need help understand IR LED TX/RX for detecting objects

[indianhits]

hello guys i am trying to do a small project on detecting objects using IR LED's but i have a few doubts as i have never done this before can you please tell me how can i set the detection range to like 1CM or 5CM is this possible using PWM.and also PWM enables us to set power but in this modulation which parameter is compromised voltage or current and which ignores ambient light photodiode or other IR LED's.

and by the way is there any good book on mechanics like working with gears,chains etc i am a noob but i want to learn Robotics!

i couldn't find any info in the WWW.

Thanks!

 

[LTX71CM]

If you're serious about robots and their related sensors Let's Make Robots! | Let's Make Robots! is a great resource. The site is very active, the members are helpful and they have plenty of tutorials. Many of those tutorials happen to be on ir range sensing, with several controllers and programing languages shown.

 

[indianhits]

is the receiver circuit any good please help me

**broken link removed**

this is a voltage comparator circuit that i plan to use if non inverting terminal has more volts than inverting terminal then i want 5V to go to microcontroller port
if inverting terminal has more volts than non inverting terminal then i want 0V to go to microcontroller port

and at the voltage divider i want 3V to appear at inverting terminal

and one more thing is IR LED same as Normal LED when it comes to forward voltage(i.e 3.3V) and current as 30mA?

Thanks!

 

[wannaBinventor]

I'm by no means an authority on anything electronics, but I have done some IR projects and I don't think that circuit will work at all.

That won't receive anything at all. You need an IR detector, not emitter for the receiving end. Look for a Vishay TSOP IR detector. It is cheap and easy to work with.

As far as the Vforward and the mA.....
Not sure about forward voltage, I think that it's usually a little more on IR leds. The mA is usually pretty beefy to enable good range. I think the ones I used could take something crazy like a 800mA BURST (as in just a low duty cycle "on" time).

I've never used it for range detection, but I think the idea here would be to use two 555 timers, or one 556 timer. One is for generating the carrier frequency (say, 38Khz depending on the receiver) and the other is for the modulation. If you don't modulate it that the receiver (TSOP) will greatly attenuate the signal. The idea is that you transmit it in front of the device and the IR will bounce back to the receiver -- detecting an object. You use a potentiometer to essentially make the IR transmitting circuit less efficient. I think you can either use it on the carrier wave 555 or the modulating 555, but I'm sure one is probably more proper --- I'd guess the modulating 555. Thus, this will (should) change how well the receiver receives the IR bounce back.

Clear as mud, right?

Also, check me against some other folks by looking at a tutorial on this.

 

[cr0sh]

Something else to keep in mind: It is best when designing such a system that the IR LED and photo-transistor are a "matched pair". Sometimes you can buy them in this manner (that is, they are sold as a pre-matched pair), other times you have to do a little research. The key part is the output frequency of the IR LED vs the frequency that the IR photo-transistor is most sensitive; the datasheets for the parts will tell you this (provided they are available). You won't get a "perfect" match (not even the matched pairs are "perfect"), but generally you can find an IR LED that will cover a broad enough frequency range where its peak output will be close to the center-line of the peak detection frequency of the photo-transistor. Matching the IR LED and photo-transistor in this manner will allow you to get peak sensitivity, as well as range from the devices prior to any amplification on the transmit or receive end of things.