Thermocouple amplifier wrecked by LEDs / Steppers

I am using a MAX31855 to measure a thermocouple (TC). In my system I also have an LED array (18 LEDs) and some stepper motors.

Normally the TC reads 23C (my room). As soon as I switch on the LEDs, it shows 50C - WTF? :o If I move the steppers, the TC goes haywire, jumping between 0 - 200C and also giving errors on some readings.

I tried adding lots of caps, made a low-pass filter to power the MAX31855, etc. Nothing works. I'm out of ideas.

The MAX31855 is powered by the Arduino MEGA 5V line (from USB) while the rest of the components are off a LM7806 6V regulator which is getting juice from a power supply (~10V in).

Who has some ideas?

Are you using a breakout board?

[quote author=Coding Badly link=msg=3285014 date=1496352557] Are you using a breakout board?

[/quote]

Yes, from Adafruit. And a breadboard for everything else.

Bad ground.

Most likely your power supply is inadequate and injecting noise in the system. Thermocouples are a worst case situation for noisy power.

Post a wiring diagram (hand drawn is fine, Fritzing is not).

I added a 2 more 2200uF caps, one on Power supply - ground and one on LM7806 output - ground. Seems to have fixed the problem.

I thought Satan entered my system, how did some LEDs give me double temperature? Weird.

I'd post a wire diagram but the setup looks messier than my pubic bush so...

Ground currents perhaps? - use star grounding. Simply drawing the wiring diagram will show you where the currents are - draw the supply and ground wires that carry current to stepper and LEDs in thick or colour. If the current path to the thermocouple amps shares any part of thats drawn in thick/colour, you have noise injection direct to your sensitive analog circuitry from the high current circuitry - that's always to be avoided.

You may also need a cleaner supply at the thermocouple amp, some supply filtering might be needed.

Hi,

I'd post a wire diagram but the setup looks messier than my pubic bush so... :o :o :o

That would possibly be that cause :o :o , you need to layout your wiring so input signal wiring, such as the Thermocouple does not come anywhere near the LED array and Stepper Motor wires.

Please, persevere and draw a circuit diagram, it will help you trouble shoot your circuit and provide a good reference for later.

Tom.... :)

MicroBubble: I thought Satan entered my system, how did some LEDs give me double temperature? Weird.

Are you using PWM to drive them ?

MicroBubble: The MAX31855 is powered by the Arduino MEGA 5V line (from USB) Who has some ideas?

Generally i avoid using USB supplies for anything analog. Use a battery for development at least, it is one less fault to find.