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7. Electronics Design

Week Assignment

  1. Test the operation of a circuit board (group).
  2. Design a hello-world board with additional buttons and LEDs (individually).

Design a Hello-World Board with Additional Buttons and LEDs

I designed a hello-world board using an ATtiny1614 with an additional LED and button. The design process involves three main steps:

  1. Defining the schematic
  2. Designing the PCB with the traces
  3. Building the PCB

As we were introduced to KiCad during the class, I used the ATtiny1614 datasheet as a base for my design.

Example ATtiny1614 Board

attiny1614 example

I opened KiCad and created a new project. Using the FAB library that we added during the class, I redrew the hello-world board example with an ATtiny1614, a UPDI connector, a capacitor, and an FTDI connector. I also added an LED, a resistor, and a switch.

To determine which pin to use for the LED and the button, I referred to the following diagram:

Attiny1614

Initially, I used pin number 8, but later I realized that all pins except Ground, VCC, UPDI, and TX/RX were available options.

Initial Attempt

I first created a schematic with the 3216 microcontroller but later corrected it to use the 1614. I kept the file name as 3216, as advised by Oscar, to avoid potential bugs. However, I found that the microcontroller was not utilized effectively in this design.

first attempt

During the lab session, I started exporting the .svg file to open it in Inkscape and convert it to a suitable .png. An instructor pointed out that I should move the LED to another pin to make the design functional. I revised the schematic, adjusted the connections, and added a new resistor.

Options to Check When Exporting to .svg:

  • Copper layers: F.CU
  • Technical layers: Edge cuts
  • Print mode: Black and white
  • SVG page size: Board area only
  • Print board edges
  • Pagination: All layers in a single file

Preparing the .png in Inkscape

After organizing the components, I created the outline and exported the design to .svg. I opened the file in Inkscape and created three layers:

  1. Background
  2. Traces
  3. Interior

first second attempt

  1. Background Layer: Added a large black rectangle.
  2. Interior Layer: Moved the outline into this layer and filled the figure with white using the bucket tool.
  3. Traces Layer: Moved the traces into this layer and turned them white.

I exported the interior and traces separately. For the image definition, I used 1000 dpi.

After exporting, I used Mods to mill the PCB.

During the milling process, the instructor noticed that my traces were too thin and the UPDI connector was placed behind the capacitor. I corrected these issues in KiCad, adjusting the trace thickness and repositioning components to make better use of space.

Final Design

For the final board, I selected different pins for the LED and switch to facilitate programming. I also added two 1k resistors, one for the LED and one for the switch.

last attempt schematic last attempt

Components Used:

  1. ATtiny1614
  2. Capacitor 1µF
  3. UPDI connection
  4. FTDI connection
  5. 2 resistors (1kΩ)
  6. LED
  7. Switch

I used the alternative corner for milling as the left-bottom corner was not well leveled. I set the Z-axis to -0.5mm for a proper cut.

board different traces

I tested the boards for shorts and connection issues. The LED worked as expected!

finished board connected

To program the board, I used the FTDI and UPDI connections from week 4 and followed the instructions on this page.

I used Arduino IDE to install megaTinyCore, selected the ATtiny1614 microcontroller, and configured the proper port. I encountered issues on my Mac, which seemed related to the USB connector type.

/*
Blink
Turns an LED on for one second, then off for one second, repeatedly.

BOARD: ATtiny1614/1604/814/804/414/404/214/204
Chip: ATtiny1614
Programmer: jtag2updi (megaTinyCore)
*/

#define LED_BUILTIN 2 //PA6 (Pin 2)

// the setup function runs once when you press reset or power the board
void setup() 
{
    // initialize digital pin LED_BUILTIN as an output.
    pinMode(LED_BUILTIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() 
{
    digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(1000);                       // wait for a second
    digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
    delay(1000);                       // wait for a second
}

programming

Files

Find all the files here:

Design Rule Check

To properly use KiCad, I followed the beginner guide to KiCad. I also consulted this tutorial on running the Design Rule Check. Initially, I used the default settings for trace width and spacing but found them too thin. I adjusted the settings as follows:

  • Min Track Width: Changed from 0.2mm to 0.3mm
  • Min Via Size: Changed from 0.4mm to 0.8mm

The Design Rule Check button displays a modal where these parameters can be defined. Errors are indicated with a white arrow and detailed in the modal.

  • Clearance: By Netclass
  • Min Track Width: 0.3mm
  • Min Via Size: 0.8mm

Testing the Board with the Multimeter

Since I was unable to join the group for Raspberry Pi testing, I fulfilled the assignment by testing my new board with a multimeter. I watched this video on how to use a multimeter to guide me through the process.

I compared the board against my blueprint and checked the schematic for correct polarities. Before connecting the board to power, I verified the following:

  • Checked for shorts between VCC and GND
  • Ensured the microcontroller was soldered in the correct position

Measurements taken included:

  • Voltage
  • Resistance: To verify resistor values
  • Continuity: To test for open or shorted conductors, switch operation, and clear circuit paths
Last update: September 16, 2024