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Changing ADC level changes input impedance to a value as low as 20 k ohms. With 0.1 uF value as shown in the BOM, the high-pass cut-off is:

1/(2*pi*20k*0.1u) = 79.6 Hz
|h|dB = 20*log10[ sqrt((s*r*c)^2)/sqrt(1+(s*r*c)^2) ]
|h|dB = -12.2612

A change to 1 uF will have the following effect:

s = j2*pi*20
r = 20k
c = 1u

fc=1/(2*pi*r*c)
fc = 7.9577

|h|dB = 20*log10[ sqrt((s*r*c)^2)/sqrt(1+(s*r*c)^2) ]
|h|dB = -638.2644m

The proposed DSP high-pass (DC removal) filter is also designed for 8 Hz cut-off, which yields another -638 mdB for a combined response of -1.28 dB at 20 Hz and -55mdB at 100 Hz (99%).

TLV320AIC3104 datasheet page 36:

In most cases, the analog input pins on the TLV320AIC3104 should be ac-coupled to analog input sources, the
exception to this being if an ADC is being used for dc voltage measurement. The ac-coupling capacitor causes a
high-pass filter pole to be inserted into the analog signal path, so the size of the capacitor must be chosen to
move that filter pole sufficiently low in frequency to cause minimal effect on the processed analog signal. The
input impedance of the analog inputs when selected for connection to an ADC PGA varies with the setting of the
input level control, starting at approximately 20 kΩ with an input level control setting of 0 dB, and increasing to
approximately 80 kΩ when the input level control is set at –12 dB. For example, using a 0.1-μF ac-coupling
capacitor at an analog input results in a high-pass filter pole of 80 Hz when the 0-dB input level control setting is
selected

It is cause of confusion that the left-right ordering of the channels is reversed between the "enabled" header and the "gain" header.

https://forum.bela.io/d/207-testing-out-the-audio-expander-caplet/2
https://forum.bela.io/d/161-instrument-control-w-a-feedback-loop-aiming-100us-latency/21

when open the bela_cape_rev_v3 project using kicad, bela_cape-eagle-import.kicad_sym not found, where can get it?

Two pads on J10 are currently nc but could conveniently be connected to ground.

Wishlist:

Pin 15 of the TLV320AIC3104 , with a couple of resistors should do it .
Check out "11.2.2 Typical Connections for AC-Coupled Headphone Output With Separate Line Outputs and External Speaker Amplifier" pag 86 of the datasheet."

Raised here: http://forum.bela.io/d/73-microphone-to-speaker/4

Hello,

Does Bela community planning to release hardware schematics of the Bela Mini Project?

Change the input protection circuits on BelaMini to use Schottky diodes like the cape

On the PB:

1. VBUS.RAW (the 5V in from the µUSB on the PB) is connected through a ferrite bead (FB1) to the VIN.USB signal (broken out on P1.07 and labelled USB1.VIN). This is also connected to ball J16 of the BGA, which is USB0_VBUS. This has the following consequences:

• if power is supplied through USB0 (µUSB on the PB), then USB1.VIN will also be powered.
• if power is supplied through USB1 (header), then the AM335x will think that USB0 has power.

2. the OSD335x checklist (https://octavosystems.com/app_notes/osd335x-schematic-checklist-am335x/) says

USB VBUS Sense Input: USBx_VBUS is a voltage sense input and NOT a power output pin. Check that a valid voltage (>=4.4V) is present on the pin to enable the USBx peripheral.

3. the TPS65217 can allow large currents from input to the Vsys output, and ranges can be set in software:

4. Jason K is happy to review the amended design.

to avoid loud static noise when the codec is powered down (high impedance) and you are going into a high impedance (DI) input

minimum load is specified as 16ohm http://www.ti.com/lit/ds/symlink/tlv320aic3104.pdf

The lack of it can cause problems in creative and unexpected ways

https://forum.bela.io/d/1376-new-board-new-problem/2
https://forum.bela.io/d/1438-mux-capelet-errors

When you want to force booting from the SD card, you hold press the USER button (which effectively shorts P8_43 to GND). This changes the boot order to:

• SPI
• SD card

Sometimes (often?) the board fails to boot, possibly because it receives some stray signal on spi0_d0 or spi0_d1 (check the BBB's manual to see which one is expected to be used for iincoming data). Possibly, adding a pull down there could resolve this issue.

This is more of a documentation note than an actual feature request, as a resistor there may have negative effects on the bandwidth of the SPI bus.