infrared reciever ksm803 issue

[Ahmed Wahdan]

i have infrared reciever ksm803 , i connect it and test it with TV remote and it work ( using LED blinking ).
i use 950 nm LED IR transmitter , input of this led is 38 khz signal with 50% duty cycle ( as IR reciever has 38 khz filter )
my problem is :
reciever output should be low when IR signal recieved .
but i have this beaviour :
at start , IR signal found , output of IR reciever is High
IR disappear , nothing happened.
IR appear again , the reciever output has a low pulse and then return to high .
what i have missed ??

 

[hexreader]

Check the datasheet - there are minimum and maximum pulse width specs (500 to 700 us).

Most 3 pin IR receivers will not work with steady 38kHz signal, the signal needs to be modulated.

If my reading of the datasheet is correct, this particular receiver looks to me to be unsuitable for TV remotes in any case.

 

[Ahmed Wahdan]

i found that if the tx work send all time the recierver will not sense it , should be off time so the reciever can sense the signal .
i want to count no of users passing a door , how can i achieve that ?

 

[hexreader]

Your transmitter needs to work as follows:

1) send 38kHz for 600 us
2) send nothing for 600 us
3) repeat forever

... or put another way: modulate your 38kHz signal with a 1.7 kHz square wave.

You will need to detect presence or absence of 1.7 kHz at the receiver.

Note that this is theory from reading the datasheet. I have never tried this myself. I have only ever worked with domestic TV IR protocols.

 

[shihab_leo]

you can send a pulse train with 800us time period and 50% duty cycle(400us burst of 38kHz and 400us space). on receiver side, if off period is greater than 400us -- it means someone or something is in the path

 

[Ahmed Wahdan]

i read that if signal is continous reciever will ignore it .
now how i can control range of IR transmitting ?

 

[shihab_leo]

send a pulse train with 800us time period and 50% duty cycle(400us burst of 38khz and 400us space)

this way you are not sending a continuous signal. you will send 400us burst of 38kHz and then idle period for 400us.

To control the range, you should control the transmitting power (current to IR LED). if you need long range, consider using hi-power LED