Glitchy Audio when running Bela Mini with Lipo Battery

Kunsf

Hey there! I just finished my first project with Bela Mini, using a piezo as an audio input and gyro for controlling parameters from Pd. Everything sounds clear when running plugged to pc or with a phone charging adapter through USB but when I use a 3.7V 900mAh lipo, it sounds glitchy (no hum, or noise). I tried increasing block sizes but there is no change. I want to use a lipo battery because my case is designed for it, what should I do?

giuliomoro

This is unexpected. What sort of glitches are you getting? Also, how are you powering the gyro? 3.3V or 5V? The 5V supply rail will be actually about 3.7V when powered from lipo, so that may be one source of problem.

Can you let it run on the lipo for a bit, make sure the glitches happen, then connect the USB and check the log in the IDE: do you see any useful message?

Kunsf

<< piezo attached to my desk and I'm tapping. Usb one is the desired sound and with lipo, it sounds like this. (blocksize 64)

ADXL 326 was powered from 5v but unfortunately, switching to 3.3v doesn't solve it.

Now I don't have any messages on IDE, but last night I got these when I plugged Bela after the problem with lipo, maybe it helps to understand.

make: Warning: File 'build/core/default_libpd_render.d' has modification time 61426846 s in the future
make: warning Clock skew detected. Your build may be incomplete

giuliomoro

Kunsf make: Warning: File 'build/core/default_libpd_render.d' has modification time 61426846 s in the future
make: warning Clock skew detected. Your build may be incomplete

that's just normal when running headless.

I will check on a LiPo here as soon as I have a chance. Can you try to just play a sinewave (e.g.: run the 01-Basic/sinetone example) and see if that is also affected by running on the lipo?

giuliomoro

is the piezo going into the audio input?

Kunsf

Yes, with some 2.2M resistors

giuliomoro

Kunsf Yes, with some 2.2M resistors

where is the resistor going? Can you post the full diagram?

Kunsf

Sinetone is not affected, and the resistors are hooked like one of this https://raw.githubusercontent.com/wiki/BelaPlatform/bela/Images/EXAMPLES/04-Audio_samples-piezo_x3.png

giuliomoro

those resistors are only needed if you use the analog inputs. In your case you are using the audio inputs so you should be able to do without the resistors. Try that and see if anything gets better.

Kunsf

I connect it directly but it's the same. When plugged to pc it's fine and clear, but with lipo full of bleeps and bloops.

giuliomoro

Can you try to use a different source as an input, e.g.: a mobile phone or something like that?
Also, where are you taking your ground from?

Kunsf

Same glitches happen with different audio sources. I use P2 pin 15 for battery.

giuliomoro

and what ground for the audio?

Kunsf

piezo's ground is connected to the outer pin of 3 pin inlet (IN) the middle is empty and the other cable is connected
on the inner.

Kunsf

Also, the ADXL326's x,y,z is connected to A0, A1, and A2, Vin to 3.3V and GND to GND right next to it.

Kunsf

I disconnected the sensor while Bela was powered through USB same glitchy sound appeared. When there is no data coming to analog inputs it goes randomly up and down, so those were the reason (they were affecting my pitch shifter patch). Maybe 3.7 lipo is not enough for powering the ADXL326 because it's acting like there is no connection when powering with it.

What can I do alternatively? I really want to work it with rechargeable batteries, but open to the other solutions as well.

giuliomoro

Kunsf Maybe 3.7 lipo is not enough for powering the ADXL326 because it's acting like there is no connection when powering with it.

That is possible, although not what would appear from its datasheet.

Kunsf I disconnected the sensor while Bela was powered through USB same glitchy sound appeared.
When there is no data coming to analog inputs it goes randomly up and down, so those were the reason (they were affecting my pitch shifter patch).

This actually makes me think that Bela's analog inputs wouldn't work when powered with 3.7V: the internal voltage reference is 4.096V, and that is unachievable in this setting. It can possibly be switched to use 3.3V as a reference. The datasheet is not extremely clear on this. I will have to test it.

lokki

use a 5v phone charger battery pack? they come in different sizes, maybe you can find a suitable one.
alternatively charge pump your lipo voltage to 5v:
https://www.sparkfun.com/products/10255