# Electronic design

For this week we are making a start at designing pcb's. Im excited for this week because I can finally make my own circuits instead of using unreliable breadboards. With designing I'm starting out with KiCad.


## No symbol table
When I first tried to start a project for kicad it asked for a symbol table. 

![alt text](image.jpg)

Apparantly KiCad doesn't come with it on Linux systems (I don't know about windows). So I needed to install an extra package called `kicad-library`. After that I could use the standard symbol library. Later on I also found out I needed to install the 3D-models libary. Everything of KiCad on Linux comes separately.


## The assignment
For this weeks assignment henk wanted us to design a pcb with at least a led, a switch and then we had a choice between a speaker and a sensor. I wen't with a speaker because I could use that for my final project.

### KiCad
I'm going to do this in KiCad because it is the only software I know thanks to the lecture on thursday. I first started out dragging all the parts I needed onto the schematic editor.

![alt text](image-12.jpg)
Using the `A` key while in this screen you can open the component selector and search for the components needed.

![alt text](image-13.jpg)

After that I needed to think how I wanted to connect everything. I wanted to use the switch as a power switch and the led as some sort of status indicator. wiring up the speaker is going to be the hardest part.

I first started off with the easier parts. So I started with the LED. I accidentally found out when you hover click a part and press `D` you directly go to the data sheet of the part so that's a nice shortcut. 

#### Connecting a LED
When reading the datasheet I found this graph. With a relation to voltage and mAh of the LED.

![alt text](image-14.jpg)

If I supply the LED with 20 mA it should run at 1.8V. The supply voltage is 3.3V so.
```math
R = V / I \\

R = 3.3 / 0.02 \\

R = 165 Ohm
```
So I will need a 165 Ohm resistor.

![alt text](image-15.jpg)

This is how I connected my LED. I chose to use the MCU as a ground because Henk once explained how it's better for the MCU and that it could handle more led's or other connections that way.

#### Connecting the speaker
Now I wanna drive the speaker. But to do that we need some sort of driver because I don't think the mcu's has enough power to drive the speaker.

When searching online and on older fab academy projects I found that people everywhere use IC's to drive them. I wanted to try to make one without an IC because I have seen my friend make one when he was doing electrical engineering. When looking around online all the circuits look super confusing. For example the one on [this forum](https://www.physicsforums.com/threads/amplifier-circuit-driving-an-8-ohm-speaker.967270/) doesn't have any ground symbols.

After searching for a while I found [this](https://www.instructables.com/How-to-Make-Simple-Amplifier-Circuit-Without-IC/) on Instructables
![alt text](image-16.jpg) 

##### Understanding resistors
The only step I needed to figure out is why it work like this and why doesn't the speaker blow up when connected because there is 9 volt on the circuit and the speaker is rated for 1 volt. I still have a lot of trouble wrapping my head around how voltage drops because of a resistor.

Voltage can be seen as the speed of water traveling through a tube. A resistor makes the tube smaller for a small part so the water slows down. So the voltage drops.

Resistors always cause a voltage drop. How big the drop is depends on the amount of current going trough it and the resistance (Ohm)

```math
V = I * R
```
This is Ohms law. So to keep a constant voltage you need to make sure your current is also constant and not changing constantly. In that way you can keep a constant voltage.

#### Back to the speaker
I watched [this](https://www.youtube.com/watch?v=U0FIG2J6Zls) video and now understand the fundementals of a amplifier. The only thing necessary is something that can make an small signal big. For that I can use a MOSFET. I also need to make sure the MOSFET doesn't over current the speaker so that's why it needs a resistor before the gate pin. And I need some sort of buffer for the speaker once it needs a lot of power.

![alt text](image-17.png)

When I was looking for MOSFET's through the Fab library I found 2 type of MOSFET's P channel and N channel. I quickly searched what it does.

![alt text](image-18.png)

So for my use case I will need a N channel MOSFET that can work output a linear voltage based on what is supplied on the gate.

![alt text](image-19.png)

I first had this setup. But then I asked AI for feedback and it told me I used the wrong transistor because it could only be on or off and not anything in between.

![alt text](image-20.png)