Connected SPI device causing M0 to not boot [solved]

[mwolter]

Hello,
I am in the process of moving a project from a Moteino to a Moteino M0 and ran into an issue with an Adafruit MAX31855 thermocouple amplifier. If I have the MISO pin from the 31855 connected to the M0, it will not boot when power is applied. I have to remove the pin, then reconnect it after the M0 has booted. After it's booted, I reconnect the MISO port and the temperature is read properly and the M0 functions just fine. As far as I can tell, there doesn't appear to be anything wrong with my code and this worked fine on a Moteino previously.

Is there anything I should be doing differently with the M0?

Below is my code related to the 31855:

Code Select Expand

#include <Adafruit_MAX31855.h>	//get library from: https://github.com/adafruit/Adafruit-MAX31855-library tested using Sept 26, 2016 version

int oilTempCsPin = 2; // spi client select (CS) pin
unsigned long oilTempLastRead; // millis of the last read interval
int oilTempUpdateInterval = 300; // interval for temperature readings in ms
double oilTemp = 0; //most current temperature reading
int oilTempErrorCount = 0; //count of thermocouple read errors

Adafruit_MAX31855 oilTempObj(SCK, oilTempCsPin, MISO);

void loop() {

		if (millis() - oilTempLastRead > oilTempUpdateInterval) { // successive temp readings faster than 220ms will cause errors and the temp will remain constant

			double f = oilTempObj.readFarenheit();
			if (isnan(f)) { //was there a communication with the thermocouple
				oilTempErrorCount++;
				if (oilTempErrorCount >= 5) {
					oilTemp = -999;
					oilTarget = -999;
					SerialUSB.println("{\"Error\":\"Oil Temp Sensor Malfunction. Unplugged?\"}");
				}
			}
			else {
				oilTempErrorCount = 0; //reset error counters
				oilTemp = f;
			}

			oilTempLastRead += oilTempUpdateInterval;
		}
}

[Felix]

What exactly do you mean by not "boot"?
There is a bootloader which always runs when you plug it in. If there is a sketch it will jump at that location, otherwise it will stay in the bootloader. FWIW a double RESET-tap would also put it in bootloader.

Can you confirm that your M0 does not get into the SKETCH ?
By putting something like a BLINK pattern followed by a delay(), before running your sketch code?

[mwolter]

A better explanation is that it does not run the sketch. Still learning the Moteino M0 The sketch does a serial print of the thermocouple value every four seconds, so this is my sketch run indicator.

With the MISO pin connected, I do not receive the serial print. Tried power cycling the MISO pin connected, tried pressing the reset button, M0 still does not run the sketch.

I have to physically remove the MISO pin, reset the M0, restart the serial monitor, wait for the error reports (because the pin is disconnected), then insert the MISO pin. When I do this procedure, everything works fine. Obviously, this is not ideal since a normal power outage will cause the sketch to not load.

[Felix]

I'm not sure how to try to reproduce this without the actual hardware and code you're using.
If you're up for sending your setup over I can give it a go. I know it's inconvenient but ... unless you have other suggestions I'm not sure how to help.
Do you have a logic analyzer? I would probe the SPI bus during boot and see what's going on there.

[mwolter]

Switched to a generic MAX6675 module using the code below and it works fine. Not sure what the issue was but I know this is good.

Code Select Expand

#include <SPI.h>

int oilTempCsPin = 2; // spi client select (CS) pin
unsigned long oilTempLastRead; // millis of the last read interval
int oilTempUpdateInterval = 300; // interval for temperature readings in ms
double oilTemp = 0; //most current temperature reading
int oilTempErrorCount = 0; //count of thermocouple read errors

float thermocoupleReadC(int _tcCsPin) {
	bool _tcFirst = true;
	float _tcTemps[6];

	unsigned int tcData;
	float tcTemp, tcAvgTemp;

	//read the temperature

	SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV16, MSBFIRST, SPI_MODE1));

	digitalWrite(_tcCsPin, LOW);
	tcData = SPI.transfer(0x00) << 8;
	tcData |= SPI.transfer(0x00);
	digitalWrite(_tcCsPin, HIGH);

	SPI.endTransaction();

	if (tcData & 0x0004) {                  //open thermocouple circuit
		return -1.0;
	}
	else {
		tcTemp = (tcData >> 3) / 4.0;         //calculate deg C
		if (_tcFirst) {                       //if first time through, fill the readings array
			_tcFirst = false;
			for (int i = 0; i<6; i++) {
				_tcTemps[i] = tcTemp;
			}
		}
		for (int i = 0; i<5; i++) {           //shift prior readings
			_tcTemps[i] = _tcTemps[i + 1];
		}
		_tcTemps[5] = tcTemp;                   //put the new reading in at the top end of the array
		tcAvgTemp = 0.0;                      //calculate the average
		for (int i = 0; i<6; i++) {
			tcAvgTemp += _tcTemps[i];
		}
		tcAvgTemp /= 6.0;
		return tcAvgTemp;
	}
}

float thermocoupleReadF(int _ssPin) {
	float tcTempC;

	tcTempC = thermocoupleReadC(_ssPin);
	if (tcTempC < 0.0) {
		return tcTempC;
	}
	else {
		return tcTempC * 9.0 / 5.0 + 32.0;
	}
}

void setup() {
	pinMode(MOSI, OUTPUT);
	pinMode(MISO, INPUT);
	pinMode(SCK, OUTPUT);
	SPI.begin();                            //initialize SPI

	pinMode(oilTempCsPin, OUTPUT);
	digitalWrite(oilTempCsPin, HIGH); //Start de-selected
}

void loop() {
		if (millis() - oilTempLastRead > oilTempUpdateInterval) { // successive temp readings faster than 220ms will cause errors and the temp will remain constant
			
			oilTemp = thermocoupleReadF(oilTempCsPin);
			oilTempLastRead += oilTempUpdateInterval;
		}
}

[Felix]

Ok .. interesting.
Is this considered solved then?

[mwolter]

Yessir, I'll just stick with this amp. Don't need negative temp readings, so this should be fine.