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What is burst of 38 kHz?

Suraj143

Active Member
It says the infrared receiver supporting 38 kHz range.

It means 26.3 uS time for one pulse (100% duty cycle).
13.15uS if it is (50% duty cycle)

Turning on a bit for 13uS & off the other 13us will generate a 38 kHz wave with 50% duty cycle.

I need to know what is burst of 38 kHz?

Thanks
 

Suraj143

Active Member
In Sony the logic zero represented by 600uS.Is this a collection of 26.3uS time?

Then do I need to call my 13uS on / off routine 23 times [600/26 = 23] to represent 600us in Sony?
 

Suraj143

Active Member
Hi is it tutorial number 5 but it has all receiving side.receiving part ok for me.

I need the transmitting part.generating 600uS,1.2mS in 38khz range.
 

Suraj143

Active Member
Hello I cannot see any transmitting part.All I see is decoding TV remote codes in tutorial 5.

can you tell in which tutorial does it have the transmitting part?
 

Suraj143

Active Member
Hi I found that I read it thanks.

But I have a problem.

In sony 600uS time is a burst of 38 kHz. Then in a burst it has high & low pulses.Ex:13uS on 13uS off.

When decoding the pulses from a PIC cant the PIC detect the high & low pulses within a burst?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
No, it doesn't see them, the IR receiver IC demodulates the bursts and outputs a simple pulsed signal, representing the original pulses (but not identical to them).
 

Suraj143

Active Member
Nigel & audioguru please answer me.

Picture 1 shows a burst of 600 uS in a Sony pulse (logic zero).
Picture 2 is the inside of that burst part.

One cycle’s length is 26 uS followed by a 50% duty cycle that is 13uS mark time & a 13uS space time.

From the datasheet of receiver module

Burst length should be 10 cycles / burst or longer.

What does it means by burst length?
Does it mean it needs 10 cycles?

One cycle length = 26uS
Then in the above example it is 26 uS X 10 = 260 uS minimum time needed to receive a signal? Tell me am I right or wrong?

From the datasheet of receiver module

After each burst which is between 10 cycles and 70 cycles a gap time of at least 14 cycles is neccessary.

I cannot understand this.
 

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audioguru

Well-Known Member
Most Helpful Member
Read the datasheet of a TSOP1738 receiver IC.
They have an automatic gain control that reduces gain if the 38kHz is continuous because then it might be interference from a compact fluorescent light bulb. The IC expects data which is in bursts of 38kHz pulses. The bursts must be 10 cycles of 38kHz or longer. After each burst which is between 10 cycles and 70 cycles a gap time of at least 14 cycles is necessary. For each burst which is longer than 1.8ms a corresponding gap time is nexessary at some time in the data stream. The gap time should have at least the same length as the burst.

The TSOP1138 requires fewer cycles of 38kHz during each burst because it can operate at a higher data rate.
 

Suraj143

Active Member
The bursts must be 10 cycles of 38kHz or longer.

What does means by 10 cycles? Does it means 26uS X 10 = 260uS time?
 

Suraj143

Active Member
I see now, thanks.

1 cycle (13uS on & 13uS off) is not enough to detect by the receiver.It needs minimum 10 cycles (260 uS).

And also it needs a gap time after each burst.It needs minimum 364uS time.

All the protocols follow these rules.

I asked because I need to turn on an LED through IR pulses.Earlier I did sending just a 1 cycle (26uS) but it didn't work.

Now I know why it didn't work because the burst must hold at least 260uS followed by a gap time.
 

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