hi,

i am building a robotic system...in that the system should be able to sense the object automatically....i am using ir transmiter(555 ic and ir led) and ir receiver(tsop1738)...ir sensor should be able to sense the ir light coming after reflecting from the object...

when i placed the reciever and transmitter face to face its working properly ....but when i placed both facing the same side, the sensor is able to sense only vey near object,about 5cm....i need to get a larger range...when i tested my sensor with tv remote, the sensor is able to sense object at a long distance....so i think the problem is with my transmitter...i also tried to give the 38khz wave from function generator to drive the leds,...i am attaching my transmitter circuit diagram

if any of you a ir transmitter circuit pls provide that to me....hope you will help me in trouble shooting the problem

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change the base transistor that is 4.7k top something smaller, so that the transistor opens more and therefor makes the led pulse more brightly. but bare in mind, that this may burn out your Diode.

Edit, even better ideea is to totaly get rid of the resistor that is in series with the IR diode. 47ohm it is.

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NOT a good idea to remove the 47 ohm, but you should make it much smaller, 4.7 ohm or so would help considerably, and change the 4.7K to 470 ohms for more base drive.

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2N2222 transistor is general purpose transistor and can have very low gain,
as low as 35 (there are big variation even between transistors with same
part number). If you heat it too much during soldering, this can get even worse.
To drive IR LED at 50% you will want some 40-50mA. If transistor has gain of
30, base current has to be at least 1.66mA. If the high of 555 output is close
to 5V and Vbe is some 0.7V, current through R4 is only
Ib=4.3V/4700Ohm=0.91mA
If you ask me, I would first change the R4 to 2.2K (red-red-red).
That should guarantee base current of at least 1.9mA.
Don't go too crazy on lowering R3 values because your remote only works for a
second or two. Your sensor might have to run continuously. If you lower the
value of R3 do it gradualy.

 

removing the 47 ohm resistor and driving the IR led in a low dutycycle power bust mode..in which a high current is passed , for a very short duration.

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Read the data sheet for the tsop receiver too.... it attenuates the signal after a short time of continuous receive - it's worth using the trigger function to turn the signal on/off inline with the duty cycle.

it may help.

best regards,
colin

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