SPI programming

Using Arduino Programming Questions
1

Hi, I am trying to program for a pressure sensor which uses the SPI protocol. However, it seems like that my code doesn't run properly. Can some one help me with this? I appreciate that a lot!!!

Here is the datasheet

#include <SPI.h> // include the SPI library
const int cs = 10;
const byte sample = 10000011;
const byte resend = 01010000;

void setup(){
  pinMode(cs,OUTPUT);
  Serial.begin(9600);//initialize the serial monitor 
  Serial.println("Initializing the force monitor");
  delay(50);//give the numatac some time to setup
  SPI.begin();//begin SPI trasaction
  digitalWrite(cs,HIGH);
  }


void loop(){
  //Set up SPI bus
  //set the clock speed to be 5 Mhz, most significant byte first, and data trasfer mode 0
  SPI.beginTransaction(SPISettings(4400000,MSBFIRST,SPI_MODE0));
    uint8_t MSBbyte, LSBbyte;
    digitalWrite(cs,LOW);
    SPI.transfer(sample);
    SPI.transfer(sample);
    digitalWrite(cs,HIGH);
    delayMicroseconds(50);
    digitalWrite(cs,LOW);
    MSBbyte = SPI.transfer(resend);
    LSBbyte = SPI.transfer(resend);
    SPI.endTransaction();
    digitalWrite(cs,HIGH);

    MSBbyte = unsigned(MSBbyte)>> 1;
    LSBbyte = unsigned(LSBbyte)>> 3;
    LSBbyte <<= 3;

   unsigned int rawdata = MSBbyte*256 + LSBbyte;
   unsigned int pressure = unsigned(rawdata) >> 3;
    Serial.println(pressure);
2

by the way, I just want to get the fluid pressure which is Pdc.

3

While listening to the responses from the NumaTac the host should write 0x0001 to the MOSI lines to avoid errors.

You don't seem to be doing that.

4

I added this line "SPI.transfer(0x0001)" either before or after the 50 microsecond delay, but it still doesn't work. Could you please give some some advice? I am beginner of SPI protocol, and I have no idea what to do next. :slightly_frowning_face: Thanks.

    digitalWrite(cs,LOW);
    SPI.transfer(sample);
    SPI.transfer(sample);
    digitalWrite(cs,HIGH);
    delayMicroseconds(50);
    SPI.transfer(0x0001);
    digitalWrite(cs,LOW);
    MSBbyte = SPI.transfer(resend);
    LSBbyte = SPI.transfer(resend);
    SPI.endTransaction();
    digitalWrite(cs,HIGH);
5

I think you want:

    digitalWrite(cs,LOW);
    SPI.transfer(0x83);  // Sample Command for Channel 1
    SPI.transfer(0x00);  // Eight bits of Don't Care
    digitalWrite(cs,HIGH);
    delayMicroseconds(50);
    digitalWrite(cs,LOW);
    MSBbyte = SPI.transfer(0x00);
    LSBbyte = SPI.transfer(0x01);
    digitalWrite(cs,HIGH);
    SPI.endTransaction();

Note: You can't write binary constants as a string of 0's and 1's. What you wrote was "sample = Ten Million and Eleven" and "resend = Octal 1010000" (that's decimal 266,240). The leading '0' makes it an octal (base eight) constant. Naturally neither of them will work as expected. The way(s) to write a binary constant:

const byte sample = B10000011;  // Arduino-form binary constant
const byte resend = 0b01010000;  // Non-standard C binary constant

Most programmers write binary constants in HEX.