Lab 12: One Watch, Five Modes

This is the big one. Everything you've built so far comes together into one watch. Press MODE to go from one mode to the next:

Weather → Analog → Digital → Stopwatch → Timer → and back to Weather.

A row of five dots at the bottom of the screen shows which mode you're in. The bright dot is the one you're on.

What You Will Learn

• how one program can run five different watch faces
• why a program should only load what it needs
• how a stopwatch or timer keeps going when you're not looking at it

Run It

Open 12-main-template.py in Thonny and click Run. The watch sets its clock from the internet, then starts in Weather mode. Press MODE to step through the others.

Weather	Analog	Digital	Stopwatch	Timer

The Buttons Changed a Little

In this watch, the MODE button's job is changing modes. So the stopwatch and the timer can't use MODE the way they did in labs 10 and 11. Here's how they work now:

Mode	UP	DOWN	MODE
Stopwatch	start / stop	lap while running, reset while stopped	next mode
Timer	start / pause, or +1 when setting	reset while paused, or −1 when setting	next mode

To set the timer, hold MODE down for one second. While you're setting it, MODE moves from the minutes to the seconds, and it won't change modes until you're done. That way you can't leave by accident in the middle of setting it.

Only Load What You Need

Think about your school backpack. You could carry every textbook you own, every day, but it would be heavy, and you'd only use a few of them. It makes more sense to pack just the books for today's classes.

This watch works the same way. Each mode is a separate file: mode_weather.py, mode_analog.py, mode_digital.py, mode_stopwatch.py, and mode_timer.py. Only the mode on the screen is loaded into the Pico's memory. When you press MODE, the watch:

1. tells the current mode to stop
2. unloads it, freeing up its memory
3. loads the next mode and tells it to start

However many times you press MODE, the watch always has about 380 KB of memory free.

Modes That Keep Going

What happens to a stopwatch that's running when you switch to the weather? It keeps running! When a mode stops, it can hand the watch a note to remember, like "I started at this moment" or "I'll reach zero at this moment." When the mode loads again, it reads its note and carries on.

• A running stopwatch is still running, with the right time, when you come back to it.
• A running timer keeps counting down. When it reaches zero, the watch jumps straight to the timer and sounds the alarm, whatever mode you're looking at.
• The weather remembers its last forecast, so it doesn't have to ask the internet again every time you pass by.

Make It Your Watch

Save a copy of this program to the Pico as main.py, along with the five mode_ files. Now whenever the Pico gets power, it becomes your five-mode smartwatch, even with no computer attached.

For the curious: how to add a sixth mode

Every mode file has the same four functions, and that's all the watch needs to know about a mode:

Function	When the watch uses it
start()	when the mode is loaded: draw the whole screen
update()	about 100 times a second: redraw whatever changed
stop()	when you switch away: hand back a note to remember
on_mode()	when MODE is pressed. This one is optional.

To add a sixth mode, copy one of the mode_ files, change it, and add its name to the MODES list at the top of 12-main-template.py. You don't need to add a dot: the watch always draws one dot for each mode in the list.

Try This

1. Change START_MODE = 0 to START_MODE = 1. Which mode does the watch start in now?
2. Start the stopwatch, switch to the weather, wait 10 seconds, then go back. Is the time right?
3. Set the timer for 20 seconds, start it, then switch to the analog face. What happens when it reaches zero?
4. Take mode_analog out of the MODES list. How many dots are there now?

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