Lab 07: Set the Time with the Buttons

What if there's no WiFi? A real watch lets you set the time with its buttons. This lab does too:

Button	What it does
MODE	Steps through: run → set hour → set minute → run
UP	Adds one to the highlighted number
DOWN	Takes one away from it

The part you're changing is highlighted in yellow. Hold UP or DOWN and the number keeps changing by itself, so you don't have to press 45 times to get to 45 minutes.

What You Will Learn

• why a single press can count as three (and how to fix it)
• how "hold to repeat" works
• how to set the Pico's clock from a program

Run It

Open 07-set-time.py in Thonny and click Run. Then:

1. Press MODE. The hour turns yellow.
2. Press UP or DOWN to change it.
3. Press MODE again. Now the minutes are yellow.
4. Change them, then press MODE once more to get back to running.

Setting the minutes also sets the seconds to zero. That way you can match another clock exactly: set the minutes one ahead, then press MODE right when the other clock gets there.

Problem 1: Bouncing Buttons

Inside a button, two bits of metal touch when you press it. But they don't touch just once. They bounce, like a basketball, touching and letting go several times in a few thousandths of a second. The Pico is so fast that it sees every bounce as a separate press, so one push could move the hour three places!

The fix is called debouncing: after the button changes, ignore it for the next 40 thousandths of a second (40 milliseconds, or ms). By then, the bouncing has stopped.

DEBOUNCE_MS = 40

Problem 2: Hold to Repeat

Pressing a button 45 times would be miserable. So if a button is held for half a second, it starts "pressing itself" about 8 times a second until you let go:

HOLD_MS = 500      # wait this long before repeating
REPEAT_MS = 120    # then repeat this often

Both of these fixes live inside a class called Button. A class is a blueprint: the program makes one Button from it for each real button, and each one keeps track of its own bouncing and holding.

Setting the Pico's Clock

Once you change a number, the program writes the new time into the Pico's clock, the RTC:

rtc.datetime((year, month, day, weekday, hour, minute, second, 0))

That means lab 03 and lab 05 will show your new time, too, as long as the Pico stays plugged in.

Try This

1. Change DEBOUNCE_MS to 0. Can you get one press to count twice?
2. Change REPEAT_MS to 40. Now how fast does it count?
3. Make the highlight color green instead of yellow. Look for HIGHLIGHT_BG near the top of the program.

Next: Lab 08: A Digital Watch Face