DIY Digital Caliper - CALIPATRON

Description

Most of us have seen the videos and articles about "hacking" digital calipers. 99 percent of them talk about reading the caliper value out of a port on the side of the device. I don't know about you, but using a port as per design does not represent true hacking to me. I decided to make a digital caliper from scratch. Make my own boards and write my own code. There are few goals I want to set first. I want this to be an exemplary project. What does this mean to me. I want everything to be well documented. All schematics, gerbers, code etc. must be kept up to date, so that anybody could take them and make their own. A set of clear build instruction. I think I document my projects well, but unfortunately this is not the case. One too many times I have return to a project after a few months and found some crucial piece of information is missing. I have not written down the correct value of a resistor, or the PCB has changed and I did not save it.

Components

1 × STM32F103C8T6 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers

1 × USB C

1 × TPS79333-EP LDO

1 × 0.91 inch Winstar OLED Display Module

1 × 3-1437565-0 Switches and Relays / Switches

Project Logs

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I am stuck
Dimitar • 08/01/2025 at 09:46 • 0 comments

Hi all,

Jay remaindered me about the patents and I went to search in them for answers.

Good news / bad news type of situation.

Bad news: I still don't know the answer of any of the questions from last log.

Good news:I found the answers to a questions I did not ask.

Does the size of the pattern matter and how?

In short - yes. You can think of it this way - 0.01 mm out of 1 mm is far greater than 0.01 mm out of 2.5mm. Smaller pattern greater sensitivity.

What are those capacitors on the back for?

Read more »
Generation
Dimitar • 07/13/2025 at 12:55 • 5 comments

Hello all,

Another session with ChatGPT and some googling I made a short python script to generate the patter that we use for excitation of the sensor. The code is already uploaded for you to play with

Read more »
Simulation
Dimitar • 07/11/2025 at 13:44 • 0 comments

Hello all,

I have decided to do something that probably I should have started with. A simulation!

Here you can find a python script that uses matplotlib to graph the excitation signals and the resulting signal.

It is not very sophisticated, but it seems to match the real world to a great extend.

Read more »
Open questions
Dimitar • 07/05/2025 at 20:16 • 0 comments

Hello all,

The project is still going! Lately I have been overwhelmed with some personal issues and did not have much time to tinker.

However quite a number of people have contacted me about the project and expressed interest. So this motivates me to keep going.

There are still some open questions regarding the project.

1. How is this signals generated? Why this frequency? It looks like PDM but not quite.

2. My footprints do not match the ones form a caliper I bought. The example pads do not align as neatly as mine. I put both scale and sensor on my scanner and this is the result. Why do they did that?

Read more »
Kevin's software breakdown.
Dimitar • 12/31/2024 at 10:13 • 0 comments

Hello all,
You may know Kevin Lynagh form "I made a cell phone" talk (and many more places), he has been interested in the project on the software side of things. He made a breakdown of his implementation of the SW.
You can take a look here: https://kevinlynagh.com/calipertron/
Happy new year to everyone!
Cheers,
M
Type 2 Hardware available.
Dimitar • 11/14/2024 at 20:49 • 0 comments

Hello all,
There are a few people that were interested in the project. It would not be very fun if you don't have hardware to tinker with. So you got two options.
A - Is to get the files gerber files and the BOM from the repo and make yourself a board with the STM32
B - You can order a Type 2 kit from my tindie shop
There are a few differences to consider A is cheap to make. It is only 2 layer PCB and you can scavenge a blue pill to take the parts. But this comes with a cost of lower resolution.
Example B is a bit nicer you can choose what XIAO board to use and it better resolution. But it is 4 layer board and a bit more expensive.
Cheers,
M
Type 2 hardware fix
Dimitar • 10/24/2024 at 15:19 • 0 comments

Hello all,

This is how the fix looks like

Now it looks quite bad, but it works kind of good. This is wat we have now on the ADC pin of the XIAO

Now there are a few differences. Because the excitation pads are smaller the charge on the them is smaller and the useful signal is smaller. This makes the noise to signal ration bigger. And this is why we see a bit fuzzier signal.

The high part of the signal is sloped. My theory about that is there is a bit of overshoot on the excitation signals. This is normal since I soldered a bunch of signals.

A think when I put the shift register on the board this will be mitigated to a large extend.

Time for some KiCAD action.

Cheers,

M
Calipatron type 2
Dimitar • 10/22/2024 at 08:05 • 0 comments

Hello all,

I wrote on the previous build log that we have a different flavor of HW. For now we will call it type 2.
I was hoping that this would be just scaling the bigger footprints down and subtitling the MCU with headers, but it was not meant to be like that :)
When I got the the hardware I saw this on the scope.
I was thinking at first it is noise from the switching of the PDM and I added some RC network to each pad. This only made the thing worse. Also I was thinking that the XIAO boards are noisy. Even I striped the copper surrounding the T-scale thinking that it was picking up some noise. The problem becomes obvious once we zoom in even closer.
This is what one of those peaks look likes on the 2us scale. For the original hardware running the ST I was using port register to switch the state of the excitation pads all at once. But running the XIAO board I was switching them one by one and then we get this ladder effect.
Now the quick solution would be to do the same for the XIAO board, but not all the pins are on the same port. Further more what happens if we put RP2040 or other controllers. We need a way of switching everything robustly and with every MCU provided.
The solution for now would be to add a shift register like the 74HCT595D from NEXPERIA. I have some laying around and will make a test.
Also for bonus points a played around with the signal generation and I have modified the pattern a little bit so we get even nicer signals. You can get it from the repo.

