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I'm new to electronics.

Attempting to bench-test a SilentStepStick stepper driver board, (based on a TMC2130)

Using: Arduino Uno, a SilentStepStick driver board, a 0.6A stepper motor, and waterott example code (using SPI).

The motor turned as expected, code and wiring appeared to function, for about 30 seconds, Then "all the smoke leaked out" of the ATmega328P, in the Arduino, and the Stepper Driver burnt out also.

Process & Problem Description:

  1. Turned on 24v power, as per datasheet 24v must be connected before 5v (VIO).
  2. Plugged in arduino USB-B plug, did notice some faint blue sparks, between the grounding parts of the connectors. Didn't realise significance.
  3. Motor turned, code worked.
  4. After about 10 seconds noticed a very faint burning smell, disconnected arduino and checked motor and driver for heat, none found.
  5. Reconnected for 10 seconds, faint burning smell resumed again, disconnected arduino.
  6. Reviewed code, found example code was setting current to 50%
  7. Changed code, lowered current to 6%.
  8. Reconnected, motor turned ok, smell returned, then a few seconds later the ATmega328P visibly fried, stepper driver was fried also.

I have triple checked all wiring prior to posting this, all seems correct. Perhaps too much current was applied?
If so, I am unsure why that would affect the arduino - isn't it just providing signalling? Or did 24v somehow make it's way to the arduino?

Here is the wiring diagram: enter image description here

I have power from the arduino 5v rail to Vio, and GND->GND, and the 24v power supply is connected to VM & the second ground. All SPI and stepper control pins are connected.

Why did it blow up?

UPDATE:
-If I measure voltage between the ground of the USB cable, and the arduino ground, when the cable is not plugged into the arduino - then I see 24 volts (!) - It is clear that 24v is going through the driver, and into the arduino, over the 5v rails (Vio).

  • Per helpful advice from comments, issue is likely with grounding: Arduino is powered via USB, from an Intel NUC Desktop, which is powered by DC only - no ground.
  • The 24v power supply is grounded to earth.

UPDATE - Solved:
-Thanks to the gracious advice from the comments, solution found.
-The Arduino logic power suppy was via USB, from a "Intel NUC" DC-powered desktop - there is no earth.
-The 24v comes from an earthed power supply. -The two devices do not share a common ground, & the 5v is not earthed. I presume this to mean the 5v power supply is "floating" relative to the 24v power supply, and this is what caused the issue. -The problem was resolved by obtaining an earthed 5v DC power supply, and connecting the ground of the 5v supply to the ground of the 24v power supply. -Images provided below to clarify. Only power wiring shown for clarity

Original Problematic Wiring: Problematic Wiring

Solution Wiring enter image description here

I would be very happy to accept a formal answer to this - if someone wishes to state in technical terms, what likely occurred in the first wiring diagram, that would be great and perhaps make this a useful question.
Summary: In the first diagram, one power supply was not earthed, and the two power supplies did not share a common ground. The result was: a visually burnt TMC2130 driver, a visually burnt ATmega328p in the arduino, and some black burn marks in some sockets on the breadboard.

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  • \$\begingroup\$ What 24V power supply are you using? Is it a decent supply, or a cheap wallwart? \$\endgroup\$ – Tom Carpenter Sep 16 '18 at 21:27
  • \$\begingroup\$ A decent one, 41.7amps \$\endgroup\$ – Mtl Dev Sep 16 '18 at 22:53
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    \$\begingroup\$ Hmm. I'm wondering if there is an earth problem somewhere - getting sparks when you plug the USB cable in suggests that the power supply ground (and hence circuit ground) is leaking current from the mains, hence you get a spark when you plug in to your computer. \$\endgroup\$ – Tom Carpenter Sep 16 '18 at 23:03
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    \$\begingroup\$ Right now, just touching the outer part (shielding) of the USB-B plug from my computer, to the outer part (shielding) of the female USB socket on the arduino - there are clearly visible sparks. Checked with multimeter - 24volts is there.(!) Removed all wires from Arduino - except 5v lines, still have 24v. So 24v is coming into the Arduino from the GND and Vio pins on the driver. How is this possible? What to do? \$\endgroup\$ – Mtl Dev Sep 16 '18 at 23:57
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    \$\begingroup\$ Thankyou Sam, I understand. I will not give up, I will keep trying until I figure this out, I will post an answer if/when I do. FYI I am not convinced the 24v-only test is valid either, I made a separate question to ask that and only that question. It seems strange to me that I am seeing 24v on the 5v rail - and for sure the arduino was seeing 24v too. FWIW, the board schematics are here \$\endgroup\$ – Mtl Dev Sep 19 '18 at 15:44

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