Help required with TSOP1738 Ir Detector

[suhasm]

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?

 

[Boncuk]

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

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

Boncuk

 

[suhasm]

Do you mean that i have to build another astable and connect the output of that to the reset pin of the 38kHz astable?

And do u mean 50-100 microseconds or milliseconds?
milliseconds seems to be too large a time interval to me...

 

[blueroomelectronics]

The TSOP is designed to work with short bursts of data, not a steady modulated beam. SB-Projects: IR remote control

 

[suhasm]

@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?