I have a question about using external devices connected to the 3.5mm headphone jack that I haven't found answered elsewhere.
Initially I used a powered speaker (which has it's own battery) plugged into the headphone jack. Worked just fine.
Since I want to have speaker audio in my project, I next went to one of the cheap little PAM8403 stereo amplifier boards mounted in the same enclosure and powered from the same +5V power supply that provides power to the Teensy and Audio Shield. This means there is a common ground connection between the 5V return and the Teensy GND pin, but per the caution silkscreened on the board, I did not connect the headphone ground (HPVGND) to the Teensy GND. I'm pleased that feeding the audio from the L or R pins on the headphone jack to this audio amplifier seems to work just fine (i.e. with only the signal pin(s) connected and no connection the the headphone jack ground).
Since it works I can't see anything wrong with this approach but would appreciate any comments. I could provide AC coupling between the two grounds (i.e. with a capacitor between HPVGND to GND) but I don't think it will make any difference. The fact that this works as it does is a plus for my project.
Bob
Initially I used a powered speaker (which has it's own battery) plugged into the headphone jack. Worked just fine.
Since I want to have speaker audio in my project, I next went to one of the cheap little PAM8403 stereo amplifier boards mounted in the same enclosure and powered from the same +5V power supply that provides power to the Teensy and Audio Shield. This means there is a common ground connection between the 5V return and the Teensy GND pin, but per the caution silkscreened on the board, I did not connect the headphone ground (HPVGND) to the Teensy GND. I'm pleased that feeding the audio from the L or R pins on the headphone jack to this audio amplifier seems to work just fine (i.e. with only the signal pin(s) connected and no connection the the headphone jack ground).
Since it works I can't see anything wrong with this approach but would appreciate any comments. I could provide AC coupling between the two grounds (i.e. with a capacitor between HPVGND to GND) but I don't think it will make any difference. The fact that this works as it does is a plus for my project.
Bob