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I'm using a MCP3008 8ch 10bit ADC to expand the Analog Inputs for the project I'm working on. The only library I can find for it is here the library is ported from Adafruit's Raspberry Pi library here. From what I can tell the library uses bitbanging as opposed to hardware SPI in order to communicate. I would like to use hardware SPI, but don't have the skills to write a library to communicate with it myself. Are there any resources for how to write a library like that, or anything I can read about on how to convert a library from bitbanging to hardware SPI?

  • What Arduino is this for? – Nick Gammon Mar 27 '16 at 4:25
  • It's for a PCB I designed based on the Atmega 1284 with hardware support added to the IDE with MightyCore found here: github.com/MCUdude/MightyCore – TheAutomator Mar 27 '16 at 4:30
  • Typically, the library has a "sendByte" function in which it sends through "software spi" you would only have to re-write that. – Paul Mar 27 '16 at 13:53
  • The library uses some weird form of SPI. As it sends only 5 bits, and then reads 12 bits. SPI is normally a multiple of 8 bits. – Gerben Mar 27 '16 at 15:53
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The standard AVR library has SPI handling. See, for example: http://www.gammon.com.au/spi

You don't have to write a library if you don't want, just communicate directly using SPI.

The datasheet for the MCP3008 has some tips for using an 8-bit SPI system to communicate with the device. In particular this chart:

MCP3008 timings

You can see from that, that you will need 3 x SPI.transfer. I don't have one here to test with, but the code would look like this:

digitalWrite (SS, LOW);  // select device
int result;
SPI.transfer (0x01);  // start bit
result = SPI.transfer (0b10000000);  // single, ch0
result = (result & 0b11) << 8;  // move to high-order byte
result |= SPI.transfer (0);   // lower order byte
digitalWrite (SS, HIGH);  // deselect

Untested, but this should be roughly it.

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Turns out my google-fu needs work. I found this that works great using hardware SPI! Thanks everyone!

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