Input Devices
Group Assignment:
Probe an input device(s)'s analog levels and digital signals
Document your work on the group work page and reflect on your individual page what you learned
Individual Assignment:
Measure something: add a sensor to a microcontroller board that you have designed and read it
Have you answered these questions?
Linked to the group assignment page ✅
Documented what you learned from interfacing an input device(s) to your microcontroller and optionally, how the physical property relates to the measured results. ✅
Documented your design and fabrication process or linked to the board you made in a previous assignment. ✅
Explained the programming process(es) you used. ✅
Explained any problems you encountered and how you fixed them. ✅
Included original design files and source code. ✅
Included a ‘hero shot’ of your board. ✅
Group assignment
Probe an input device(s)'s analog levels and digital signals
Document your work on the group work page and reflect on your individual page what you learned
For the group assignment, aiming to probe the analog levels and digital signals of an input device, my colleague Omar provided valuable assistance. He explained in more detail how analog and digital signals work from a physical and technical perspective.
Here is the link to learn more about the group project.
For the group assignment, I met virtually with colleagues from the academy to compare our progress and the sensors we were using. During the meeting, we shared our screens and presented the results obtained with tools such as the oscilloscope, observing and comparing the analog and digital signals generated by the sensors. This allowed us to discuss adjustments, optimize our implementations, and identify similarities and differences in the results.
Reflections
Through the exploration of input devices such as the LDR (Light Dependent Resistor) and the TTP223 touch sensor, I've gained valuable insight into the nature of analog and digital signals. The oscilloscope has been an indispensable tool in observing these signals, providing a clear visualization of how they respond to environmental changes like light intensity and physical touch.
The LDR sensor demonstrated how an analog signal smoothly varies in response to light, while the digital touch sensor allowed me to understand how simple high/low values are used to trigger events in a system. This learning emphasizes the importance of input devices in modern electronics and how sensors can provide real-time data for system interaction. By using tools like the oscilloscope, I now better understand the practical applications of these sensors and the significance of accurate signal interpretation in circuit design and analysis.
Individual assignment
Measure something: add a sensor to a microcontroller board that you have designed and read it
In the week 9 assignment, we were asked to measure something: add a sensor to a microcontroller board we had designed and read its value. To do this, I’m sharing the links to weeks 06 and 08, where you can view the design and fabrication of the board I will be using. Electronics Design, Electronics Production.
Team training
Our instructors, Ulises and Roberto, prepared a class to help us understand a bit about electronics and, especially, to learn about this week's topic: input devices. We joined the class, and it was really clear and dynamic. I’m sharing the link so you can access this training: Video link. For those who don’t know anything about electronics, like me, this video is perfect; it will help you understand several key concepts that are useful for the assignment.
Exercise with the instructors 1
One of the basic exercises we did and that I document here was a simple simulation on the Wokwi platform, where we learned how to light up an LED.
I copied the same code from Wokwi to Thonny, and the only thing I did was change pins 3 and 4. In my PCB, the LEDs worked correctly. In the code, the sleep value was set to 0.5, a time that can be adjusted to control the LED's on and off.
from machine import Pin
from time import sleep
print("Hello, Fab Academy 2025!")
pinLed = Pin(3, Pin.OUT)
while True:
#pinled.toggle()
pinLed.value(0)
print("Apagado")
sleep(0.5)
pinLed.value(1)
print("Encendido")
sleep(0.5)
Exercise with the instructors 2
Now I will make the button work, first I did the simulation on Wokwi.
Here, on the LED pin, I can change the values of the LED, which are 3 and 4, since I have two LEDs. I can also configure the sleep, and in this case, I set it to 0.1 seconds.
from machine import Pin
from time import sleep
print("Hello, Fab Academy 2025!")
pinLed = Pin(3, Pin.OUT)
pinBut = Pin(2, Pin.IN)
while True:
print(pinBut.value())
pinLed.value(pinBut.value())
sleep(0.1)
This is the code I used in Thonny for the button.
Now I will do this exercise individually using two sensors: one is the 4-pin LDR Sensor Module and the touch sensor. I'm a bit nervous and relaxed at the same time, I feel like it's going to be easier, although I’m a little scared that I might damage the components. So, let’s take it easy! ✨😊
1. Programming Process - 4-pin LDR Sensor Module
I Chose the Module
To begin, I selected the sensor modules I would use: a 4-pin LDR sensor and a TTP223 touch sensor. These input devices helped me understand both analog and digital signals.
The module I used for this is the 4-pin LDR Sensor Module. This sensor measures the ambient light intensity and has 4 pins:
A0 (Analog Output): Analog output that varies depending on the light.
D0 (Digital Output): Digital output that indicates whether the light exceeds a threshold.
GND (Ground): Connection to the circuit ground.
VCC (Voltage Common Collector): Connection to the power supply (5V or 3.3V).
I Made a Simple Sketch
Before jumping into code, I made a small conceptual sketch to visualize how I would connect and program the components, helping me organize the pin assignments and behavior I expected from the circuit.
Here is a diagram explaining the connection of the LDR Sensor:
VCC of the LDR sensor → +5V of the XIAO RP2040.(PORT 4)
GND of the LDR sensor → GND of the XIAO RP2040.(PORT 4)
D0 of the LDR sensor → D0 (PORT 4) to read the digital value.
A0 of the LDR sensor → D1 (PORT 4) to read the analog value.
I Simulated the Circuit in Wokwi
I used Wokwi, an online simulator, to create a virtual version of my setup. This allowed me to write and test code using components like LEDs, buttons, and sensors before applying it to my real board. I simulated how the LED reacts to the button and sensor inputs.
