Proximity Sensor Project

Discussion in 'The Projects Forum' started by mogi88, Aug 3, 2008.

  1. mogi88

    Thread Starter New Member

    Aug 3, 2008
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    Hi forum readers. I'm new to electronics but am dying to make this gadget.

    I carry my bikes on a roof rack, which can be hazardous if you accidentally drive beneath something that has low clearance, as I did recently. This happens a lot with people carrying their bikes on top, so I figured a simple proximity sensor would help keep that from occurring.

    The sensor would easily clip on to the handlebars of the bike that is mounted on the roof of the car, and is directed forward. When it senses something - a low hanging carport, for instance, at a given preset distance it turns on an alarm so that the driver is reminded to stop. The alarm will sit on the dashboard and will be connected to the sensor via a long wire that runs across the seal of the door. The alarm needs to have have an on/off switch.

    Questions:
    1. Is infrared or sonar a better proximity sensor considering that this will be used outdoors in a moving vehicle and in sometimes rainy/snowing weather. I was considering the LV-MaxSonar-EZ0 proximity sensor. Other suggestions?
    2. Is anyone able to help me wire the alarm portion? I know this is pretty simple, but I am a total novice.
    3. Any comments about a power source? Battery vs. drawing from the lighter jack in the car?

    Thanks.
     
  2. AlexR

    Well-Known Member

    Jan 16, 2008
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    Given the average driver reaction times and car stopping distances (see this link) I very much doubt that a proximity sensor would be of much use.
    I think you would find that by the time a sensor detects a low obstacle and sound the alarm you will just have time to glance up at the rear-view mirror to see your bike (or parts thereof) flying backwards at a great rate of knot towards the road surface and/or any other following vehicles.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    1) At what maximum distance do you want to detect the low object?
    2) At what max speed will the car me moving that needs protection? (I am assuming obstructions are more of a problem in a parking lot than on the open highway.)
    3) How will you aim the device once it is attached to the handlebars? That is, a small error in aiming each time you attach it to the handle bars could have a dramatic effect on detection of obstacles at say 100ft.

    Assuming you are considering detection at 50 to 100 ft., I think a laser-based method would give you better results than sonar, mainly because you can keep the beam narrower.

    John
     
  4. mogi88

    Thread Starter New Member

    Aug 3, 2008
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    1) Want to detect low object at about 5-10 meters
    2) Car is moving at low speeds - basically while in parking lots, entering garages, etc.
    3) Good question. Vertical angulation could make a big difference at larger distances.

    An additional problem is detection on the periphery since I also want to be alarmed when I am turning into a garage. That's why I initially thought a wide beam would be better.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Assume you want 10 meters, then consider the "spot" size of the measurement cone for ultrasonic and laser. I do not have that number, but you can probably assume the ultrasonic will be a lot larger. A larger spot size will mean more false echos, which will give more false alarms.

    For proximity measurement, you might consider the Stanly TLM-100 (77-910), which uses a laser to measure distance by TOF. Apparently, that is an older model and is available new for about $50 .

    The Stanley site shows that the spot size for the laser at 50 ft is 0.6"; whereas, the spot size for ultrasonic distance measurements at 50 ft is 106" (almost 9 ft.).
    If those numbers hold, the ultrasonic would obviously not work well for telling whether a ceiling or obstruction is a little too low.

    How frequently can one take a laser distance? I was able to do it about 2X per second just using my finger on the button. A hacked unit using a repetitive test signal might exceed that frequency. I have no idea how long the laser would last at a higher frequency. What I am thinking here is that if the TLM-100 were on your bicycle, if there were no obstruction, it would return an error. If there were an obstruction, then it would return an actual distance to the obstruction. By hacking the device, you could control it from within the car.

    A simpler solution to detect but not provide range to an obstruction might be to simply attach a laser pointer or laser line projector to the bike. If you could see the dot or line on the obstruction, you would know it was too low.

    John

    Edit: Remember, the laser will be fixed relative to the axis of the car, so if you are going down a ramp or up an incline, the result may be misleading. I don't think an auto-leveling laser line projector will help in that regard.
     
    Last edited: Aug 3, 2008
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