Hi there
I'm using a Teensy 3.2 to make potentiometer readings for a MIDI controller. The idea is that the controller is USB powered.
I know USB power is very noisy, that's why I've tried everything in my hand to filter that noise:
- In this FTDI application note recommends to use a filter just before the usb 5v pin.
- This filtered voltage goes to a LDO to get 3.3v, and from there to the potentiometers and also to the AREF pin.
- The cursor of the potentiometers have a capacitor to AGND. The pots are also AGN grounded.
- Also I'm using some software filtering to smooth the readings.
After the LDO the noise is reduced a little bit, but it looks like the poor LDO can't handle the spikes. Trying to figure out where this noise is coming from, I was that without the Teensy connected to the circuit the USB power, although noisy, is "quiet" compared to when the Teensy is plugged in (see attachments). First file with Teensy unplugged, second with Teensy plugged. The yellow measurement is taken directly from the USB 5v pin (1), and the pink one is taken after the passive filter (2).
So, is that normal? Are this spikes coming from the Teensy itself, or maybe they come from the computer, when a load is connected? I tried with 3 different Teensy 3.2 boards, and results are the same, so maybe is the second option...
Anyway, any ideas on how to improve this?
Thank you!
I'm using a Teensy 3.2 to make potentiometer readings for a MIDI controller. The idea is that the controller is USB powered.
I know USB power is very noisy, that's why I've tried everything in my hand to filter that noise:
- In this FTDI application note recommends to use a filter just before the usb 5v pin.
- This filtered voltage goes to a LDO to get 3.3v, and from there to the potentiometers and also to the AREF pin.
- The cursor of the potentiometers have a capacitor to AGND. The pots are also AGN grounded.
- Also I'm using some software filtering to smooth the readings.
After the LDO the noise is reduced a little bit, but it looks like the poor LDO can't handle the spikes. Trying to figure out where this noise is coming from, I was that without the Teensy connected to the circuit the USB power, although noisy, is "quiet" compared to when the Teensy is plugged in (see attachments). First file with Teensy unplugged, second with Teensy plugged. The yellow measurement is taken directly from the USB 5v pin (1), and the pink one is taken after the passive filter (2).
So, is that normal? Are this spikes coming from the Teensy itself, or maybe they come from the computer, when a load is connected? I tried with 3 different Teensy 3.2 boards, and results are the same, so maybe is the second option...
Anyway, any ideas on how to improve this?
Thank you!