Discovering I can just treat Sparky Danger Organ like a piezo buzzer for making music was great, it opened up a world of already-written Arduino sketches playing music with tone(). Now Sparky is getting its 15 minutes of fame with Emily’s This Is How Electronic Ignition Works And Also How To Make A Spark Plug Play Music published on The Autopian.

In Emily’s article, she compared modern electronic ignition with electromechanical ignition from BC (before computers) era of cars. The distributor diagram is a pretty good explanation why I couldn’t do very much with an old ~1950s Chrysler ignition coil my neighbor had sitting on a shelf: I needed something to interrupt power to the ignition coil so its primary winding’s 12V field can collapse and induce high-voltage in its secondary winding. Since I usually play with electronics manipulating 5V or less, at well under 1A, I didn’t have anything on hand suitable to handle such power.

However, a modern electronic ignition coil has that switch built-in. (The “Igniter” box in the LS1 Coil diagram of Emily’s article.) So to repurpose a retired coil+plug only requires a 5V, low-current, digital control signal to be sent on its IGT pin. Now that’s something Arduino tone() can do easily and help Sparky find its singing voice.

So what’s next? There was a bit of confusion between Emily and I about Arduino tone(). She referred to an installed library, but I found it as a built-in function. Investigating this confusion led me to https://github.com/bhagman/Tone where I learned we were both right. There’s a full non-core version that Emily had to install into her (presumably older) Arduino IDE, and Arduino had incorporated a simplified version of this library into core which is what I found. The simplified version can only generate one voice. The full version can generate more voices: one per hardware timer on the AVR chip. ATmega8-based chips have two timers so two voices. ATmega328P (like that on the Arduino Nano I used) can do three voices, and an ATmega1280-based board like the Arduino Mega can control six spark plugs. Useful facts to keep in mind whenever Emily or I get our hands on more retired electronic ignition coils.