Scooter Speedometer

Or, perhaps the most whimsical thing I have made since the Covid Hat . Although that may be debatable.

Bits needed

Pi Pico - https://www.pishop.ca/
A3144 hall effect sensor https://www.amazon.ca/gp/product/B07QNX6HWT/
Little strong magnet https://www.amazon.ca/dp/B09CNJ4GN8/
SSD1306 OLED Display https://www.aliexpress.com/item/32717542815.html

LED
220 ohm resistor
10K resistor

And some way to hook them all up.

Getting Ready

Get MicroPython from https://www.raspberrypi.com/documentation/microcontrollers/micropython.html
Install MicroPython on your pi pico by downloading the .uf2 image and dragging and dropping it onto the Pico in boot mode.

Install Thonny if not already done apt install python3-tk thonny
Install the library for the ssd1306

Click on Tools > Manage Packages to open Thonny’s package manager for Python libraries.
Type “ssd1306” in the search bar and click “Search on PyPI”

(Image credit: Tom's Hardware)

Click on “micropython-ssd1306” in the returned results and then click on Install. This will copy the library to a folder, lib on the Pico.

Wiring

Reality part 1

Reality Part 2

Wire Wrapped

Software

Building the large characters

Pick a monospaced sans serif font and increase the font size to a suitable sized font
Type 0-9 and a decimal
Take a screen shot
Use the Gimp to carve out the characters to 11 separate images
Convert each character by running each of the 11 images through img2bytearray.py (https://github.com/novaspirit/img2bytearray)
Copy and paste the byte arrays into the source code.

Calculate the speed

There are four magnets attached to the non-driven rear wheel. Hence four hits (interrupts) on the hall effect for each revolution.
The wheel is 18cm in diameter so the circumference is π x diameter.
Set a timer for a second
Count the interrupts in a second, divide by 4 multiply by 3600 gives cm/hour
divide that by 100,000 gives km/hour
Distance = Distance + Circumference * interupts / 4 / 100,000

Code

Prototype 1

Everything in famous zip lock bag

One magnet

Prototype 2

How to build a box.

https://www.thingiverse.com/thing:2594893
Box template

// General Settings
comp_size_deep = 43; // Depth of compartments
comp_size_x = 65;        // Size of compartments, X
comp_size_y = 45;        // Size of compartments, Y
wall = 2.5;                 // Width of wall, see `internal_wall` below for alternate inner wall size.
repeat_x = 1;           // Number of compartments, X
repeat_y = 1;           // Number of compartments, Y
tolerance=.15;      // Tolerance around lid. If it's too tight, increase this. If it's too loose, decrease it.

// Box Rounding
box_corner_radius=0; // Add a rounding affect to the corners of the box. Anything over `wall` will cause structure and lid problems.
internal_corner_radius=0; // Add a rounding affect to the inside.
mesh_corner_radius=0; // Leave a radius around each corner of the mesh. May hep with bridges.
corner_fn=30;

OpenSCAD

https://ultimaker.com/software/ultimaker-cura/

Ultimaker Cura - slice the drawing to 3d printer layers

Assembly - notice the zap straps on the bottom.
Especially the one pushing the BOOTSEL button.
This took us a while to figure out.

All together with the zap strap moved to not push the BOOTSEL button.

With the cover installed. You will note that there are two ways to install the box. Facing back (correct) and facing forward (wrong). We of course first installed incorrectly. But actually we didn't because the steering will turn 180 degrees - and it was. So we fixed it incorrectly.
Finally we had a coffee and then zap strapped it on correctly. Only two zap straps were sacrificed.

There are now 4 magnets and less electricians tape.

The hall sensor has been glued on in a holder.

Prototype 3

perhaps the finished product

This will include a box with printed holes rather than drilled
Velcroed to the handlebars rather than zap strapped.
Perhaps a black box - although the orange is growing on me
A 24v to 5V buck converter so the speedometer can use the scooter battery rather than using a separate battery.