I have a Teensy 4.1 based, USB MIDI Host Synthesizer that I'm controlling with a NuEVI (or NuRAD) USB device midi controller.
The NuEVI and NuRAD controllers are based on Teensy 3.2. These controllers have internal batteries as does my USB MIDI Host Synth.
Problem: when I run the Host Synth on its battery and the NuEVI on its own battery and then I turn off the Host Synth with the NuEVI still on, I noticed that the NuEVI is putting out dc voltage on the USB device data+ pin with a spurious signal on it. The spurious signal is making its way through to the 3.3V supply and then to the audio circuit (basically the same audio circuit as the Audio shield), and out the head phones. This causes an unpleasant, restroom-ish sound for a second or two while the synth is powering down.
I checked the NuEVI usb device port while not connected to anything and the data+ pin is outputting about 1.7V (with no spurious signal). When connect to the Teensy 4.1 host port the data+ pin is about 1.3 V with the spurios signal on it.
The NuEVI has the usb device port connect directly to the Teensy 3.2 inside, and the host port on my synth is connected directly to the host pins on the Teensy 4.1.
The question is: is it a problem to have the about 1.7 volts on the data pins from the Teensy 3.2 driving the data pins (data+) of the host port on the Teensy 4.1 when the Teensy 4.1 is not powered on?
The NuEVI and NuRAD controllers are based on Teensy 3.2. These controllers have internal batteries as does my USB MIDI Host Synth.
Problem: when I run the Host Synth on its battery and the NuEVI on its own battery and then I turn off the Host Synth with the NuEVI still on, I noticed that the NuEVI is putting out dc voltage on the USB device data+ pin with a spurious signal on it. The spurious signal is making its way through to the 3.3V supply and then to the audio circuit (basically the same audio circuit as the Audio shield), and out the head phones. This causes an unpleasant, restroom-ish sound for a second or two while the synth is powering down.
I checked the NuEVI usb device port while not connected to anything and the data+ pin is outputting about 1.7V (with no spurious signal). When connect to the Teensy 4.1 host port the data+ pin is about 1.3 V with the spurios signal on it.
The NuEVI has the usb device port connect directly to the Teensy 3.2 inside, and the host port on my synth is connected directly to the host pins on the Teensy 4.1.
The question is: is it a problem to have the about 1.7 volts on the data pins from the Teensy 3.2 driving the data pins (data+) of the host port on the Teensy 4.1 when the Teensy 4.1 is not powered on?