Gallery, Projects and General > Neat Stuff
Micro DRO made from tyre tread depth gauge
kd0afk:
I think that is just the reader head. If the pcb strip is made the same way as the ones in the digital tire gauge then I think the resolution should be better if used with the cheap Chinese dro heads. I sent an email to the folks at Wixey to get the measurements.
BillTodd:
--- Quote ---I don't doubt you but it just seems a bit sophisticated for a device this cheaply made.
--- End quote ---
They are cheap because they use pretty standard printed circuit manufacturing techniques to form the sensor strips. Expensive (accurate) ones will have additional laser trimming and checking phase, taking extra time and hence money to make).
They all use chip-on-board bonding (i.e. rather than use a separate plastic package for the silicon chip, the chip is glued onto the PCB directly) with an elastomer (conductive rubber sandwich) connection to the LCD.
kd0afk:
When I said PCB I am speaking of the slide. The sensors in the read head read the distance between the gaps in the copper pads on the slide pcb. If the dimentions of the strips are the same ie: copper pads are the same width and the gap is the same, you will have the same accuracy as with the caliper head or the tire depth gauges. Pretty sure the level of accuracy is established in the read head itself.
BillTodd:
--- Quote ---When I said PCB I am speaking of the slide.
--- End quote ---
As was I.
--- Quote ---The sensors in the read head read the distance between the gaps in the copper pads on the slide pcb
--- End quote ---
Yes, they read the change in the capacitance at the edges - The accuracy is wrapped up in the measuring of the change in capacity, straight clean edges of all the parts contribute.
The tyre depth gauges use exactly the same heads as the cheap callipers :) They're just re-purposing the heads to find a niche in a flooded market place.
I guess the Wixey devices have the same kind of accuracy (~10um) but have chosen not to display it (it's only wood after all)
[edit] interestingly the early callipers used a 24 bit binary output format that resolved to 1/20480th of an inch (~2um) but the LS bits are too noisy for any kind of use.
kd0afk:
Just got a reply from Wixey and the pitch of the pattern and gap is the same. Should have the same accuracy as a digital caliper. Most of what I do is accurate to the hundredth and if I need to get down to the thou I use a mic.
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