max31855

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Elsa_FrozenFever
 
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max31855

Post by Elsa_FrozenFever »

Hello Team,

I designed a custom PCB to interface with four thermocouple sensors. The schematic I used is based on Adafruit's MAX31855, and I’m using a Teensy 4.0 microcontroller to read the data from the sensors.

However, my serial monitor is showing the following error messages:


Internal Temp = -0.06
Thermocouple fault(s) detected!
FAULT: Thermocouple is open - no connections.
FAULT: Thermocouple is short-circuited to GND.
FAULT: Thermocouple is short-circuited to VCC.
I’ve tried replacing the thermocouple sensors, but the issue persists. I measured the voltages across the pins, and the following readings were observed:

CS pin: 3.3V
SCK pin: 0.56V
MISO pin: 4.01V
Supply voltage: 3.3V
I'm particularly puzzled by the MISO pin outputting 4.01V, even though the supply voltage is 3.3V. I would expect the MISO voltage to be around 3.3V.

Has anyone encountered a similar issue or have advice on what might be wrong? Any help would be greatly appreciated!

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T_Mo
 
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Re: max31855

Post by T_Mo »

(Community member)
No direct experience with that.

Just for additional info, what supply voltage are you running to the Teensy?

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Elsa_FrozenFever
 
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Re: max31855

Post by Elsa_FrozenFever »

The teensy is powered by 12V, but the MAX31855 is powered by separate 3.3V supply

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T_Mo
 
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Re: max31855

Post by T_Mo »

Are you using this?
https://www.adafruit.com/product/4323

If yes, then its max input voltage is 5V, via USB or the VIN pin.

Internally it runs from 3.3V via a regulator. So there should be nothing that would explain the 4V you see on MISO.

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Elsa_FrozenFever
 
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Re: max31855

Post by Elsa_FrozenFever »

ok, then you mean to say the voltage levels are correct??
I'm wondering then why I'm not able to read the sensor values

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T_Mo
 
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Re: max31855

Post by T_Mo »

then you mean to say the voltage levels are correct??
No, quite the contrary. If you connected the Teensy or the sensor to 12VDC, then it could have been damaged.

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