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Help required with TSOP1738 Ir Detector

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New Member
Hi ,

I'm using a infrared LED pulsing at 38kHz and a TSOP1738 receiver to receive the signal from the LED.

I have checked the transmitter through an o'scope and it seems to be pulsing at 38kHz with ~50% duty cycle.
The IR LED is being driven by a BD139 with on current = 100ma.

The TSOP1738 responds to pulses from the TV remote and i can see the pulses on the o'scope.

But , when i turn on the Ir transmitter , the output of the TSOP goes low for around 1.5s , then goes high again. This is happening from atleast 10 feet.
(which is more than enough range for me)

I understand that this is due to the gain suppression by the TSOP when it detects a continuous signal to reduce noise.

How do i make a circuit such that the output of the TSOP is continuously low , when the the IR LED is pulsing and it is continuously high when it is not pulsing.

I dont want to use and nor am i very comfortable with programming microcontrollers. I want to finish this with using only ICs and transistors.

I read the datasheet but did not understand much about the transmission protocol.
Should we first send our data in less than 70 cycles of 38kHz ?
then should we wait for 4 times long? (70*4 = 280 cycles)

all this is getting pretty confusing for me...
can sum1 please explain how the TSOP expects the IR light to be modulated and show a simple circuit that demonstrates how to do this?


New Member
You are supposed to transmit bursts of pulses, not continous pulses.

Use a dual timer and interrupt the 38KHz signal every 50 to 100ms.



New Member
@blueroomelectronics thanks for that link...

i followed boncuk's advice and made another astable with period = 70milliseconds and connected the output of that to the reset of the 38kHz carrier astable.

The TSOP seems to be detecting the signal continuously now. Thank you :)

Can any1 tell me how to send data through a microcontroller through Ir. Can i just modulate data in the normal serial format or do i have to use some other encoding?
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