Part 4: Designing The Keyboard PCB

Many weeks later.... I have come up with the final design for sound generation (the keyboard). I decided on 12 separate 555 timer circuits. The limitation with running all the keys off of one or two timers is that I wouldn't be able to play two notes at the same time. No fun!

I decided to use easyEDA to design the circuit, mainly because it has JLCPCB and LCSC plugins for parts and footprints. Since we are doing manufactuing through JLCPCB, it was an obvious choice. KiCad was a close second, as they also have a JLCPCB plugin. However, I had never used it before, and I didn't want to waste time on the learning curve. In the future, I'd like to try KiCad, it seems a little more user friendly than easyEDA and EagleCad.

The most important thing I learned in the design process was using modules. For my first iteration I did all twelve 555 circuits by hand, copy and pasting and adding in values. For the final design, I made one 555 circuit, then saved it as a module. Then I changed the specific frequency resistor values (this set the frequency, ie. the note) in the BOM.

Here is the final PCB design. The biggest challenge was reducing the footprint to fit inside the box.

The Final PCB Design

I decided to make the PCB yellow, as a treat.

The final PCB in 3D with yellow PCB color. Everything is to by placed by JLCPCB except the 555 timers.

This is the final schematic, as you can see, it's a lot to do by hand.

THE FULL SCHEMATIC

This is the module I built with AR3 being the specific frequency resistor.

The module. There is a different value for each R3 and a 5k trim pot for fine tuning of each note.

Things I would do differently:

• figure out how to use layers in the schematic design.

• Start with parts selection and design around that instead of vise versa

• Start with modules

• Onboard power module