Reading Digital caliper with Arduino

[Vinny]

Got my scope going (finally) and decided to take a look at my caliper. Mine's the older one and nothing was making sense at first but eventually I got it figured out.

This one is POS ground, and the data is inverted. If it's high it's 0, if it's low it's 1. But you still read on the rising edge of the clock. The first 24 bits are pretty meaningless since they're absolute position from when the battery was inserted. The second 24 bits are the the relative position from where it was last zeroed.

After figuring out the oddness of the data, I take the binary data, invert and feed it into a binary calculator backwards (LSB is sent first). Convert that to DEC and divide that number by 20480. I had the caliper set to 1.0005" and it sometimes read 1.001. The number I got was 20498. Divide that by 20480 and got 1.00087890625 (I doubt they're that accurate) so it explains why it was bouncing between 1.0005 and 1.001.

I think Chuck's is easier to read.

Edit: I didn't check the other calipers I have. One has a funky door and the plug won't go it (without case mods) and the other is upstairs in the office and I didn't feel like climbing them steps again.