well we just built an ir emitter circuit emitting a 38kHz signal. we r confident that works. however the ir detector shows either high or low (when i block the signal with my hand). why does it not show a 38k signal?
Assuming you're using an IR receiver IC that's how it's supposed to work, it demodulates the incoming IR and 38KHz carriers, and outputs the original modulation.
However, they are designed for data, not a plain carrier, and using a plain carrier will drastically reduce range.
Like I said, it's working exactly as expected then - if you want an AC output from the receiver you need to modulate the 38KHz in the transmitter - this will also massively improve range.
well we just built an ir emitter circuit emitting a 38kHz signal. we r confident that works. however the ir detector shows either high or low (when i block the signal with my hand). why does it not show a 38k signal?
Very simple concept.. it's this property helps it to use i r as proximity detector...
See.. there are two separate parameters.. 1. range 2. ability to pass through an object (transparency..)...both are independent factors...
*1. first thing you should remember is: if you want to improve the range.. then you are to reduce the duty cycle to 10 %... ( but you dont want this...)...
*2. second thing you should remember is: i am sure ..the ir rays never pass through an opaque object... Sometimes your detector gives high and sometimes low...
Reason 1 : very simple ... light travels at speed of 3,00,000Kms / sec. and hence it might be reflected many times before it reaches detector..
As Sir Nigel said, 38 kHz signal has to be modulated and and most IR receivers have a maximum of 600uS pulse width modulation, longer than this will not be received.