IR COMM. without modulation

[khansaab21]

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

 

[FvM]

It can work with unmodulated IR if you are able to distinguish 0 and 1 state unconditionally, also in presence of ambient light. Are you?

Obviously, a project specification is necessary to decide about. Standard remote control receivers and a respective modulation have been used with success for low speed (1-2kbps) serial communications. It can't work for higher speeds anyway. You may want to check the IRDA specification and devices, that work up to 115 kbps on short distance.

 

[khansaab21]

I am not really sure about the ambient conditions. But following is the block diagram of my project.

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

Max. distance between transmitter and receiver is 1m

Any suggestions to improve the design and again the same question, looking at this block diagram of project, the data have to be modulated or a simple TX transmission will serve the purpose

And incase if ypu suggest to modulate the data, is there any way that i can generate
NAND(PWM+DATA) directly from PIC

 

[khansaab21]

Plz any of you out there plz help as i dont have much time and have to get started

 

[betwixt]

You CAN use IR without a carrier but your range and reliability will be very much reduced. The idea of the carrier is that you can treat the signal as bursts of AC rather than DC so it become much easier to filter out unwanted frequencies the detector will pick up.

To 'nand' the signal, if that's what you really want to do, set up an output with a constant signal, this could be from a PWM module or a timer, then use the TRIS register bit for the output pin to switch the signal on or off. When set to input mode (tris bit is 1) the pin will float rather than drive the signal out.

If you are using a receiver module intended for use in IR communication, such as the ones found in domestic equipment, it already has filtering built in so you MUST use a carrier for it to work.

Brian.

 

[bobcat1]

HI

Most IR detector IC use modulation in order to prevent interference from light sources

So if you plan to use IR detector IC in your project you will have to use modulation

But if you plan to build a discreet detector(using a pin photo diode and op amp) and you are transmitting from a very close distance (less the few centimeters) you can use IR without modulation

All the best

Bobi

The microcontroller specialist