Speaker OUT To MIC IN

[Suraj143]

I want to use ISD1820 voice recording 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 ISD module.
Please see the attached file.

Thanks

 

[Nigel Goodwin]

A series resistor should be all you need - historically the original Philips cassette recorders used a 1.5Meg inside the DIN plug to make a mike input into a line input. The value obviously depends on the input impedance of the mike input.

 

[ChrisP58]

In addition to a resistor, you'll probably also need a DC blocking capacitor as the SIM800L supplies DC to power the electret mic that it's expecting.

 

[Nigel Goodwin]

In addition to a resistor, you'll probably also need a DC blocking capacitor as the SIM800L supplies DC to power the electret mic that it's expecting.

If you're using a 1.5Meg resistor, as I suggested, it's probably not going to be an issue.

 

[KMoffett]

Will the fact that the ISD1820's speaker output is not ground referenced make a difference? Maybe capacitive couple both sides. Followded by a voltage divider.

 

[Nigel Goodwin]

Will the fact that the ISD1820's speaker output is not ground referenced make a difference? Maybe capacitive couple both sides. Followded by a voltage divider.

No, you only need to use one of the outputs - think how a bridged amplifier works, and you will understand why. You 'could' add a coupling capacitor, but I suspect it would make little difference - particularly with a high value series resistor rather than an actual voltage divider (the second resistor is the input impedance you're feeding).

 

[Suraj143]

OK, I can connect the two speaker wires directly to the MIC input via a single 1.5Meg resistor (It can be placed any side of these two wires).The spec sheet I posted have a MIC impedance is maximum of 27K.Is this 1.5Meg ok in that case?

 

[Nigel Goodwin]

OK, I can connect the two speaker wires directly to the MIC input via a single 1.5Meg resistor (It can be placed any side of these two wires).The spec sheet I posted have a MIC impedance is maximum of 27K.Is this 1.5Meg ok in that case?

Try it and see, adjust as required - you only use ONE of the speaker wires (for bridged outputs), the other connection is ground.

 

[Suraj143]

If you looked at the attachment on my first post it doesn't have a common ground in either MIC IN (sim 800l) or speaker out (isd1820). It shows SP+ SP- & MIC+ MIC-.

 

[Nigel Goodwin]

You could connect two resistors if you wanted?, from +ve to +ve and -ve to -ve, or one resistor from +ve to +ve and ground the -ve input.

 

[Suraj143]

You could connect two resistors if you wanted?, from +ve to +ve and -ve to -ve, or one resistor from +ve to +ve and ground the -ve input.

Ok thanks I'll do like that.

 

[Suraj143]

Did like this.Quite ok. But there is a noise coming out.Noise means a background noise (the sound like when tuning a FM radio).Any method to cancel the noise?

 

[Nigel Goodwin]

What happened to all the discussion about resistor values for attenuation?, you're sticking massive signal levels in to a mike input. R2 needs to be a great deal larger.