Get "On Star" -like system for your car, free.

With a cheap mobile phone and a DTMF (dual tone multifrequency) decoder, you can get a system to unlock your car's doors, to turn off the engine, to trigger the siren or horn, or just about anyting you can think of with remote control (from any place you can dial up to your car's phone number).

Step 1 Get your stuff.

You'll need:

-A mobile phone that has a hand free port. And which you can configure to self answer any incoming call. (Motorola C133, which I used has this feature).
-A hand free for your cell phone. (got it for 1 US at Waldo's 1 dollar mart)
-A car charger/adaptor for your cell phone (Waldo's to the rescue)
-The most critical of all: a CM8870 dtmf decoder IC. In Mexico, AG electronica has them. It is considered obsolete in USA, but If you can get it in Mexico, you can certainly get it in the US.
-a 3.579545MHz quartz crystal
-2 x 100 KOhm x 1/4 W resistors
-1 X 330 KOhm x 1/4 W resistor
-3 X 100nF ceramic capacitors
-7805 voltage regulator IC
-1000 uF X 25 V Filtering capacitor
-4 x 12 V Relays (I used automobile type)
-4 x BC548 or any small power PNP transistor.
-4 x 4.7 KOhm x 1/4 W resistors
-4 x 1N4001 diodes (to dissipate back emf from the relays)
-Printed circuit board (prototype board)
-A nice plastic housing (I used a discarded wireless phone base station)

Comments

[Mythbuster Kid]

Seems a little bit over complicated.

[Chebog]

Sir, question? how many source is required in the circuit? is it 2 source? Source from the 7805 voltage regulator to supplied to the circuit and the 12volt for the relay? or is it the same source to use in the relay?

[Chebog]

Hello Sir, I have a question?. The voltage regulator IC has a Input, common, and output, is the common pin there serve's as the Ground?.

[Chebog]

sir good day again can something about relays.what relay could turn on and off a bulb with 220V and what DIODES and transistor can amplify or power up that relay?.tnx

[unknownpocketnerd]

I've already explained that. You need to find yourself some basic electronics handbook. The automotive relays I suggest cannot handle 220V, they are low voltage high current relays designed for no more than 40 V. However there are PCB mounted relays that handle up to 400 V. The diode is to eliminate the back emf after the relay switches off so the transistor and IC do not get damaged. 1N4001 will do. For transistors: BC548, 2N2222 just about any small signal npn transistor will do.

[Chebog]

Thank you very much sir, I really appreciate it...

[Chebog]

What i mean is where do the supply of the relay goes?in order for it to function?

[unknownpocketnerd]

Just read along the rest of the comments.

[Chebog]

Sir good day.can i ask you again about where do the goes in the relay is it connected on the coil to drive it? and do the ground goes is it on the common of the voltage regulator IC?please reply.

[Chebog]

good day, i just would like to ask you again regarding with the transistor.If where is the collector and emitter connected to the circuit.

[unknownpocketnerd]

I have already answered that, just read the blog.

[Chebog]

excuse me sir. is it OK to use any type of cellphone just like nokia phones?.or motorola phones only?.

[unknownpocketnerd]

Motorola phones have the behaviour that this gadget demands: They can be set to auto answer even when the hands free and charger are plugtged. I tried a nokia one, but it didn't work the same way. Old motorolas worked for me.

[Chebog]

ahmm,good day sir.regarding on your circuit how about the relay how do you connect it?.because my relay comes with no diode inside.

[unknownpocketnerd]

DTMF outputs small current 5/0 V states, thus to drive a relay, a transitor is used. The base is connected thru a resistor (4k7) to the DTMF. The emmiter to ground, the collector thru the relay's coil to 12 V. This is the most common way to drive a relay. Use any small signal generic npn such as 2N2222.

Then use the realy's contacts as you please.

[Chebog]

THANK YOU Sir for your reply i really appreciate it.tnx again.

[giacomine]

Como eu faço a ligação do celular para o circuito? E como eu faço a programação do celular (teclas)? Obrigado!

[giacomine]

How I make the linking of the cellular one for the circuit? E as I make the programming of the cellular one (keyboard keys)?

[unknownpocketnerd]

Sorry I don't read/speak Portuguese. Can you write that in English?

[giacomine]

How I make the linking of the cellular one for the circuit? E as I make the programming of the cellular one (keyboard keys)? Thank you!

[unknownpocketnerd]

How does the phone connect to the circuit? I just indicated it: Using the handsfree cable earpieze wire. It is and audio signal, and the DTMF decoder needs an audio signal coupled thru a cap. So just connect the audio signal from the phone's handfree to the DTMF input.

[Chebog]

Hello Mr. Author.can i if where do the 4.7 resistors go in the circuit?because I'm trying your project and I really can't figure it out where the resistors goes in the circuit.please tell me what to do?.thank you......

[unknownpocketnerd]

the 4.7 k resistors go between the DTMF decoder outputs and the transistors' bases. 

[insaneidiotic]

hey iam trying your project to my car actually . iam not that high knowledge to do it .
iam an automobile engineer actually which makes me geek to your project...

hey please assist me with your content that u made for this project .
ill be very happy if u help me out .

since iam weak with the circuit i gonna make it through my friend to fix it in my car as considered to my car how all should i change the settings and pls help me out through mail since iam not a premium user iam not given the contents so pls do try to provide me fully.

iam from india:

my mail ID [e-mail]
contact no:[phone]

ill be very helpfull if u provide me your contents of the circuit where will the major fault occur while doing this project pls assit me.....!!!!!!!!!!!!!

