line-in connections

[milton59]

I have a noob question about hooking up a line-in audio jack to pin A2 on a teensy 3.2. I have built the recommended circuit shown on the audio system design tool page for ADC input. My question is should I tie the ground "common" wire from the line-in cable to pin to the teensy "GND" pin or the "AGND"pin or does it matter?"

 

[GremlinWrangler]

If you have a multimeter first sanity check that the shield really is the same voltage as the Teensy ground (test AC and DC). Then you would normally use AGND is it's got some additional filtering that may help reduce noise at the Teensy end if it's doing things. AGND most effective with things like sensors where you can control all the elements of your measurment. The filters don't like high current flows hence check of that your line in doesn't have half mains or anything present on it.

 

[milton59]

If you have a multimeter first sanity check that the shield really is the same voltage as the Teensy ground (test AC and DC). Then you would normally use AGND is it's got some additional filtering that may help reduce noise at the Teensy end if it's doing things. AGND most effective with things like sensors where you can control all the elements of your measurment. The filters don't like high current flows hence check of that your line in doesn't have half mains or anything present on it.

Thank you for your reply, my line-in is a headphone jack from my cell phone. I measured ac volts at between 1 and 2 volts and very little current and am using the suggested circuit for audio into the ADC which looks like a voltage divider and filter connected across AGND and 3.3 volt output from the teensy. I am powering the teensy from a 5 volt/ 10 amp switching PS. I will try grounding the line-in through AGND. Thanks again.