Exercise: Digital Read Serial

Objective

Measure a binary physical property as a single-bit number.

Some devices in the physical world do approximate a digital reality: switches are usually either on or off. But even these devices have non-ideal properties reflecting the physical reality, e.g. switch contacts can “bounce” as they make contact, creating a momentary pulse train rather than a clean on/off transition.

Steps and observations

1. Load and run the DigitalReadSerial sketch.
2. Observe the numbers printed in the serial monitor as the switch changes state.
3. Try to observe switch bounce, e.g. several transitions measured for a single physical transition. Using a pushbutton instead of the switch and getting rid of the delay can help in catching a bounce.

Comments

A digital input is essentially a single-bit analog-to-digital converter, albeit with an ambiguously defined threshold between the voltages representing zero and one. The digital input sampling rate can be much higher than the 10-bit ADC, so much higher frequency digital signals could be processed with careful real-time programming.

A related challenge exercise is the Arduino RCtime tutorial in which a photoresistor-capacitor circuit is used to form an ad-hoc ADC using a single digital I/O pin. Multiple bits of conversion resolution are obtained from measuring the single input bit over time.

Other Files

1. digital-read-serial.fzz