tl;dr NO (see below for oscilloscope traces)
I'm a bit of a noob when it comes to electronics, but I have a project using the X27 motor which is surprisingly difficult to find information about.
- You should both absolutely use a stepper driver board, and it's completely unnecessary.
- It's both completely safe, and unsafe to use them direct on PWM GPIO pins on a classic microcontroller with and without diodes.
- Break-out boards are on the market with and without place for flyback (EMF, etc) diodes.
As a rule you should plan with 2x the driver voltage for a flyback diode for any inductive load;
I planned to use the X27 motor on a 3.3v power supply from an STM32 micro controller on a custom PCB, however coarse reading in the internet left me with questions if that's safe; forums (Arduino forums, naturally) recommend using an Arduino as they are "more tolerant".
I found in the STM32F103 datasheet that it's absolute max tolerance for a GPIO pin is 9v, and I'll be powering that with a 5v supply, even though it's a 3.3v logic level.
For the ATMega32U4 on the Arduino Leonardo, the max tolerated voltage is VCC+0.5 (see "ยง29 Electrical characteristics")
These two traces show that at worst there's about 5v on the bus, which seems to be outside the Arduino's tolerance, but it has ran perfectly OK for more than a week unattended on my desk, and it's well within spec for my STM32 project goals.
I assume this is something to do with driving AC loads with PWM but I can't say for sure. I may also be measuring this wrongly as I grounded the probes to the arduino ground, and not to the "ac" ground.
In the end, I'm just happy that it looks like driving these directly with an STM32 without any diodes or custom driver board should work just fine.
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