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  • Author Author: colporteur
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IR sensor: all that glitters is not gold

colporteur

"All that glitters is not gold" is a concise statement stating that not everything that looks precious or true turns out to be so. I can say that about IR sensor only from experience.

I pride myself on due-diligence before using a technology. A recent project that relied on IR sensor has caused me endless problems. I have taken a step back from using IR sensors. IR noise is a problem that is not easily solved. I wanted to share my experiences in the hope that others can avoid the pit falls or at least be aware they are there.

I started using an ubiquitous IR sensor. I believed the claims. There were numerous examples of using the device. At no point did anyone mention an issues.

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I used the IR Sensor in this project to detect a model train. IR sensors under the track are used to detect if a model train was present. I successfully completed the project development and then took the design on the road. I can only say, the road show failed miserably!

My windowless, IR noiseless development environment came back to haunt me later on. The amount of IR noise present in the production environment resulted in reducing the IR sensitivity so much that the sensor failed to detect. Sunlight, halogen lights, LED fixtures and even a desk lamp produced enough IR noise to swamp the sensor and made them unusable.

If you are planning on using IR technology, you need to consider that noise will impact the device operation.

Those familiar with RF know that if you are located adjacent to a RF broadcast tower it can create problems. The signal invades other technology and you are left scratching you head for solutions.

My old flat screen TV has issues with IR noise generation. Three brands of IR extenders fail if they are located near the TV. Turn on the LED pot lights in the living room and the extenders range gets poor. What gives?

I suspect much of new light technology is generating noise in the spectrum our eyes cannot see. Those inexpensive LED lights might look bright but outside of what our eyes see, the spectrum is getting lambasted. What you don’t see doesn’t bother you, right?

My friend garage door opener failed to operate after he replaced the incandescent bulbs in the garage with low energy LED bulbs. Only through the grace of his technology knowledge did he track down why the 20 year old garage door opener had issues after changing light bulbs.

After discovering the difficulties with IR on my project, I did a search for issues using the technology. Noise in the spectrum is a problem, that is not easy to solve. I'm forced to find another solution to detect the model train. IR has left me feeling like I am in the game of snakes and shoots and I just landed on the snake that took me back to the beginning. Ask the right question and all that IR glitters is not gold

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  • Thanks for the response folks.

    The IR sensor solution is working in the development layout. Two model trains alternate switching onto a loop of track controlled by IR sensor readings feeding a Arduino Mega. I've had model railroaders go through the exercise of manually switching the trains and then flip a switch to have the whole sequence managed by a microcontroller. They are impressed.

    When the design was taken to a different location it failed. The amount of IR noise between the two environments made the sensor unreliable. This is the point in the project I discovered these sensors have limitations. Oh how I wish I had of discovered that weakness during development.

    I don't want to diminish any ones suggestions by responding with "I've tried that, it can't or doesn't work". Lets just say IR limitation are known. Unfortunately before now, not by me:( This company recognized the issues and used modulation to minimize the problems.

    image

    "Principle: The emitting part of the laser sensor is a 180KHz oscillator emitted by an oscillator tube, amplified by a triode, the laser tube emits light, and the receiving part receives the returned light intensity from a matching 180KHz receiver tube. Since the laser sensor uses modulation processing, the receiving tube can only accept the reflected light of the same frequency, so the influence of visible light on the reflected laser can be effectively prevented."

    These units are five times more per unit than an IR sensor. 

    This post was just me licking my wounds after discovering what I thought was a working solution,(because it worked) had weaknesses that I wasn't fully aware of. If someone is considering these IR sensor modules in a project, just be aware of some constraints. Who knew turning on a halogen light under the layout to provide some light to work with, flooded the sensors and made them unpredictable.

    I'm currently exploring break-beam sensors using laser light as a solution. It is not ideal but does work reliably. Each model railroad layout environment have their own caveats that limit options. Getting it to work and getting it to work within the clients requirements has its challenges.

  • in reply to colporteur

    Hi Sean,

    IR works really well, but the original boards did not use modulation, so they are not really usable in conditions where changing ambient light cannot be kept away from them.

    The TL1838/VS1838 IR sensors as shown in the photo earlier are much cheaper. They use modulation. They are under $1 USD for a quantity of 10. Paired with an IR LED (similar cost) and a series resistor, operated by an Arduino timer output (or PWM) pin, the total cost would be under $0.20.

    image

    There's examples online showing how to connect up the sensor:

    image

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  • in reply to colporteur

    Hi Sean,

    IR works really well, but the original boards did not use modulation, so they are not really usable in conditions where changing ambient light cannot be kept away from them.

    The TL1838/VS1838 IR sensors as shown in the photo earlier are much cheaper. They use modulation. They are under $1 USD for a quantity of 10. Paired with an IR LED (similar cost) and a series resistor, operated by an Arduino timer output (or PWM) pin, the total cost would be under $0.20.

    image

    There's examples online showing how to connect up the sensor:

    image

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