A unique IR Receiver problem.

[savage67]

Hi friends,

Last day i came across with a little weird problem.
I have built a IR receiver circuit for my project. In this project there is no communication problem in the 1-7 m distance range but if i put the remote controller very closed to the IR receiver (5-10 cm) there is no communication between.

Could you please try to explain this problem if you have any idea.

Regards.

 

[sky_123]

Maybe your IR transmitter is not switching off totally.

 

[keith1200rs]

Or overloading the receiver - recovery from overloading can be slow.

Keith

 

[savage67]

I think it is related with irradiance parameter but i have no deeper information.

 

[BradtheRad]

Reduce intensity a bit by holding a sheet of paper in between.

Or perhaps the sending LED has such a narrow beam that it misses the detector when held close?

 

[DineshSL]

Hi friends,

Last day i came across with a little weird problem.
I have built a IR receiver circuit for my project. In this project there is no communication problem in the 1-7 m distance range but if i put the remote controller very closed to the IR receiver (5-10 cm) there is no communication between.

Could you please try to explain this problem if you have any idea.

Regards.

Do you use 36kHz modulated IR communication ?. If so, that may be due to back and forth reflection between transmitter and receiver; this may spoil 36kHz modulation. Also IR transmitter may radiate weak IR, that may sensitive to receiver even after it is off in 36kHz modulation.

 

[sky_123]

If so, that may be due to back and forth reflection between transmitter and receiver; this may spoil 36kHz modulation

This would be some unique physics?!

 

[DineshSL]

This would be some unique physics?!

See shiny faces of IR transmitters & receivers, that can act like face to face mirrors in close proximity.

 

[sky_123]

It would need perfect alignment, and mirrors 99.99999999% reflective to keep the photons bouncing long enough (of the order of 1/36kHz).. it's just never going to happen.

 

[DineshSL]

May be, it's also not proved.
IR reflects well and don't think need of 100% alignment. IR tr and rc have angles of view. Surround components of tr and rc can also reflect IR since close proximity. I didn't guess it happens in a straight line (example of mirrors is not exactly correct). Since closeness, situation may behave like closed space and can trap the IR.

 

[sky_123]

May be, it's also not proved.

It's not a hard thing for you to read up on mirror reflectivity, the speed of light and intensity decay on mirror bounce. I'm not going to read up on that for you. Common sense indicates that the conditions would never _ever_ exist for "trapped IR" in the user's scenario.

 

[keith1200rs]

I have to agree with sky_123. Light would have to bounce around for around 5 miles to upset a 36kHz modulation (and not be significantly attenuated!).

The ludicrous suggestions are ignoring the obvious likely possibilities - signal overload or the LED has such a narrow beam that it misses the detector when held close. I am not sure if the last of those two suggestions is likely without knowing the physical setup. No details have been given at all about the setup, devices being used etc. Overload can easily be checked with a neutral density filter.

Keith.

 

[FvM]

If you are e.g. using a standard RC receiver like TSOP1736, you'll notice that there's an Eemax maximum irradiation specification. Depending on the sender half angle and power, it can be easily achieved at 5 to 10 cm distance. Similar saturation problems can be expected with most receiver designs.

 

[D.A.(Tony)Stewart]

What is the dynamic range of your AGC? Without a schematic and readings, one can only guestimate.