If you're thinking of building a Shumatech 350 based DRO, this is a cautionary tale of the relevant scale.
I purchased a pre-built 350 board via eBay, and wired it into an enclosure bought separately. As with all things electronic where I have even an ever-so-small role in the assembly, I held my breath, blocked my ears, crossed pretty much everything and plugged it in.
The board fired up perfectly with the welcome message, and I was able to scroll through the setup process with the function keys. I started breathing again.
Next, I made up some cables to connect to the cheap callipers I also purchased via eBay through a vendor in Hong Kong. The measuring unit on the callipers is identical to the pictures shown on the Shumatech website (which is why I ordered them), so what could possibly go wrong?
Well, er - nothing. That is, nothing was showing on the 350's Display. Nothing, notwithstanding that the DRO was providing power to the callipers and successfully switched them to fast mode. I tried all 3 callipers and all 3 inputs sockets. I checked the cables. I reversed the clock and data wires, and tried that. Nada.
The very helpful guys in the Shumatech Yahoo group let me know that the callipers or scales I need for the 350 with Revision 4 software must be 24 bit protocol, and that those that look like mine but with the 24 bit protocol can only be identified by the small crystal on the PCB (disassembly required to check) rather than just by similarity to the pictures I had found.
Going forward, how does someone contemplating a 350 DRO build proceed with confidence in their scales? One of the guys in the Group said that the very cheap scales sold in Hong Kong and by one large US business are not 24 bit. He said that the scales he had purchased in the past through Wildhorse, Neiko and Virtual Village were all 24 bit, and he had purchased some from Virtual Village 3 months ago that worked fine.
I cannot vouch for what he says (yet) but I have no reason for doubt. I have now ordered some from Wildhorse as I have purchased from it before, and its website refers to the scales as 350 compatible. I have no affiliation with any of the above.
The Fignoggle mini-mill DRO plans also mention Shars as a supplier of scales that work with the 350.
In any event, a confirming email to the vendor about compatiblity and a refund may a good idea (note how I ignore my own advice).
I hope this helps someone not waste money on non-24 bit scales. The bright side is that I have more than enough cheap digital callipers for the workshop so I don't lose them all amid the mess.
Mods, please edit if you aren't happy with me naming names based on heresay.