View Full Version : IR sensor

06-21-2005, 03:31 PM
I was tryin the IR reciever-transmitter ckt using IR LED and TSOP1738..
the LED glows well as i saw it thru webcam..

The problem is tht the TSOP gives a low output only momentarily when the LED is witched on and despite the LED being "on" it then returns to high voltage
Is this correct cos i think it shud give a const. low in presence of IR radiation.
Please help

06-21-2005, 07:02 PM
Hope you are giving the input IR pulses in pulses..

because the Datasheet clearly states that continuous 38Khz wave is take for a disturbance signal...


check the datasheet..

Are you using the EFY tras-rec ckt???


06-21-2005, 08:42 PM
I dont know if the ckt is in EFY but it wa son this website tself and uses the 555..
I guess from the datasheet its clear tht "after a burst of 20-70 cycles a gap of min 14 cycles is neccesary"
This i dont think is the case if im jus givin a continuos 38khz using a 555

I suppose thts the mistake..But how do i rectify it??
Like how do i limit the pulse train???


06-21-2005, 11:59 PM

To get the spaces between the packets of pulses you could connect two 555 timers together in the tone burst occillator configuration. Say you want 20 pulses on, 20 pulses off (time period of T = 1/38,000s). Make the first 555 timer's time period 40T , 50% duty cycle and connect its output (pin 3) to the reset pin (pin 4) on the second 555 which should be running with a time period of T. Connect your IR LED to the output of the second 555 which will have the desired waveform.


06-22-2005, 12:59 AM
yeh i thought thts the only poss way since only a 555 can do ne sort of timing but if there is any easier way do tell me
Thanks for tht anyways!!!

12-02-2005, 12:50 PM
i hope tat u r modulating the signal with 38khz....
drive the base of a transistor from the output of 555 and have the ir led in the collector arm of the transistor....
supply more current to these ir leds.....