Build a GPS cruise control for your car using any Smartphone, or iPad

Picture of Build a GPS cruise control for your car using any Smartphone, or iPad
We will show you how your car can automatically slow down in speed zones.

 It will make your drive easier, more relaxing in ways you can't imagine.
My wife has one, and even though women-hate-gizmos, she uses it every day!

It works ON ANY CAR newer than 2000.

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Step 1: Parts list and schematic for Box labeled "2 Instructable"

Picture of Parts list and schematic for Box labeled
Parts List:

Buy or build this board I copied from:
(they also give eagle-cad schematic).

The razor board has inputs:
1) Audio
2) +5vDC

The razor board outputs:
TTL levels when the audio is DTMF 0,1,...9,#,*

You will need two relays.
(radio shack Model: 275-001 or anything similar)

Step 2: Wire the DTMF/Audio

Connect the Razor-audio to the cellphone-earphone jack.

Since cellphone headsets are cheap, I would start with that
and cut the end and solder it right on the razor-audio jack.

Just solder it on the razor board, no need to buy yet another connector...

Step 3: Connect 5v to the razor board

First you have to test in your apartment, right?
So get a wall-wort.
E.g    110v to 5v DC converter.
You can get them at the Good-Will or Radio Shack

Use a voltmeter to verify its 5v DC, not AC.

Connect it to the 5v on the razor-board.

Step 4: Get the app

Go to the Android Market and get the app called,
"Back Seat Driver, Pro".  

It will cost you a dollar and 30cents of that goes to Google and 70 cents goes to the nonprofit called wikiSPEEDia.org

In the menu, click on "Cruise Control". Then click on ON, OFF.

You should see the LEDS on the Razor board light on.

If the LEDS don't change, adjust the volume-control on the razor board.

Step 5: Email me

I am constantly working on the Cruise-control part of that app.

Email me and make sure you have the latest.


Step 6: How to clip onto your cars existing Cruise Control Wires in the Steering Column

Here's how to clip onto your cars cruise control.
All car manufacturers use the same concept, resistors, but each manufacturer uses different resistors.

There are several ways to figure out which wires to use, and what the resistor values are:
There are four ways, but if you are lucky you will only need the first way.
I have listed them in order of hardness, easy first.

1) First look here to see if your car is listed.

or 2) Take apart your cruise-buttons (in the steering wheel) and use an ohm meter as you press the SET, DECEL, RESUME buttons. Trace the wires to under the dash past a thing called a "REEL" (fancy name for brush).

or 3) Go to your library, ask to use the computer which has a goofy database called,
"ALLDATA". For example, I live in Memphis, and here is some info on ours.
In ALLDATA, look under cruise control. It will show the resistors for the SET, DECEL, RESUME functions of the cruise control. Write down the color of the wires and the resistor values.

or 4) Tell me your car and I will look it up for you.

Step 7:

Step 8: Parallel two wires across your cars cruise control wires.

All cars use 2-wires for all the cruise functions, SET, DECEL, RESUME like this:

                         SET                     DECEL                     RESUME
                              |                             |                                   |
                            R1                        R2                               R3
                             |                              |                                   |
                              \                              \                                  \  pushbuttons
                             |                              |                                  |

There is also a crappy video there:

Under the dash, find the two cruise wires.
To make sure you have the right ones, you can put an ohm meter across them and hit the SET, DECEL, RESUME buttons. You should see the resistance jump up to values in the 1kohm range. THEN you know you have the right two wires.

Attach wires to them in parallel.
Run these two parallel wires up and connect them to the relays on your DTMF-PCB.

FYI, I situated my DTMF-PCB in front of my odometer and hid my wires in the steering column... I also added a 4pin connector on it to hold the wire-1, wire-2 and additionally +12v, GND which will be used to power the DTMF-PCB. You can get +12v, gnd from just about anywhere under the dash.

Step 9: Example wiring on a Dodge Caravan

Picture of Example wiring on a Dodge Caravan
Heres a real picture of the 2 cruise wires on my minivan.

Yours will be different, but its real easy to get the right wires by simply ohming it out and hitting the SET, DECEL buttons.

Step 10: Initial testing

1) On the Android application called "Back Seat Driver", hit the test button called DTMF-0

2) Put an ohm meter across the 2-cruise control wires.

3) You should see the relays fake-out your cruise control and you should see the resistance jump to the right value, R1, R2, R3.

4) Now its time to drive the car and see if SET works.

Step 11: Final testing

After both SET and DECEL work,

1) Turn your cruise control on as you normally would.

2) Drive until you see the speedlimit show up on your Android phone running the app called "Back Seat Driver".

3) Drive a little above the speed limit and you should hear the SET click on.

Don't forget, you can listen to the SET signal by unplugging the headphone jack.

Email me if you get stuck.