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Topic: Making a tsop ir receiver with discreet components? (Read 2104 times) previous topic - next topic

Oddwired

Im looking at the tsop4838 ir receiver modules and I want to use them in a laser circuit however I can't find a laser that is both safe and capable of working with the sensor so I want to build one of the detectors out of discreet components and tailor it to work with a red or green laser pen.

From the documentation it appears a photodiode is connected to an amplifier (which I assume is a transimpedance op amp circuit) then a band pass filter and then a demodulator.

Would this just be a matter of a few simple op amp circuits or would it get more complex than that and can anyone explain why there is a demodulator in the circuit? I can't see which signal is being demodulated as i thought the circuit just passed through whether the signal was high or not and whatever microcontroller the tsop was attatched to did all the demodulating?

Wawa

Building a sensitive IR receiver from discrete components is not that easy.
TVs from the seventies and eighties (e.g. Philips K9/K11) had discrete receivers.
Maybe you can dig one up, and mod it.
What is your project. Why a laser.
There are high power narrow beam IR diodes that might be ok for what you're trying to do.
Modulated IR is used to make data transmission immune to ambient light.
Leo..





runaway_pancake

Can / Can't / Maybe
Attached is a schematic for an IR remote receiver, based on an old (obsolete?) IC.

Maybe research light beam communicator.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

Boardburner2

#3
Sep 16, 2015, 03:22 am Last Edit: Sep 16, 2015, 03:49 am by Boardburner2
and can anyone explain why there is a demodulator in the circuit?
iR remotes are driven with high current pulses to increase the range.
Pulse position modulation is normally used.

Back then a custom chip did the demod although these days a micro can do it.

Laser diodes can only be modulated between about 20% to 100%, they are not digital , so a carrier may be needed depending on what you are trying to achieve.

The reciever you mentioned uses a carrier frequency but gives a digital output signal that can be decoded by a micro.

Edit

Mixing my tenses.
The origional remotes used baseband on off switching of the led.
These days modulation seems to be the norm.

be80be

You'll have to make this to
http://pdf.dzsc.com/UPC/UPC1373H_1261351.pdf

lasercn

I think you get the ir receiver modules from the B2B marketplace ,their are many supplier to supply the ir receiver modules ,so you can select the best suitable , like the alibaba ,made in china and en.ofweek is a good choice!

be80be

Here something that gets you over 30' with a red pin laser https://dmohankumar.wordpress.com/2012/11/17/laser-based-alarm-system-sensor-circuit-17/

Chagrin

A laser will certainly work with an IR receiver (been there / done that with TSSP4038, specifically). be80be kinda beat me to the punch but the range you'll get is limited primarily by how well you can aim the laser. Make sure you get a laser module with an adjustable focus so you can UNfocus it and get a larger spot that doesn't require precise aiming.

Grumpy_Mike

The real reason modulated light is used is to make it immune from background light.
The amplifier has a band pass filter designed into it so that steady background light doesn't get amplified but the pulsing light does. It is this pulsing light at typically 38KHz that gets demodulates in the chip. It converts pulsing light into a high and no light into a low. The data you are trying to convey is then modulated onto that modulated light and that is what the micro decodes.

Wawa

Google "SFH400".
Glass lens narrow beam (~7 degrees) IR diodes like that easily bridge 10meters with a standard 3-pin receiver.
Leo..

Oddwired

#10
Sep 16, 2015, 08:49 am Last Edit: Sep 16, 2015, 08:50 am by Oddwired
Ah I see! So even if you shone an infrared lamp at it it wouldn't pass the signal through because the frequency of ir pulses (it wouldn't even be a pulse, just constant on) would be outside the accepted range?

krupski

#11
Sep 16, 2015, 09:02 am Last Edit: Sep 16, 2015, 09:07 am by Krupski
Im looking at the tsop4838 ir receiver modules and I want to use them in a laser circuit however I can't find a laser that is both safe and capable of working with the sensor so I want to build one of the detectors out of discreet components and tailor it to work with a red or green laser pen.

From the documentation it appears a photodiode is connected to an amplifier (which I assume is a transimpedance op amp circuit) then a band pass filter and then a demodulator.

Would this just be a matter of a few simple op amp circuits or would it get more complex than that and can anyone explain why there is a demodulator in the circuit? I can't see which signal is being demodulated as i thought the circuit just passed through whether the signal was high or not and whatever microcontroller the tsop was attatched to did all the demodulating?
What's the point of using a red and green laser? Is that for encoding something?

Normal IR communications consist of pulses of IR at 38 or 40 khz. The IR is pulsed at 40 khz so that only that frequency is recognized and ambient light "noise" is ignored.

The data stream usually consists of pulses of IR with three different timings:

The header
A Mark
A Space

TYPICALLY (although not always), a space is 500 or 600 milliseconds of IR pulses at 40 khz, a Mark is twice that and a header is twice as long as a mark (that is, typically a header is 2400 ms, a Mark is 1200 and a Space is 600).

The long header pulse carries no information... it just allows the IR receiver AGC to set itself to the IR intensity.

Then, the actual data is sent, a "1" bit is a Mark-Space and a "0" bit is a Space-Space.

Now, at 40 khz, each IR cycle is 25 microseconds (T=1/F). So, to send out a 2400 millisecond header, you need to send 2400 / 25 = 96 pulses of 40 khz. So it follows that you send 48 pulses for a mark (1200 ms) and 24 for a space (600 ms).

The attached sketch (image sketch, not Arduino sketch! :) ) should clarify it.



Check out this link also for more info: http://www.righto.com/2010/03/understanding-sony-ir-remote-codes-lirc.html
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

Wawa

Ah I see! So even if you shone an infrared lamp at it it wouldn't pass the signal through because the frequency of ir pulses (it wouldn't even be a pulse, just constant on) would be outside the accepted range?
Yes, the receiver only amplifies the base frequency, and ignores the "static" sun light, and mains frequency modulated light.
TSOP4838. The last two digits is the frequency. 38Khz.
If you look at the waveform picture from Krupski, you see the thin lines representing the base frequency.
The receiver removes them, and just outputs the big blocks. The actual data.
Leo..

Grumpy_Mike

Ah I see! So even if you shone an infrared lamp at it it wouldn't pass the signal through because the frequency of ir pulses (it wouldn't even be a pulse, just constant on) would be outside the accepted range?
Yes but it would not even be a constant on because the light is constant it would register as off.

krupski

Yes, the receiver only amplifies the base frequency, and ignores the "static" sun light, and mains frequency modulated light.
TSOP4838. The last two digits is the frequency. 38Khz.
If you look at the waveform picture from Krupski, you see the thin lines representing the base frequency.
The receiver removes them, and just outputs the big blocks. The actual data.

Leo..
Yes, the diagram shows the (actual) 40 khz IR pulses as the thin lines and the decoded data stream as the thicker lines. If you put an oscilloscope on an IR receiver module, you would only see the waveform shown by the thick lines, you wouldn't see the thin "raw" 40 khz IR carrier frequency.

Sort of like AM radio. You see the detected audio, but not the much higher frequency RF carrier.....


Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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