How to increase IR transmitting distance?

Thread Starter

dhanasingaraja

Joined Nov 25, 2011
12
I'm doing a bidirectional visitor counter.i m using TSOP 1738 at receiver side,and 38KHZ astable multivibrator at transmitter side.everything works fine.but it can't work if the distance between Tx,Rx is above 8cm.It's very short distance,so i can't use it in real time.I picked up sony IR LED from my old TV remote.now also it can't works for long diastance.I have attached my circuit diagram.I have used R1=1k,R2=1.394k,c=0.01up.
please...... help me!
 

Attachments

John P

Joined Oct 14, 2008
1,749
I can see two potential problems. First is that your 38KHz oscillator depends on components that may not be in the tolerance you need. Have you adjusted it with an oscilloscope? You'd be better off with a crystal-based oscillator, anyway.

Second, those TV remote receivers have built-in gain control. If they receive a continuous signal, they turn down the gain. What you need to do is send a burst of 38KHz, pause, then send another burst. I'm not sure what the duty cycle should be, but certainly no more than 50%. Maybe 10%.
 

MrChips

Joined Oct 2, 2009
19,160
I have recently witnessed IR communications achieved down 30 metres of hallway using standard IR emitters and 38KHz IR receiver modules.
 

bertus

Joined Apr 5, 2008
19,951
Hello,

The TSOP has an automatic gain control build in.
This will reduce the gain if to much IR signal is recieved.
You will need to pulse the IR signal in order to have the wanted gain from the TSOP.

Bertus
 

Thread Starter

dhanasingaraja

Joined Nov 25, 2011
12
thanks to every one.i m clear now.i should use a second 555 to cause a break in the 38KHz 555, say 50 pulse periods On 20 pulse periods Off.but how can i control a astable multivibrator by another.could i control one by controlling reset bin? or could i do AND operation for both the outputs?
 

Thread Starter

dhanasingaraja

Joined Nov 25, 2011
12
why? controlling reset pin cause any problem? or is it not possible for practical.pls help me.i want to know that.
 

MrChips

Joined Oct 2, 2009
19,160
why? controlling reset pin cause any problem? or is it not possible for practical.pls help me.i want to know that.
Actually, I've changed my mind. You can do either. Just be aware that resetting the 555 will lengthen the width of the first pulse.
 

Thread Starter

dhanasingaraja

Joined Nov 25, 2011
12
Thanks,
I have used two timers as you told.the distance also increased from 8cm to 50cm.but i want 1m distance for my application.how can i get this?
 

John P

Joined Oct 14, 2008
1,749
Forget NAND gates. Just run the LED so one end of it goes to each 555. (With a resistor included, of course.)
 

Thread Starter

dhanasingaraja

Joined Nov 25, 2011
12
hi,john what a mind for u? excellent
i modified my circuit like this......
pls say what's wrong with this
 

Adjuster

Joined Dec 26, 2010
2,147
You may want to look at the quality of the current waveform through the LED (look at the voltage across the resistor)

What is the duty cycle of the drive current? If the current is passing for too large a percentage of the time, the carrier content will be impaired.
 

Thread Starter

dhanasingaraja

Joined Nov 25, 2011
12
I m getting 3.3v at 33R. this is my circuit.......
pls say what's wrong with this.i m giving 33% duty cycle for the drive current
 

Attachments

Thread Starter

dhanasingaraja

Joined Nov 25, 2011
12
success! success! success!

My circuit works fine.it works for more than 3 meter.nothing is wrong with my 2nd circuit.i did mistake in bread board connection.now i have corrected it.

thanks friends,
thanks for spending your valuable time for me
thank u very much
 
Last edited:
Top