till-s / kicad-dicebug

School/kids project; an electronic dice

The DiceBug

by Till Straumann, 2023

Introduction

This is a simple electronics project that I have created to teach kids how electronic circuits are "built" -- in a physical sense. They don't have to understand how it works (6 year olds have assembled the bug) but just have fun placing the small components on the board, watching the solder melt in a toaster oven and walk away with the finished product.

The cute bug features a motion sensor and operates as an "electronic dice" cycling throught the familiar patterns of pips we know from traditional dice. The cycling is randomly triggered by hand motion and happens too fast to control the outcome. When the hand is withdrawn the bug will show a random facet.

The bug's preferred meal is a CR2032 lithium battery. A small power-switch is located at the tail end of the animal.

Occasionally, the motion sensor may have to recalibrate itself (the dice seems to be "stuck" when that happens). Just leave it alone for several seconds (no touching) and it will come back to life.

Since the battery is exposed don't store the or operate the device in a conducting bag or box.

Warning

Keep (any type of) batteries away from small children. Swallowing batteries can be life-threatening!

Assembly Instructions

Prerequisites

PCB

You need to have the PCB manufactured. There are many companies (mostly in China) who do this cheaply. I found, however, that most manufacturers would not offer the red solder mask combined with black ink (silkscreen) that I liked. Eventually, I came across elecrow who would make the PCBs the way I wanted them (slightly more expensive "premium service").

Make sure to also order a couple of stainless steel stencils (more than one if you work with groups of kids). PCB manufacturers often also offer stencils and you save on shipping cost when ordering from a single source...

Parts

The parts can be obtained from the usual electronics distributors (DigiKey, Mouser, Farnell, ...). These sources also sell solder paste; I had good results with lead-free low-temperature paste, Chipquik TS391LT50, which melts around 138degC.

Brass-plated nails, 1.2mm (dia) x 12mm (length), which I found at a DIY shop make nice legs.

For the actual soldering you'll need a cheap toster oven or a hotplate, YMMV. There are many instructions available on the internet.

IQS211 Capacitive Sensor Programming

Azoteq's IQS211 is very versatile and ideal for this kind of application. I have regularly found it at Mouser; DigiKey sometimes don't have them.

Note that you need to configure ("burn") the IQS211's OTP options prior to using it in your application. Unfortunately, this means that you need the Azoteq CT210 Programmer (also available from distributors) and a programming socket (e.g., here).

The configuration value is stated in the schematics.

Assembly

Nothing special here; I have a bunch of tweezers that I lend to the kids so that they can work in parallel. Usually a kid's eyesight is good enough to see the 805 parts perfectly. Adults may need glasses.

Spend some time on the internet if you have never done this; there are many resources available that teach how to harness SMT.

Obvously, you only install the battery into the holder after soldering the board.

Feet

After assembling and soldering/toasting the board I use a small hammer and carefully hit the small nails just enough so that they hold on in the mounting holes. Turn the bug on its feet to verify that it stands nicely tweaking the feet if necessary. Eventually, you use a conventional soldering iron and (lead-free) solder to fix the feet permanently.

Good luck!

License

This project is licensed under the OHL-S open-hardware license; the artwork was created by my kid Adam and is licensed under CC-BY-NC-ND.