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Speaker OUT To MIC IN

Suraj143

Active Member
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
 

Attachments

Nigel Goodwin

Super Moderator
Most Helpful Member
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

Well-Known Member
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.
 

KMoffett

Well-Known Member
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

Super Moderator
Most Helpful Member
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

Active Member
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

Super Moderator
Most Helpful Member
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

Active Member
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-.
 

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