Need some input on another DIY DRO kit

ycroosh

ycroosh

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I'm working on a DIY kit for Glass and Magnetic scales and have a few design decisions to make:
1. I can use PCB-mounted DB9 connectors that will look neater and more rigid, but since different scales have different pinouts, that means that it will be necessary to modify the cable to fit the adapter's pinout (re-solder some wires). Alternatively, I can go with 4-pin headers and panel-mounted connectors. That way the scales will stay stock, but there will be a bit more work with the connectors. Also, the second option is about $6 more expensive (for some reason PCB mounted connectors are much more expensive)
2. I can use a single resistor network to pull down all 8 input pins, or 8 individual resistors. Since all of the glass and magnetic scales I've ever encountered use some sort of sourcing output, this will work fine. Unfortunately many rotary encoders use sinking output. With individual resistors I can add a way to select pull-up or pull down option per axis input; with the network it will need to be either all up or all down.

Practical implication is that if I go with panel mounted connectors and a resistor network the kit will cost around $50 + shipping, if I go with individual resistors and PCB mounted connectors, it will be closer to $60 + shipping (and will be more complicated). I'm leaning towards simpler is better. Do y'all have any thoughts or strong opinions?

Also, to pre-empt some questions I can foresee:
  • The kit will run the same firmware as the pre-assembled board but will have only single-ended inputs (A' and B' lines on differential scales will not be connected; scales will still work fine).
  • I hope to have it ready by the end of April, assuming I can get the boards dialed on the first revision (the PCB fab house I use has 2-4 lead time).
  • I will likely try to do a "beta" batch first, so let me know if anyone is interested in participating.
  • Hardware and firmware is not open source, but I will post the schematic and scratch-build instructions as well, since all of the parts are obtainable in through-hole configuration.
Regards
Yuriy
 
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If you decide to do a beta batch let me know.
 
Fantastic! For DIY, more flexibility is definitely an advantage. Thinking along the lines that anyone who's happy building a kit rather than buying pre built is more likely to have some oddball setup.
Personally I'd be happy to see panel mount connectors and individual resistors, but more from a flexibility point of view than cost. Panel mount also gives greater freedom with enclosure form factor.
 
I also would prefer increased flexibility over reduced price and complexity.
 
OK, then another question: how many people use (or would use) non-linear scales for a DRO?
 
I've not heard of non linear scales before, but interested?!
 
Lo-Fi,
That would be rotary encoders, either in a rack-and-pinion configuration, or reading directly off a lead screw. For smaller machines (i.e. not things used to machine aircraft carrier propeller shafts), I can see someone wanting to use a rotary encoder on the compound slide screw since there isn't that much space to mount glass scales. In practice I've only seen something like this on a miro lathe - a guy had encoders mounted where the dials would normally be.
Regards
Yuriy
 
Ah, of course. Thanks Yuriy! I've thought about geared rotary encoders and suchlike, but it seems like an opportunity for introducing backlash and other such issues. Interesting, though.
 
How about bringing the db9 pins out to pads and the input to the cpu to another set of pad. Through-hole would probably be easiest for most to modify but surface pads would also work. Traces for "the most common" pattern (you get to choose what that means) aready on the board. For 'non-standard' connections, user cut the traces with an xacto knofe, solders the appropriate jumpers, done.

Saves having to stock an assortment of 'adapter' connectors and offers some 'on-site' flexibility should the user need to change the configuration.
 
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