Hello Everyone,

I am working on project, which is based on ISD1820 module?

For voice amplification I have connected ISD1820 with LM386 module. Everything is done only one problem which I am facing is strange sound comes as soon as it plays the recorded sound. I need the output upto 86db from the speakers, so I have used LM386 Module.

While recording there is minimal background noise, but it makes sound as soon as the playback is started in loop. I am not able to figure out how to eliminate that voice.

Though I have read the topics here about including RC combination between pin 1 & pin 8. Do i need to do same with the LM386 module? or the modifications are just for those, who r using LM386 ic?

 

Have you tested it with the loudspeaker connected directly to the ISD1820 ?

The boards should be connected by linking the 0V and connecting just one of the audio outputs from the ISD1820 to the input of the amplifier.

Make sure that neither of audio outputs from the ISD1820 is connected to ground.

 

THanks for your reply.

The one speaker came with the device I checked it with that. The voice was less audible to I used larger output speaker.

But the other speaker with higher output range I connected it through LM386, the sound is louder but there is some additional noise that comes out.

and yes only speaker input is connected to LM386 & not the ground. Only the main Vcc & ground is connected via source.

 

Can you provide a diagram showing exactly how everything is connected?

 

Sir,

Here is the circuit diagram, I hope it will be helpful though the diagram is not proper I made it in hurry. But suggestion from you would be really helpful.

 

There is a risk that noise from the DC-DC converter is entering the audio path so try powering the circuit from a non-switching power supply or a battery.

Any noise in the supply ground to the LM386 will be amplified just as if it were an input signal so be careful where you connect this cable.

There is nothing to attenuate the output from the ISD1820, it could be that the amplifier is being over-driven.

 

Note that the ISD1820 has two differential speaker outputs, use only ONE of them, do not ground the unused output.

When the chip powers up to play a sound, the audio output will jump from zero volts to approximately 1/2 Vcc, this is going to give you a loud THUMP in the speakers as your amp's coupling capacitors charge up.

I did this once before with an ISD chip, I ended up needing to mute the audio amp for a 100 ms or so at the beginning of playback, to suppress that nasty THUMP!

Alternatively, you could transformer couple the signal, using a 600:600 coupling transformer across BOTH audio outputs, the thump will be suppressed, same as when you have a speaker directly connected, since both outputs wake up at the same time, there is no transient. (well... almost no transient)

This would also help your ground noise issue, if that indeed is the problem.

 

ok,Thank you for providing information.7

But I am not able understand this thing properly ( 600: 600 coupling). Can you please elaborate this & explain?

 

Hi anuragm,

As suggested by blocco, the noise coming from the DC-DC converter might be the culprit here. Use a scope to check if your amplified signals are clear without any noise (you can worry least about this if the audio plays smoothly after the buzzing sound.

I have used the LM386 IC as an amplifier for one of my Arduino project. I also remember that I also got a small buzzing sound every time I powered on the circuit. But once its powered in I had not problem with its performance . The link for that project is given below for you to check its audio quality.
https://circuitdigest.com/microcontroller-projects/arduino-audio-music-player

Also I have used a 8ohm speaker directly with ISD1820 and had no problem with its audio quality as well. Yes, as you said the speaker provided by the vendor was not loud enough so I also have changed the speaker. The link for that project is also given below for you to check
https://circuitdigest.com/microcontroller-projects/esp8266-based-iot-security-system

 

ok,Thank you for providing information.7

But I am not able understand this thing properly ( 600: 600 coupling). Can you please elaborate this & explain?

Google 600 ohm to 600 ohm audio coupling transformer.

Connect primary side to both ISD ouputs, ground one side of the secondary, right at the input of your amp, the other terminal goes to the amp input.

This transformer then provides coupling, conversion from differential to single ended, and isolates the ground.

 

Hello! I cannot understand the list of componet values of resistors and capasitors in the diagram of datasheet of the lm386 . What is 104 on the left and 4.7 o on the write?

 

Hello! I cannot understand the list of componet values of resistors and capasitors in the diagram of datasheet of the lm386 . What is 104 on the left and 4.7 o on the write?

104 is the value code of the capacitor, in picofarads, similar to the color bands on a resistor. In this case it is a 1, followed by a 0, followed by four zeros, so 100,000 pF, or 0.1 uF.

The 4.7O indicates 4.7 Ω. The 'O' is there just to let you know that it wasn't supposed to be 'K' or 'M' or anything else. Sometimes 'R' is used for the same purpose.

Another convension that use to be very common in the days of hand-drawn and poorly copied/treated printed schematics was to replace easily messed up period with the prefix letter. So "4R7" would mean 4.7 Ω while "4K7" would mean 4.7 kΩ.

 

Instead of copying errors or wrongly guessing, use the LM386 circuit shown by its manufacturer in its datasheet: