Collected from various spots around the Web, including evanescent eBay listings, and reformatted to make sense, these specs describe the 2M415 stepper driver: a smaller sibling of the 2M542 family.

Blurb

• +15 to 40VDC Supply Voltage
• H-Bridge, 2 Phase Bi-polar Micro-stepping Drive
• Suitable for 2-phase, 4, 6 and 8 leads step motors, with Nema size 16 to 23
• Output current selectable from 0.21 ~ 1.5A peak
• Compact credit card size package
• Optically isolated single ended TTL inputs for Pulse, Direction and Enable signal inputs
• Selectable resolutions up to 12800 steps
• Over Voltage, Coil to Coil and Coil to Ground short circuit protection.

Electrical specs

Mechanical specs

Dimensions

2M415 Footprint

Wiring diagram

2M415 Wiring

Notice that the driver requires a positive voltage for the optoisolators.

Of course, the box from halfway around the planet contained HB-415M drivers. Should you go looking with the usual keywords, you’ll find that HB-number turns up mostly “House Bill number” citations from various state legislatures. Popping the top off the drive reveals www.sikesai.com, which eventually produces a description and PDF datasheet for the driver. It turns out to be an “Ultra Low Noise” driver, whatever that means, with reasonably standard specifications that correspond more-or-less to the 2M415 drivers I thought I was getting.