Interfacing MCP3302 ADC with Arduino Micro SPI Help

Question

I am very new to hardware design and am making an optical detection circuit using a photodiode. I simply need to interface with the photodiode and save the output voltage values on Arduino IDE

Hardware setup:

• Photodiode (BPW21R) connected in transimpedance arrangement with 100K feedback resistor and OPA350 op amp
• Output signal from the transimpedance amplifier is connected to CH0 on the ADC (MCP3302)
• Op amp and ADC to be powered to +5V using Arduino Micro power pin

ADC <-> Arduino Micro Connections:

• VDD and VRef <-> +5V Power Pin
• CS/SHDN <-> RX_LED / SS
• DIN <-> MOSI
• DOUT <-> MISO
• CLK <-> SCK

My two questions are:

• Are my connections between ADC and Arduino Micro correct to communicate by SPI protocol?

• In Arduino IDE, how can I edit the code so that the Arduino Micro receives data from the ADC by SPI protocol and displays it in the serial monitor?

  #include <SPI.h>

  void setup() {

  pinMode(SS, OUTPUT);
  pinMode(MISO, OUTPUT);  
  
  digitalWrite(SS,HIGH);
  Serial.begin(115200);
  

  }

  void loop() { byte c;
  digitalWrite(SS,LOW);

  Serial.println(analogRead(MISO));
  
  digitalWrite(SS, HIGH);
  delay(100);
  

  }

Answer 1

This is NOT how an SPI ADC works.

Your approach is mixing the digital and the analog worlds in the weirdest way possible.

The external ADC stores the data bytes in a register after data is sampled. Values must be queried using the appropriate commands through a library or custom set of instructions using the SPI communication protocol

The way you are trying to read the value from the ADC by expecting an analog value in the MISO pin is simply wrong and makes no sense.

Read the device's manual and figure out what commands you need to send to it to request the digitised values.

Also, get a good understanding on how the SPI protocol works. That's going to be extremely helpful.

This library might be of help: https://github.com/bakercp/MCP3XXX

I reiterate, as many wise men use to say: RTFM!