Cheers,
M
Production files
Dimitar • 09/15/2024 at 12:23 • 0 comments
Hello together,
Here you can find the necessary files to create your own boards. Since the design is two layer only it is possible to CNC the boards. You should only take care to isolate the back of the board where the scale is sliding with some tape:
Here is the link: https://github.com/MitkoDyakov/Calipatron/tree/main/Hardware/V1.2
You will find:
- gerber files
- POS files
- Schematics
- mounting diagram
- BOM
- KiCAD footprints
- step models
- 3D renders
If you like the project and you want to join now is a good point. Still the project has a long way to go and it could be improved, but I feel the HW is in a working state and could be used in POC for your intended use.
Cheers,
M
We are still kicking!
Dimitar • 09/11/2024 at 11:28 • 0 comments
Hey everyone,

I know it is been a while. The project is still alive. I just had a rough patch designing PCBs for the project. For some time I did not had s solution for the noise problem, but now I do and here is the update. I tried addressing it with a the twin t-notch filter. That was not eliminating the problem, but rather putting a band-aid on it. Also fixed a few other minor things.
- T-scale bar was wrong. The board was kind of working with the old one (on top) so it did not made an impression on me at first. But digging into the project it was getting clear that there was something off with the signal we puck up. Also for bonus points I added millimeter scale silkscreen.
- On the front of the board. I finally fixed the display pinout. It took me a few tries. I added the twin T-notch filter and ran the ground closer to the excitations signals. We have a name "CALIPATORN" - I did not come up with the name :|
- The big big change is on the back of the board and the one that brings the major improvement. What should strike you is the keep out area around the excitation/pickup pads. The ground plane was the source of the 50/60hz noise. When the T-scale was out of alignment it coupled with the ground and introduced the AC signal through the op-amp which amplified it and we could clearly see it on the measurement
The board above is our technology demonstrator. There are many other MCU on the market that are both cheaper, faster and with more feathers than the STM32F103. There are also people that don't like ST MCU in general. To address this I am working on this board. This contains the power supply and the op-amp part of the tech demo, but has a socket that holds XIAO style board. The good part is that you can have Arduino, Raspberry Pi or ESP-32 powered Calipatron. This board has a few glitches to iron out, but I will get there soon.

I now feel good about the CALIPATRON V1 that I recommend interested people to get some boards to experiment with. To do this in the near future I will upload schematics, gerbers, component position files, BOM and assembly schema. If on other hand you want a complete board you will be able to find some on the tindie shop.
Cheers,
M

View all 25 project logs

Discussions

Jay wrote 06/02/2025 at 17:30

Could you please release the kicad files as well? I was going to try and build up a board with an STM32H7 - just to see if I could try and implement https://kevinlynagh.com/calipertron/ with better visualization using high speed USB on the H7

Are you sure? yes | no

Dimitar wrote 06/03/2025 at 07:57

Hi Jay, you can find gerbers and schematics on the github repo. If you need the project files (KiCAD) you will have to wait a few days. I am on a trip, if I forget please DM me.

Are you sure? yes | no

Jay wrote 06/03/2025 at 11:37

Thanks Dimitar, I will use the schematics posted on github - thanks for releasing all this info - this is awesome!

Are you sure? yes | no

Dimitar wrote 06/03/2025 at 15:51

Let me know if you need anything.

Are you sure? yes | no

mborji32 wrote 07/16/2024 at 13:53

hi where is software?can i make this caliper by arduino?what is the code in arduino?/

tnx

Are you sure? yes | no

Dimitar wrote 07/16/2024 at 18:56

We still don't have running example. Not long ago we where dealing with hardware issues. As soon as we get some viable example we will post it. Please stay tuned.

Are you sure? yes | no

SoLongSidekick wrote 06/29/2024 at 21:23

Being as obsessed with calipers as I am I'm totally going to make this one of my first projects I try with my new PCB mill. It looks like you're using capacitive touch or something very similar. I wonder if it would be possible to make the slide component double as a MIDI keyboard.

Are you sure? yes | no

Dimitar wrote 06/30/2024 at 18:39

Actually it is 2 layers on the PCB, so CNC milling will be perfect. I would do digital MIDI trombone if I was you :D

Are you sure? yes | no

SoLongSidekick wrote 07/01/2024 at 16:48

DUDE that is freaking GENIUS! That is so much more badass and clever than whatever I would have thought up. I'm capable of making any changes that might make a milled PCB more reliable and will absolutely shoot them back to the documentation so they can be added if so. If there's any changes that are too complex for me I'll shoot them your way and you can decide if they're worth your time to either help me or do yourself. I don't expect anything so no worries there.

