Smart Car Sensor


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Smart Car Sensor

Home Automation is really cool. Watch this video that shows one of the ways my computer system utilizes these smart car sensors. Click here if you want to learn more about Home Automation.

For some time I wanted our HAL 2000 system to know when my wife or myself was home or away.  Now, don’t get the wrong idea!  I just wanted to make our home smarter and be able to adapt to our lifestyles based on which of us is home.  In order to accomplish this I would need to have a system that would be able to identify each car individually, and be able to tell the difference between coming home or going away. 

Of course, I looked into burying a sensor in the driveway, but that could not tell the difference between my car, my wife’s car, or even uncle Sammy (the guy who visits my wife when I am at work.)   I had to come up with a smarter system.

Next, I looked into RFID  This is the technology that is incorporated into the Mobile Speed Pass.  This system allows you to pull up to the gas pump, pump your gas and drive away without swiping your credit card.  The cheapest RFID systems that might work in this application were around $2000.00.  No way!

Finally, I looked into the transmitters and receivers that are incorporated into wireless home alarm systems.  I knew I would be able to wire them into the car and have a unique signal for each automobile.  I also knew they would be relatively secure since they are used for home security.  I spoke to my friend Frank Rico who is also a HAL 2000 user and an expert in the alarm and lock industry.  Frank did some research and found the perfect pair or transmitters and receivers that could be easily adapted for this project. 

Visonic Ltd makes a transmitter and receiver that transmit around the 315 MHz range and have up to 16,000,000 codes. 

  This transmitter and receiver are ideal for this project because:

bulletThe transmitter can be connected directly to a 12v relay wired to the car’s ignition.
bulletThe transmitter can be configured to send (toggle) a unique signal if the car is turned on (leaving) verses turned off (coming home).
bulletThe receiver can be wired directly to a SECU-16 digital input (or a X-10 PowerFlash module) since it has a “FORM 1C” relay output.
bulletThe receiver’s relay would remain latched (on) until the car returned home.  It would not time out and falsely indicate the car had returned when it had not.

You will need a separate transmitter and receiver for each automobile you wish to automate.

You will also need a 12-volt power supply to power the receiver and a 12-volt automotive relay to interface between the transmitter and the car’s electrical system. 

If you plan on automating two or more vehicles, multiple receivers if wired in parallel can share a single power supply.

Once you get all the parts for this project it is necessary to “pair” the receiver to the transmitter.  You will have to do this independently for each vehicle.  It is much easier to do this on a workbench where both units can be next to each other, rather than after they are installed.  Before we connect the power supply lets set all of the jumpers and dipswitches in both the receiver and transmitter:


Set the relay output jumper to: PULSE


Set the dip switches as follows:
SW1 = OFF (UP)
SW2 = OFF (UP)
SW3 = ON (Down)
SW4 = OFF (UP)

In order to “pair” the units you will have to provide power to the receiver, so now is a good time to wire the 12-volt power supply to the receiver.  Be careful to connect the (+) positive wire of the power supply to the (+) terminal in the receiver and the (-) wire to the (-) terminal.  This will prevent smoke from filing up your work area and irritating you wallet.

Once you power the receiver you will need to move the jumper temporarily to the “LEARN” mode.  Carefully follow the instructions to pair the receiver to the transmitter. 

Important Note: When you are pairing the transmitter do not actuate the reed switch with the magnet to send the RF signal.  You will instead want to use a jumper to connect the Aux. input terminals together to send the RF signal.  Once the unit has successfully be paired move the JUMPER back to the "OPERATE" mode setting.  Test the units together.  You should hear the relay click in the receiver (and the RED LED will light) when you connect and disconnect a jumper between the Aux. Inputs on the transmitter.

Once each unit is paired it may be useful to identify each transmitter and receiver combination that will be associated with each vehicle.  I wrote our names on each to indicate which transmitter had been paired with which receiver.


Installing the Transmitters

You cannot wire the transmitter directly to the car’s 12-volt electrical system. Therefore, we will first connect the transmitter to the 12-volt relay, then connect the relay to the automobiles electrical system.

