How to improve the distance in IR communication?

[dhanasingaraja]

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!

 

[chuckey]

Have you got a good filtering system for your 38 KHz signal? Are you running some real power into your transmitting LED(s) have you got some focussing optics?
Frank

 

[dhanasingaraja]

tsop internally has a bandpass filter.i don't use any focusing optics.tv remote works for more than 10m without any focusing optics.but why my circuit not working? this is my transmitter circuit

 

[emresel]

Hi;
Check first if your ir led emitter is at 950nm. Because your receiver is tuned to that wavelength.
On the other hand your multivibrator applies continuous pulses to IR led. But your receiver saturates its output after a number of pulses. In spec it is wrtitten that;

After each burst which is between 10 cycles and 70 cycles a gap time of at least 14 cycles is neccessary.

You can test it by placing some obstacle between them, and see if receiver generates any output, at the time you remove obstacle.
(I mean simulate burst packages with time gaps, in a short easy manner)

Also consider if your ir emitter led can sink current in such a continous pulse driving mode.
In remotes there is relatively high current to increase distance, but applied in short durations, so that IR led can stand it (no damage).

Hope helps

 

[dhanasingaraja]

Thanks emresel,
receiver generates output,when placing a abstacle.not generates output when removing.and i can't find the wave length of the ir led.i'd used several ir leds one by one.but i can't get lange distance output still now

 

[dhanasingaraja]

please help me........................

 

[hexreader]

Have you checked the datasheet for the IR receiver that you are using?

The receivers that I use have a maximum 'mark' time for a signal and are not designed for continuous 38kHz operation.

I suspect that this may be your problem. I suspect that the 38kHz transmit signal needs to be modulated, not steady, requiring two 555 timers rather than one.

Hope this helps

EDIT: sorry, this repeats the information already given. please ignore my post

 

[dhanasingaraja]

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?

 

[s_guria]

control the reset pin(pin4) of 38KHz 555. connect the output of second multivibrator to it.

 

[dhanasingaraja]

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?

 

[emresel]

what is the resistor value from 5V to IR led. Try to decrease it (supply more current to LED). But be carefull, avoid to defect LED.

 

[dhanasingaraja]

33 ohm.i think,can't decrease below this

 

[emresel]

What is the voltage on 33R when transistor is on? Do you have any scope to measure it (waveform)? May be we can calculate the current and decide.

 

[dhanasingaraja]

I m getting 3.3v at 33R. this is my modified circuit.......
pls say what's wrong with this

 

[emresel]

I m getting 3.3v at 33R.

means 100mA over LED, so you may try to decrease resistor value a little bit.

50 pulse periods On 20 pulse periods Off

Beside it decrease on period (ie 50 to 10) and increase off period (ie 20 to 50). So led can stand higher currents i think.
On the other hand, do you apply supply filter for tsop1738?
See datasheet page2, 100r in series on supply line then cap to the ground.
I advise greater value rather than 4.7uF. This should also effect receiving sensitivty of tsop.

From my point, that's all what i can suggest on this issue.
Good luck.

 

[wa1kij]

Perhaps you should add some gain to the receive side.

---------- Post added at 18:22 ---------- Previous post was at 18:12 ----------

In effect, your receiver is a radio receiver whose antenna is a photodiode or phototransistor. If you tuned it to 38Khz, say with an active filter, it would be more sensitive to your light source, and less sensitive to ambient light.

 

[Pjdd]

Your second (modified) circuit should work. The output stage and the on-off ratios could be improved for efficiency, but it should easily work at 1m even at a much lower drive level, that is, at a lower LED current. Calculations using your component values yield a nominal burst length of about 26 cycles ON and 52 cycles OFF, which should be OK for a TSOP1738.

Here are some thoughts:
1. Is there a strong ambient light shining on the receiver module? Other light sources can reduce the sensitivity of the receiver. It should be shielded in directions other than the front. A guide tube at the front will also help.

2. Judging by your resistor values, I assume you're using 1% types. What about the timing capacitor? If you're using a ceramic disc capacitor, they have wide tolerances and could place the frequency well of the ideal 38kHz. Do you have any way of checking the frequency?

3. As someone else pointed out, the LED's wavelength should be 940 or 950nm. If the ones you're using happen to be, say 850nm types, that will greatly reduce the sensitivity too. If you don't know, can you get known ones? For example, the Vishay TSAL6200 is a good one.

I've been working a lot with IR transmissions for some time now. With about the same LED current as yours (~100mA peak), I get reliable reception at 4-5m using no-name IR LEDs from the local market, and up to 15m using Vishay TSAL6100 LEDs. The 6100 is more sharply focused than the 6200 and has a stronger axial intensity, but has a narrow angle of emission and is best suited for fixed point-to-point communication.

 

[dhanasingaraja]

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 invaluable time for me
thank u very much

 

[Pjdd]

Congratulations! Here are some suggestions for improvement:

You don't really need the output transistor. A bipolar 555 (not the CMOS version) can easily drive the IR LED at the required current level. You can connect the LED cathode directly to the output of the 555 while still retaining the series 33-ohm resistor. That will reverse the duty cycle ratio and is preferable as it means less power drain and lower dissipation for the LED. It will give you a peak of about 60mA.

The sensitivity of receiver modules like the TSOP1738 depends largely on the peak pulse rather than the average. If you use 18k for R1 and 10k for R2, that will further reduce the duty cycle to about 26%, thereby reducing dissipation and power drain.

You could also use 0.1uF for C3 and 10k each for R3 and R4, reducing charge and discharge currents.

 

[dhanasingaraja]

hi,
Is 50% duty cycle not necessary for 38khz?.