IR Sensor help please

Thread Starter


Joined Feb 27, 2006
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.



Joined Apr 20, 2004
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.

Thread Starter


Joined Feb 27, 2006
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.


Joined May 16, 2005
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:

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

Thread Starter


Joined Feb 27, 2006
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?