Description: The MCP3002 has a 10-bit analog to digital converter (ADC) with a simple to use SPI interface. Use this IC if your microcontroller does not have an ADC or have enough ADC lines. A great chip when you need to add additional ADC lines.
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It’s easy to use, the datasheet is excellent, and it is much faster that the built-in ADC on the Arduino. Just note that that it needs a low resistance source (see pages 11-12 of the datasheet for details), so use an op-amp if your source has high resistance, especially if you’re sampling very quickly.