[unknownpocketnerd]

Well, everything you need is right here, that's why I've wrote it as an 'instructable'.

A person who engages in building this gadget needs to be experienced in electronics, or have some one with that expertice help her/him out.

The hard part is to get the IC. Newark sells it here in Mexico, but I don't know about India.

Anyway thanks for your post.

[Chebog]

Mr. author good day, can i ask you something where do the 4.7K resistor go in the schematic?please reply.cause I'm working on that project of yours.

[insaneidiotic]

It was nice hearing from you ...iam trying out in my car..... here the IC is easily available...:-) thats great of it...:-)

i have done the circuiting with my friend as explained in the picture.

sorry man that guy just did the circuiting and gave it to me. he just did not fix it to my car ... so only asking these questions.... sorry again....

My doubts .......:-)

hey man .... there is no steps after connecting to the relays, should theses realys be the command giver to the mechanism used in the car. where should i give the relays connected to...

how do i find the input from the headset of the phone it has two ends of ear peice.... which one will do for the project ?

then pls tell me about how to signal the IC through my phone this is where i hung up totally... like first call the phone number of the mobile placed in the car then should i give a combination of the numbers....... i am totally confused here ... please elaborate... how to signal the IC.... ...

hey iam at my final stage to connect to the car and work it out correctly..... if i do this i might impress my girlfriend man....... please do help me man...... whatever happens i have to do it completely.... pls help me out man.....

my face book url:
http://www.facebook.com/reflectorr

do provide me email address of yours so that i can contact u further......

[unknownpocketnerd]

The DTMF decoder needs and audio input, so the handsfree's 'ear piece' will have to be desoldered and the pair of wires soldered thru a dc decoupling capacitor to the DTMF. Then make sure you setup the phone to auto answer incomming calls.

The relays can switch on/off anything you want in your car: horn, lights, engine, locks, etc.... Just ask your friend to wire you the stuff you need to control.

Good luck impressing your fiance!

[insaneidiotic]

thaks buddy....

will soon say u a result of what happened to my car.......:-).

[insaneidiotic]

It was nice hearing from you ...iam trying out in my car..... here the IC is easily available...:-) thats great of it...:-)

i have done the circuiting with my friend as explained in the picture.

sorry man that guy just did the circuiting and gave it to me. he just did not fix it to my car ... so only asking these questions.... sorry again....

My doubts .......:-)

hey man .... there is no steps after connecting to the relays, should theses realys be the command giver to the mechanism used in the car. where should i give the relays connected to...

how do i find the input from the headset of the phone it has two ends of ear peice.... which one will do for the project ?

then pls tell me about how to signal the IC through my phone this is where i hung up totally... like first call the phone number of the mobile placed in the car then should i give a combination of the numbers....... i am totally confused here ... please elaborate... how to signal the IC.... ...

hey iam at my final stage to connect to the car and work it out correctly..... if i do this i might impress my girlfriend man....... please do help me man...... whatever happens i have to do it completely.... pls help me out man.....

my face book url:
http://www.facebook.com/reflectorr

do provide me email address of yours so that i can contact u further......

[gormly]

I am still amazed everytime I see a comment like this... sad.

[DiamondBack]

"Now call your cellphone. Once it answers ..." This is suggesting that we have a second phone line on our cell plan, am I understanding that right?

[stapler117]

 For this use, adding a second phone to your line would be necessary. it would be better to use a prepaid phone since you wouldn't use many minutes.

[Kasm279]

Yes but when the service expiration date nears you have to buy more minutes. Pretty soon the minutes pile up, even on my mom's phone that she occasionally uses...

[unknownpocketnerd]

I guess they add up.  I am not sure since the service provider some times changes its fees and policies,  but I am pretty sure the phone can take phone calls right.  Anyway, I once in a while call it to see if the phone is still alive and test the functions I have (siren, engine off, locks, etc.).  Only once I had to replace the battery of the cell phone as it was dead and wouldn't charge no more. This is something you will like to do to make sure your system is up and ready whenever you need it.

[shotbythelite]

Umm, no? No one said you needed a second plan to call your cell phone. Just call with another person's phone or your home telephone.

[AndrewNoNumbers]

Wow you must have a lot of patience to do something like this. I gave up just reading the parts list. =]

[unknownpocketnerd]

Thanks. It has proven to be very useful as one day my alarm's remote control battery died, I was unable to get into my car, so I dialed the system's phone from my cell and was able to unlock the doors then I got in and disable the alarm according to the alarm's emergency procedure (ignition on, valet parking switch pressed for 5 seconds, and so on). But I was able to get back home and then took the other remote control. It is like a "plan B" stuff also.

[y2j514]

My plan B for when my alarm remote dies is called a key.  It works pretty well - you put the key in and the door unlocks =D

I mean sure the alarm goes off but you do the emergency override.

[unknownpocketnerd]

I forgot to mention that I disengaged the keylock from the shaft that drives the mechanism, so the only way to get in the car is by means of the electric locks (I am afraid of lock picking).  So my key only works on the ignition switch (for now).