Simply connect a two-conductor wire between the transmitters “Aux. Terminal Inputs” and pin’s 2 and 6 of the relay.  Be sure to give yourself enough length of wire to run from the car’s fuse panel to the top of the dashboard.  Now connect a RED (+) wire to PIN A of the relay and a black (-) wire to PIN B of the relay.  (In my picture I am using a green wire since I did not have RED)  Use electrical tape and fully insulate the relay so no wires are exposed.

Smart Car Transmitter

Transmitter Open

12-Volt Relay Close Up

It is VERY important to mount the transmitter on the dashboard or higher.  If the transmitter is installed under the dash it will not have the necessary range to communicate with the receiver since it is surrounded by metal.  (Yes, I learned this the hard way.)  Use double stick tape and secure it in an area that will not block the driver’s visibility.  I painted the transmitter covers to match the vehicles interior.  I was worried about the temperature here in the Florida sun, but I have had this installed for about 6 months now without any problems. 

Transmitter Installed on Dash

To wire the relay to the automobile; connect the BLACK (-) ground wire of the relay (PIN B) to the chassis (-) "ground" of the car.  Using a multi-meter identify a fuse in the fuse panel than switches on and off with the ignition, but does NOT turn off when the engine is cranking.  Connect the RED (+) wire of the relay (PIN A) to the “load” side of the fuse.  (The “load” side of the fuse will NOT have power on the terminals when the fuse is removed from the fuse panel.  It is basically the “cold” side of the fuse.)  This will ensure the fuse will blow if there is a short rather than smoking you out of your car.  For additional protection, you may want to wire an in-line fuse on the positive (+) RED wire as close to the fuse panel as possible.  Use tie wraps to dress any loose wires.  You wouldn’t want these wires falling down from the dash while someone is driving.

When you start or stop the car, the transmitter will send a corresponding signal to the receiver.  


Installing the Receivers

You will need to mount the receivers as close to the car as possible in a dry indoor location.   I installed them in my garage and found they work well from about 100 feet even through our metal garage door. Do not try to extend the length of the receiver’s antenna.  It is tuned for the specific frequency and lengthening the wire will actually make the reception worse.

Both Receivers Installed

If you are connecting the receiver to an Adicon Secu-16 digital input you can install the E.O.L. (End of Line) resistor (included with your SECU-16) between the “common” (C.) and “normally open” (N.O.) terminals on the receivers relay.  (As seen in the photograph below)  Next, run a two-conductor wire between the same connections on the receivers relay going to an available digital input on the SECU-16.  Remember to connect one wire to a “common” terminal on the sensor input side of the SECU-16 and the other wire to an unused input.  Make sure you leave the “jumper” installed in the SECU-16 signifying the digital input is being used.  Document which input number you selected for each vehicle.

Receiver Open

Receivers connected to SECU-16

If you will be using a X-10 Powerhouse PowerFlash interface, instead of the SECU-16, simple connect these two wires to the two available connections on the PowerFlash module.  Set the input switch to “A” and the mode switch to “3”.  Set, and document, the house and unit code for each vehicle.

Connect and wire up the 12-volt power supply to each receiver.


Setting up HAL2000

Now you will need to create your automobile sensors in HAL.   Go to the “Automatic Setup Screen” and select SENSORS then ADD.  Proceed to add a sensor for each vehicle giving them a descriptive name than can be used in rules. For example:


I also added 4 flags (2 for each car) that indicate whether each car is home or if it just got home.  This way I can easily use them in various rules.  FLAG example names:


  From here we can use these flags in rules to do just about anything.

bulletHAL greets each of us by name when we come home.
bulletHAL turns on inside and outside lights at night, before we even get out of the car.
bulletHAL sets the answering machine to answer on 2 rings when both cars are not home.
bulletHAL announces who is arriving or leaving the house.
bulletHAL plays my favorite music on the DMC when I arrive home.
bulletHAL sends an e-mail (text message) to our cell phones indicating the other has just arrived home, but only when the other is not home.

The following screenshots show how I set up some of my rules. 

Announcing Cindy is home

Greeting Cindy upon entering the house

Turning on lights when we arrive


Documentation and where to purchase

Visonic MCT-302 Transmitter  ($38.39)
Purchase it here
Visonic MCR-304 Receiver ($45.69)
Purchase it here
Radio Shack 12-Volt Relay Cat# 275-218
Purchase it from Radio Shack
Radio Shack 12- Volt DC Power Adapter CAT# 273-1774
Purchase it from Radio Shack