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6. Electronic Design

Design Concept

Building towards my final project, I wanted to design a board that uses capacitive touch — carving the touch pads directly into the copper of the circuit board itself.

Before opening any software, I started with pencil and paper. Sketching the concept first helped me think through what I actually needed: how many pads, what they would trigger, how the components would relate to each other. This turned out to be an important step — coming to KiCad with a clear idea of what I wanted made the whole process much less intimidating. The concept: three copper pads on the board that, when touched, give a single LED three different blinking commands and rhythms. In a later iteration I want to connect the touch input to a stepper motor that will drive my kinetic sculpture. [Sketch of initial concept here]

What is Capacitive Touch — and What’s Actually Happening?

Capacitive touch is worth understanding properly because it’s not just a software trick — there’s real physics behind it. A capacitor is any two conductive surfaces separated by an insulator. When you bring a finger close to a copper pad, your finger — being conductive — adds to the capacitance of the system. The pad and your finger together form a temporary capacitor, with air or the PCB surface acting as the insulator between them.

The ATtiny1614 has a built-in PTC (Peripheral Touch Controller) peripheral that continuously charges and discharges the pad and measures how long that cycle takes. The timing is everything: * No finger present: small capacitance, fast discharge → no touch registered * Finger present: larger capacitance, slower discharge → touch detected * The key insight for the circuit design is that each touch pin (PA4, PA5, PA6) can sense independently — one pin, one pad, no separate send/receive pair needed. This keeps the circuit simple.

What I Learned About Electronics Design

The honest takeaway from this week is that electronics design is more approachable than it looks. It’s not magic — it’s a patient art. If you slow down, read the datasheet, check your connections, and take it one component at a time, everything starts to make sense.

A useful mental model I developed: always keep voltage, resistance, and current in the back of your mind while designing. Think of it like water in a pipe — voltage is the pressure pushing it, current is how much is flowing, and resistance is how narrow the pipe is. These three things are always in conversation with each other (V = IR), and every component decision is really a decision about managing that relationship. Too much current through an LED and it burns out. Too little resistance on a programming pin and a surge can kill the chip. Keeping this in mind while placing components turned abstract numbers into something more intuitive.

A few more specific things I learned:

  • Capacitors as shock absorbers — I learned that capacitors placed near the power pins of a chip (called decoupling capacitors) act as a local reservoir of charge. When the chip suddenly demands more current — which happens constantly as it switches on and off internally — the capacitor supplies that burst instantly, before the power supply has time to respond. Without it, those sudden demands create tiny voltage spikes that can interfere with the chip’s operation or damage it over time. The capacitor smooths those spikes out, acting like a shock absorber for the electrical current.

  • Voltage drop — every component in a circuit consumes some voltage. An LED, for example, needs a specific forward voltage to light up, and anything above that needs to be accounted for with a resistor. Understanding voltage drop meant I could calculate the right resistor value rather than just guessing.

  • Grounding — every component needs a return path to ground. A floating ground causes unpredictable behavior. I made sure every component in the schematic had a clear, labeled ground connection before moving to the footprint stage.

KiCAD Design

Schematic Design in KiCad

With the sketch done, I moved into KiCad to build the schematic. The schematic is the logical map of the circuit — it shows what connects to what, without worrying yet about physical placement or size. The circuit has three main parts:

  • 3-pin programming header (UPDI)

  • Pin 1: GND — labeled and connected to the shared ground rail

  • Pin 2: PWR — connected to VCC (5V from USB)

  • Pin 3: UPDI — connected through a 470Ω resistor to the PA0 of the ATtiny. The resistor is there to protect the chip from voltage surges during programming.

  • PA0 is dedicated to UPDI only — it cannot be reassigned.

  • LED circuit A current-limiting resistor regulates the voltage reaching the LED. The LED (LED_4206) connects after the resistor. The other leg connects to ground

  • Capacitive touch pads Each pad (PA4, PA5, PA6) connects through a small series resistor to protect the chip from electrostatic discharge The pads themselves are not components — they get drawn directly onto the copper layer in the footprint stage I kept referring back to the ATtiny1614 datasheet throughout this process to confirm the right resistor and capacitor values. The datasheet tells you exactly what each pin expects and what limits not to exceed.

Footprint Design in KiCad

With the schematic complete, I moved to the PCB layout in KiCad — this is where the schematic becomes a physical board. The main steps: * Place components — KiCad imports the components from the schematic. I arranged them to minimize crossing traces, keeping the touch pins on one side and the programming header accessible at the edge.

  • Route traces — connecting the components with copper traces, keeping clearances within the design rules.

  • Draw the capacitive touch pads — since the pads are part of the board itself rather than separate components, I drew them manually using the Circle command on the copper layer. I opened the circle properties, filled it using the fill tab, and relabeled each one: PAD 1, PAD 2, PAD 3.

  • Draw edge cuts — I switched to the Edge Cuts layer and drew the board outline, defining the physical boundary of the PCB.

  • Run the ERC (Electrical Rules Check) — KiCad’s built-in checker scans the schematic for errors: unconnected pins, missing power flags, short circuits. I ran the check, reviewed the results, and confirmed the design was clean and ready for fabrication.

Group assignment

The group assignment for this week is here

I learned how to use a logic analyzer understanding the internal funtions of the stepper driver. Unlike the usual drivers the one we used used 4 pins rather than the Typical DIR and STEP.By connecting the logic analyzer to those pins we were able to see how the electic pulsing works and even how the pulses were out of step for the purpose to deterimining the direction and speed of the stepper.

Design Files

Download KiCAD Schematic

Download KiCAD Footprint