For Electronics Design I finally have the chance to start working on my final project. For this week we need to design a “Hello World” PCB with a micro-controller, one button and one LED. As my final project is going to need a lot of buttons, this is a good chance to start the design of a single button and have the chance to test it.

Think

My final project is going to consist of a keyboard with 24 buttons for the right hand, four buttons for the left hand and a rotary encoder. The buttons should be:

• easy to press,
• make quick contact without a “click”
• be pressure sensitive after the button is pressed
• be able to emit light.

The requirement to be able to emit light makes it impossible to use capacitive sensors. To achieve both a switch and a pressure sensor, the switch circuit should not be an existing button but rather be part of the PCB design.

Eventually the switch will be part of the pressure sensor.

To have a switch like this I would need to make my own PCB footprint in KiCAD.

Make

Bill of Materials

My HelloSwitch board will need the following components:

Custom parts

To have the switch and the pressure sensor on the board I have to make custom parts in KiCAD. A part consists of a symbol and a footprint. Symbols can be drawn in any shape but must have pins defined that match with the pins on the footprint.

The switch is going to be a classic “normally open” switch, so I decided to “borrow” and edit the symbol from the “fab” parts library.	The sensor is essentially a variable resistor, so this symbol is also “borrowed” from the kiCAD libraries itself

For the footprints I needed to estimate the eventual size these buttons are going to have. To determine the size of the footprints I photographed and measured my own hand to see what size of keyboard would be comfortable to play.

Original image of my own hand being measured.	In Rhino I Estimated the keyboard pattern based on the measurements.

From the analysis of my own hand I determined that a key, if round, would have a diameter of 20mm. I decided to draw the PCB layouts of the sensors in Rhino, so I would have slightly more sophisticated drawing methods at my disposal.

Both the switch and the sensor drawn in Rhino	The resulting exported vector files couldn’t directly be imported in KiCAD because Rhino doesn’t export filled polygons.

I had to use InkScape to import the polygons, join them with by selecting the nodes and pressing shift-j and then filling them.

Eventually I could use my footprints in my schematic.

The siwtch…	…and the sensor as to separate footprints.

The schematic

I chose to make the schematic as a whole instead of using a lot of labels.

The schematic. Labels are used for the connectors to reduce clutter.

The PCB could then be created. A ground-plane fills all the empty spaces.

While drawing the PCB I found I needed some 0Ohm resistors to be able to have all the GND pins connected.

Check

The PCB was eventually milled and it worked, as can be seen in the documentation for Embedded Programming and Input.

The PCB worked. I could control the RGB LED and the analog input returned significantly different values when a piece of carbon foam was pressed to it.

Electronics design in FabAcademy

Here’s an overview of all the PCBs I designed and made during the entire cycle. The design files can be found here.

Theatrum Control Board

This board got made for the machine week. Eventually we chose to go for another solution.

Schematic	PCB	Result

I2C Squeeker

This board got made for the Networking and Communications assignment. It tought me the method of connecting devices on a bus using ribbon cables.

Schematic	PCB	Result

USB2Midi converter for the Feib

This board converts USB-Midi to serial Midi. It actually works very well but it didn’t make it into the final project as I had difficulties mixing 3.3v and 5v devices on the same i2c bus.

Schematic	PCB	Result

OLED2I2C Header

This board served as a connector converter to make the OLED display compatible with the I2C ribbon cable.

Schematic	PCB	Result

Feib main board

These were variations of boards that would act as the main board for my final project. Unfortunately neither of them made it into the project as I was running out of time. A perfboard solution would have to do.

WEMOS D1 Mini version

Schematic	PCB

ESP12f version

Schematic	PCB

Tiny DAC

This board got made during the output devices week. It contaiuns an SMD piezo speaker connected to the DAC of an Attiny416

Schematic	PCB	Result

WS2812 Button

I planned to make a small PCB for each button on the Feib instrument. Eventually I saved some time by cutting up an LED strip.

Schematic	PCB	Result

I2C Level converter breakout-breakout

I thought I could mix logic levels on the I2C bus of my final project by using an AdaFruit level converter board. I made this board to convert logic levels and essentially end up with 2 busses. It didn’t work.

Schematic	PCB	Top	Bottom

Theatrum Luminus LED board

The Theatrum machine needed a very bright LED. Four Luminus LEDs would certainly do. They were controlled using a MOSFET on a nother board.

Schematic	PCB

A silhouette of a lightbulb, found using google image search, served as the outline of the board.	The picture of the resulting PCB is of an earlier version

Group Assignment

The group tested some electronic components using the measurement equipment available.

The multimeter was used to measure voltage. In this case the voltage of a 9v battery.

The most used function of the multimeter is to measure wether current can flow through a conductor.	The diode test can be used as a connectivity test

Alternating voltages over time other than very slowly changing voltages can’t be measured using a multimeter. Here we try to measure the voltage drop over time of a capacitor. There’s certainly a change but we can’t see how the capacitor discharges over time.

To measure changing voltages over time we used the oscilloscope.

By measuring the voltage between the positive and the negative side of an electrolytic 100nF capacitor…	…the oscilloscope shows us the change of voltage over time when the capacitor is discharging.

A microcontroller generates changing voltages over time, in this case to switch LEDs on and off very fast.	These signals can be nicely visualized as block-waves on an oscilloscope.

Files

• All the kicad designs