IRForum

Hello, wanted to ask a question that google does not seem to be my friend with, what is an infrared burst length?
From what I understand its the minimum length that you need to transmit an infrared burst for it to be picked up by the sensor.
I am looking particularly at the TSOP4856 I have been in contact with vishay about it and they tell me the minimum burst length is 10 cycles which apparently is 1.8ms.
Now there data sheet shows tests with a space of 600us and a mark of 600us and on the milestag website for infrared laser tag kits they use 600 for space and 0's and 1200 for 1's and 2400 as a header so why are people using below the minimum burst length if that is the specification for it do you think they meant to put 1.8us in the email.

Thanks, Chris.

1 cycle length is determined by the carrier frequency.

So at a carrier frequency of 40kHz, the period is 25 uSecs, which is the same as the cycle length.

So in this case, if the minimim burst was 10 cycles, it would be 250 uSecs @ 40kHz.
(1,000,000/40,000 = 25 uSecs)

In practice, it would be less than this in many environments. For example some protocols would have minimum legnths of 167 uSecs (also know as the mark duration)

also at 56kHz the period is 17.85 uSecs, so 10 cycles would be 178 uSecs. (it looks like your calculations were out by a factor of 10)

There is also a minimum gap (or space) after each burst and usually considerations on burst length vs gap and burst rate.
These are all specified in the data-sheet for each receiver model.


Note: some receivers will be 'tuned' for particular IR protocols ( and burst lengths).

In general, I would suggest sticking with mark/space lengths being used in existing protocols - where possible.