This Digital Measuring Wheel Supports Three Modes of Operation

The idea

When it comes to measuring distances or the length of an object, most people reach for a tape measure or ruler. The main problems with these tools is that they have a finite distance that can be measured, putting objects longer than the tape or ruler out of reach. To combat this problem, Albert Barber has created a project he calls the Digital Measuring Wheel that aims to enable users to measure things up to 100 meters long, in comparison to the typical tape measure with a limit of around 7.6 meters.

Electronic components

To build this, Bartber chose to use a rotary encoder that works by sending a coded pulse on each rotational step, giving both positional and velocity data to the connected Arduino Pro Mini board. Displaying all of the necessary information to the user is handled by a 0.96" OLED screen, while a single 1S LiPo battery pack powers the entire device. Last of all, a pair of momentary push button switches allow for user input.

Designing the wheel

One big challenge in designing the digital measuring wheel was figuring out how to maintain accuracy while also preventing damage from occurring to any components while in use. Barber came up with a mechanism that relies on a single large, spinning wheel embedded with a series of 48 teeth. Meanwhile, the stationary internal assembly contains the PCB, electronics, and a secondary gear on the rotary encoder with a mere 8 teeth for a ratio of 1:6. The outer wheel is held in place by a set of four screws and glides easily over two rings of ball bearings that reduce friction.

Assembly

After receiving his custom-designed PCB, Barber set to work on soldering all of the components onto the board, including the Arduino Pro Mini, OLED screen, rotary encoder, buttons, and the USB charging module. From here, one end of the wheel's shell was attached along with a set of ball bearings. The PCB was then set in place along with the wheel and another handful of ball bearings. Finally, the top shell was combined with the remainder of the assembly to complete this sandwich of 3D-printed parts and electronics.

The program

Most of the magic comes from the firmware Barber wrote for the Arduino Pro Mini. It configures the board's interrupt pins to trigger whenever a signal is registered from the rotary encoder and either increments or decrements a counter, depending on the direction of rotation. Then after a set amount of time, this value is read and used in a simple calculation to determine either the distance or speed of the outer wheel, as its diameter is known in advance as well as the gear ratio.

Measuring objects

To measure something, the user must first select their desired mode by double-tapping the 'Z' button, while a single press resets the value to zero. Switching between metric units and imperial units can be done by pressing the button labeled 'M'. Because of how inches are traditionally written in fractions rather than decimals, the closest value to 1/16" is used to maintain readability while taking care to not reduce resolution.

To see the Digital Measuring Wheel in action, you can watch Barber's video here on YouTube or read more about the project on Instructables.