GND is the reference point to decide whether a signal is high or low. In electronics, connected GND is almost always required/assumed with only a few exceptions.
Did you also check SS with the oscilloscope?
Typically, SPI does not require pull-ups/downs. Unless explicitly mentioned in the datasheet of the MCP3911 or related evaluation boards, you probably don't need them.
Open up the example: File-Examples->10.Multitasking->TimerLibrary.
Then replace the Sketch on the first tab with the Sketch below. This Sketch sets up a timer to trigger every 500 ms. In the timer trigger function, it sets a flag that is used in the main loop to do an analogRead(). Do not perform analogRead() in the trigger function. This function is executed in the ISR context and should contain as minimal code as possible.
#include "Timer.h"
volatile uint8_t adc_flag = false;
Timer myTimer;
void timerFunction()
{
adc_flag = true;
}
// Add setup code
void setup()
{
Serial.begin(115200);
Serial.print(Timer_getNumTimers(), DEC);
Serial.println(" timers");
Serial.print("myTimer.begin... ");
myTimer.begin(timerFunction, 500);
Serial.println("done");
Serial.print("myTimer.start... ");
myTimer.start();
Serial.println("done");
// Set the analog resolution to 14 bits
analogReadResolution(14);
}
// Add loop code
void loop()
{
if (adc_flag) {
adc_flag = false;
uint16_t adc_val = analogRead(A0);
Serial.print("Analog value: ");
Serial.println(adc_val);
}
}
Thanks to @reivilo for putting this timer library together.
