bicycleguy
Well-known member
FYI
The SPI for the SD-card on the audio board running at 24MHz is intolerant of long signal lines on its bus. On a project using the Teensy 3.2, audio board and an I/O expander MCP23S08 a breadboard project (and subsequent PWBs) worked great.
However, when the I/O expander was moved to its proper location about 8 ft away all kinds of ringing, noise and fun ensued. The SD-card and MCP23S08 libraries allow the bus speed to be changed between devices but that wasn't enough. Solutions that would help one device hurt the other. Note, a good oscilloscope with SPI decoding was essential in diagnosing.
A 74LVC126 tristate output buffer solved the problems. No software changes were required. When the CS line for the audio is pulled down it disconnects the bus from the slower SPI devices and their cable reflections ect.
I know this isn't the greatest way to handle remote stuff but it seems to work reliably.
The SPI for the SD-card on the audio board running at 24MHz is intolerant of long signal lines on its bus. On a project using the Teensy 3.2, audio board and an I/O expander MCP23S08 a breadboard project (and subsequent PWBs) worked great.
However, when the I/O expander was moved to its proper location about 8 ft away all kinds of ringing, noise and fun ensued. The SD-card and MCP23S08 libraries allow the bus speed to be changed between devices but that wasn't enough. Solutions that would help one device hurt the other. Note, a good oscilloscope with SPI decoding was essential in diagnosing.
A 74LVC126 tristate output buffer solved the problems. No software changes were required. When the CS line for the audio is pulled down it disconnects the bus from the slower SPI devices and their cable reflections ect.
I know this isn't the greatest way to handle remote stuff but it seems to work reliably.