MCP3008 raspberry pi ADC error - c

Question

I am getting an error when reading from the mcp3008 ADC. The function below returns 127 when receiving a 3.3V input. Since it is a 10 bit ADC, it should return 1023.
I have defined my pin numbers correctly, and included both stdio.h and wiringPi.h. Any help is appreciated.
int main(void) {
int adcValue = 0;
wiringPiSetup();
pinMode(csPin, OUTPUT);
pinMode(sclkPin, OUTPUT);
pinMode(mosiPin, OUTPUT);
pinMode(misoPin, INPUT);
while(1) {
delay(10);
adcValue = readADC(CHAN0);
if (adcValue == -1)
printf("Error reading from %i \n", CHAN0);
else
printf("Chan0: %i \n", adcValue);
}
}
int readADC(int adcChan) {
// Variables
unsigned char dataOut = 0;
unsigned char adcout = 0;
int i, j = 0;
if ((adcChan > 7) || (adcChan < 0)) {
return -1;
}
digitalWrite(csPin, HIGH);
digitalWrite(sclkPin, LOW);
digitalWrite(csPin, LOW);
dataOut = adcChan;
dataOut |= 0x18;
dataOut <<= 3;
for (i = 0; i < 5; i++) {
if (dataOut & 0x80) {
digitalWrite(mosiPin, HIGH);
} else {
digitalWrite(mosiPin, LOW);
}
dataOut <<= 1;
digitalWrite(sclkPin, HIGH);
digitalWrite(sclkPin, LOW);
}
adcout = 0;
for (j = 0; j < 12; j++) {
digitalWrite(sclkPin, HIGH);
digitalWrite(sclkPin, LOW);
adcout <<= 1;
if (digitalRead(misoPin)) {
adcout |= 0x1;
}
}
digitalWrite(csPin, HIGH);
adcout >>= 1;
return adcout;
}

Answer 1

Your adcout is a char and can't hold the 10-bit value. Use an unsigned int instead. Also, you should not shift back your value with adcout >>= 1;, it's already good.

Answer 2

You are returning a variable unsigned char adcout = 0; which of a size 8 bits NOT 10 bits. Also you are right shifting it by 1 before returning,So most probably you are getting :
255 Right shifted by 1 = 127.

Answer 3

use python and spidev module!
It will look something like!
import spidev
spi = spidev.SpiDev()
spi.open(0,0)
def read(ch):
adc = (spi.xfer2([1,(8+ch)<<4,0])
data = ((adc[1]&3 << 8) + adc[2]
This should give u proper readings from the mcp3008 chip.
I am currently using this chip in a sensor module for connecting my analog sensors. Ch is the channel on the mcp3008 (0-7)