Request Speaker PHAT Internals Information

Discussion Raspberry Pi
1

I will be using the Speaker PHAT with STM32 processor; not a pi zero. I’ll be using it only for its audio capabilities. I’m looking at the data sheet for the MAX98357 and have some questions:

  1. How is the GAIN_SLOT pin wired? The gain_slot pin on the chip sets the gain. Depending on how it is connected – if at all – the gain can vary from 3 to 15 dB.)

  2. How is the SD_MODE- pin wired? That determines whether left channel data is output, right channel data is output, the average of left and right channels is output, or the chip is placed in standby mode. It would be neat if we could access this pin to put the chip in low power mode, but I understand that probably wasn’t a design consideration.

  3. Which pins on the header are connected to which signals on the chip? Specifically, which header pins connect to each of the following signals?

  • LRCLK
  • BCLK
  • DIN

I suppose if I take out my ohm meter and get a decent magnifier and needle probes, I could figure this out, but I assume someone could just look at the schematic and let post the information.

Thanks,

Ken

2

Hi Ken!

  1. The gain is left floating for 9dB gain. You can solder a 0 ohm resistor for 12dB or a 100k resistor for 15dB to the empty 0603 resistor landing near the amp chip.

  2. It’s wired to the Pi’s 5V rail via a 1M ohm resistor, thus mixing both channels.

LRCLK -> BCM19
BCLK -> BCM18
DIN -> BCM21

3

Thanks, Niko.

That’s just what I needed.

Regards,

Ken