IR software & hardware basics

[flotulopex]

Hello,

I've been looking around this forum and the Internet about basic information on IR communication. But there's so much information I can't make up my mind what kind of components I should get started with and, hence, what software method I should apply.

For a start, I have 2 questions.

A.- As IR-emitter, one use IR-LEDs. As IR-receiver, one can use IR-LEDs, phototransistors or IR-Modules. What makes the difference between all these receivers?

B.- Some IR-LED's datasheet mention pulse frequencies (mostly 38kHz and 40kHz), other don't. Why, what's the difference between those LEDs?

Here are some of the sites I already visited:
http://www.rentron.com/Infrared_Communication.htm
http://www.winpicprog.co.uk/pic_tutorial5.htm
http://www.ustr.net/infrared/infrared1.shtml

[skimask]

A.- As IR-emitter, one use IR-LEDs. As IR-receiver, one can use IR-LEDs, phototransistors or IR-Modules. What makes the difference between all these receivers?
B.- Some IR-LED's datasheet mention pulse frequencies (mostly 38kHz and 40kHz), other don't. Why, what's the difference between those LEDs?

If this is what you wanted to know:
TX:
IR emitter - could be just an IR LED, could be a premodulated IR LED with a built in oscillator running at 38khz (give or take, it varies)
IR LED - just that, an infrared LED, generally, if you want to use it in an IR comm scheme, you have to modulate it.
RX:
IR LED - not really a receiver, but you could use it in the way that I used them in my touchless sensor project.
IR phototransistor - = IR detector, does just that, detects IR, turns on a transistor, generally doesn't to any 'detecting' of a 38khz carrier
IR modules - have a built in IR phototransistor/diode and a filter to detect a 38khz carrier wave, generally pulls an output to ground when a carrier is detected.

The datasheets that mention 38khz/40khz/whatever mean that the specific module is set up to either TX or RX an IR beam modulated at that frequency. If you're just dealing with a 'beam breaking' application (like a garage door sensor), you don't need to modulate anything. If you want to send some data, you want to modulate the signal.
Think AC vs. DC. You can't send any useful information over a DC line. Once you start changing the DC line, it becomes AC and you can send info. (and I'm using AC kinda wrong in this instance, I should be calling it pulsing DC).

Don't know if it helps much. I've done a little bit with IR Tx and Rx, modulated a carrier, detected a carrier here and there. I used the old Sony IR protocol to handle the data transfer, works for me... I guess I need more info from your end on what you want to accomplish...

[flotulopex]

Thanks for all these infos, skimask.

I've started a simple remote control project.

The TX side is not an issue curently.

For the RX side, I found some "old" phototransitors (could be SFH309).

The problem I see now, is the reception sensitivity.

I use my TV remote as test IR generator and can measure some signal for a maximum of 30 centimeters away from the phototransistor. above this distance, I can't se any more signal.

Is there any trick to make the receiver more "sensible"???

[dhouston]

I recommend starting with a TSOP1100 which is a wideband receiver (33-57kHz carrier, 940nM which is the wavelength used by consumer IR devices) and connect it as shown here...

• http://davehouston.net/learn.htm

before trying more complex things like a phototransistor.

[flotulopex]

Dave,

Why do you think a phototransistor is "complex"?

I connected it just like you show it up in your webpage and it works. I have connected a BC237 to amplify the phototr's signal but this doesn't make it more reactive.

The only problem is sensibility. Or am I wrong and maybe I should measure the sensibility another way?

I don't know to make it better...

Nevertheless, I'm going to by some IR modules to make some tests.

[skimask]

Dave,
Why do you think a phototransistor is "complex"?
I connected it just like you show it up in your webpage and it works. I have connected a BC237 to amplify the phototr's signal but this doesn't make it more reactive.
The only problem is sensibility. Or am I wrong and maybe I should measure the sensibility another way?
I don't know to make it better...
Nevertheless, I'm going to by some IR modules to make some tests.

Do you have any lenses in the way of the emitter or detector?
How much ambient light do you have in the room?
What kind of lights do you have in the room where you are doing your testing?
All of these can kill an IR signal...

[dhouston]

Dave,

Why do you think a phototransistor is "complex"?

I connected it just like you show it up in your webpage and it works. I have connected a BC237 to amplify the phototr's signal but this doesn't make it more reactive.

How are you measuring/detecting the output?

With a phototransistor you will receive the carrier frequency, usually in the 36-40kHz range. It's difficult to measure the amplitude of a 25-28µS pulse and the output of the phototransistor circuit will be a series of bursts at the carrier frequency. You'll have to count the number of such pulses to determine the duration of the bursts and decode the transmission. Or, you'll have to use a low pass filter to demodulate the signal to recover the data envelope.

An IR receiver demodulates the transmission and outputs the baseband data envelope with the width of the spaces (it's active low) proportional to the duration of the bursts. It's an order of magnitude or two simpler to deal with.

I suggest the TSOP1100 (available from Mouser) because you don't have to worry about matching the carrier frequency of the IR remotes you might come across. Read the datasheet for the TSOP1100 - it's got a lot stuffed into that small package.