See pictures below. I bought a bunch of these on Ebay they work pretty good. But the microphone is low quality. What I want to do is ditch the microphone and use the headphone jack on my computer as a source to record sound. I believe I can remove the microphone and R3 and attach the input directly to C4. As I understand it I might need a voltage divider to attenuate the signal from my headphone jack but I have no clue how to do it or the resistor values. Could I just use a very low volume on my computer instead? Do I need a resistor to match impedance?

 

This chip wants Mic in less than 100 mv P_P.
I would guess about 50:1 would be the maximum attenuation you would need.
With a volume control in the computer, maybe 5:1 max attenuation.
Zin is 10K, so 39k in series with the computer or a 1K volume control pot after a 3.9K resistor from the computer.
Make sense?

 

Awesome thanks. I'll go with the 39k in series.

 

Awesome thanks. I'll go with the 39k in series.

Did this worked for you, can you share the circuit diagram and final product picture.

 

I landed on this thread because I wanted to do the same thing - drive a cheap ISD1820 board from a computer headphone/line-out instead of the on-board microphone. Turns out it's simpler than you might think!

Components:

1. 3.5mm headphone jack (TRS - 3 pole).
2. 10uF ceramic capacitor.

Process:

1. De-solder the on-board microphone.
2. Solder a short wire between the ground of a 3.5mm headphone jack and one of the microphone pads on the board.
3. Solder a 10uF capacitor between one of the channels of a 3.5mm headphone jack and the other microphone pad on the board.

I found a volume level of about 25% on the computer gives the right balance between signal and noise (the on-board automatic gain control compensates). You can test that by setting the pass-thru jumper on the 1820 board, so you can hear the level.