# Reading a digital caliper with an Arduino

Discussion in 'Embedded Systems and Microcontrollers' started by chucketn, Aug 27, 2015.

1. ### chucketn Thread Starter New Member

Jan 22, 2012
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One of my hobbies is machining. I have a small machine shop where I make models of steam engines, tooling and other stuff.
I have successfully used an Arduino to control and index a Rotary Table to make gears and such.
I would like to add a Digital Read Out to my metal lathe, using cheap Chinese Digital Calipers, and an Arduino to interpret the caliper output.
Has anyone here successfully used an Arduino to read and display the output of a low cost digital caliper of the type sold by Harbor Freight ?

Chuck

Feb 5, 2010
3,851
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3. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,504
512
Thank you for the link. I will have to try that.

To OP. In the article at the link they mention how to read the low voltage output of the caliper. They mention that uC input might be as high as 0.7xVcc. Normal Arduino Vcc is 5 volts. Which means in this example that to uC to read digital 1 it must see 0.7x5=3.5 volts. Your 1.5 volt caliper is way below that 3.5 volt. That is why you need an additional circuit to make 5 volt Arduino see the caliper data.

But... there are some Arduino boards that don't use 5 volts "system". Arduino Due uses 3.3 volt "system". Since 1.5 volt output of the caliper is much closer to 0.7x3.3=2.31 volts input of Due, Due or another 3.3 volt Arduino might be a better choice for this project.

My advice is to download datasheet for the 5 volt Arduino and 3.3 volt Arduino, and see what are their thresholds for reading digital data.

Last edited: Aug 27, 2015
4. ### JohnInTX Moderator

Jun 26, 2012
2,394
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Yeah, thanks @Kermit2
For @chucketn be sure to check your cheap Chinese calipers for accuracy before going to the trouble. I was given a pair by a guy for whom I was doing an XYZ display/control setup for milling machines. Scrapped it after finding out it could be as much as .020" off over the scale. Personally, I use Mitutoyo.

You might consider using conventional glass scales with quadrature outputs. Not too hard to interface..

EDIT: Searching on glass scales got this link. They don't like the Chinese caliper approach either.

Last edited: Aug 27, 2015