How to increase IR transmitting distance?

dhanasingaraja · Nov 25, 2011

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!

ericgibbs · Nov 25, 2011

dhanasingaraja said:
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!

hi,
If your IR emitter is sending a continuous 38KHz signal, the TSOP will not work correctly, there has to be breaks in the 38KHz transmission, look at this clip from the datasheet.

dhanasingaraja · Nov 25, 2011

thanks ericgibbs,
but i can see this also in datasheet (in features)
"Continuous data transmission possible (up to 2400 bps)"
what mean for that?

ericgibbs · Nov 25, 2011

dhanasingaraja said:
thanks ericgibbs,
but i can see this also in datasheet (in features)
"Continuous data transmission possible (up to 2400 bps)"
what mean for that?

Data transmission is not the same as the 38KHz frequency.

dhanasingaraja · Nov 25, 2011

ok,how should i modify my transmitter circuit? pls..........help me

ericgibbs · Nov 25, 2011

dhanasingaraja said:
ok,how should i modify my transmitter circuit? pls..........help me

You could use a second 555 to cause a break in the 38KHz 555, say 50 pulse periods On 20 pulse periods Off

dhanasingaraja · Nov 25, 2011

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?

ericgibbs · Nov 26, 2011

dhanasingaraja said:
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?

hi,
I would use a Reset on the 555 emitter driver

Boncuk · Nov 26, 2011

Hi,

I guess this what ericgibbs mentioned.

U1 generates approximately 38KHz, while U2 generates a lower frequency.

With U1 being reset at the low frequency the output should look like the blue trace on the scope. The yellow trace shows the output signal of U2.

With a constant carrier frequency the TSOP assumes disturbance and cuts back on receiver sensitivity, thus making the signal unusable for long range.

Use a TSAL6100 IR-TX-LED for max range. It can work with a constant If of 100mA.

Boncuk

jpanhalt · Nov 26, 2011

Here is an almost identical circuit with values that give the proper packets of pulses. I used a 556, which is a dual 555. The pin nmbers for using two 555's will be different, but the pin names will be the same. Capacitor values are in microfarad, unless specified differently.

John

dhanasingaraja · Nov 26, 2011

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?

jpanhalt · Nov 26, 2011

Please post your circuit and details. Read the datasheet carefully where it describes what is required in terms of the signal for best sensitivity. Some mechanical changes, such as a putting the receiver at the end of a tube (light shield) to decrease interference from outside. Are you using it in a room with fluorescent light bulbs? John

dhanasingaraja · Nov 26, 2011

yes,i m using this in a room with fluorescent light.i have attached my circuit diagram.

jpanhalt · Nov 26, 2011

That circuit is not like either Boncuk or I recommended. It will not give you the 38 KHz "carrier" modulated on/off at about 1 KHz, as required for maximum distance. If you are using 555's, you must have two. Fluorescent lamps will seriously interfere unless you use the proper modulation. It is even described in the datasheet you have.

John

audioguru · Nov 26, 2011

How do you tune the 555 to exactly 38kHz?
How do you power the TSOP IR receiver?
Are your fluorescent lights the old long tube ones or are they new compact fluorescent light bulbs that cause 38kHz interference?

dhanasingaraja · Nov 26, 2011

oh!!!sorry, i wrongly sent my old circuit. i modified my circuit like this......
pls say what's wrong with this

audioguru · Nov 26, 2011

Your circuit is different to the circuit that works.
Get rid of the 7404 and correct the values of R4 and C3.

jpanhalt · Nov 26, 2011

I ran those values through a calculator and get approximately 38 KHz at 51% duty cycle for the "carrier" and 481 Hz for the modulation. The modulation has a duty cycle of 67%, which is why I suspect the original designer of that circuit added the inverter. A more common modulation frequency is about 1 KHz at 50% duty cycle (like my design above).

That gets us to the point of: 1) Analyzing another circuit for why it doesn't work; or 2) Asking why the OP here didn't go with either suggested circuit given here? The other circuit should work. Does it work and at what range? Have you confirmed all of your connections? Have you triple checked all component values?

If the output of the inverter were connected to an LED through a resistor instead of to the second 555, it's output frequency is a bit too high for most most people to see it pulse. You might be able to see a flicker out of the corner of your eye. If you see a steady on, try looking at it through a fan for something to get a strobed effect. That won't tell you its frequency, but it will tell you whether it is flashing. If it is flashing, then the problem is probably somewhere else.

John

dhanasingaraja · Nov 30, 2011

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

ericgibbs · Nov 30, 2011

dhanasingaraja said:
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

hi,
Well done,
Please post your working circuits so that others can benefit from your work.

How to increase IR transmitting distance?

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