Input Devices¶

Group Assignment:¶

• Probe an input device(s)'s analog levels and digital signals.

1. Overview & Objectives¶

In embedded systems, an input device (or sensor) converts a physical quantity—such as position, distance, light, or temperature—into an electrical signal that a microcontroller can process.

For this group assignment, we explored and probed two fundamental categories of input signals:

• Continuous Analog Signal: Measured using a potentiometer.

• Digital & Pulse-Width Signal: Measured using an Ultrasonic Distance Sensor (HC-SR04).

2. Analog Input Device: Potentiometer¶

To probe this signal, we connected the potentiometer's wiper (center pin) directly to an oscilloscope probe channel, with the ground clip attached to the circuit's GND. The oscilloscope was set to a DC-coupled input with a voltage scale of a few hundred mV/div, so the full rotation range could be seen on screen.

Observation: as the shaft was turned, the trace showed a smooth, continuous line moving up or down between roughly 0V and the supply voltage — with no steps, edges, or repeating pattern. This confirmed the potentiometer output is a purely analog, continuously variable voltage, directly proportional to the wiper's mechanical position.

The video below demonstrates the continuous probing and response of the potentiometer input:

3. Digital & Pulse Signal: Ultrasonic Sensor (HC-SR04)¶

For this device, we probed control line with the oscilloscope.the channel on the Echo pin, referenced to the sensor's GND. The time base was set fast enough (µs/div range) to resolve the short trigger pulse and the longer echo pulse on the same screen.

Observation: the Echo line went HIGH for a much longer, variable duration — its width changed directly with the distance of the object placed in front of the sensor: the closer the object, the shorter the Echo pulse. This confirmed that the HC-SR04 does not output an analog voltage at all; it encodes the measured distance purely in the timing of a digital pulse, which the microcontroller must convert back into centimeters (distance = pulse width × speed of sound / 2).

• Echo Pin (Output from sensor): Outputs a digital HIGH pulse whose duration; corresponds to the round-trip travel time of the ultrasonic wave.

The video below shows the active probing and real-time response of the ultrasonic sensor:

4. Conclusion & Comparison¶

Probing these two devices side by side with the oscilloscope made the practical difference between analog and digital signals very clear: