Adruino SPI

Using Arduino Programming Questions
1

Hey all, I posted a similar topic in sensors but I think that it should actually be posted here, anyways here goes:

I have a humidity sensor that uses SPI, and since I'm a complete noob at it I can't seem to make it work

Sensor SPI data:http://sensing.honeywell.com/spi-comms-with-digital-humidity-temp-sensors-tn-009071-1-en-final-07jun12.pdf

From this I developed code that I thought would work but seems to just return two full bytes:

#include <SPI.h>

byte slave1 = 48;

void setup() 
{
  // put your setup code here, to run once:
Serial.begin(9600);
Serial.println();
pinMode(slave1, OUTPUT);
digitalWrite(SS, HIGH);
digitalWrite(slave1, HIGH);
pinMode(MISO, INPUT);
///////////////////////////////////////////////////////////
SPI.begin();
SPI.setClockDivider(SPI_CLOCK_DIV32);
SPI.setBitOrder(MSBFIRST);
SPI.setDataMode(SPI_MODE0);
}
///////////////////////////////////////////////////////////
 String MeasurementReady()
 {
   digitalWrite(slave1, LOW);
   delay(10);
   digitalWrite(slave1, HIGH);
   delay(10);
   digitalWrite(slave1, LOW);
   byte a = SPI.transfer(0);
   byte b = SPI.transfer(0);
   digitalWrite(slave1, HIGH);
   String Result = String(a,BIN);
   Result = Result + String(b,BIN);
   return Result;
 }
//////////////////////////////////////////////////////////


void loop() 
{
  // put your main code here, to run repeatedly:
Serial.println("Test");
Serial.println(MeasurementReady());
while(1);
}

Can someone tell me where I am going wrong please.

Thanks.

2

I got this far on the first page of the datasheet you linked. Section 2.1.

By default, the digital output humidity sensor performs humidity
measurement and temperature measurement conversions
whenever it receives a measurement request (MR) command;
otherwise, the sensor is always powered down. The results are
stored after each measurement in output registers to be read
using a data fetch (DF) command.

Are you sending those commands? I don't see where you are sending any commands to the sensor.

3

I want to but if you check the pin out of the sensor it only has MISO, so I can only receive data from the sensor not send it, my understanding is that the MR command is just setting the SS low and not taking a reading then setting it high again, and DF is setting slave low and taking a reading, I am pretty unsure how this particular setup works.

4

Next section:

2.2 Humidity and Temperature Measurement Request
To wake up the humidity sensor and complete a measurement
cycle, an MR command is used. The complete measurement
cycle performs a humidity measurement and a temperature
measurement and stores the results. As shown in Figure 3, an
MR command is a read of eight or more bits, ignoring the data
that is returned.

Try throwing one transfer in between the low and high.

5

No change