Lab 08: Set the Clock from the Internet

The Pico forgets the time whenever it loses power. Real clocks that hang in stations don't have this problem, because a master clock keeps them all right. Your clock will do the next best thing: ask the internet.

Welcome to Lab 08

This is the lab where your clock goes online. After this, it can set its own time anywhere there's WiFi, the same way a phone does. Let's make time tick!

What You Will Learn

• how the Pico joins a WiFi network
• what a time server is
• what time zones and daylight saving time are
• how to keep a password out of your code

Before You Run It

The Pico needs the name and password of your WiFi network. They go in a special file called secrets.py:

1. Find the file secrets-template.py in the kit folder.
2. Copy it, and name the copy secrets.py.
3. Type in your network's name and password:

wifi_ssid = "your-network-name"
wifi_pass = "your-network-password"

1. Save secrets.py to the Pico.

Keep Secrets Secret

Never put a password right inside a program, because programs get shared. Keeping it in its own file means you can share every program without sharing your password. This repository's .gitignore keeps secrets.py from ever being uploaded to the internet.

Run It

Open 08-wifi-sync-time.py in Thonny and click Run. The screen tells you what's happening, one step at a time:

1. Joining your-network-name
2. IP 10.0.0.22, which means your Pico is on the network
3. Asking pool.ntp.org, which means it's asking a time server
4. Time set 10:10:25, and the time appears in big green numbers

How It Works

Special computers on the internet called time servers do nothing but tell other computers the exact time. They follow a set of rules called NTP, the Network Time Protocol. The Pico asks one, and in a fraction of a second it gets the answer.

All of that happens in one line of the program:

if wifi_time.sync_time(display):

sync_time() lives in the kit's file wifi_time.py. It joins your WiFi, asks a time server, fixes the time zone, sets the Pico's clock, and then turns the WiFi off again to save power.

Time zones

A time server answers in UTC, the time in London, England (in winter). So the program adds the number of hours in TIMEZONE_HOURS from config.py:

Time zone	TIMEZONE_HOURS	When it's noon UTC, it's...
Eastern	-5	7 AM
Central	-6	6 AM
Mountain	-7	5 AM
Pacific	-8	4 AM

Daylight saving time

In most of the United States, clocks "spring forward" one hour in March and "fall back" one hour in November. The program works out whether today is in daylight saving time and adds the extra hour when it is. If you live in Arizona or Hawaii, where clocks don't change, set USE_US_DST = False in config.py.

Try This

1. Change TIMEZONE_HOURS to -8 and run the program again. What time does it say now?
2. After this lab finishes, run Lab 07. The face shows the right time, because the Pico's clock keeps going until the power is unplugged.

If It Doesn't Work

• No secrets.py on the Pico. You forgot step 4: save secrets.py to the Pico.
• WiFi failed. Check the spelling of the network name and password. Capital letters matter! Also, the Pico only connects to 2.4 GHz networks.
• The time is off by exactly one hour. Check TIMEZONE_HOURS and USE_US_DST in config.py.

Your Clock Is Online!

You joined a WiFi network, asked a time server for the exact time, and kept your password out of your code. Next, you'll set the red hand in motion.

Next: Lab 09: Tick Tock