Audio filter between ISD1616 Audio Output and SIM808 Mic Input

Thread Starter

HighVoltageJoe

Joined Jun 1, 2017
25
Hi all,

I have a project in which a ISD1616 audio recording chip is fed to a SIM808 chip mic input with a simple filter so that when the SIM808 makes a phone call, it will have an automated voice recorded message. The problem is that I get a bunch of static and no voice after I record. I don't know why that would be, other than I made a chinsy filter. Attached is my audio filter. The two green lines on the bottom go to the mic input on the SIM808. Any help is greatly appreciated!

Thanks,
Joe M
 

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Thread Starter

HighVoltageJoe

Joined Jun 1, 2017
25
Your circuit is missing many parts that are shown on the datasheet.
I was going to ask why you take the speaker output instead of the AUX output until I noticed that the datasheet is written in a foreign language (Chinese?).
Thank you for your reply. I did not see this in the schematic that I was looking at. Maybe I was looking at a simplified version of the datasheet. Thank you for pointing that out!
 

ebeowulf17

Joined Aug 12, 2014
3,139
Your circuit is missing many parts that are shown on the datasheet.
I was going to ask why you take the speaker output instead of the AUX output until I noticed that the datasheet is written in a foreign language (Chinese?).
Interesting circuit. Most of the mic related components look familiar, but I would've expected the bottom of R3 and C1 to go to ground (or common, whatever you choose to call it in this scenario.) They have it going to the LED pin, which seems odd.

Any idea what that's all about? Is this a power saving measure? That one pin activates the LED and the mic, and any time it's not "on" it prevents wasted current from being spent biasing the mic? If so, wouldn't it still be better to connect directly to chip pin, not far side of 1k resistor? This all seems odd to me!
 
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