Assignment 6 (Electronic Design)

individual assignment: • use an EDA tool to design an embedded microcontroller system using parts from the inventory, and check its design rules for fabrication • extra credit: simulate a circuit • extra credit: try another design workflow • extra credit: design a case

Design Concept

Building towards my final project I wanted to design a board that uses Capacitive touch, but carving in Capacitive pads on the copper circuit board itself. Capacitive touch allows the micro controller to sense human touch and even proximity to a Conductive Pad that acts as a capacitor with a varying capacity. Using the ATtiny which have a build in capacitive touch sensing ability (pins PA3, PA4, PA5) the microcontroller can detect that change in how long the capacitor discharges. The ATtiny’s PTC peripheral continuously charges and discharges the pad, timing how long it takes. A longer discharge time = more capacitance = finger present.

No finger: small capacitance, fast discharge → no touch registered. Finger present: larger capacitance, slower discharge → touch detected.

I would like to design a board with three copper pads that when touched give a simple LED three different commands and rhythms of blinking. In a later design I will link the capacitive touch with a stepper motor which will move my kinetic sculpture.

ATtiny pin to components

Power (pins 1 & 14) — VCC gets 5V from USB, GND connects to the shared ground rail. Straightforward. Touch pads (pins 2, 3, 4 — PA4, PA5, PA6) — these three are part of the ATtiny 1614’s built-in PTC (Peripheral Touch Controller) peripheral. This is the key insight: you do NOT need a separate send/receive pair per pad. Each of these pins can sense capacitance directly on its own. One pin, one pad. This simplifies your circuit significantly compared to what you originally sketched. LED output (pin 9 — PB0) — any general-purpose I/O pin works for the LED. PB0 is a clean choice, away from the touch pins and easy to route on the PCB. UPDI programming (pin 13 — PA0) — this is the dedicated programming pin. It goes directly to your 3-pin header. One important note: PA0 is UPDI only — you cannot use it for anything else. Spare pins (5, 6, 7, 8, 10, 11, 12) — six pins completely free. Good news if you ever want to expand the project.

Schematic Design

I worked with Claude to help guide me through designing the schematic for my PCB. It’s fairly a simple design with a small number of components.

3-pin header that has a pin for ground, PWR, and UPDI.

Label the ground so it connected to the ground pin in the ATtiny Add a PWR_5V to the second pin so it will connect with VCC at the ATtiny For the 3rd UPDI pin which is in charge of the programming, we need to add a 470 resistor. This is to protect the chip from surges. After adding the resistor connect to the UPDI so it will connect to the UPDI pin in the ATtiny, which is PA0.

LED circuit

Add a resistor to regulate the voltage reaching the LED. Connect the LED_4206 component Then connect to the ground pin of the ATtiny

Touch Pads

Since the touch pads will be engraved into the copper board then, instead of adding a component, we can just add a label and draw it on the boards, when designing the footprint. However, each Pad needs to be connected to a resistor. Also, to protect the chip from surges

Footprint

After making a few adjustments, to ensure little crossing across the components and ensuring the clearances within the limit.

I drew the capacitive touch Pad using the circle command. Then by double clicking the circle to open the properties tab. I filled the circle with the fill tab. Then Relabel the circle to PAD 1. I did the same thing for the rest of PAD 2 and PAD 3.

Steps

Draw Edge cuts

Go to the edge cut layer and draw the edge cuts.

Check Electric Rule Checker (ERC)

Electric Rule Design

Add Text