Duggle Posted July 18, 2010 Report Share Posted July 18, 2010 Hi there, Ive developed a16 colour (using red/green tricolour LED) linear display strip. It features 4 i/o bits per LED. (Off, plus 3 levels of Red, 3 levels of Green, 3 levels of Orange, 6 in-between shades of orange) The linear strip is designed to be mounted above/behind a midi keyboard key array. Possible display modes include noteon/off monitoring and showing the position of keyboard splits and zones. Anyhow, once tested this will all be documented on my midibox blog. One octave requires 6 shift registers. I have drafted a strip module pcb design that covers one octave. As many octaves as required are chained together. For my own use will be 2x4 octave (2x48 notes) in 2 strips. This adds up to 48 shift register chips. So my question relates to the maximum number of 74hc595 that can be chained. I understand it is the capacitive load of SCLK and RCLK signals to each chip that creates the limit. Possible strategies: 1) Reduce the clock frequency of the SPI port. (Using DMA, this should have a very minimal, or negligible adverse effect on performance and is the preferred solution). Question: Where (in MIOS32) is the sr clock speed defined? 2) Provide a (stronger) buffered output to SCLK and RCLK (a buffer line driver at the start of the chain to drive these signals harder than the STM32 with pullup resistors.) Question: suggested device? thanks Quote Link to comment Share on other sites More sharing options...
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