Why Does My DIY Circuit Produce Unwanted Noise?

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The discussion centers on troubleshooting a DIY circuit that produces unwanted noise when powered on. The user suspects issues with the shield wire, potential mis-soldering, or a misplaced capacitor. Other participants suggest that the circuit functions as an audio amplifier and emphasize the importance of having a schematic for effective debugging. The user lacks measurement tools but plans to purchase a digital multimeter for further testing. Proper understanding of components and connections is highlighted as crucial for successful circuit assembly.
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Hi!
I was working on a circuit today.I soldiered all the capacitors, resistors, transistors,... just as the paper-guide said except the Microphone;Because it was said in there that if you want to use this kit as an earphone, simply solder the MIC to the board,else use a "shield wire(?)" to attach the MIC to it's slots...I assumed that shield wire is simply the ones that have some golden torn wires as their kernel...I used a 3.5 mm standard headphone
But after plugging the batteries, some irrelevant noise(not the environment sound) and sometimes continuous beep is heard (However, when I blow to the MIC some relevant noise can be heard)
WHERE IS THE PROBLEM?
My suspects[!]:
-the "shied wire"?
-mis-soldering the shield wire to the MIC?
-mis-soldering the battery wires?
-I misplaced a 4.7 capacitor in a 0.47 capacitor,then I desoldered it with lots of troubles[!]. Perhaps the capacitor failed?

This is a picture of my cuisine[!]:
http://i52.tinypic.com/339n0qg.jpg
I will be glad if you help...
Thanks
 
Last edited:
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Pooya_M said:
Hi!
I was working on a circuit today.I soldiered all the capacitors, resistors, transistors,... just as the paper-guide said except the Microphone;Because it was said in there that if you want to use this kit as an earphone, simply solder the MIC to the board,else use a "shield wire(?)" to attach the MIC to it's slots...I assumed that shield wire is simply the ones that have some gold torn wires as their kernel...I used a 3.5 mm standard headphone
But after plugging the batteries, some irrelevant noise(not the environment sound) and sometimes continuous beep is heard (However, when I blow to the MIC some relevant noise can be heard)
WHERE IS THE PROBLEM?
My suspects[!]:
-the "shied wire"?
-mis-soldering the shield wire to the MIC?
-mis-soldering the battery wires?
-I misplaced a 4.7 capacitor in a 0.47 capacitor,then I desoldered it with lots of troubles[!]. Perhaps the capacitor failed?

This is a picture of my cuisine[!]:
http://i52.tinypic.com/339n0qg.jpg
I will be glad if you help...
Thanks

Welcome to the PF.

It almost looks like a transmitter and receiver together? I see the microphone in the picture, but also see what looks like an earpiece jack. Is this meant to be a wireless microphone, or a wireless receiver? Or can it do both somehow?
 
a 3.5 mm headphone would be plugged into the down left device in the picture
I think it is just a sensitive amplifier.
 
Pooya_M said:
a 3.5 mm headphone would be plugged into the down left device in the picture
I think it is just a sensitive amplifier.

Ah, I see. It is an audio amplifier from the microphone to the earphone jack.

Can you post a copy of the schematic? That would be helpful in debugging the circuit operation.

Also, what measurement equipment do you have? Do you have a digital multi-meter (DMM)? How about an oscilloscope?
 
berkeman said:
Ah, I see. It is an audio amplifier from the microphone to the earphone jack.

Can you post a copy of the schematic? That would be helpful in debugging the circuit operation.

Also, what measurement equipment do you have? Do you have a digital multi-meter (DMM)? How about an oscilloscope?

Here:http://www.freeimagehosting.net/t/ea24f.jpg
Sorry about photo's poor quality
Well,I don't have any measurement tools yet!(Say, I am a first year electrical engineering student and I don't even have a multimeter!)
Going to buy a good DMM tomorrow... (It is 2:15 A.M now in here!)
 
Do you have the schematic? That is the paper diagram of the parts, and how they are connected together. The photo that you posted just now is the "layout" of the circuit, not the "schematic".
 
berkeman said:
Do you have the schematic? That is the paper diagram of the parts, and how they are connected together. The photo that you posted just now is the "layout" of the circuit, not the "schematic".

you mean kind of these things:[PLAIN]http://www.dekits.com/images/images_big/shematic8.jpg
No,I don't.
BTW,the picture in this post is something like my circuit
 
Last edited by a moderator:
Pooya_M said:
you mean kind of these things:[PLAIN]http://www.dekits.com/images/images_big/shematic8.jpg
No,I don't.
BTW,the picture in this post is something like my circuit

The schematic example link at dekits.com is not working.

It will be very difficult to help you debug the problem without the schematic for the kit. Can you get it from dekits.com somehow?
 
Last edited by a moderator:
Pooya_M said:
Well,I don't have any measurement tools yet!(Say, I am a first year electrical engineering student and I don't even have a multimeter!)
Going to buy a good DMM tomorrow... (It is 2:15 A.M now in here!)

I've been using the http://www.shopextech.com/c938/multimeters.php, less expensive than a Fluke and seem to be competetive in quality.

Scopes are expensive, no way around that. I picked up a 20MHz one online that wasn't terribly expensive. It seems to do the job for me.
 
  • #10
It isn't my circuit's schematic.But I think it is similar to it in practice:
http://www.freeimagehosting.net/e7b2d
 
  • #11
Also:
Pooya_M said:
I assumed that shield wire is simply the ones that have some gold torn wires as their kernel..

Never assume anything when building circuits. *wink*
 

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