To start, you will need a few basic components that can be found at all electronics stores. Including the reusable breadboard, you can probably get all of the components you need for about $25.
A breadboard will let you experiment with different component values and connect components together without soldering. It makes testing and prototyping quick and easy and can be reused on your next circuit design projects as well. Find more information about breadboards here.
The chip we’ll be using for our synth is the CD40106. (datasheet, PDF) which is a hex inverter with hysteresis, also known as a Hex Schmitt Trigger. It works with a wide range of voltages, but we’ll be using it primarily with 9V batteries. If you’re interested, this page has a good simple explanation of hysteresis.
Photoresistors, also called Light Dependant Resistors (LDRs), are a passive component whose resistance changes based on the amount of light that on the component’s surface. They are cheap and a lot of fun, but hard to control with any precision.
Potentiometers can be used as either variable resistors (like LDRs) or voltage dividers. They allow you to smoothly and precisely adjust the amount of resistance (or voltage) in a circuit. We’ll use them as pitch and volume controls, but you might find other uses for them as well!
Pushbuttons are simple components that simply make and break connections, letting you turn things on and off. There are different kinds of pushbuttons, but we’ll primarily be using momentary buttons which make a connection while the button is depressed and break the connection when it is released.
Toggle switches are a lot like buttons, but instead of momentarily making a connection they hold the connection closed or open, making or breaking the circuit. Toggles work well as power switches and are useful for turning part of your synthesizer on and off. They can also be used to switch where your signal goes.
Resistors are one of the most common (and cheap) electronic components. They limit the current flowing through your circuit, slowing down the flow of electrons. Resistors are used in countless ways, and we’ll use a bunch of them in building our synthesizers.
Capacitors store and discharge energy, allowing you to create periodic behavior. Capacitors come in two main varieties, ceramic capacitors (smaller storage, non-polar) and electrolytic capacitors (larger potential storage, polarized). We’ll talk more about polarized vs. non-polarized components later.
Battery clips simply allow you to connect a battery to your circuit. Be very careful when connecting your battery, if you accidentally attach your battery backwards you could ruin your chip. Take your time when connecting your battery (and buy a few extra chips).
A 1/4″ output jack will let you connect your synthesize to an amplifier, mixer, or effects processor/guitar pedal. If you plan on connecting your synth to a little bluetooth speaker or something with an aux input, you might consider using an 1/8″ jack instead.
We’ll be using standard 9V batteries for this project. I highly recommend investing in a couple rechargeable batteries. They will quickly save you money and battery waste is extremely toxic to the environment. Rechargeable energy! A pair of rechargeable batteries costs around $25 and will last you for years. Again, be careful to connect your battery to the clip correctly.
Adding a little amplifier chip to your circuit will let you to connect a speaker for a self contained synth. There are lots of cheap readymade amplifier boards for a few dollars, but the cheapest solution by far is the LM386 audio amplifier IC. There is an entire page of information on amplification options.
If you are using a built in amplifier, you’ll need a speaker component as well. Speakers range from a couple of dollars (pictured) to very expensive. For our purposes, a cheap speaker will do just fine. I like building synthesizers right into cheap old speakers. They sound great and it’s a readymade enclosure — all about that reanimation.