I designed the synthesizer to have direct feedback, bright colors, and big parts. This makes it easy to understand, easy to use, and fun for children of all ages. Even if the person using it does not quite understand what all of the buttons and knobs are doing, it is fun to just smash buttons, and flick switches and listen to the sound change.
Overall, I am pleased with how this came out. I am hoping that my nephew will enjoy playing with this half as much as I do.
Step 1: Kid-Friendly Design
For starters, I decided to use big colorful arcade buttons because of their sturdy construction and inviting appearance. I tested this theory on the Instructables resident toddler and she seemed more than pleased to smash away at the button panel, whether or not the buttons did anything. I next decided to replace the switches, sliders, and potentiometer knobs with home lighting fixture parts. From my experience, I find that small children like to play with light switches and other big buttons. Unfortunately, they were not very colorful and inviting. I solved this problem by adding colored resin to the tops of each of the knobs.
The power switch was also a challenge. I wanted it to be easy enough that my nephew could feasibly use it himself, but difficult enough that he would not get the immediate feedback of turning the synthesizer on and off repeatedly (which would defeat the point of all other switches). I resolved upon a lamp pull switch for this task. Toddler testing thus far has proven successful.
One more thing I had to keep in mind was how to make changing the battery easy enough my sister could do it, but impossible for my nephew. I didn't want him to be able to get into the case and tug at the wiring. I resolved to use a hatch system with two child-proof magnetic latches. In order to get into the inside of the case, you need to know to carefully place a magnet on two specific places on the hatch. This makes the case both seamless, and easily accessible (to those in the know).
The one weak point in the case is the speaker grill. I considered reinforcing this with a metal mesh, but ultimately decided against it. I'm just hopeful he won't try to jab anything long and skinny inside the holes. I did, however, water seal speaker cone, because - well - you never know.
Beyond that, I simplified the synthesizer circuit that I was working with to only include functionality that gave immediate or near immediate feedback. While some knobs may not work when some of the switches are toggled, my nephew will never be far from making it create some sort of noise, or toggling it back into some sort of highly playable state. This makes it fun enough for a toddler to wail away on, but complex enough that it will still be rewarding as he gets older. This toy is compelling to children of all ages.