void spi_cs(int f)
{
  if (f) {
    digitalWrite(2, HIGH);
  } 
  else {
    digitalWrite(2, LOW);
  }
}

void spi_ck(int f)
{
  if (f) {
    digitalWrite(3, HIGH);
  } 
  else {
    digitalWrite(3, LOW);
  }
}

void spi_do(int f)
{
  if (f) {
    digitalWrite(4, HIGH);
  } 
  else {
    digitalWrite(4, LOW);
  }
}

int spi_di()
{
  return digitalRead(5);
}

unsigned short spi_transfer(unsigned short v)
{
  int i;
  for (i = 0; i < 16; i++) {
    spi_ck(0);
    if (v & 0x8000) {
      spi_do(1);
    } 
    else {
      spi_do(0);
    }
    delay(2);
    v <<= 1;
    if (spi_di()) {
      v |= 1;
    }
    spi_ck(1);
    delay(2);
  }
  spi_do(1);
  return v;
}

unsigned short sample_ch0()
{
  spi_cs(0);
  int v = spi_transfer(0x6800) & 0x03ff;
  spi_cs(1);
  return v;
}

unsigned short sample_ch1()
{
  spi_cs(0);
  int v = spi_transfer(0x7800) & 0x03ff;
  spi_cs(1);
  return v;
}

int get_temperature()
{
#if 0
  return (int)((sample_ch0() / 1023.0 * 5000 / 4 - 424) / 6.25 * 10);
#else
  return (sample_ch0() * 50000L - (1023L * 424 * 4 * 10)) / (25 * 1023);
#endif
}

static int temparray[16];
static int tempindex;

void setup()
{
  Serial.begin(9600);
  pinMode(2, OUTPUT);  
  pinMode(3, OUTPUT);  
  pinMode(4, OUTPUT);  
  pinMode(5, INPUT);  

  for (int i = 0; i < 16; i++) {
    temparray[i] = get_temperature();
  }
}

void loop()
{
  int t = 0;
  for (int i = 0; i < 16; i++) {
    t += temparray[i];
  }
  t /= 16;

  if (t < 0) {
    t = 0;
  } else if (t > 999) {
    t = 999;
  }
  char buf[100];
  sprintf(buf, "%2u.%01u\n", t / 10, t % 10);
  Serial.print(buf);
  delay(1000);                  

  temparray[tempindex] = get_temperature();
  tempindex = (tempindex + 1) % 16;
}