Fast Resistor Sorting with DIY Ohmmeter Encased in Lego Bricks

Invariably, hobbyists end up with a pile of unsorted resistors at the end of a project, or perhaps have purchased a mixed-lot of assorted resistors to begin with. Resistors have color bands printed on them, rather than numeric values, which makes them more difficult to sort.

There are a number of common approaches to organizing resistors:

All of these methods are satisfactory, but time-consuming. So, I created a device built from Lego bricks and minifigs that measures the resistance, displays the standard value, and speaks the resistance using text-to-speech (TTS).

Multimeter made with Lego minifigures and bricks

Multimeter made with Lego minifigures and bricks.

A resistor is placed in the hands of the minifigure for measuring. Wires have been threaded through the arms to make electrical contact with the resistor.

Lego minifig holding resistor in hands

Lego minifig holding resistor in hands.

The meter also has a slot for placing AA or AAA batteries, to measure their voltage. A metal wrench from a dollhouse connects to the top of the battery.

Battery tester Lego minifig with metal wrench

Battery tester Lego minifig with metal wrench.

A USB cable comes out the side of the case to connect to a personal computer.

USB cable hole

USB cable hole.

A microcontroller inside the meter communicates the measured values to a .NET application running on the PC.

Minifigure Multimeter NET screenshot

In fact, the .NET application is actually in charge. The application issues a series of commands (turn on a specific known resistor, set the gain, read the analog value) to the microcontroller, and then switches known resistors to narrow down the actual value of the resistor being measured.

This process repeats over and over, until approximately the same value has been calculated twice in a row. At that point, the application displays and speaks the results.

If the user removes the resistor or battery from the device, the application sees a change to an extreme value (very high resistance or very low battery voltage), and stops updating the screen so that the user can observe that value at their convenience.


The overall solution turned out very well. Here is the meter in action:

Cool, huh? Let’s see how it was made.