Cheap Idea for a DRO

[1113562]

The PIC will do all the decoding and sampling and filtering and will upload a value on request from the display processor. It is fronted by a dual comparator to do the level shift and generates a PWM output to drive the -1.5v charge pump. The output will be in native format (note that the reader always outputs in imperial, metric conversion is done by the display processor)


No, not looked but doubt you will find one...


The 'machined bar' is a PCB, under the graduated label... see here for more info. This makes it hard to extend, but easy to cut down...

Thanks for that Irvine,

Thats interesting. Re the reader units. Am I correct in thinking that the 4 bit BCD type readers do change the transmitted values when switching between metric and imperial? If that is the case it would be a lot easier to get the reader to do the conversion rather than the top end.

Thank's for the insight into the capacitive sensor operation. I was not aware the bar has a strip pc under the label. That's a bit of a nuisance as my plan was to buy cheap 6" calipers and fit longer bars. making long strip pcb's is not out of the question but I guess that the whole reader accuracy relies on the pitch accuracy if the T and comb? Do you know if the comb fingers are isolated from each other or linked together, its hard to see on the photo. It looks like the Ts are isolated from each other.

[irving2008]

Am I correct in thinking that the 4 bit BCD type readers do change the transmitted values when switching between metric and imperial? If that is the case it would be a lot easier to get the reader to do the conversion rather than the top end.

Cant say, I have never seen a BCD one, all 5 of mine are the 24bit type. My DRO processor/display will always display in mm as I dont use imperial for metalworking - but if i did it wouldn't be hard to add a in/mm button. Anyway how difficult is adding:

 
double reading_in_mm[3];
for(int I=0;i<2;i++)
  reading_in_mm[i]=reading_in_inch[i]*25.4;
display(readin_in_mm[]);

Do you know if the comb fingers are isolated from each other or linked together, its hard to see on the photo. It looks like the Ts are isolated from each other.

Not looked closely, but I'd say they were...

[1113562]

Not looked closely, but I'd say they were...

I have had another look at the photo and it does look like the fingers are all linked together with a thin continuous strip of copper along the bottom edge. I will have to pull the graduated label of mine to check. This would make butting two strips together to make a longer length tricky as you would need to retain this electrical connection across the joint. Better obviously not to try and butt together and to make as one length. Etching a long PCB would be difficult due to need for long light box, long artworks and etching tank etc.