NXT : I2C communication with PCB

[mattallen37]

Instead of using:

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WriteBuf[1] = 0xf+(~ReadBuf[0]) ;

Why not something like this:

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WriteBuf[1] = 0xff-(ReadBuf[0]) ; //You may need the NOT bitwise operator in there, I don't know, as your code is incomplete)

just for simplicity.

Or, you could break out the individual bits, and rewrite the output value based on their values (or whatever other values).

[angusfr]

if found the solution before i saw your answer ^^

My complete code based on "RXC touch sensor Mux" :

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#define I2Cport S4
#define I2CAddr8574  0x40                         // I2C Address pour 8574

unsigned byte WriteBuf[]={I2CAddr8574,0x00};               // adresse - données
unsigned byte ReadBuf[];                                   // Lecture PCF8574
int RdCnt=5;                                      // Nb byte a lire
unsigned byte lightLed = 0x00;


int GetTouchSwitches()
{
  do
  {
    I2CBytes(I2Cport, WriteBuf, RdCnt, ReadBuf);
  }while (ReadBuf[0] == WriteBuf[1])           // instead of do "ReadBuf[0] == 0xff", i check if the data change. That's how i can light more than 1 led at the same time (if i write 0xff, i turn off led)
}


task main()
{
  ClearScreen();
  SetSensorLowspeed(I2Cport);
  WriteBuf[1] = 0xff;                         // turn off leds
  while(true){
    GetTouchSwitches();                    // get button pressed
    ReadBuf[0] >>= 4;                        // readbuf = 4byte for button and 4 byte for led, i only need informations about button then i delete led bytes
    lightLed = ~ReadBuf[0];                // ~ operator convert 0 to 1 and 1 to 0   (button pressed is high level 1 but i need a low level 0 to ligh a led)
    lightLed = (lightLed) & (WriteBuf[1]);        // i use an AND operator to keep previous light leds
    WriteBuf[1] = lightLed;                            
    I2CBytes(I2Cport, WriteBuf, RdCnt, ReadBuf);   // i send data to PCF8574 
    Wait(100);
  }
}

Some comments are in french, don't blame me for that x)

Next step for me is to turn off a led when the linked button is pressed for a second time without turn off the other leds. Display wich leds are ON or OFF on NXT screen would be nice too.

I'm gonna take a look about my switch too (on A0,A1,A2) ...

See you