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Automatic Garage Doors and Infrared Tripwires

with 2 comments

I like things that make life easier. One of the first things we installed when we first moved into our house was an automatic garage door. Getting out of the car to open the garage door in the rain is for chumps!

Knowing when to close the garage door is tricky.  We had been guesstimating by using a chalk mark on the wall, but that’s fairly inaccurate – the car bumper has been scratched by a closing garage door on more than one occasion (mostly by me). The solution would to install something that can tell when the car is fully in the garage. And the first solution I thought of (me being an engineer) was an infrared tripwire.

An infrared tripwire works by shining a beam of light at a sensor across an open space. When a solid object disrupts the light beam, such as a car or a person, it triggers an alarm of some sort – usually a buzzer or light. Shops often use infrared tripwires to detect patrons entering or exiting the store.

There are a few ready-made tripwires available on the market, ranging from $100-$150, but I found this kit at Jaycar (the Kemo B216N “Infrared Light Barrier 5m”) that apparently does the same thing for only $15 (plus around $30 for housing and connectors) – just need to solder it together. No sweat. The guys at Jaycar in Maddington also threw in a 12v power supply in for free. Thanks guys – free stuff good 🙂

Dusting off my soldering iron, I assembled the kit over a few nights. It took about 2 hours in total to solder in and test all the components. It didn’t work straight away so I gave it to my dad, the electronics engineer, to diagnose. He found that the instructions had capacitors C8 and C9 switched around, a fact that is obvious once I looked more closely at the photo. It took about another hour or so to prepare the cabling and housing.


When I finally tested the tripwire, it worked great – at night time. During the day it didn’t work at all, as its sensor couldn’t tell the difference between the its tiny infrared LED and the sun. It was particularly bad in the afternoon, when the sun shines directly into the garage. Curse you big flaming ball of infrared energy!

I needed another solution. After a lot of blasphemous remarks about sun-related deities (and words rhyming with “trucking”), I settled on a kit that was cheap, quick and easy to install, accurate to the millimetre and works in all light conditions:

A feature comparison between the Kemo kit and the tennis-ball-hanging-from-the-ceiling kit:


Infrared Tripwire




$0 (recyclable components)

 Construction time

3 hours

3 minutes

 Installation time

1 hour

15 minutes







 Works during the day?




Sometimes the simple solutions are the best ones.

Written by Richard

26 March, 2009 at 10:11 pm

Posted in tech

2 Responses

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  1. I’ve been using this technique in my garage for years.


    31 January, 2013 at 3:20 am

    • Funnily enough, so have I!


      4 February, 2013 at 9:31 pm

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