How do I wire this voice recorder?

Thread Starter

Arjune

Joined Jan 6, 2018
182
Voice Recorder

Do someone know how to wire the voice recorder in the above link? I bought it on eBay. Also I want to use a dynamic microphone. I don't have a condenser mic. How do I wire push button switches for record and play on the board, etc.Does the speaker require a capacitor to block dc?

Thanks
 
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KeithWalker

Joined Jul 10, 2017
2,306
A dynamic microphone is low impedance and produces a low voltage signal. You will need a pre-amplifier to use it with this board because it is designed to use an electret microphone which has a built-in amplifier transistor. This is how you connect it:
VoiceRec.jpg
 

Audioguru again

Joined Oct 21, 2019
4,537
Absolutely not! An electret mic has about the same 10mV output level as a dynamic mic. The Jfet is an impedance converter, not an amplifier.
To use a dynamic mic a coupling capacitor is needed in series with it.
 

Thread Starter

Arjune

Joined Jan 6, 2018
182
I believe the average output of a dynamic mic of low-impedance is five millivolts. I believe a capacitor in series with the dynamic mic at the positive input should work. Is there any way to clear the recording. There are two unused spots left on the diagram Keith.
 

KeithWalker

Joined Jul 10, 2017
2,306
I believe the average output of a dynamic mic of low-impedance is five millivolts. I believe a capacitor in series with the dynamic mic at the positive input should work. Is there any way to clear the recording. There are two unused spots left on the diagram Keith.
I don't know what the extra pads LP and LB on the circuit board are for. The module will only save one message so the way to erase the recording is to record over the previous message.
 

Thread Starter

Arjune

Joined Jan 6, 2018
182
I attached a radio shack microphone element which is condenser type to the circuit that I bought on eBay and the circuit worked great for a few times but then it stopped working. I used the single playback button and the single press and hold to record button and things were okay. When working the unit made one beep to record and two beep as I release the button to end recording. I wired a second recorder and the result was silent meaning not working. I am using 5 volts DC to power the module. I did not attach a DC blocking capacitor from output to the speaker. I'm going to try to guess at what else I can do.
 

Audioguru again

Joined Oct 21, 2019
4,537
The first circuit stopped working and the second circuit did not work because you bought cheap Chinese junk on ebay.
The circuit probably uses a bridged amplifier that does not need a DC blocking output capacitor.
 

KeithWalker

Joined Jul 10, 2017
2,306
The first circuit stopped working and the second circuit did not work because you bought cheap Chinese junk on ebay.
The circuit probably uses a bridged amplifier that does not need a DC blocking output capacitor.
The circuit does use a bridged amplifier and does not need a blocking capacitor. I have used several different recording modules including this type from AliExpress and I have never experienced a problem with any of them. I consider them to be great value for what little they cost.
I would suggest that the failures were caused by mishandling of the bare boards. The boards are small and delicate. It's very easy to accidentally short out the non-insulated modules. It is also easy for an inexperienced person to damage them while soldering on the peripheral wires.
 

Thread Starter

Arjune

Joined Jan 6, 2018
182
I added a DC blocking capacitor for the speaker and the second board is now working so far. I used 470 microfarads. The positive polarity is on the left side towards the ground connection. The negative end of the capacitor goes to the speaker and the other connection of the speaker goes to the other speaker connection on the board. I don't feel I bought something inferior because it's on eBay and made in China. Shouldn't we give the Chinese some love for the ingenuity?
 

Audioguru again

Joined Oct 21, 2019
4,537
The amplifier in the module is a bridged type that has two amplifiers, One amplifier for each speaker wire. Then the AC signal voltage to the speaker is doubled which double the speaker current resulting in 4 times the output power of a single amplifier.
Measure each speaker wire to see that they are the same, about half the supply voltage. Since the speaker wires have the same voltage then the speaker has no voltage across it then it does not need a DC blocking capacitor.

ebay sells some cheap fake and defective junk from CH***.
 

KeithWalker

Joined Jul 10, 2017
2,306
ebay sells some cheap fake and defective junk from CH***.
I have always steered clear of ebay because I suspect that a lot of the sellers are just out to make a fast buck. They buy cheep reject electronics and re-sell them as new with a big fast profit. The source companies for AliExpress stand by their products. I only ever received one item that did not work. They refunded my money promptly without asking me to return it. I even feel a little guilty sometimes, paying so little for such high tech devices. I couldn't even mail them locally for the price of some of the "free shipping items" that I have purchased.
 
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Thread Starter

Arjune

Joined Jan 6, 2018
182
Is there a simple circuit I can use to merge both halves of the bridge into one output so I can use that one output with the speaker and the common ground using the same power supply of 5 volts?
 

KeithWalker

Joined Jul 10, 2017
2,306
Is there a simple circuit I can use to merge both halves of the bridge into one output so I can use that one output with the speaker and the common ground using the same power supply of 5 volts?
Not that I am aware of. Why do you want to do that? It's much easier to just connect the speaker across the two output terminals. There is no need for a ground connection to the speaker coil.
 

Audioguru again

Joined Oct 21, 2019
4,537
The bridged amplifier has two amplifiers. Simply connect a coupling capacitor (it blocks the DC) to one of the outputs with a speaker connected to the output of the capacitor and to ground. Then the power in the speaker will be 1/4th the power produced by the bridged speaker connection.

One amplifier with a 5V supply produces an output voltage swing of maybe 4V peak-to-peak which is 1.414V RMS. Then the power in an 8 ohms speaker is 1.414V squared/8 ohms= 0.25W.
The bridged output produces double the 4V p-p and double the 1.414V RMS of 2.828V RMS. Then the power in the 8 ohm speaker is 2.828V squared/8 ohms= 1W. The coupling capacitor is not needed with a bridged output because the DC is the same at both outputs.
 

Thread Starter

Arjune

Joined Jan 6, 2018
182
Thank you much for your patience audio guru. By the way the first board is now working again with a 470uf DC blocking capacitor to one of the bridge output. Thank you very much Keith for the original diagram.
 
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