Lab 04: Ask the Internet What Time It Is

The Pico forgets the time whenever it loses power. Real smartwatches never seem to have this problem. They ask the internet for the correct time. In this lab, your watch will do the same.

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, secrets.py, means you can share all your programs without sharing your password. This kit's secrets.py is set up so it never gets uploaded to the internet.

Run It

Open 04-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 10:09:20, 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). When it's noon there, it's still early morning in Minnesota. 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? Where in the country would that be right?
2. After this lab finishes, run Lab 03. The time is still right, 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.

Next: Lab 05: An Analog Watch Face