IR LED motion trap

[P4d0uch]

Hi, I wanted to make an IR LED motion trap, using IR LED and IR phototransistor, to know, if someone entered or exited a room. But the problem is, that the range is only about 10-15cm. Is there any way to make the range at least 1m?

Currently the LED is powered by 5v source with current limiting resistor of 150 ohm.

Thank you for any answers.

[mattmiller]

More LEDs?

[P4d0uch]

I've just looked at the specification of the IR LED and found out, that it is one of the weakest. I will try to buy some more powerfull ones.
It should not be a problem to get a range of 1m right?

[mattmiller]

Its just a matter of power really - you could need a bigger sending diode or multiple ones

[P4d0uch]

yeah I had some 3mm at home. And then I've found out that the power is only 3.2 - 20mW/sr and the better ones are over 100 mW/sr. That might be it.
I will buy some 5mm and more powerfull LEDs

[W0LFIE]

The ones used in remote controls usually have a good output, actual power unknown, usually from a 3V Power supply from AA or AAA cells.

But if you have a scrap Remote kicking about... Robert could be yer mother's brother.

[P4d0uch]

You're right. I had one remote from old DVD around. And with a bit of tunnig of the resistor values on the phototransistor side, I got around 1m of range with no problems.

The key is to have the diode and transistor aligned perfectly, so I will buy another LEDs and use at least 2 to make it easier.
Thanks for your help.

[W0LFIE]

I expect that you know you can "see" IR LED(s) using the camera on your phone?

Always a useful tool for testing such things..

Wolfie tip #112

[P4d0uch]

Yes. That is useful when working with IR.
I've got it working, but I will need to make a better solution to limit the current to the LEDs, because the limiting resistor gets very hot. For now I used 1W resistor but it is very hot to touch.

[texy]

Alternatively you could use ultrasonic range finder, eg HC-SR04

Texy

[P4d0uch]

Yes I've got 2 at home but I thought that IR would be better in this application.

[texy]

Yes I've got 2 at home but I thought that IR would be better in this application.

As long as you can get it working, yes.
The advantage with the HC-SR04 is that it doesn't need anything on the other 'side' of the door frame, ie it is a transceiver.
Texy

[P4d0uch]

That is true. Maybe I will give them a try.