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Reload this page1.6 - Norsk Data projects

SWT001 - Thumbwheel CKN1187, BCD

The project

  • How does a thumbwheel switch works?
  • Let's figure it out in this project using a 10 position BCD switch.
  • All the switches used in this project are taken from the ND Memory Trace Module.
  • Just reading the thumbwheel setting and display the current BCD value is a bit too easy so we throw in some extra functionality as well.

How it works

I have used the thumbwheel with negative logic. Which means that all the thumbwheel signals are pulled high at the Arduino side, and then drawn low by the connections inside the thumbwheel.

When you change the setting on the thumbwheel you will notice that the signals and values briefly shows an "odd" value. This is due to imperfections in the thumbwheel, f.ex between 1 and 2 will the connections break and the value will be 0 for a short while.

ThumbwheelSignals on
thumbwheel pins
Logical value
0 picture


  • Cut the stripes on the stripboard at the shown places.
  • Solder all the components to the stripboard.
  • Solder all the wires on the back of the stripboard.


  • With a simple program for the Arduino board, we can now watch the current setting of the thumbwheel.
  • The program itself has none commands, it will only print a status line according to the switch settings.
  • This program can be downloaded and uploaded to the an Arduino board using Xloader.
  • After downloading you can connect to the Arduino board using f.ex HyperTerminal.
  • The SWT001 board has three run modes (switch 7103):
    • (Auto) Automatic - Display a status line every time the thumbwheel value is changed.
    • (Cont) Continue - Display the status line repeatedly, this will show that the thumbwheel is not perfect and may show an "odd" value while moving from one position to the next.
    • (User) Manually - The status line will only be displayed when the user press the push button.


ND noProductLanguageReleaseTitleDownloadFilesSizeOriginalType
292010.A00ArduinoENAug. 2017SWT001- -- YesSW
292010.A01ArduinoENDec. 2018SWT001ZIP file14.8 KBYesSW
292010.A02ArduinoENDec. 2018SWT001ZIP file15.0 KBYesSW

Version history

  • Hardware (PCB 9002)
    • A00 - 2017.08.19 - Arduino Uno interface board
  • Software
    • A00 - 2017.08.19 - Original version (internal version)
    • A01 - 2018.12.20 - Rewritten to comply with coding standard, first released version
    • A02 - 2018.12.30 - Prell on the user push button corrected, added version info


  • Do you have all the parts required to build PCB 9002, that I can buy?
  • No, sorry. You have to find/buy them other places.

  • Can I buy an Arduino Uno and/or Arduino prototype board from you?
  • Yes, but IT IS much cheaper to find and buy it on the internet.

  • Can you build or help me build this project?
  • No, you are totally on your own and YOU have to build it yourself.

  • Can I have the Arduino source sketch so I can modify it myself.
  • No, you can NOT. You have to write your own sketch.
Component side

Solder side

Side view

Hooked up to the Arduino board

Circuit diagram

Snapshot from a run

This page was last updated 06. Nov. 2023
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