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Old 12th February 2011, 12:34 AM   #1
maurycy is offline maurycy  United States
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Default Microphone to speaker circuit

Not sure if my title is correct. I have a LED vu meter that connects to speaker terminal of my receiver. I would like to convert it to a wireless device by adding a microphone. Does anybody know of a circuit that will convert microphone source to a signal that can be connected directly to speaker?

My VU meter is based on LM3915 chip.

Thanks.
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Old 12th February 2011, 03:42 AM   #2
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Microphone to the speaker or did you mean microphone to the LED metering?

G
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Old 12th February 2011, 03:47 AM   #3
maurycy is offline maurycy  United States
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Quote:
Originally Posted by stratus46 View Post
Microphone to the speaker or did you mean microphone to the LED metering?

G
Yes, that's what I want to do.
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Old 12th February 2011, 08:36 PM   #4
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Quote:
Originally Posted by maurycy View Post
Yes, that's what I want to do.
I still don't know what you want. You cannot answer an either/or question with Yes/No.

G
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Old 12th February 2011, 09:02 PM   #5
maurycy is offline maurycy  United States
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OK. Let me start again. This is the circuit that I am going to build:

10 LED VU meter

It connects to the speaker output on the amplifier. Now, I want to make it wireless so I want to add a microphone. Now, what I need is a circuit between the microphone and the above VU meter. I assume that the microphone signal is too weak so it would have to be amplified. Probably by LM386 chip?

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Old 13th February 2011, 01:25 AM   #6
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Quote:
Originally Posted by maurycy View Post
OK. Let me start again. This is the circuit that I am going to build:

10 LED VU meter

It connects to the speaker output on the amplifier. Now, I want to make it wireless so I want to add a microphone. Now, what I need is a circuit between the microphone and the above VU meter. I assume that the microphone signal is too weak so it would have to be amplified. Probably by LM386 chip?

Thanks.
I thought that was what you had in mind. You will need a preamp and likely not an LM386. Rod Elliot's site is a good place to start.

ESP Projects Pages - DIY Audio and Electronics - Audio test equipment

An electret mike requires power to run whereas dynamics do not. Often the mic manufacturer offers simple examples to use their product. The gain of the preamp will likely end up between 50 and several hundred but this depends heavily on what mic and how loud you consider '0'.

The LM3915 requires up to 10 Volts to drive to 0 while mic output tends to be in millivolts. 1 mV boosted to 10V would be a gain of 10,000 though as I said, I expect your gain in the 200 +/- 2 times. Do not attempt to get high gains in a single stage. For 10,000 it could be two cascaded gain of 100 amps

National, Analog Devices, THAT corp, TI (Burr Brown) and others offer mic preamps and examples of how to use the chips in specific applications.

BTW when things are called 'wireless' it's assumed to be RF (radio, wifi etc) and not acoustically coupled as you have in mind.

G
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Old 13th February 2011, 01:43 AM   #7
Pano is offline Pano  United States
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Wow, I'm glad you figured that out, G2!
When I read wireless and microphone - I thought he wanted to rig the input into a wireless mic and transmit it to a remote or portable VU meter. Yikes.

Turns out to be much simpler.
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Old 13th February 2011, 02:38 AM   #8
maurycy is offline maurycy  United States
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Thanks for the info G2. With my limited knowledge of electronics, I guess I will build the wired VU meter first and than play with additional board for the mic and preamp. If I expand the original schematic in the beginning, I will most likely introduce a lot of errors.
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Old 13th February 2011, 06:05 AM   #9
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Modular is an excellent way to go especially in the beginning. The metering is already working so half the battle is done. You then get the mic amp working and simply substitute the speaker signal with the mic signal and adjust the gain to get the readings you want. Sounds like fun.

G
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Old 14th February 2011, 02:14 AM   #10
maurycy is offline maurycy  United States
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I also found this schematic that has LM386 incorporated between mic and vu meter. I may give it a try since it looks easy.

schematic
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