While I'm FAR from as capable on CAD as I should be by now I've been 3D printing since ~2011 (FDM and mSLA) so I'll take a crack at designing a printed enclosure to chuck back upstream as well. Once I have a useable stock board (unedited except for maybe small changes to make it more millable) I'll post and let me know if you want a couple, I'd love to be able to add to the project. The workflow I've been creating creates what I call "80% PCBs" (I actually think they're going to be better than 80% of what professional fab houses can do but it's kind of a play on the 80% AR receivers that can be completed at home legally, shut up I thought it was funny haha). They're milled, black or green (I prefer black but can do any color, black and green is what I have on hand though) solder mask applied then either laser or CNC etched (haven't decided which gives results i like better yet - oh yeah I have a laser engraver too), and the last thing I'm working on is the silk screening. Luckily that's an established, pretty easy concept I'm just trying to adapt the screen creation process to be laser cut for better results. I recently discovered that xTool offers a laser cut silk screening setup so I'm trying to figure out exactly what they use for their screen creation for the best laser cutting, although I'll probably end up buying their screen system as - though pricey - it allows multiple screens to be used with a single frame that stretches the screens out when locked in. Not having to have a seperate frame for each circuit design would be huge (especially with how relatively tiny PCBs are) as that cost adds up super fast. I'll update as I make progress, thanks for the warm welcome!

Are you sure? yes | no

Dimitar wrote 07/01/2024 at 18:02

I love your enthusiasm!!! I am always down for a fun project, so send schematics, models etc. and I will review them. Note that I don't have formal educations about this, so I figure stuff as I go :)

Are you sure? yes | no

Stefan de Bruijn wrote 06/25/2024 at 09:49

Very interesting. I'll keep it brief... I'm one of the founders of a popular open source CNC firmware. When testing normal calipers I noticed that there's a huge time delay between the measurement and the actual position, rendering it virtually useless for motion control. It's probably because there's no need to have a fast measurement. What I'd like to see is if I can combine the timing of the diy caliper with (fast) motion of a known frequency and time delay. I'm particularly interested in a linear encoder here, ideally absolute, but response time is key here.

I am aware of glass scales and rotary encoders. They all have their advantages and perks.

If you have a design with schematics and some pcb's somewhere, I'm happy to just order a few and test it out. Also feel free to drop a message.

Are you sure? yes | no

SoLongSidekick wrote 07/01/2024 at 16:49

I'm curious exactly what kind of delay you're talking about, because my Mitutoyo calipers seem pretty instantaneous. If you're talking micro-seconds though that's entirely moot as my dumb meat eyes can't even detect that fast.

Are you sure? yes | no

Stefan de Bruijn wrote 07/01/2024 at 17:33

The cnc firmware i work with has a step rate of 125 kHz. Not even my mitutoyo calipers give data at that rate. I need to know the delay between motion and measurement, the delay between measurement and data (observation) and information about the consistency/delay of the timings.

Are you sure? yes | no

NM wrote 06/21/2024 at 19:33

I'm really excited about this project too! Would it be a good time to try reproducing it? I'd like to see if it can be made slightly smaller, and used as an encoder for a linear axis. Looking forward to future updates. :)

Are you sure? yes | no

Dimitar wrote 06/22/2024 at 21:04

Thank you for the comment, we have a new version of the PCB. I am going to test it next week and if all is fine I will post the schematics and the gerbers on the git repo for everybody to play with. I do have a few extra board I could send your way if you want to join the project. Just send me a pm.

Are you sure? yes | no

Lucas wrote 05/13/2024 at 10:13

Thinking about the mechanical stiffness issue. I propose trying to bond the pcb to a piece of glass with superglue or uv cure.
I remember watching this [video](https://www.youtube.com/watch?v=c7A6QDj5Lbw) by diffraction limited showing that glass is surprisingly flat and looking it up on ebay it doesn't seem prohibitively expensive.

Love the project btw! Very interested to see how accurate the diy digital calipers can get.

Are you sure? yes | no

Dimitar wrote 06/22/2024 at 20:57

The glass would defiantly work for the flatness, but there are more things to take into account such as alignment and repeatability in movement. And to be hones its remarkable how much stuff I drop on a daily basis, so the glass will take a beating. On the mechanical front Ryan made a lot of progress.

Thank you for the comment, we have a new version of the PCB so stay tuned.

Are you sure? yes | no

Stefan de Bruijn wrote 06/23/2024 at 11:52

If you get rid of the edges, simple U or square aluminium extrusion profiles are also remarkably straight. Looking forward for the new PCB, I have a nice application in mind where this could be very useful.

Are you sure? yes | no

Dimitar wrote 06/25/2024 at 07:43

@Stefan de Bruijn do tell!

Are you sure? yes | no

DIY Digital Caliper - CALIPATRON

Description

Components

Project Logs

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I am stuck

Generation

Simulation

Open questions

Kevin's software breakdown.

Type 2 Hardware available.

Type 2 hardware fix

Calipatron type 2

Production files

We are still kicking!

Discussions

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