mortonkopf
Well-known member
Hi All. I have been working on project with an SPI bus driving eight chained port expanders (MCP23S17) with T3.6, a set of Adafruit Trellis button pads, and an ILI9341 screen. Moving from breadboard to a more permanent setup I extended the SPI bus wires and immediately ran into problems with signal integrity. Lots of malfunctioning at the rotary encoders that are attached to the chips. I thought it was my soldering, that perhaps a trace had broken on my homemade PCB, or that I simply blew something. As i was resoldering, switched on again after I was done and I moved the data and clock lines to the first chip. Immediately there was an improvement in chip response. I then realised that every time I touched these lines, there was a response of some kind.
So, I found that I was acting as an earth. I wound an earth wire around the SPI data and clock, and hey presto, perfect functioning of high speed polling of chips.
Question is, do you think that it could be that the SPI bus needs this shield, or am I masking something more fundamental about a poor circuit that will come and bite me later. When I say 'long' cable, I am only talking of moving from 10cm to 30cm in length.
All the best.
m
So, I found that I was acting as an earth. I wound an earth wire around the SPI data and clock, and hey presto, perfect functioning of high speed polling of chips.
Question is, do you think that it could be that the SPI bus needs this shield, or am I masking something more fundamental about a poor circuit that will come and bite me later. When I say 'long' cable, I am only talking of moving from 10cm to 30cm in length.
All the best.
m