Speaker OUT To MIC IN

elyas721 · Jul 14, 2023

I want to use dfplayer modules speaker output to connect to SIM800L MIC IN Pins.Can this being done? How to connect it?
In other words Instead of a MIC input on SIM800L module, I use the sound out of the dfplayer module.
Please see the attached file.

What is the reason for the noise? How can I fix the noise? Can you guide me by schematic?

Thanks

Nigel Goodwin · Jul 14, 2023

You can't feed a speaker output into a microphone input.

Historically, the original Philips Cassette recorders had a microphone socket only, and to use it as a line input you added a 1.5M resistor inside the DIN plug, in series with the input pin.

As you're using balanced connections it's a little more complicated, have a look at this page:

Uneeda Audio - Build your own attenuator pads

Build your own attenuator pads

www.uneeda-audio.com

You'll have to sort out the values to meet your requirements.

elyas721 · Jul 14, 2023

Nigel Goodwin said:
You can't feed a speaker output into a microphone input.

Historically, the original Philips Cassette recorders had a microphone socket only, and to use it as a line input you added a 1.5M resistor inside the DIN plug, in series with the input pin.

As you're using balanced connections it's a little more complicated, have a look at this page:

Uneeda Audio - Build your own attenuator pads

Build your own attenuator pads

www.uneeda-audio.com

You'll have to sort out the values to meet your requirements.

I tried the file attachment, it didn't work, it still makes noise

Nigel Goodwin · Jul 14, 2023

You've got hardly any attenuation there, try a 470K instead of 4.7K in a.png for a start and see what happens. However, layout 'could' be an issue, with ground loops etc.

elyas721 · Jul 14, 2023

Nigel Goodwin said:
You've got hardly any attenuation there, try a 470K instead of 4.7K in a.png for a start and see what happens. However, layout 'could' be an issue, with ground loops etc.

I will test with a resistance of 470 ohms and let you know

But what do you mean by arrangement? What should be the layout?

Nigel Goodwin · Jul 14, 2023

elyas721 said:
I will test with a resistance of 470 ohms and let you know

But what do you mean by arrangement? What should be the layout?

In audio circuits you can get induced signals via ground connections, which is why a comon technique is a single standard ground connection that everything goes to.

elyas721 · Jul 14, 2023

Nigel Goodwin said:
In audio circuits you can get induced signals via ground connections, which is why a comon technique is a single standard ground connection that everything goes to.

What should the ground connection look like in my circuit, what did I do wrong?

Nigel Goodwin · Jul 14, 2023

elyas721 said:
What should the ground connection look like in my circuit, what did I do wrong?

Have you tried a 470K resistor (not 470 ohm) yet?, it may not be a ground loop problem - which are often difficult to cure.

rjenkinsgb · Jul 14, 2023

It could be that the dfplayer output needs a load resistance across it (output pin to ground pin), eg. a 47 or 100 Ohm, to stabilise it?

Then use a high value resistor from the output pin to the mic input of the next module?

elyas721 · Jul 14, 2023

rjenkinsgb said:
It could be that the dfplayer output needs a load resistance across it (output pin to ground pin), eg. a 47 or 100 Ohm, to stabilise it?

Then use a high value resistor from the output pin to the mic input of the next module?

I did it, it didn't work

elyas721 · Jul 14, 2023

Nigel Goodwin said:
Have you tried a 470K resistor (not 470 ohm) yet?, it may not be a ground loop problem - which are often difficult to cure.

I did this method, the hissing increased, it is completely hissing

dfplayer music sound
Nothing is played

rjenkinsgb · Jul 14, 2023

OK, try leaving the load resistor connected at the DFPlayer module, and using a voltage divider at the input of the SIM800L?

eg. 1K directly across the mic input and 10K series resistor from dfplayer out to mic in?

Also, as Nigel said, ensure the ground / 0V connection between the two is short and quite thick wire, to avoid any ground noise.

elyas721 · Jul 14, 2023

rjenkinsgb said:
OK, try leaving the load resistor connected at the DFPlayer module, and using a voltage divider at the input of the SIM800L?

eg. 1K directly across the mic input and 10K series resistor from dfplayer out to mic in?

Also, as Nigel said, ensure the ground / 0V connection between the two is short and quite thick wire, to avoid any ground noise.

Do you mean to test like this?

rjenkinsgb · Jul 14, 2023

The 1K across the SIM800 inputs, plus the 47 or 100 ohm load where you show the 1K.
And 10K (at a guess) between dfplayer out and sim800 mic in.

The 10K series and 1K shunt would form a voltage divider, reducing the level while keeping a fairly low impedance, so hopefully limiting the noise pickup.

elyas721 · Jul 14, 2023

rjenkinsgb said:
The 1K across the SIM800 inputs, plus the 47 or 100 ohm load where you show the 1K.
And 10K (at a guess) between dfplayer out and sim800 mic in.

The 10K series and 1K shunt would form a voltage divider, reducing the level while keeping a fairly low impedance, so hopefully limiting the noise pickup.

I used 1k and 10k resistor but it has no effect

rjenkinsgb · Jul 15, 2023

Try a larger resistor in place of the 10K, or smaller in place of the 1K.

The higher the ratio between the two, the smaller the signal will be at the mic input.

What effect are you getting? Overload / distortion, noise??

Can you add a photo of the actual devices & wiring as you have them connected?

elyas721 · Jul 15, 2023

rjenkinsgb said:
Try a larger resistor in place of the 10K, or smaller in place of the 1K.

The higher the ratio between the two, the smaller the signal will be at the mic input.

What effect are you getting? Overload / distortion, noise??

Can you add a photo of the actual devices & wiring as you have them connected?

I connected two resistors of 10k and the noise decreased a lotNow every few seconds a short noise is created and removedDo you have a solution to completely remove the noise?

elyas721 · Jul 15, 2023

rjenkinsgb said:
Try a larger resistor in place of the 10K, or smaller in place of the 1K.

The higher the ratio between the two, the smaller the signal will be at the mic input.

What effect are you getting? Overload / distortion, noise??

Can you add a photo of the actual devices & wiring as you have them connected?

made a mistake with the series of two 10k resistorsThe sound just got weaker, so I couldn't understand the noiseI only did it by wiring to remove the noise, I will close the working circuit cleanerI put a 10k and 680 ohm resistor, but it still had no effectI put the same power supply for sim800l and dfplayer with 3.9 voltage

Nigel Goodwin · Jul 15, 2023

Remove the DFPlayer, and connect a microphone to the input of the SIM800, does it work OK then?.

elyas721 · Jul 15, 2023

Nigel Goodwin said:
Remove the DFPlayer, and connect a microphone to the input of the SIM800, does it work OK then?.

Works well with microphone

Speaker OUT To MIC IN

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