NOTE 7/2020: I have discovered a limitation on how fast the saddle can be moved without losing Z counts. I assumed this would be faster than would be possible to crank by hand, but it turns out that you can lose counts even at moderately fast cranking speed – somewhere around 2″/sec carriage movement. For now I can manage by watching my handwheel speed, but it appears a faster uC than the MSP430 is needed. I will update when I have a solution.
This is an outstanding machine DRO for hobbyists, not just an outstanding DIY project, but a super DRO even compared to high-end pro machines. The beauty of TouchDRO is that it uses a (cheap) Android tablet for the display and control (I used a 1st-generation Nexus tablet – $50 on eBay) while the scales connect to a small (user-built) box that wirelessly sends data to the tablet via Bluetooth. The extra cute thing about this particular DRO installation is that all that parts are very small and don’t interfere with any travel distances or setups on this already smallish machine.
Below are a schematic and a link to the TouchDRO website.
TouchDRO Link: http://www.yuriystoys.com/p/android-dro.html
This particular circuit is designed for quadrature-output scales only. It will not work with the cheaper Chinese “caliper” or other similar scales (though TouchDRO *can* work with those as explained on their web page). Examples of quadrature output scales are optical scales and some magnetic scales. In my particular case, I used magnetic read heads made by Renishaw (Model LM10) and linear magnetic tape that I purchased used on eBay. This choice was made to get the smallest linear measurement parts possible.
Below are links to Eagle files for the above circuit. Note that you can get an MSP430 Launchpad board for less than building the above board, but I wanted tiny size and compatibility with the header connectors on my read heads, so I designed my own board and made PCBs at OSH Park.
Eagle schematic: https://dl.dropboxusercontent.com/u/2186623/MSP430_TOuchDRO_surf.sch
Eagle PCB layout: https://dl.dropboxusercontent.com/u/2186623/MSP430_TOuchDRO_surf.brd
Or, if you want to just use my layout, you can order blank PC boards from OSH Park here: https://oshpark.com/shared_projects/QH96j7xH
Read heads are Renishaw LM10s off eBay for about $100 each. These can be expensive, but I wanted the tiny size. I also got the linear magnetic scale tape off eBay. Total cost was about the same as a good Chinese DRO package like Sino.