A few quick questions - 4.1 with Audio shield Rev D

C

ChrisKelly

Member
Hi

These are pretty basic questions so please bear with me! ;)

- on the 4.1 board, do all 3 GND pins need connecting to 0V/ground for correct functionality?
- are the two 3.3V pins meant as outputs/voltage sources or do they need a separate 3.3V voltage connection?

When using the 4.1 with the Rev D audio shield:
- on the audio in and line out connections, are DC blocking caps redundant?
- do both the audio in and line out connections need both signal and GND pins connecting to analog GND?
- is best practise to limit analog inputs to the 4.1 pins not used in conjunction with the Rev D board i.e/ try to just use A8, A3, A2, A0 ?

thanks

Chris
 
ChrisKelly said:
Hi

These are pretty basic questions so please bear with me! ;)

- on the 4.1 board, do all 3 GND pins need connecting to 0V/ground for correct functionality?
- are the two 3.3V pins meant as outputs/voltage sources or do they need a separate 3.3V voltage connection?

When using the 4.1 with the Rev D audio shield:
- on the audio in and line out connections, are DC blocking caps redundant?
- do both the audio in and line out connections need both signal and GND pins connecting to analog GND?
- is best practise to limit analog inputs to the 4.1 pins not used in conjunction with the Rev D board i.e/ try to just use A8, A3, A2, A0 ?

thanks

Chris
Click to expand...

On the Teensy 4.1, all 10 ground pins are inter-connected. The ground pins are:
  • Ground pin next to pin #0;
  • Ground pin between VIN and 3.3v
  • Ground pin between pin 13 and pin 41/A17;
  • Ground pin in the middle row in the back between the reset button and the micro SD drive);
  • Ground pin within the micro SD card reader;
  • Ground solder pad in the first set of solder pads under the teensy;
  • Ground solder pad in the second set of solder pads under the teensy;
  • Two ground pins in the USB host breakout; (and)
  • Ground pin in the ethernet breakout.

Similarly the 6 3.3v pins are all interconnected (i.e. there is only one 3.3v regulator):
  • 3.3v pin between the ground pin and pin 21/A9;
  • 3.3v pin between pin #12 and pin #24/A10;
  • 3.3v pin in the middle row of pins between the reset button and the micro SD card reader;
  • 3.3v pin within the micro SD card reader;
  • 3.3v pin in the first group of solder pads underneath the Teensy; (and)
  • 3.3v pin in the second group of solder pads underneath the Teensy.

In hooking up the audio shield, you will need to connect the 3.3v pin between the ground pin and pin 23/A9. You will need to connect 2 ground pins (the one between VIN and 3.3v, and the one next to pin #0). The reason you need to connect the two ground pins is the audio adapter shared a lot of the design with the earlier audio adapters for the Teensy 3.x processors. In the 3.x processors, the ground pin between VIN and 3.3v was an analog ground pin. While the other ground pin next to pin #0 was the normal digital ground pin. The 3.x audio shield used the analog ground pin for the sound components, while it used the digital ground pin for the micro SD card reader and the flash memory solder pads. The Teensy 4.x microprocessors don't have a separate analog ground pin, but the audio shield doesn't interconnect the two ground pins.
 
One last question:
- when connecting to the audio input on the audio shield, and when taking a line out signal, do the corresponding GND pins need connecting to my analog (audio)? Or can these be left unconnected?

Thanks again
Chris
 
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