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Confused about tuned oscillator behavior.

AdhiWay

Mar 15, 2022
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Hi everyone, I'm kind new in electronics and I like it it's my hobby.
I have made a tuned oscillator circuit i struggle a lot to make it work and finally seems working fine, I don't have oscilloscope so I'm testing it by using LED connected in series with transistor which it base connected to the output of the oscillator like in the picture below, I have tested it with LED with both transistors PNP-NPN and the LED lighted up in both ways, so I think that the oscillator is working which means it generate AC signal, but it made me confused because when I tried to connect a diode in series between the oscillator output and LED transistor base the LED didn't light up, I have connected the diode with both sides with the NPN and PNP transistors, and LED didn't work, the diode is fine, is not broken, so I'm confused it seems to me strange!!. I would like to know what's the problem or if I'm missing something, I appreciate your help.IMG_20230617_205549.jpg
 

AdhiWay

Mar 15, 2022
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I know those websites and I know how to build a tuned oscillator, I have build one but it didn't work although that I build it exactly like those websites explain, so I have relied on myself 100% to solve the problem and eventually made it work, the simple question I asked is when I connected a diode between the signal output and transistor base that switch the LED on, it didn't work, and the PNP-NPN that I talked about are the LED switch transistors not the amplifier.
it seems that nobody try to give a help expect you, although that I thought that I asked a simple question, thanks anyway.
 

Harald Kapp

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I tried to connect a diode in series between the oscillator output and LED transistor base
Effectively in series with D1 and D2? In that case the current, limited by the 5.7 kΩ or the 10 kΩ resistor, respectively, is way to small to light up the LED.
 

danadak

Feb 19, 2021
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The above a sound card oscilloscope. Good to ~ 20 Khz. Make sure you protect your sound card inputs, google
"sound card oscilloscope protection circuits"


If youd ecide to go this route also buffer the generator output, eg. sound card output.

Some folks have gotten throw away sound card dongles to insure protection for PC. Or
just keep a spare sound card on hand in case you hose it. But if you provide adequate
protection for inputs and outputs you should have no problem on "normal" low voltage
stuff or use 10X, 100X probe interface, on top of the protection.



Regards, Dana.
 
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AdhiWay

Mar 15, 2022
38
Joined
Mar 15, 2022
Messages
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Effectively in series with D1 and D2? In that case the current, limited by the 5.7 kΩ or the 10 kΩ resistor, respectively, is way to small to light up the LED.
Thank you for replying, I have tested without resistors at the transistors bases, it didn't work, I was also struggling with a phase shift oscillator but fortunately I made it work and I tested the LEDs with it with the diodes like I did in this circuit and the LEDs worked fine!.
 
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