IR Sensor help please

Discussion in 'General Electronics Chat' started by Hurdy, Oct 25, 2007.

  1. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Hi everyone,

    I am looking to build a simple circuit that detects when a car approaches my gate that will then sound a buzzer or something similar back at my house.

    I'm thinking that an IR sensor is the best approach. Either have a break beam sensor or a reflective IR sensor.

    Now, I have a few questions that I need clarifying.
    The distance from the gate to my house is about 150-200 meters.
    If I go for an IR sensor that is rated at 5V supply would the run be too long?

    I have been browsing suppliers such as RS components and noticed that they do IR sensors that need a supply of 10-30V. Is this voltage level used because of long distances and voltage drop?

    What I'd like is some kind or IR sensor that detects a car then triggers some simple logic circuit which will pulse a buzzer high and low using something like a 555 timer.

    Is this a good approach? Does anyone have any comments that could aid me in my design choice.

    I thank you all for your time reading this and appreciate any feedback possible.

    Rob
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You could just get a PIR floodlight and use it. The floodlamps could be optional, but it would be easy to get a signal sent to the house.

    It is going to be difficult to come up with something that does not have false triggers. A beam can have a large dog or even a piece of trash blow through, and the PIR sensors will trigger on animals and even high wind gusts.
     
  3. Salgat

    Active Member

    Dec 23, 2006
    215
    1
    Could he prevent this with a small delay in trigger (since cars are longer)? Something like a capacitor and an SCR?
     
  4. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    how about an ultrasonic sensor

    moz
     
  5. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    The is the option of having to IR beams. As a car is generally of a certain length, an anaimal or piece of paper would only break one beam at a time where as a car would trigger the two.

    I could use ultrasonic or even a proximity sensor. It's all really a case of price and reliability.

    What kind of voltage levels will I need to work with? Would 5V be enough to run a distance of say 150meters from the control box to the sensor? Anyone have any thoughts on this matter?

    I've browsed at some sensors and found ones of 5v and 10-30v ratings. 5V would be easier as I could create some simple logic circuit to trigger a buzzer but it wouldn't be a problem having to step down a higher voltage signal to 5V.
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Another option would be to bury a 2 meter dia. loop of insulated wire under the driveway (unless the driveway is already in place) and use this loop in an oscillator. When a car-sized lump of steel moves over the loop, the frequency will change. Difficult to implement if the driveway is already poured, though...

    Regarding the 150-200 meter cable run, resistance will depend on wire size. There are several charts on the internet which list ohms per 1000 foot of common wire sizes.

    Here's one: http://amasci.com/tesla/wire1.html#awg

    Remember: you have length going to the gate, and length coming back as well. Both will have resistance.
     
  7. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    cool chart. Thanks thingmaker3.

    Hmmm your loops frequency thing sounds quite interesting. Might be worth looking into. Is there a specific name for this type of system that I can use to google for more inforomation?
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    It's called a "metal detector." :)
     
  9. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    lol yes ofcourse :).

    hehe thanks
     
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