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Why does the "generated" signal fail to work?

 
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Rhye




Joined: 23 Feb 2018
Posts: 1



PostLink    Posted: Mon Feb 26, 2018 7:25 am    Post subject: Why does the "generated" signal fail to work? Reply with quote


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I am trying to replicate the remote control for my Sony home theater system. I started with anaylzing the demodulated signal of power on button using a TSOP1738 IR demodulator(http://www.kynix.com/Detail/840529/TSOP1738.html). It looks like this:



You can see the signal (along with the decoded command). Next I replicated the signal using the Arduino (and as per SIRC protocol, chose 1/4 duty @ 38Khz). Below is the signal of a complete one to show the code sent and a zoomed one to show the 38Khz 25% duty burst within the signal.





Now to drive an IR LED using this signal, I fed this into a 2N2222 NPN BJT transistor's base with its collector connected to +5V and base to IR LED -> Series Resistance -> GND. And to test the signal I fed this "generated" signal through the TSOP1738 again and probed the output.



The signal I get looks like an IR signal except for the 1's (when TSOP1738 goes LOW) instead of being LOW for a duration, as in the first image. I see a lot of toggling going on:



The "generated" signal, of course, does not work. Any idea what's going in here ?
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barclay66




Joined: 27 Jun 2011
Posts: 1291
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Mon Feb 26, 2018 10:28 am    Post subject: Reply with quote

Hi,

The series resistor to the tranistor's base should be much lower, between 1K to 4.7K. Otherwise, the transistor isn't switched off reliably when the arduino's output goes low...

Check this out: http://forum.arduino.cc/index.php?topic=147852.0

Regards,
barclay66
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