A small exercise was done in Wokwi, where the sensor is selected and the option for Photoresistor (LDR) appears, and the amount of light varies as the bar is moved. Inside, a number can be seen that changes; this happens because I was moving the bar.
I Transferred the Code to Thonny
After making sure everything worked in Wokwi, I copied my code into Thonny, which I used to program my actual PCB. I only had to adjust the pin numbers to match those used in my real board.
from machine import Pin, ADC
from time import sleep
pinPot = ADC(Pin(27))
while True:
pot_value = pinPot.read_u16() # read value, 0-65535 across voltage range 0.0v - 3.3v
print(pot_value)
sleep(0.1)
This is the LDR sensor code. Here, only the pin number is changed to ensure the analog (pin 27) and digital (pin 26) signals work correctly.
I Tested on My PCB
Finally, I connected the real components on my custom PCB and ran the code. The LED responded correctly to the button press and sensor readings, confirming that the simulation matched the physical implementation.
Now I will proceed to test the sensor. To do this, I used the light from a lamp and moved it closer and farther from the sensor. At the bottom of the Thonny program, you can observe the numerical variation, which represents the change in light intensity measured by the LDR sensor.
When measuring the LDR (Light Dependent Resistor) sensor with a multimeter, I encountered difficulties due to the nature of the measurement and the characteristics of the sensor. An LDR is a component whose resistance varies depending on the amount of light it receives. This means that the measurement with a multimeter is neither direct nor constant, as the resistance changes with the light.
When you use a multimeter to measure resistance, the reading will not be stable if the LDR is exposed to different lighting conditions. If the light is variable, the resistance will change constantly, making it difficult to obtain an accurate reading. Additionally, common multimeters are not designed to measure the dynamic response of components like the LDR, which depend on external factors such as light intensity. Unlike sensors like a touch sensor, which have a more stable signal, the LDR fluctuates depending on lighting conditions, resulting in inconsistent readings.
Programming Process - Touch Sensor TTP223
I Chose the Sensor
The Touch Sensor is a device that detects human contact through the conductivity of the skin. This sensor has various applications, such as activating lights, contactless switches, and as an input device in electronic systems. It generally has three pins:
VCC (Voltage Common Collector): This pin is connected to the power supply, typically 5V or 3.3V, depending on the system being used.
GND (Ground): This pin is connected to the circuit ground or negative to complete the current flow.
SIG (Signal):This pin generates a digital signal (HIGH/LOW) when a touch is detected. The HIGH value indicates that the sensor has been touched, while the LOW value indicates no touch.
I Made a Simple Sketch
Touch Sensor Connection with XIAO RP2040:
VCC→ +3.3V or +5V of the XIAO RP2040 (It is recommended to use 3.3V).
GND→ GND of the XIAO RP2040 (Any available GND pin).
SIG→ D3 (Or any available digital pin to read the sensor state pin 29).
I Transferred the Code to Thonny
from machine import Pin
import time
# Define the pin for the touch sensor (in this case D3)
touch_pin = Pin(29, Pin.IN)
# Function to read the touch sensor value
def read_touch_sensor():
if touch_pin.value() == 1: # If the value is 1, the sensor is touched
return True
else:
return False
# Main loop
while True:
if read_touch_sensor():
print("Touch sensor touched")
else:
print("Touch sensor not touched")
time.sleep(0.5) # Wait for 0.5 seconds before the next reading
The code I generated for this is based on the following prompt used in ChatGPT:
"Generate a Python code to read the state of a touch sensor using the XIAO RP2040 microcontroller. The code should check if the sensor is touched (connected to pin D3) and print a message to the console every time a touch is detected. The reading should be done in an infinite loop, with a 0.5-second delay between each reading."
I Tested on My PCB
Touch Sensor Test with PCB: The touch sensor test with the PCB was a success. It works perfectly. I was really excited when I saw that I had completed my task correctly. Although it took me a bit of time to make the connections, I made sure they were connected to the correct pins to avoid any potential mistakes. Ensuring the VCC pin is connected to the appropriate voltage (3.3V or 5V) and the SIG pin is in the correct port for reading the signal is crucial for optimal sensor performance.
I also measured with a multimeter to observe the type of signal being emitted. In this case, the variable is numerical. Without contact, the reading was 0.0002 volts. When I placed my hand on the touch sensor, the reading immediately rose to 5V.
Reflections
During the development of the assignment, I didn't encounter any issues initially, as the system worked correctly at first. However, when my instructor Cristian reviewed my work, he pointed out several errors in the pin connections, which surprised me since everything had worked fine earlier. Despite this, I had noticed that my LDR sensor was overheating, which made me suspect there might be connection issues.
At first, I felt frustrated for not having done it correctly, but I decided to take a more careful approach and rechecked the connections patiently. The mistake I made was relying on the schematic diagram instead of following the PCB layout, and also not consulting the microcontroller’s datasheet properly. These details were overlooked during my initial review.
Thanks to my instructor’s explanation, I was able to identify these mistakes and correct them in time. From this experience, I learned the importance of always following the PCB design and carefully reviewing the technical specifications of the microcontroller before making any connections.
In this exercise, I was able to integrate sensors with a microcontroller board, which allowed me to measure physical properties such as light intensity and touch contact. The experience helped me better understand how sensors interact with the environment and how to read their signals, whether analog or digital, using a microcontroller.
Additionally, I faced the challenge of working with sensors like the LDR (Light Dependent Resistor) and the touch sensor, and I learned to program in Python to get accurate readings of their values. Using simulation platforms like Wokwi made it easier to test concepts before actual hardware implementation.
Regarding the problems I encountered, at first I felt a bit unsure about how to handle the connections and ensure that the values read were correct. However, practice and reviewing the code allowed me to troubleshoot and obtain the expected results.