6. Electronics Design¶
Ohm’s law¶
We started the group assignment by learning about Ohm’s law and how to use a multimeter:
First, we powered a 4m thin wire with 1V power supply. We measured the voltage between the ground and several points of a thin wire. The voltage was proportional to the length of the wire measured.
Then, we “cut” the wire in two with a resistor. We again measured the voltage and noticed that the voltage difference was close to 0 before the resistor and close to one after.
Voltage divider¶
We started to learn about voltage divider. This is an important circuit that is used to measure of input devices such as Light Dependent Resistors.
We found a formula to calculate the resistors values starting from Ohm’s law:
Then we built a voltage divider using a 610 Ohm resistor and another resistor with unknown value.
Using the variable power supply, we set the input voltage to 5V and used the oscilloscope to measure the output voltage. With these two voltages and the known resistor value, we were able to calculate the value of unknown resistor.
Observing PWM with an oscilloscope¶
Then, we explored the differences between an analog and digital signal.
We tested the function analogWrite(pinNumber, D) with the Arduino. This function creates a PWM signal with a duty cycle of D/255 * 100%.
We used this code on an Arduino:
int pinNumber = 9;
void setup() {
}
void loop() {
analogWrite(pinNumber, 50);
delay(50);
analogWrite(pinNumber, 100);
delay(100);
}
We observed the signal for analogWrite(pinNumber, 100);
And for analogWrite(pinNumber, 50);
Observing I2C communication with an oscilloscope¶
We then observed I2C communication using the oscilloscope.
We used this code:
#include <Wire.h>
void setup() {
Wire.begin(); // Join I2C bus as Primary
}
void loop() {
Wire.beginTransmission(0x2A); // Start communication with Secondary (address 0x08)
Wire.write(0x01); // Send a single byte
Wire.endTransmission(); // Stop transmission
}
The hexadecimal number 0x2A translates to 0101010 in binary. Since we didn’t have another Arduino, there was no response to the request of writing, so the microcontroller was sending the address in a loop without writing any byte.
