7. Electronics design
Intro
Tasks
Hello future student, perhaps Henk has sent you here. Perhaps you're struggling with Electronics design and you're a total noob to electronics and Henk told you that I was a noob once, just like you. Well, before you do anything this week, watch these three videos:
Basic Electronics for Beginners in 15 Steps
How to Make a Circuit Board (Beginner's Guide)
Aalto FabLab KiCad tutorial and use Nadieh's notes
Other useful resources
Group assignment
Electronics concepts
Voltage (V, Volt)
Is measuring how much electrons would like to go from one place to another. Something pushes / motivates the electrons to move, and we observe by how much. The force getting them to move. Push enough against those electrons and they will jump.
In the example below, Angel falls is an example of high voltage because there is a lot of force behind the water / "electrons" moving to ground.
Niagara falls is more low voltage, as it's a wide, short drop.
Current (I, Ampere)
The total amount of electrons in a circuit. Angel falls might be considered as having low current, whereas Niagara falls has lots of it.
NB. The sum of all voltage in a loop = 0. All of the voltage is used as it returns to the end of the circuit
DC - direct current. Always positive.
AC - alternating current. Its polarity switches positive to negative.
Power (P, Watt)
Voltage x Current (V x I)
Energy is Power over Time (eg. kWh)
Components
Resistors (R) Is a current limiter. It creates resistance for electrons.
If there is too much voltage being resisted, the energy will be dissipated in heat. The heat can/will destroy the circuit.
Two main types of resistors: pin and service mount.
Rings on pin resistors will tell you its value > the first two are numbers > next is the additional zeroes > last is the degree of accuracy (eg. 5% meaning the results will be between 95 and 100ohms)
SMD — first two are the numbers, last one is the zeros
They have no polarities.
Resistance = voltage / current
Capacitor (C)
- Storage tank for electric fields.
- Store them and they will retain the charge.
- Often used in filters to block out the wrong kinds of currents. This also helps smooth out the signal that's delivered.
- They can be polarized or not.
Diode / LED (D)
- They act as a one way valve for electrons.
- “bridge rectifier”
- Can use to make an AC signal a DC signal.
NB. In a closed circuit, you don’t lose current (amps), you lose voltage.
Coil (L)
- A storage tank for magnetic fields.
- Short circuit for DC current.
- Typically used in relays and motors.
- Magnetism can be used to create motion (motors).
- Relay is a switch that’s controlled through the magnet
There can be quite a lot of energy stored in the coil, if you suddenly yank the power, there can be issues. But, a flyback diode can dissipate the magnetism -- it's like a bleed resistor for a capacitor. Somewhere to manage the release the stored energy in a coil or capacitor.
Transistor (Q)
- Amplifier and/or switch.
- Bipolar — small current can amplify a large current.
- JFET - P / N.
- MOSFET: metal oxide field effect transistor — small voltage can drive a large current.
- Most digital systems we use MOSFETs.
Microcontroller (U, IC)
- Built from millions of MOSFETs in an area and in a certain way.
- Inputs, outputs, memory, calculations (ALU).
- Essentially, “being a computer” by sending signals to other devices to do the different kinds of heavy lifting.
Measuring devices
Multimeter
- They measure voltage and current.
- The black cable should always be ground.
- For DC signals, the multimeter is perfect.
- For signals that alternate, multimeter is not the best tool — multimeter will average out readings.
Oscilloscope
X and Y axis visualizations of a current, shown on a screen that's divided into squares, whose values can be adjusted in order to help better visualize the current.
NB. Always connect the ground first with any measuring tool.
ffmpeg gif making
To make the gif: ffmpeg -i osc.MOV osc.gif
To make a gif that's less enormous: ffmpeg -i osc.MOV -vf "fps=10,scale=400:-1:flags=lanczos,split[s0][s1];[s0]palettegen=max_colors=64[p];[s1][p]paletteuse=dither=bayer" -loop 0 osc.gif
I tried using gifsicle to decrease the file from 2mb, but it just made it 1.9mb: gifsicle -O3 --lossy=80 -o osc.gif osc-lossy.gif
Used ffmpeg to trim the loop and got it down to 996kb: ffmpeg -i osc.gif -ss 00:00:00 -t 00:00:02 osc4.gif
Above is a gif of the oscillator in work. It shows how long it takes before the signal starts again. From one point in the wave until the same measurement at the beginning of the next wave is how you measure its period.
