- group assignment: - use the test equipment in your lab to observe the operation of a micro controller circuit board
- individual assignment:
- use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller
- extra credit: try another design workflow
- extra credit: design a case for it
Group Assingment
The full group assigment can be found:
https://fabacademy.org/2025/labs/cuenca/generic.html#week6
This week we got familiar with different different equipment in the lab specifically we looked at:
- the multimeter
- the logic analyzer
- a power suppy and
- the oscilloscope.
Oscilloscope
While the multimeter takes and average of the signal at point in time giving a single value, the oscilloscope is used to measure an electrical signal dynamically throughout time.
In this video you can see the signals as we change from DC to AC.
For this purpose we run a micro python program where we turn on and off a pin in the Xiao ESP32S3 micro controller.
from machine import Pin
from time import sleep
on_pin = 4
pin = Pin(lon_pin, Pin.OUT)
for i in range(1200):
pin.on()
sleep(1)
pin.off()
sleep(1)
print("on",i+1) In the video above, the bottom labels indicate:
- The vertical separation on the vertical axis (in this case 2 volts)
- The attenuation of the probe,
- The horizontal separation of the measurements in the horizontal axis (in this case 5\(\mu\)S)
- and the type of current being measured (AC/DC)
The following video provides a tour of the oscilloscope functions (Spanish).
Power Suppy
The Hanmatek 305 is a power suppy with two knobs to control the voltage and the amperage in a range of 0-30 Volts and 0-5 Amperes respectively. In addition, there is a safety button to stage the changes made in these knobs. We used the device to to run different sizes motor to guess what were the operating ranges by varying the voltage and amperage.
Individual Assingment
I wanted to be able to design and Printed Circuit Board (PCB) that allowed to test the different peripherals I will be using for my final project.
Development board
Module 1: Interface to motor
The configuration of the development board will depend on what I intend to test. In my case one important output is motor(DC) rotation for rolling the used tape of the smart trap and I would like to test my motor by changing speed and possible rotation direction.
For motor functioning I will use a half bridge and therefore it is important to half data connection and electricity connections as inputs to the motor driver. Below you can find a picture of the motor driver I plan to use and I have scribbled what each pin does.
So we will need routing as inputs to: STBY, PWMA, AIN2 and AIN1 that will use 4 data pins in addition to VCC and GND.
Module 2: Interface to sensing equipment
For the temperature and moisture sensor I will use three pins: PWR, GND and data. Howeve, it might be nice to have more data pins in case we would like to connect output devices like an OLED to display values when we are not connected to a computer.
Module 3: Control Buttons
This third module would have buttons to decrease and increase the speed of the motor. So at least we will need two data pins and connections to PWR and GND. Ideally these buttons would be somewhat separated from the rest of the board.
Pull up and down resistors
Some points:
- In a button energy can bombard a pin that is floating which can producerandom high and low voltage values.
- Adding a 10 k resistor will pull up 5v.
- If one pushes the button the microntroller sees 0 otherwise it sees 5
- Some micro controllers have already built resistance
- Pull down to ground or pull up to a voltage supply
Xiao ESP32S3 sense
Here you can see the back of the card where we can find BAT+ and BAT- which are terminals for a battery connection.
and the front. Note I have not included the camera part of the board.
Therefore, it would be important to account for all the pins that will be necessary in our Kicad design.
| Module | Ctrl | E | Pin |
|---|---|---|---|
| Motor driver | 4 | 2 | D0 D1,D2,D3 |
| DHT22 or other | 3 | 2 | D4, D5, D6 |
| Buttons | 2-3 | 2 | D7, D8 |
| Battery charger | 0 | 2 |
The assignment is limited components to the inventory. Below one can find Eagle and Kicad libraries.
Kicad
At this time the most up to date library is Kicad so I decided to use this software. I followed this tutorial for building my development board.
https://www.youtube.com/watch?v=d3H3tfU4zBI&list=PL-Hb9zZP9qC7-j4MKZNYg5i8rwu_ejkwW
Kicad is a collection of tools for PCB development:
File = > New project
to import libraries => preferences=> manaege symbol or footpring then go to the library with the file symbol.
Below you can see some key buttons from the menu of the schematic tool.
Some commands to manipulate symbols:
- G grab moves components keeping connections
- M moves compenents breaking connections - only the componet
- R: rotate can combine it with M for example
- A: to add a component
In order to modify a symbol you can double click on it.
Symbols will characterize the pins e.g. power input, input or passive etc.
Also you have footprints which will create a footprint with the component real dimensions allowing the physical representation of the component.
The goal is to create a representation of the components in the schematic tool including how the components are related e.g. which pin will communicate with another in another component.
Once we are happy with a design we go to the PCB editor to design the arrangement of the components and board shape and dimension.
If you wanted to modify the design rules you can do this in the board set up you can use the constraints to set minimum values but you can also set a net class for custom requirements. Also if you wanted to modify a track in the editor you can select the track then press U to select all the tracks associated with it and then hit E which defaults to properties and change the width value. Ideally you use a net class from the beginning.
One can set constraints
as
well as classess
Finally here is the board I designed.
Schematics:
Routings:
Printed board:
SVG file:
Some thoughts about this week
- I spent a lot of time doing the schematic tool what I would be doing in the PCB editor. Just get the schematic done as best as I can and then spent some time in the PCB designer.
- Make sure you comply with the design rules and constraints specified by the manufacturer.
Final project…
Here you can find a link to my project development page to see some additional info in regards to my final project :project development