Hi,
I have been following this tutorial:
https://learn.adafruit.com/ir-sensor/ir-remote-signals
The section "IR Remote Signals" shows how to visualize the undecoded IR signal at 38kHz. I am not able to replicate this with my o-scope. When I use an IR photodiode in reverse bias, it seems that the input impedance of the o-scope will "decode" the raw IR signal and I can no longer see the carrier. What needs to be done to prevent this?
TIA,
AP
Visualize undecoded IR signal
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- Franklin97355
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Re: Visualize undecoded IR signal
Which IR device are you using?
Were you able to before?and I can no longer see the carrier.
- apuder
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Re: Visualize undecoded IR signal
This one here: http://a.co/7lshqgCfranklin97355 wrote:Which IR device are you using?
Sorry, poorly worded. I was never able to see the carrier.Were you able to before?and I can no longer see the carrier.
- Franklin97355
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Re: Visualize undecoded IR signal
How are you wiring and reading them? These are not the same as those in the tutorial as they have no demodulator circuit.
- apuder
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Re: Visualize undecoded IR signal
I am trying to replicate what is explained on this page:
https://learn.adafruit.com/ir-sensor/ir-remote-signals
The author writes "We'll hookup a basic light sensor (like a basic photocell!) and listen in. We won't use a decoder like a PNA4602 (just yet) because we want to see the undecoded signal."
The author shows some screenshots but not the parts list or wiring for that particular setup. I've been trying what the second responder suggested on this page:
https://electronics.stackexchange.com/q ... cilloscope
I can see a small change in amplitude but not the distinct discrete signals that are shown in the Adafruit tutorial.
Thanks for taking the time to respond!
AP
https://learn.adafruit.com/ir-sensor/ir-remote-signals
The author writes "We'll hookup a basic light sensor (like a basic photocell!) and listen in. We won't use a decoder like a PNA4602 (just yet) because we want to see the undecoded signal."
The author shows some screenshots but not the parts list or wiring for that particular setup. I've been trying what the second responder suggested on this page:
https://electronics.stackexchange.com/q ... cilloscope
I can see a small change in amplitude but not the distinct discrete signals that are shown in the Adafruit tutorial.
Thanks for taking the time to respond!
AP
- Franklin97355
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Re: Visualize undecoded IR signal
That is because the device in the Adafruit article is an IR Demodulator not an IR receiver diode. They are not the same. Again, how are you connecting the diode for testing?
- apuder
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- Joined: Thu Jun 29, 2017 2:51 pm
Re: Visualize undecoded IR signal
The wiring I did is according to the second link I mentioned in my previous post.
To put it in simpler terms: what parts and wiring are needed to replicate the screenshots shown on this page:
https://learn.adafruit.com/ir-sensor/ir-remote-signals
To my understanding, the screenshots show the IR carrier wave and the author explicitly mentioned that he did *not* use an IR decoder.
AP
To put it in simpler terms: what parts and wiring are needed to replicate the screenshots shown on this page:
https://learn.adafruit.com/ir-sensor/ir-remote-signals
To my understanding, the screenshots show the IR carrier wave and the author explicitly mentioned that he did *not* use an IR decoder.
AP
- Franklin97355
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- apuder
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Re: Visualize undecoded IR signal
Thanks, I'll give that a shot.
AP
AP
- apuder
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- Joined: Thu Jun 29, 2017 2:51 pm
Re: Visualize undecoded IR signal
well, I just looked at the data sheet for the TSOP38238:
https://cdn-shop.adafruit.com/datasheets/tsop382.pdf
The block diagram shows a demodulator. How will it be possible to measure the 38kHz carrier wave if there is a demodulator? Once again, I'm trying to replicate the screenshots on this page:
https://learn.adafruit.com/ir-sensor/ir-remote-signals
https://cdn-shop.adafruit.com/datasheets/tsop382.pdf
The block diagram shows a demodulator. How will it be possible to measure the 38kHz carrier wave if there is a demodulator? Once again, I'm trying to replicate the screenshots on this page:
https://learn.adafruit.com/ir-sensor/ir-remote-signals
- Franklin97355
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Re: Visualize undecoded IR signal
And I keep telling you that is what they used in that tutorial.Once again, I'm trying to replicate the screenshots on this page:
https://learn.adafruit.com/ir-sensor/ir-remote-signals
- apuder
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- Joined: Thu Jun 29, 2017 2:51 pm
Re: Visualize undecoded IR signal
I know the TSOP38238 is mentioned at the beginning of the tutorial and that it is used for the IR sensor they build at the end of the tutorial. In the middle of the tutorial they show the raw carrier wave and they even mention that they do NOT use a decoder. Since the TSOP38238 has a demodulator I just wonder how it is possible to measure the 38kHz carrier wave that is shown in the screenshots.
Anyways, I have already too much of your time. Thanks.
AP
Anyways, I have already too much of your time. Thanks.
AP
- Franklin97355
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Re: Visualize undecoded IR signal
OK, I see where you are pointing and I don't have an answer but someone else may.
- apuder
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Re: Visualize undecoded IR signal
As a way to provide closure to my own question I wanted to respond with a solution. I found a local expert who helped with this problem. First of all, the other poster on this thread is not correct when suggesting to use the TSOP38238 mentioned in the IR tutorial. The TSOP38238 demodulates the IR carrier so it is no longer visible. One has to use an IR photodiode to receive the raw, modulated IR carrier. One issue is that the amplitude is not big enough to use as input for a logic analyzer. My local expert suggested an op-amp to amplify the signal. Attached is his wiring diagram that works beautifully. Huge thanks to Kevin @ SFSU. Also thanks to the other poster for taking the time to reply to my question.
AP
AP
Please be positive and constructive with your questions and comments.