Maximal power to drive IR LED

[ROSELEE]

I'm making a light barrier and working on a "sender" part right now. The main thing I want to achieve is the maximum distance. I'm using Vishay TSSP4038 for receiving signal.

In the datasheet it's stated that it can work on distances about 30m. I can't get even close. With 350mA (1W) LED it's about 3m max (outdoors).

Here is my current schematic:

T1 is NPN transistor. Q2 is N-channel mosfet. .ATTINY25 turns the LED on/off 38000 times per second (kHz). So effectively I can double max current through LED (change R3 to 2.5). I also have some 1W chinese LEDs from ebay, which do work better (distance-wise), but I'm not sure how much more current I can give them without burning.If you think that the transmitter is good then should I provide receiver details ?

I would be very thankful if someone better than me in electronics would check the schematic and maybe give me some advice or tell if something is really wrong.

 

[DIWdiver]

First off, it looks like you are only getting about 120 mA. Vbe of the ss8050 is typically only about 0.6V, so to get 350 mA, you'd need R3 to be 1.7 ohms. If the duty cycle is 50%, I'd probably go with 1 ohm.

The other thing that will have a huge impact on range is the optics of your LED. In particular, the 'viewing angle'. The smaller it is the longer range you'll have but the more important it will be to aim well.

One other thing is that infrared leds typically have quite low Vf, so 1W is probably more like 800 mA.

 

[ssanasisredna]

Are you shielding your sensor on the receiving end so that it gets as little ambient light as possible. Bottom of some black plumbing pipe pointing at the transmitter will help.

 

[Steve K]

Mr. DIWdiver has some great observations. I've played around with IR emitters and receivers, and optics are half the battle. Some familiarity with the idea of "signal to noise ratio" can help too. 30m is quite a distance, so you'll want to focus the light of the emitters, and make the receiver as sensitive as possible to light coming from the emitter and not sensitive to other light.

Have you considered some sort of modulation of the transmitted light, which when properly demodulated, should help reject the ambient light?

Since this is a light barrier, are you allowed to simply have a retro-reflector 30m away, and have the detector located next to the emitter? This might make modulation and demodulation easier, as well as only having one package of electronics.

Many years ago, I built a little IR beam device using a little 5mm IR LED and a white reflector. It had a range of 2m, and was used to detect if the cat had gotten up on the countertop. With decent optics and a much more powerful IR LED, a 30m range should be very possible.

 

[ssanasisredna]

Have you considered some sort of modulation of the transmitted light, which when properly demodulated, should help reject the ambient light?

It is modulated.