IR Info...

[surjo_dm]

Hi,
Can any body give me some info regarding different IR sensors available today or atleast provide a link? Along with that i would also love to know all about the IR receiver of a TV remote control.
Thanks,
Surya

 

[crust]

The IR modules used in TV remote controls incorporate the phototransistor, gain amplifier, and demodulator in a single package. They usually output an inverted bit stream.

Sharp GP1U52X
Vishay TSOP1140 (I prefer this one)

 

[surjo_dm]

Thank u crust,
But u wrote,"They usually output an inverted bit stream". What does that mean. Maybe i got it wrong. Can u please xplain me?
Thanks..
Surya

 

[kinjalgp]

Inverted bit stream means when the sensor detects IR carrier or signal, its output goes from logic-high to logic-low. i.e Active Low Output.

So if you send 1100 through IR LED, the receivers output will be 0011.

 

[Nigel Goodwin]

Thank u crust,
But u wrote,"They usually output an inverted bit stream". What does that mean. Maybe i got it wrong. Can u please xplain me?
Thanks..
Surya

The output of the receivers is usually an open-collector output, which means that it requires a pull-up resistor to work. This output is normally switched off, so is pulled high by the pull-up resistor. When it receives a suitable IR modulated signal the output is turned on, pulling the output low. So 'on' is low, and 'off' is high, which is the opposite way to normal convention.

There are some details on IR communication in my PIC tutorials at - they are based on the Sony SIRC remote system.

 

[kinjalgp]

The output of the receivers is usually an open-collector output, which means that it requires a pull-up resistor to work. This output is normally switched off, so is pulled high by the pull-up resistor. When it receives a suitable IR modulated signal the output is turned on, pulling the output low. So 'on' is low, and 'off' is high, which is the opposite way to normal convention.

There are some details on IR communication in my PIC tutorials at - they are based on the Sony SIRC remote system.

The output are not open collector. They are internally pulled-up by a high value resistor. For SFH505/506 this value is 100k and for all Vishay Telefunken receivers ie. TSOPxxxx series it is 80k.

 

[Nigel Goodwin]

The output are not open collector. They are internally pulled-up by a high value resistor. For SFH505/506 this value is 100k and for all Vishay Telefunken receivers ie. TSOPxxxx series it is 80k.

Interesting, I've never actually seen a datasheet on the devices, but every circuit I've ever seen (and I've seen a great many!) all use an external pull-up resistor. I've had a TV last year, a brand new Sony set out of a box, where the resistor (SM) wasn't fitted during manufacture - the remote control didn't work until the resistor was fitted.

Obviously the values you quoted are pretty high, and it's quite possible most uses would require an external resistor.

If I get time tonight I'll disconnect the pull-up resistor on one of my IR Boards and see what voltage I get on the output pin (without any connection to any kind of load of course).

 

[crust]

I concur with kinjalp that in fact they are *not* open collector outputs. You can definately use them without an external pull-up. Having said that, I always use external pull-ups because the high-z internal pull-ups dont seem to provide as much noise immunity as a 1k or so external pull-up.

In this **broken link removed** a 30k pull-up is shown in their internal schematic.

 

[Nigel Goodwin]

If I get time tonight I'll disconnect the pull-up resistor on one of my IR Boards and see what voltage I get on the output pin (without any connection to any kind of load of course).

Just to let you know that I did disconnect the pull-up resistor and measure the voltage, as you say there does seem to be a weak pull-up on the output pin - using a 10MOhm meter it reads about 0.1V lower than at the top. I can't be bothered to work that out

Regardless, I'm not planning ever using one without a pull-up resistor, it appears to be normal practice commercially (where they save every resistor they can) - so I'd sooner stick to proven reliable practice.

But thanks very much for the info!.

 

[surjo_dm]

Thank u guys,
Can the IR component of sunlight affect such an IR receiver (the one used in TVs,VCRs etc.)? I am using a similar sensor(GP1U26R series from SHARP) for my project where it is used to receive the reflected IR signals from an obstacle. The transmitter is an IR LED operating at 1kHz. The entire unit is used for proximity detection.
:?: Hence, do i need to have any kind of covering of the unit from direct sunlight?
:? Well, i do have some understanding regarding infrared rays, but is there any link through which my knowledge regarding IR is complete so that i don't have any further misconceptions in the future?
Thanks again,
Surya

 

[kinjalgp]

The receivers in TV uses modulated infrared signal and so it has very high immunity to sunlight or any other ambient IR source. The modulation frequency for most receivers is 38kHz, however it may vary with type of receivers. Check out your receivers specs. The LED should transmit signal at same frequency which a receiver can detect. I think 1kHz is too low and I have never seen any receiver with this carrier frequency.

 

[Nigel Goodwin]

The receivers in TV uses modulated infrared signal and so it has very high immunity to sunlight or any other ambient IR source. The modulation frequency for most receivers is 38kHz, however it may vary with type of receivers. Check out your receivers specs. The LED should transmit signal at same frequency which a receiver can detect. I think 1kHz is too low and I have never seen any receiver with this carrier frequency.

I agree, 1KHz is far too low, IR receiver IC's are available with different centre frequencies, but are all around 38KHz. I've often wonder at the use of this sort of frequency, I suspect that when they changed from Ultrasonic remotes to IR they simply used the same chips in the transmitters - and it's stayed that way ever since. One interesting point, the Swedish television manufacturer B+O used to use a 100KHz carrier, which was why One For All remotes didn't work.

 

[sahu]

The output of the receivers is usually an open-collector output, which means that it requires a pull-up resistor to work. This output is normally switched off, so is pulled high by the pull-up resistor. When it receives a suitable IR modulated signal the output is turned on, pulling the output low. So 'on' is low, and 'off' is high, which is the opposite way to normal convention.


There are some details on IR communication in my PIC tutorials at - they are based on the Sony SIRC remote system.

i want it convert with NEC protocol .
pl help me