Below are the knobs that you can use to control the view on the oscillator screen.
Logic analyzer
- Basically an oscilloscope for digital signals
- It's useful for showing the relationship between multiple signals -- oscilloscope is only for two signals
Individual project
Using KiCad
Import Fab library into KiCAD:
KiCAD hotkeys (also available in the right-hand toolbar)
aplace another componentrrotates the itemmto move itwdraw wireddata sheetvvalue
This Aalto FabLab KiCad tutorial is a useful resource for the beginning steps of KiCad.
- Compile a list of parts
- Check if the EDA files are in KiCAD
- Check if they're available on DigiKey
- Download the data sheets
- Place parts in a schematic
- Search and make sure the parts have footprints
- Add headers (GND, VCC, etc)
- Add capacitors and resistors
- Give them footprints
When the circuit seems ready, open the Electrical Rules Checker to see if there are any Violations. The two that showed for me were because the Power pins weren't set up (solved here) and I hadn't imported the Fab library correctly (make sure to read the instructions carefully).
From Henk about this week's assignment:
build around xiao rp2040 or esp32-s3 button led (external, so the button on the xiao don't count) and then either a SPEAKER 8OHM 250MW SENSOR PHOTO 940NM TOP VIEW 1206 and all the necerserry resistors and capacitors You are free to add your own in or output device so go through documents of previous years students, go trhough datasheets and try to impress me with a functional and beautifull board
| Name | Label |
|---|---|
| ESP32-C3 | Module_XIAO-ESP32C3 |
| Button | Switch_Tactile_Omron |
| LED | LED_1206 |
| Phototransistor | PT15-21C/TR8 |
| Resistors | R_1206 |
It was at about this point that I realized I was confused, afraid to do anything, and very alone (not really). Eventually though, I had to make the jump and start putting stuff into the schematic.
Placing objects is very easy. You use the hotkey a and find the relevant part from the library. Drawing wires to connect parts is also easy. The software is not the hard part about this week's assignment. Knowing what to do when it comes to electronics is.
Eventually I realized that I didn't understand how to "design a circuit".
That sounds ridiculous, but before having that thought, I didn't even know what to search for. This video kind of helped me realize that. But mostly it was because I couldn't understand why certain things were happening in other people's schematics that seemed obvious to them. For instance:
- What is ground? How does it work? (eventually this one just makes sense)
- Does a resistor get placed before or after the LED?
- How does a circuit work?
Why can we put a resistor after an LED?
And by "after" I mean: (VCC --> LED --> Resistor --> GND).
This is what AI had to say:
A current flowing through a series circuit is the same at all points. The resistor limits the current for the entire circuit, including the LED, regardless of its position in the series. As long as the resistor is in series with the LED, it will limit the current effectively.
Instantaneous effect: In an electrical circuit, changes occur almost instantaneously throughout the entire circuit. When you connect the circuit, the current doesn't "flow through" the LED first and then the resistor. Instead, the circuit behaves as a complete system immediately.
Constant current: In a series circuit, the current is the same at all points. This is because there's only one path for the electrons to flow, like a single-lane road. The current doesn't accumulate or diminish as it passes through components.
Voltage distribution: What changes across the components is the voltage drop. The total voltage from the power source is distributed across all components in the circuit. The resistor creates a voltage drop, leaving less voltage available for the LED, thus limiting the current through the entire circuit.
Electron behavior: While individual electrons do move through the circuit, the overall effect is instantaneous. When you turn on a light switch, the light doesn't wait for electrons to travel from the switch to the bulb; it lights up immediately because the electric field changes throughout the circuit at once.
