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[on:]

I've been pounding at this all day, and I'm missing something.  If somebody can point my nose I would appreciate it.

I picked up a couple of RDA5807SP I2C based FM Radio Receiver IC's off the FleaBay a few days ago. They came in the mail, and I'm anxious to hook them up to my arduino.   They're I2C controlled, they have a couple of registers storing what looks like 2 bytes of data each, and we can manipulate these registers to control the radio.  I'm fairly new to I2C, but starting to get my feet wet, and I just can't seem to get the hang of the appropriate read/write on this thing.  I write values to the registers, but when I read them back, they're different from what I wrote. I'm not sure where to go from here.

See my attached code.

So for example, lets say I want to write the register at 0x05, and set bits 0-3 as the value 1 (forget the other bits, they're not important yet), I'm doing whats shown below.   But its not working. When I read it back, its not how I set it.  What am I doing wrong?

Code:

#include <Wire.h>

int device_address = 96;
int seekPin = 12;
int seekPinState = 0;

void setup(){
pinMode (seekPin,INPUT); 
 
Wire.begin();
Serial.begin(9600);

getVolume();
maxVolume();
getVolume();

}


void loop(){

Serial.print("Device addres is: ");
Serial.println(device_address);

seekPinState = digitalRead(seekPin);

if (seekPinState == 1) {
  Serial.println("High!");

  }

getVolume();
delay(5000);

}


void maxVolume(){
Serial.println("Setting Volume");
Wire.beginTransmission(device_address);
Wire.write(5);

Wire.write(136); // first byte 10001000
Wire.write(175); // second byte 10101111  <-- This is the 1111 for the first 3 bits of the byte.

Wire.endTransmission();

}

void getVolume(){

 Wire.requestFrom(device_address, 2);

 while (Wire.available() == 0);
 
int byte1 = Wire.read();
int byte2 = Wire.read();
String binaryByte1 = String(byte1, BIN);
String binaryByte2 = String(byte2, BIN);

Serial.print("The currnet volume setting is: ");
Serial.print(binaryByte1);
Serial.print(":");
Serial.println(binaryByte2);
}

[Reply #1 on:]

Code:

while (Wire.available() == 0);

This just hangs about until at least one byte is available.
Then:-
 

Code:

 
int byte1 = Wire.read();
int byte2 = Wire.read();

Reads two bytes. At this point the second byte almost certainly has not arrived.
So I would try:-

Code:

while (Wire.available() < 2);

I haven't looked at the rest of the code so there might be other errors as well.

[Reply #2 on:]

It's I2C Mike, not Serial.

@op:

Don't do this:

Code:

 while (Wire.available() == 0);

Wire.requestFrom blocks until it gets the data you wanted, or it never will. Better is:

Code:

if (Wire.requestFrom(device_address, 2) != 2)
  {
  // error
  return;
  }

I don't know what this achieves:

Code:

 int byte1 = Wire.read();
  int byte2 = Wire.read();
  String binaryByte1 = String(byte1, BIN);
  String binaryByte2 = String(byte2, BIN);

Just do:

Code:

 byte byte1 = Wire.read();
  byte byte2 = Wire.read();

  Serial.print("The current volume setting is: ");
  Serial.print(byte1, BIN);
  Serial.print(":");
  Serial.println(byte2, BIN);

[Reply #3 on:]

It's I2C Mike, not Serial.

Yes I know, but you still have to wait until the data arrives.

[Reply #4 on:]

My timing must be lucky - I was getting both bytes in time... but your recommended modification is certainly a good idea, I've implemented it.   So the fact remains, when I set the values, and then try to read them, they come back different. I think this is more than likely a learning curve issue... I've gotta be doing something wrong.

[Reply #5 on:]

Yes I know, but you still have to wait until the data arrives.

No, because requestFrom blocks. Building in the wait only makes an infinite loop possible.

[Reply #6 on:]

I've gotta be doing something wrong.

I've looked but I can't find the programming guide. Can you link to it please? The thing that specifies the I2C commands/responses.

[Reply #7 on:]

The chip is the same as the FM receiver that Parallax sells, so I've been using their datasheet and example code as reference.

http://www.parallax.com/portals/0/downloads/docs/prod/audiovis/27984-FM-RadioReceiver-v1.0.pdf
http://www.parallax.com/portals/0/downloads/docs/prod/audiovis/ParallaxFMRadio-spin.zip

Some additional things I don't quite 'get' ....   When I send a bitstream to try and write the register, do I send it with bit 7 first, then 6, 5, etc (like you'd write it in binary on paper)  or does it go LSB first (unlike how you'd write it on paper). Do I have to send it one byte at a time, or can I send the full two bytes at once?  I think if I can get my arms around the proper way to read and write the registers, I'll be home free.

Thx

[Reply #8 on:]

The registers are 16 bit wide therefore you have to send them in two parts.
That data sheet says the high byte followed by the low byte. So to send a value in a variable called val use:-

Code:

Wire.write(val >> 8); // hi byte
Wire.write(val & 0xff); // lo byte  

Values come back from the chip with the hi byte first.

[Reply #9 on:]

Ok so we're sending it as two bytes. I get that.    We're sending the high byte first - I get that.  So when I create the variable that is going to be split with the code you provided, do I write it with bit 15 first or bit 0 first?

[Reply #10 on:]

do I write it with bit 15 first or bit 0 first?

I don't understand what you mean by first.
Declare the variable as an int

Code:

int var;

if you want to set bit 0 then:-

Code:

var = var | 0x1;

or if you want to set bit 15 then:-

Code:

var = var | 0x8000

The bits are the same as in a normal value.

[Reply #11 on:]

So lets say I wanted bits 0123 to be 1's.    Would I write the variable as shown in A or B

A - var = "0000000000001111"
B - var = "1111000000000000"

I think I write it as A

[Reply #12 on:]

I think I write it as A

Yes so do I.

Except don't put the value in quote marks, write it in hex.

[Reply #13 on:]

So when you say var = var | 0x8000  is this simply starting at the position identified?  Like I could write just the last 4 bits of the register if I really wanted to?

[Reply #14 on:]

The | is the inclusive OR operation it is used to set those bits in the variable that are a 1 in the mask (the number you are ORing) and leave the other bits in the variable unchanged.

I could write just the last 4 bits of the register if I really wanted to?

If you want to set the variable to 0000000000001111 then you can just use:-
var = 0xf