Ambient light proof distance sensor

[samarsingla]

Can someone please give me the circuit(or link) for making an IR distance sensor resistant to ambient light?

 

[dknguyen]

You won't be able to build one for distances greater than a cm or so. Just get a GP2D12 or other infrared rangefinding module from Sharp Optoelectronics.

https://www.sharpsma.com/Page.aspx/...b-a14f-92e2bd34f1c7/Distance_and_Air_Sensors/

The distance sensors are the analog ones. The digital ones are proximity sensors which you don't want.

 

[samarsingla]

The one I made with ir led and ir photo diode can detect things about 20 cm away. This much range is enough for me. Even 10 cms will do. I want to integrate many sensors on a pcb making a mutlidirectional sensor and saving pcb space. Can you please tell how to make it?

 

[Brevor]

distance sensor

Pulse the led on and off at a low freq. The exact frequency is not critical, Just keep away from multiples of 50/60 Hz. (whatever applies to where you live) 10 Khz is good. In the receiver only amplify the ac signal - block the dc component. this will eliminate most of the effects of ambient light.

 

[Sceadwian]

You can also just use a filter. Pieces from remote controls that have black windows on the front work well.

 

[samarsingla]

How can I just amplify the ac signal and block the dc? The pulse is square pulse.. right?? so how does ac come into picture? sorry I am new to elctronics.. If I use a black filter that would still be prone to ambient IR. I want it to detect only the light my led has sent.

 

[ericgibbs]

hi samar,
An ideal 'black' filter is actually a filter that will only allow thru the IR frequencies. Light frequencies outside the pass band will be blocked.

The square wave you are using is considered an 'ac' signal, the ambient light
can be considered as a 'dc' signal, as normally it changes very slowly.

So if you 'ac' couple your amplifier, with a capacitor input, using a black light
filter, you should optimise the performance of your amp, to your IR signal.

Regards
EricG

Nigel, Re-read my original post. "An ideal black filter"

 

[Nigel Goodwin]

You can also just use a filter. Pieces from remote controls that have black windows on the front work well.

They don't 'block' visible light, they only reduce it!.

The easiest method is to modulate the IR at 38/40KHz and use an IR receiver IC for the detection - there are many such examples available on the internet.

 

[Sceadwian]

Pulsed DC is still AC. As you get further and further into electronics you'll realize how little of it is actually DC. A steady voltage/current that doesn't change can not transfer information.

 

[Nigel Goodwin]

Here's an old project of mine, using a PIC 12C508 for left/right/ahead obstacle location - as I said above, you use a 38KHz IR receiver IC, which cures all the problems.

 

[Hero999]

Why does it have to be optical?

What's wrong with ultrasonic or capacitive sensing?

You can buy modules that do this pretty effectively.

 

[Nigel Goodwin]

IR is far cheaper and easier than ultrasonic, which is why it's taken over from ultrasonic in small robots.

 

[dknguyen]

The one I made with ir led and ir photo diode can detect things about 20 cm away. This much range is enough for me. Even 10 cms will do. I want to integrate many sensors on a pcb making a mutlidirectional sensor and saving pcb space. Can you please tell how to make it?

20cm? Is it a proximity sensor or a rangefinder. If it's a rangefinder, I'm impressed!

 

[Dean Huster]

The 40KHz frequency Nigel suggested wasn't just pulled out of a hat. It's pretty must the standard for ultrasonic and IR remotes. Using the modulated IR beam and the filters will help reduce the problems with ambient light, but you'll never be able to eliminate the swamping of the input element from a strong light source no easier than you can hear the whisper of your friend six seats away at today's Superbowl -- the crowd noise swamps your ears.

Dean

 

[Nigel Goodwin]

The 40KHz frequency Nigel suggested wasn't just pulled out of a hat.

I've always assumed that the sole reason for using 40KHz (or so) for modulating IR is that they simply used the existing ultrasonic designs - essentially just replacing the ultrasonic transducer with an IR LED. Since then it's just stayed that way - although they do make a range of different frequencies these days.

 

[Dean Huster]

Yes, Nigel, when you look at some of the original National Semiconductor chips' datasheets for ultrasonic remotes, they were using 40KHz. I also assume that they simply kept the same "standard" and just swapped out the sound for the light.

It's the 40KHz that allows you to get all that distance on a remote link in the presence of other ambient sound as the receiver is "tuned" to the transmitter much like we turn a radio receiver to the station we desire to hear, eliminating all the other stations from our receiver system. If you live next door to a 100,000-watt FM station at 97.7 MHz, you'll never be able to receive the station you really like at 97.5 MHz because the next-door station "swamps" or overloads your receiver and won't let it lock on a nearby frequency. Same way with trying to use the IR remote in the presence of high ambient light. Ever try using one when the evening's setting sun is beaming through the western window directly upon the face of the receiver you're trying to control? Doesn't work well either.

Dean