Week 08 — Input Devices.

Assignments

  • Group: probe an input device’s analog levels and digital signals.
  • Individual: measure something — add a sensor to a microcontroller board I designed, and read it.

Group assignment (1–3)

We used the oscilloscope to examine a motion-sensor board. Following the clock line helped us understand the board’s timing, and we also probed several random GPIO/test pads. Some pins showed noticeably higher switching frequencies than others, which suggested different sub-circuits (e.g., clocked logic vs. slow IO/interrupt). It was a quick way to map behaviors without a full schematic.

1
2
3

Individual assignment (4–11)

For the individual part, I connected a distance/motion sensor to my board and read it from firmware. I verified the sensor on a milled test board, checked the solder joints, and then wired the sensor to the MCU headers. After validating power and IO levels, I logged the readings over serial and confirmed responsiveness by waving a hand in front of the sensor.

Sensor mounted on milled board
4
Breakout inspection
5
Back side check
6
Fixture and wiring
7
Bench wiring with laptop
8
Serial readout screenshot
9
Sensor plus connector harness
10
11

Firmware — PIR Motion Test

I tested the PIR sensor with a simple sketch. I haven’t soldered the LED yet, so the program uses the Serial monitor (115200 baud) for feedback; the LED pin is already defined and will light once the LED is added. Wiring used: PIR signal → D2, PIR VCC → 3V3, PIR GND → GND. 

const int PIR = D2;
const int LED = D3;

void setup() {
  Serial.begin(115200);
  pinMode(PIR, INPUT);
  pinMode(LED, OUTPUT);
  Serial.println("PIR sensor test start...");
}

void loop() {
  int motion = digitalRead(PIR);
  if (motion == HIGH) {
    Serial.println("Motion detected!");
    digitalWrite(LED, HIGH);   // LED will work after it’s soldered
  } else {
    Serial.println("No motion");
    digitalWrite(LED, LOW);
  }
  delay(500);
}