IR COMM. without modulation

[khansaab]

Hello guys
My current semester project involves IR transcieving using PIC (PIC16F628).
The question is
IS IT NECESSARY TO MODULATE THE DATA (38 kHz or 40 kHz) IN ORDER TO TRANSFER IT USING "IR" OR IT CAN TRANSFERRED NORMALLY (LIKE DATA STREAM THROUGH USART TX).

SECONDLY WHAT RECEIVER SHOULD I USE (IR TRANSISTOR OR IR RECEIVING MODULE) AND HOW SHOULD IT BE CONNECTED TO THE CONTROLLER

Preferably, i dont want to modulate the data as its increasing the overall project cost. I just want some guidelines about the implementation.

Plz help

 

[Nigel Goodwin]

Check my PIC tutorials, modulation is VERY recommended, and doesn't cost anything to do - it's just software.

 

[Sceadwian]

The IRDA protocol would disagree with you Nigel, as I've stated in several dozen posts over the last couple years. The base discovery protocol works at 9600 baud, 50% duty cycle, directly modulated IR, no carrier frequency, no modulation, no encoding. Pulse shaping is used at higher baud rates, and there are some techniques for much higher data transmission that are outside the scope of the question.

All that is required with transmitting IR data baseband without modulation is using packets with good error detection/correction data. So the software end of things is more important that the transmitter/receiver in such cases.

 

[Nigel Goodwin]

The IRDA protocol would disagree with you Nigel, as I've stated in several dozen posts over the last couple years. The base discovery protocol works at 9600 baud, 50% duty cycle, directly modulated IR, no carrier frequency, no modulation, no encoding. Pulse shaping is used at higher baud rates, and there are some techniques for much higher data transmission that are outside the scope of the question.

All that is required with transmitting IR data baseband without modulation is using packets with good error detection/correction data. So the software end of things is more important that the transmitter/receiver in such cases.

But only short range and fairly low reliability, 38KHz modulation costs nothing, gives good range, and allows the use of reliable, easy to obtain, receiver modules.

 

[khansaab]

I only want to clear this thing out as IR receivers currently available to me doesnt have anything to indicate their receiving frequency (in case of modulated data is used)

So I just wanted to know that whether data could be transmitted without modulation or not.

Since I have now got the answer, so thank you very much to both of you.

 

[khansaab]

Just out of curiosity
How am I going to determine the operating frequency of those IR receiving modules.
And following is the block diagram of my project. Any tips to improve the design

PC --> Serial Link --> MAX232 --> PIC(1) --> IR LED-------------------------------------
----------------------------------IR Receiver --> PIC(2) --> Motor drives --> Motors

 

[Nigel Goodwin]

I only want to clear this thing out as IR receivers currently available to me doesnt have anything to indicate their receiving frequency (in case of modulated data is used)

The frequency generally isn't very critical, but most are around 38KHz, and that happily covers the 36KHz and 40KHz ones.

The frequency is in the datasheets, if you need more accuracy.

 

[UTMonkey]

surely without modulation you would be looking at a much MUCH reduced operating range? (a couple of inches)

 

[Nigel Goodwin]

surely without modulation you would be looking at a much MUCH reduced operating range? (a couple of inches)

No, but you have to build your own IR receiver, which isn't a trivial project, and they don't work as well as the IC ones.

 

[Sceadwian]

You could always send Manchester encoded data, a 19kbaud datastream would be nominally 38khz or so I think? There's really no limit to the range except for as Nigel said on how well the receiver can sort out the modulated data from all the other IR noise that's there, which can be quiet strong.

 

[Nigel Goodwin]

You could always send Manchester encoded data.

Manchester coding is commonly used, but on top of the 38KHz modulation (such as Philips RC5).

 

[khansaab]

Yes I could use Manchester encoding but my projects requirement states that the data to the target vehicle must be sent wireless via PC. Thus I came up with project block diagram as I have posted earlier.

Since it is common all over the web to use 38kHz carrier in IR communications (although IrDA protocol doesnt have anything such), can any body plz help me to implement

NAND(PWM+DATA)

directly from PIC and without any use of other IC'S. I am using PIC 16F628 (18 pin, 1 CCP, 1 USART)

And if I dont use a carrier, will a IR diode-transistor (transmitter-receiver) pair is good enough to serve the purpose or I still have to use a receiving module for receiving the information on vehicle.

 

[Nigel Goodwin]

As in post #2, check my PIC tutorials that do what you want - NAND is neither required, nor advisible.