With that brain buster semi-understood, it was time to tackle phototransistors.
Phototransistors
C = Collector.
E = Emitter. The direction of the arrow on the emitter distinguishes between an NPN and a PNP transistor.
B = Base.
- The Collector provides the "source" of current.
- The Emitter is where the current "leaves" the transistor.
- The light shining on the phototransistor controls the amount of current flowing between the Collector and Emitter.
Arrow direction determines the transistor type. In our case, the arrow is pointing towards the emitter. This indicates an NPN transistor. If the arrow was pointing towards the base, it would be a PNP transistor.
Selecting a resistor for the phototransistor circuit comes with some considerations, like, light sensitivity. The resistor value affects the sensitivity of the phototransistor. A lower resistor value (higher current) will make it less sensitive to light changes, while a higher resistor value (lower current) will increase sensitivity.
Calculating resistors
Phototransistor resistor
- Desired collector current (Ic) -- "desired" because the data sheet lists the MAX, but we don't want that
- Collector emitter saturation voltage (VCE(sat)) Voltage between the Collector and Emitter Vce
- VCC
R = (Vcc - VCE(sat)) / Ic
(3.3-0.4)/.001 = 2.9kΩ resistor
LED resistor
I also had to figure out how much resistance I needed with the LED. I chose to have an Orange LED. Color affects the calculation because different colors have different Forward Currents.
The LED datasheet:
Button resistor
Rating (Resistive Load):
The switch is rated for 1 to 50 mA at 3 to 24 VDC. This means it can safely handle currents within this range without damage.
Ensure that the current through the resistor stays within the switch's rated range (1–50 mA).
- Choose a Target Current within the safe operating range of the switch; eg. 1 mA
- Use Ohm's Law
- VCC is your supply voltage (3.3 V)
- I is your desired current (e.g., 1 mA)
Practical Recommendations from AI
Use a pull-up or pull-down resistor between 1 kΩ and 10 kΩ, as these values are commonly used and fall within safe operating ranges for most circuits.
Button
After speaking with Sam, I learned that my button needed a pull up or pull down resistor. Otherwise, when you push the button, the circuit could short.
NB. "The ESP32C3 and a lot of other boards have internal pull-up/pull-down resistors meaning in the chip there’s already these resistors. You can use them if you declare that you want to use them in your code." - Vera
PCB layout editor
Design Rules
In order to make sure that the PCB actually works, it must follow some design rules. Those, we need to define in KiCad.
I also added Constraints settings that Vera used last year (the third photo). She made a pre-defined 0.8mm track size so that she can toggle between 0.4mm and 0.8mm. She had this to say:
From the local review I heard it’s best to use 0.4 to connect pins and 0.8 for tracks that are connected to power.
File > Board Setup > Constraints
PCB layout
Drawing traces
NB. f - finish track that's being drawn.
I imported the schematic to PCB and started laying out all of the parts. Nothing was fitting right. The pins in the PCB view weren't in the same position as in the PCB editor. The rats nest makes it quite hard to concentrate, so it helped to toggle on/off the F.Fab layer in order to hide the names of the parts.
Rejigged the pins in my schematic because my traces were blocking one another. Added labels.
I moved my LED to a lower pin (on the left hand side) and my Phototransistor to a higher one. That enabled me some space to make the traces flow easier.
Design rules checker
Lots of errors. Some silkscreen errors that I could easily fix. Others were nested under the XIAO MCU, not easy (or necessary?) to remove, and so I left those.
F.Cu + Edge.cuts
KiCad Image Converter > bitmap trace the image in black and white > save it as .kicad_mod file > save it in a .pretty library folder (I called my library Henk) > add the new Footprint library to KiCad > use a to add the file to the PCB editor
(Quick) Image transfer tutorial
(Longer) Image transfer tutorial
NB. The Fablab Aalto video, linked earlier, also explains this process.
Footprint Editor > import file > select the object > right click > properties > set Layer to Edge.Cuts > save in the correct library
Select a when in the PCB viewer and add the newly made Edge.cut file from the Henk library.
