DD4WH
Well-known member
Hi Edwin,
thanks for clearing this up and thanks for the nice schematics!
Now I understand!
Yes, I tried the same with my setup (using the builtin Teensy ADC without audio board and using a separate 3V3 LDO regulator for the preamp and mic), but the clickings remained at 384/500ksps sample rate . . .
So there seems to be a different issue in my setup.
My suspicion would be:
* the SD card writes use a lot of current (more than the Teensy 3.6 voltage regulator can provide), this causes a drop on the Teensy 3V3 line, also a drop in the ADC reference voltage leading to spikes in the recordings
* the drop in ADC reference voltage can only be eliminated in my setup, if the SD card 3V3 voltage would be separated from the Teensy 3V3 line, making it necessary to cut the SD card trace of pin 4 and deliver the SD card with a separate voltage regulator . . .
In your setup with the audio board, the ADC is in the codec on the audio board, making it easy for you to provide different 3V3 lines for ADC and Teensy, so your problem is solved. My problem with the built-in ADC could however only be solved by "hacking" the Teensy SD card 3V3 line.
Thanks a lot for these insights, have fun with the Teensy!
Frank
thanks for clearing this up and thanks for the nice schematics!
Now I understand!
Yes, I tried the same with my setup (using the builtin Teensy ADC without audio board and using a separate 3V3 LDO regulator for the preamp and mic), but the clickings remained at 384/500ksps sample rate . . .
So there seems to be a different issue in my setup.
My suspicion would be:
* the SD card writes use a lot of current (more than the Teensy 3.6 voltage regulator can provide), this causes a drop on the Teensy 3V3 line, also a drop in the ADC reference voltage leading to spikes in the recordings
* the drop in ADC reference voltage can only be eliminated in my setup, if the SD card 3V3 voltage would be separated from the Teensy 3V3 line, making it necessary to cut the SD card trace of pin 4 and deliver the SD card with a separate voltage regulator . . .
In your setup with the audio board, the ADC is in the codec on the audio board, making it easy for you to provide different 3V3 lines for ADC and Teensy, so your problem is solved. My problem with the built-in ADC could however only be solved by "hacking" the Teensy SD card 3V3 line.
Thanks a lot for these insights, have fun with the Teensy!
Frank