I am using a MCP3008 ADC connected to the Raspberry Pi SPI pins.
- MOSI → MOSI,
- MISO → MISO,
- CE0 → ~(CS),
- CLK → SPI_SCLK
Input voltage to MCP3008 is 3.3V from the RPi. Vref also 3.3. GNDs all connected to ground rail on breadboard. Analog inputs 1-7 are wired directly to GND (should be 0's). Channel 0 is connected directly to 3.3V to obtain a full 1023 reading.
When observing the output of the ADC on the RPi, I am seeing lots of noisy data across all channels and Channel 0 is not 1023 but random values between 0-1023. It appears the ADC is not correctly translating the 3.3V on channel 0 to a solid 1023 and it is also getting values for the grounded channels 1-7.
Does anyone have any suggestions? I am using all brand new out of the box parts to eliminate the possibility of damaged connections. Also, I have metered all inputs and outputs on the ADC to RPi and all check out as working except the Dout pin on the ADC (MISO). The MISO pin from the ADC reads approximately 1.6V when it should output 3.3V since Ch.0 is connected to 3.3V.