Homemade Hardware - Week 11
Alpha to Beta
After a few weeks of setbacks, making some forward progress on the final project. I’m feeling confident that I’m on a path to having a first milled board this week and toward having something pretty funky effects-wise to to mess with the tone output from a microcontroller.
First up: instead of trying to create boards that will play parts from Steely Dan’s “Peg,” I’ve shifted focus over to “Reptilia” by The Strokes. The reason is pretty simple: there are only four instrument parts I need to worry about in the latter song compared to sixteen in the former. With simultaneous tone generation it’s possible to get some chiptune-y renditions of full songs from a single microcontroller, but that makes it that much harder to then control the timbre of individual instruments with more circuitry.
My plan is to recreate the album art for Room on Fire, the album “Reptilia” is from, in the PCB design. Assuming I’m using copper clad board, I probably won’t go for a color accurate recreation (though I’m assuming I could use nonconductive acrylic paints if I wanted to go that route?) but starting from a black-and-white high contrast version to begin taking the shapes and lines and turning them into traces/places for components seems promising.
My experimentation with breadboarding guitar pedal circuits has led me to a combination of a basic boost pedal (adapted from this YouTube channel) and this LM358/LM324-based distortion. In working with the 358 I’m also drawing from what we learned about op amps in Pedro’s Electronics for Inventors class this semester.
The boost is as basic as a pedal circuit can be, basically a few caps, a transistor, a voltage divider and a knob to control volume.
At first I tried adding an amplifier using the LM358 after the boost to see if it’d effectively serve as a gain, but it didn’t really change much besides clipping the guitar amp I was testing on past a certain volume.
The distortion part of the circuit is very, very basic: it just feeds the output of the LM358 back into the input, as controlled by a potentiometer. I should try testing it with various potentiometer values before either locking to a fixed resistor or soldering on pots to the PCBs. A logarithmic A-type pot might be preferable here to the linear B-types we currently have in the shop too.
The biggest design decision moving forward with a proper beta build is which microcontroller to use. The limitations of the Playtunes library I’m using for tone output is that the ATTiny version only supports up to two tone generators. An Arduino Uno using an ATMega328 can use up to six. I know we have some of those in stock plus the 7805 voltage regulators I’d need to go down from 9V for the pedal to 5V for the chip, but I’m unsure whether those tiniest traces can be milled on our machines or if I’d have to resort to using a through-hole package. I am strongly tempted to go with the Mega, though–it’d lead to better initial sound output and make programming a hell of a lot easier when I could just treat everything like an Arduino sketch.–4/24/23