car in the garage?

[kd5crs]

I don't have an Elk so I may be missing something here. Why is everyone so concerned about high levels of accuracy? If you are only trying to determine if your vehicle is in the garage or not, there should be a measurable difference in voltage between the floor of an empty garage and a car roof parked in the garage. Install a sensor, measure the voltage with a car in the garage and that becomes your trigger level.

Because in the true spirit of HA, you mess with something until it works. Then you add features until it breaks. :+D The original request was to just tell if there was a car, but then it became a question of telling WHICH car was in the spot based on height.

If you guys get this to work I'm going to copy it, so please continue!

Brian

 

[signal15]

.1V will give 10 inches of accuracy. That's sufficient for my needs. All 3 of my vehicles are VERY different heights when measured near the back (one is a pickup).

 

[dBeau]

.1V will give 10 inches of accuracy. That's sufficient for my needs. All 3 of my vehicles are VERY different heights when measured near the back (one is a pickup).

So if my math is right, the floor 100" away (say) will read 1.0v with the Elk reporting 1/12*256=21 while a car roof 40 inches away will read .4v/12*256=8. Is the Elk's A/D converter stable enough at low voltages to consistently notice a .5v difference? I'd think that it would be but I havent tested it. Would there be any problems with wiring the output of the sensor to the input of the Elk? I'd guess the power supplies would have to share a common ground. To keep things simple, powering the sensor with the 12v supply from the Elk would be even more convenient.

 

[AutomatedOutlet]

If you can mount a sensor within about 3 feet of where the car will be parked, the 1-sided photo beam sensor is a great choice.

The sensor is a Takex Beam sensor

 

[signal15]

.1V will give 10 inches of accuracy. That's sufficient for my needs. All 3 of my vehicles are VERY different heights when measured near the back (one is a pickup).

So if my math is right, the floor 100" away (say) will read 1.0v with the Elk reporting 1/12*256=21 while a car roof 40 inches away will read .4v/12*256=8. Is the Elk's A/D converter stable enough at low voltages to consistently notice a .5v difference? I'd think that it would be but I havent tested it. Would there be any problems with wiring the output of the sensor to the input of the Elk? I'd guess the power supplies would have to share a common ground. To keep things simple, powering the sensor with the 12v supply from the Elk would be even more convenient.

If you read the FAQ on the Maxbotix site, they have a solution for an unstable A/D converter that will help smooth out the signal. It's just a cap and resistor in the line. I wish I had one to test with, but I don't really want to spend the money for something that might not work.

 

[jharrell]

What about building a inductive loop sensor like the ones used at traffic lights: Vehicle Detection

I can't seem to find any premade, but it seems like it would be a pretty simple circuit.

I would imagine the driveway sensors you can buy are based on this, but seem to be too complicated, trying to detect moving vehicles, with timed alarms etc, when you just want presence detection.

The sensor itself would just be a coil of wire under a mat or tape, unless you wanted to use a concrete saw and epoxy like they do at traffic stops ray:.

 

[AnthonyZ]

http://tonynoone.blogspot.com/2009/03/play...ultrasound.html Instead of using the outputs for LED's, you could instead interface with a relay (little baby 5 volt) to provide dry contact for zones on the Elk.

 

[PaulD]

Depending on desired level of accuracy, another approach would be to use a wireless security sensor in each vechicle. With the sensor mounted in vehicle such that it is always "secure", it should show up as "secure" anytime it is within range of your receiver. If not in range, it would show up as missing or not secure. That would tell you if your vehicle is within range of your receiver. In my case, my vehicle would only be within range if it was in my garage (no other place to park within wireless range).
Not a low cost solution unless you already have a wireless receiver in your system but it would work for me since I have a wireless receiver that I have not yet installed. Not sure how the sensor shows up when it is out of range (Missing? Not secure?) nor how it is reacquired by the receiver when I am back in range after being gone. Guess I will find out when I get a chance to experiment with it.

Same concept should apply with RFID technology but I don't have any of that to play with.

 

[jharrell]

Just as a follow-up I did find pre-made inductive vehicle presence detectors: Detectors

For $105 the EMX DTEK LP looks like a good choice.

What about building a inductive loop sensor like the ones used at traffic lights: Vehicle Detection

I can't seem to find any premade, but it seems like it would be a pretty simple circuit.

I would imagine the driveway sensors you can buy are based on this, but seem to be too complicated, trying to detect moving vehicles, with timed alarms etc, when you just want presence detection.

The sensor itself would just be a coil of wire under a mat or tape, unless you wanted to use a concrete saw and epoxy like they do at traffic stops B).

 

[dBeau]

If you can mount a sensor within about 3 feet of where the car will be parked, the 1-sided photo beam sensor is a great choice.

The sensor is a Takex Beam sensor

I gave a couple of these a try. I wired one up, turned the sensitivity all the way up, and walked around the garage with it. It worked quite well. There is an LED to indicate detection so that made the experiments easy. If it's a car you are trying to detect the range is better than the stated 1m. I think the shiny surfaces help, though too shiny (like a mirror) can be a problem. Front and back detection of a reflective surface like a marker light or license plate have the best range but lead to mounting and aiming problems for me. The best mounting position I could find in the back was about 5ft away. Detection then became subject to car placement. In the front, I could get closer, but it put the detector in a place where stuff was likely to collect and block the view.

The mounting position I really wanted was facing down from the bottom of the garage door opener. Turns out the distance to the roof of my car is just over 1m. A little double sided tape (included with the sensor) a few feet of wire, yada yada, ...the Elk knows when the cars are in the garage.