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Prototype Tool: An Arduino-driven addon for digital calipers to directly output scaled dimensions


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I'm probably not the only person who's often measured something with digital calipers, then gone and tossed the dimensions into a scale calculator to get the real dimension.  So I came up with a little hack today to try and automate the process.  Here's a picture of the prototype...

 

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As you can see, the little digital display on the breadboard is showing the scale being calculated (1:48 which is hardcoded at the moment), the length measured on the caliper (20.4mm) and how large that would be at 1:48 scale (3 feet, 2.6 inches).  As you move the caliper it automatically updates the display with new values.

 

As background, it ends up most cheap calipers have a digital port on them.  If you've got a caliper, look for a little slide off panel on the top with 4 contact stripes on the circuit board inside.   This puts out a digital signal for a DRO (Digital Read Out), as the guts of these things are shared with or very similar to DROs for benchtop mills and such.

 

Here's a bigger shot to show the whole thing.  On the left of the breadboard is a little Adafruit QT Py dev board (Arduino compatible) which is plugged into a small OLED display.  The cable coming out of the caliper takes ground plus data and clock signals to the Arduino.  The clock signal is being boosted from 1.5v up to 3.3v with a little transistor circuit in the middle.

 

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I want to keep working on this as a smaller, more self contained device, obviously without so many loose wires.

 

I also want to have it so you can set the scale you want and change units.  One interesting feature would be to let it determine scale from a drawing.  You should be able to take a ship drawing for example, measure off 10 feet on the drawing's scale, and have the device tell you what the scale of the drawing is.  Then with that scale, you can start taking dimensioned lengths directly off the drawing.

 

The cable by the way is a specialized plug that goes to an RJ-11 (phone jack).  It's the same kind of plug used on DROs, and I picked up the cable from Little Machine Shop at https://littlemachineshop.com/products/product_view.php?ProductID=3483

Tim

 

Current Build:  Swift Pilot Boat 1805 (AL)

On Deck: Triton Cross Section, Harvey (AL), Falcon US Coast Guard (AL), Flying Fish (Model Shipways)

 

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As John has said Tim, a clever and what could prove a very useful tool - I can certainly see the value in removing that external step of having to use the calculator.  I currently generate a look-up table at the scale I am working, but 5 times out of 10 the scale is not posted where I am currently working.

 

How do you see the input of the scale?  A set of preprogramed buttons, or input via an external source?

 

cheers

 

Pat

If at first you do not suceed, try, and then try again!
Current build: HMCSS Victoria (Scratch)

Next build: HMAS Vampire (3D printed resin, scratch 1:350)

Built:          Battle Station (Scratch) and HM Bark Endeavour 1768 (kit 1:64)

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3 hours ago, BANYAN said:

How do you see the input of the scale?  A set of preprogramed buttons, or input via an external source?

 

I still need to work out the interaction and interface. 

 

Right now I figure these are the basic things I'd like to be able to set...

  1. The scale to some value from a list of more common scales.  Something like hitting an "up" and "down" button to cycle through a list of common scales.
  2. Enter the scale to any number you'd like.  A bit more complex, but probably doable.
  3. Detect the scale from measurements on existing drawing.  I'd personally find this extremely useful when trying to pull dimensions off an illustration or copies of historical plans.
  4. What units to convert to (imperial, metric).  This really comes down to what you find most convenient to think of in terms of real life. 

 

My plan is to mount the screen and Arduino into a small box along with a few buttons for interaction.  Alternately a slightly larger touch screen.  And also use the screen to display help information to guide the setup of the scale.  The advantage of having a little tiny computer drive the whole thing is that you can get rather detailed (in a non-complex way) with information and options.

 

My day job is being the User Experience (UX) and User Interfaces (UI) lead for a bio/life sciences product for a company you usually assume just makes printers, so this is something I want to make easy, clean, and simple.  My mantra is that any interface that requires a manual or training video is too complex, unless you're working with a very complex task to start with.  And even then, you look for ways to make it simple.  Working out scale dimensions for a model is not a complex task - laborious yes, but not complex.

Edited by Tim Holt

Tim

 

Current Build:  Swift Pilot Boat 1805 (AL)

On Deck: Triton Cross Section, Harvey (AL), Falcon US Coast Guard (AL), Flying Fish (Model Shipways)

 

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Tim, I didn't know I needed one of these until I saw your prototype.

Perhaps one the MSW sponsers wants to put their name on this product?

🌻

STAY SAFE

 

A model shipwright and an amateur historian are heads & tails of the same coin

current builds:

HMS Berwick 1775, 1/192 scratchbuild; a Slade 74 in the Navy Board style

Mediator sloop, 1/48 - an 18th century transport scratchbuild 

French longboat - CAF - 1/48, on hold

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11 hours ago, wefalck said:

I would look into a BlueTooth connection, as a cable in practice is rather cumbersome on the worktable ...

 

Agreed, but you need the cable to connect to the semi-proprietary connector on the caliper itself.  Plus you have to power the Bluetooth, and the 1.5v battery in the caliper isn't going to cut it, not to mention you still need a computer to read the caliper and send the Bluetooth signal.

 

The whole thing could be taken down to a small add-on you just plug into the top of the caliper, but there's still the matter of powering it.  It would need its own rechargeable battery, but it would add bulk.  You would in the end still need a USB cable to charge the battery.

Tim

 

Current Build:  Swift Pilot Boat 1805 (AL)

On Deck: Triton Cross Section, Harvey (AL), Falcon US Coast Guard (AL), Flying Fish (Model Shipways)

 

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One other consideration is the RF "noise" that electric motors generate. If you have machinery running in your shop you might not be able to get Bluetooth signals. Hard wiring is much more reliable.

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One "PS" to the Bluetooth idea.  

I mentioned that the caliper itself doesn't have much of a battery - just one little 1.5v button cell.  But one of the things you can do with that external connector is send power to the caliper.  So one idea would be to have a small rechargeable battery as part of the unit, allowing you to run the caliper for much longer without having to replace those little button cells.  You could then plug it into a USB-style power connector (or USB cable from computer) to recharge it.

 

I'm about to go on a 2 week vacation and hope to dive back into this when I get back.

Tim

 

Current Build:  Swift Pilot Boat 1805 (AL)

On Deck: Triton Cross Section, Harvey (AL), Falcon US Coast Guard (AL), Flying Fish (Model Shipways)

 

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