Words you'll hear
Electronics is full of acronyms. These are the ones that show up this week, in plain terms.
Power
- GND
- Ground, 0 V. The reference point every voltage is measured from. The black probe always goes here.
- 3V3
- 3.3 V, made on the board from USB power. It's what the chip runs on, what "HIGH" means, and the most any pin can safely take.
- 5V
- Straight from USB. Useful for powering motors or LED strips. Never connect it to a D pin.
- VCC
- A generic name for "the power input" on a module. The QPAD's OLED has a VCC pin.
Signals
- GPIO
- General purpose input/output. A pin your code can either set (output) or read (input).
- Digital
- Only two states: HIGH (3.3 V, 1, true) or LOW (0 V, 0, false). Think of it as a bool.
- Analog
- Any voltage in between, like 1.27 V. Think of it as a float.
- ADC
- Analog-to-digital converter. The part of the chip that turns a voltage on A0–A3 into a number your code can use.In Arduino,
analogRead gives 0–1023. In MicroPython, read_u16 gives 0–65535.
- PWM
- Pulse width modulation. The chip can't output 1.27 V, so it fakes it: it switches the pin on and off very fast, and things like LEDs and motors average it out.
- Duty cycle
- The share of time a PWM signal is on. 25% duty on a 3.3 V pin averages to about 0.8 V.
- Pull-up
- A resistor connecting a pin to 3.3 V, so it reads HIGH when nothing else is touching it. Buttons need one. The chip has built-in pull-ups you turn on in code.
- Floating
- A pin connected to nothing. It reads random values because it picks up noise. Pull-ups fix this.
Chips talking to chips
- I2C / IIC
- Inter-integrated circuit, pronounced "I squared C". Two wires that let one board talk to many chips, each with its own address. The QPAD's screen uses it.SDA carries the data, SCL carries the clock (the tick that says "read the next bit now").
- UART / serial
- Sends bytes one bit at a time with no clock wire. Both sides agree on a speed beforehand.TX transmits, RX receives. Baud rate is the speed in bits per second, like 115200.
- SPI
- Serial peripheral interface. Faster than I2C, uses four wires.SCK clock, MOSI data from the XIAO out, MISO data back in, CSn "chip select" (the n means it's active when LOW).
- OLED
- The small screen on the QPAD. It receives pixels from the XIAO over I2C.
Code
- RP2040
- The chip itself, made by Raspberry Pi. The XIAO is a tiny board by Seeed that carries the chip plus USB and power parts.
- Arduino
- A way of programming in C++. You write a
setup() that runs once and a loop() that repeats forever, then click Upload. A program is called a sketch.
- MicroPython
- Python running directly on the chip. No compiling: you edit in an app like Thonny and press Run. It uses the P numbers for pins.
- Serial Monitor
- A window in the Arduino IDE (or the Shell in Thonny) that shows whatever your program prints. Your best friend for debugging.
Tools
- Multimeter
- Shows one number: voltage (V), resistance (Ω), or a beep for "connected" (continuity). Updates a few times a second.
- Oscilloscope
- Draws voltage over time, fast enough to see millionths of a second. "Scope" for short.
- V/div, time/div
- How much one grid square is worth, up and across. The two big knobs on the scope.
- Trigger
- Tells the scope when to start drawing, like "when the signal crosses 1.6 V going up", so the picture holds still.
