power and data can be streamed. (A usb plug next to the OBDII,sweet)

Let’s start with the diagram of how I pulled that one out:

Wiring Diagram

Wiring Diagram

As you can see,it’s pretty straight forward, Arduino reads the keypad,every press trigger some sound via piezo, 2LEDs for feedback and a relay driven with a 2N2222 transistor and protected by a  diode (THIS IS IMPORTANT,see why here)

The Arduino program is commented all the way so it’s user-friendly to modify and adapt.

DOWNLOADS: (Libraries are REQUIRED for it to work,install them according to arduino.cc directives.

Arduino Keypad Library (767)  Required

info here

Arduino Password Library (670) Required

info here

Arduino Anti-Theft Program V1.1 (1179)

To power up the arduino I’ve decided to go a different way than normal people tend to go by using a China powered USB Hub like this:



So Arduino is plugged in via USB cable and get nice 5V juice out of it. Also,it enable the software update by plugging the HUB to any laptop and the addition of 6 other USB powered devices .

As you can see,this unit is powered by a wall-wart,which is not something you find under the dashboard of a 2008 Yaris.

The solution was to cut the wall-wart and replace it with a LM7805 on perfboard which is itself plugged into the accessory line o the car,this way the arduino is up after you turn the key on,thus less battery usage.

for more info on LM7805 check here.


Tools needed:

-Soldering Iron and stuff



-Multimeter (without this,it will be very,very difficult)

As explained above,all what is needed to prevent the car from starting up is to cut the Ignition Signal Line “ISL” from the Car Key Connector. When this cable is not connected  and you turn the key to start,the signal won’t reach the computer so no vroom. This is where a relay comes in handy as it will reconnect this wire and thus provide ignition.

This is what a Ignition harness looks like:

Ignition Harness

Ignition Harness

1-Using the multimeter,locate the ground wire on the harness.

2-Connect the neg lead of the LM7805 to the ground

3-Locate the Accessory wire (on the pic it’s the big beefey orange one) by probing on ground and on all the other wires and by turning the key to ACC. to have power only when it’s on this position and connect LM7805 V+ here

4-Locate the ISL again by grounding one lead of your Multi and by probing each wire then turning the key to start your car. When you find the correct wire,cut it and try to start,if it fails,you succeed.

5-Connect 2 wires that goes to your relay switch to the ISL

6-Plugin,make it look shiny and punch in a keycode,if the relay tick,you got that time to start your car. Don’t worry about the current as it’s a Signal line (well,it is on a Yaris) and some low voltage goes through).


So here’s a video of mine in action:

YouTube Preview Image

Some pics:


-I have installed a bypass security key somehow hidden down below in case the arduino freak out.

-I’ve also installed a start engine button for the look =P

Sorry,no pics of the actual wiring because when I made it 2 days ago,I didn’t thought about posting it online but people seems to like it so…

Any suggestion or request to the software : Post in the comments,I’ll be happy to modify it to suit your needs.