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Lab 10: Set the Clock from the Internet

The screen says Set clock in big white letters. Below it are the small line Time set 10:09:20, the time 10:09 AM in big green letters, and the date 2026-10-11 in small white letters.

The Pico forgets the time whenever it loses power. A phone never seems to have this problem, because it asks the network for the correct time. In this lab, your clock learns to do the same.

Welcome to Lab 10

Chrono waving welcome This is the lab where your clock goes online. After it, your clock can set itself anywhere there is WiFi, with no help from Thonny. Let's make time tick!

What You Will Learn

  • how to keep a password out of your programs
  • what a time server is
  • why joining WiFi sometimes takes more than one try
  • what UTC and time zones are

Before You Start

The Pico needs the name and password of a WiFi network. They go in a file of their own, called secrets.py.

  1. Copy secrets-template.py to a new file named secrets.py. In Thonny, open the template from the kit folder on your computer. Choose File, Save as..., This computer, and type the new name.

  2. In secrets.py, type your WiFi name and password between the quote marks. Then save it.

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

  3. Open config.py and check the line TIMEZONE_HOURS = -6. That is right for US Central time. The table further down lists other zones.

  4. Upload secrets.py to the Pico. With the file open, choose File, Save copy..., and pick the Pico this time. Do the same for config.py if you changed it.

Use a 2.4 GHz network. The Pico 2 W cannot join a 5 GHz one.

Keep Secrets Secret

Chrono warning Never type a password straight into a program, because programs get shared. With the password in secrets.py, you can share every lab and still keep it private. This kit is set up so that secrets.py is never sent to GitHub.

If you did the Connecting to WiFi lab in Learning MicroPython, you have made a secrets.py before.

Run It

  1. Open 10-wifi-sync-time.py in Thonny and click Run.
  2. Watch the small line in the middle of the screen. It reports each step.
  3. When the clock is set, the time appears in big green letters.

The Thonny shell shows the same steps:

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10-wifi-sync-time.py v1.0
Joining your-network-name
IP 10.0.0.99
Asking pool.ntp.org
Time set 10:09:20

The numbers after IP are the Pico's address on your network.

How It Works

Some computers on the internet have one job: telling other computers the exact time. They are called time servers, and they follow rules called NTP, short for Network Time Protocol. The whole conversation happens inside one line of this lab:

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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, and shifts the answer to your time zone. Then it sets the Pico's clock and turns WiFi off again. It answers True if all of that worked, and the if shows the green time.

Joining WiFi can fail on the first try, even with the right password. The program then switches the WiFi radio off and on again, like restarting a stuck game. It tries up to three times, so if you see Try 1 failed, just wait.

UTC and Time Zones

A time server does not know where you live. It answers in UTC, short for Coordinated Universal Time, one shared time for the whole world. Each time zone is a set number of hours away from UTC. US Central time is 6 hours behind, which is the -6 in config.py.

Time zone TIMEZONE_HOURS
Eastern -5
Central -6
Mountain -7
Pacific -8

From March to November, most of the United States moves its clocks one hour ahead. This is daylight saving time, or DST. Central time is then only 5 hours behind UTC. The program works that out by itself:

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def utc_offset_hours(utc_seconds):
    """Hours to add to UTC to get local time, right now."""
    offset = config.TIMEZONE_HOURS
    if config.USE_US_DST and is_us_dst(utc_seconds, config.TIMEZONE_HOURS):
        offset += 1
    return offset

offset starts at -6. On a daylight saving day, is_us_dst(...) answers True, and offset += 1 turns -6 into -5.

Check it on the picture at the top. October 11 is a daylight saving day, so the offset is -5. For the clock to say 10:09 AM, the server must have answered 15:09 UTC, because 15 - 5 = 10.

Try This

  1. When this lab finishes, run lab 09. The time is still right, because the Pico's clock keeps counting until it loses power.
  2. In config.py, change TIMEZONE_HOURS to -8. Save a copy to the Pico and run this lab again. What time does it show? Change it back when you finish.
  3. Do the same with USE_US_DST = False. From March to November the clock loses an hour. In winter nothing changes. Why?

If It Doesn't Work

  • No secrets.py found. The file is not on the Pico. Do step 4 of Before You Start again.
  • Try 3 failed, then a red Not set. Check the name and password in secrets.py. Capital letters matter! Is the network 2.4 GHz?
  • NTP try 3 failed, then a red Not set. The WiFi worked, but the time server did not answer. Your secrets.py is fine, whatever the screen says. Run the lab again.
  • The time is off by exactly one hour. Check TIMEZONE_HOURS and USE_US_DST in the copy of config.py on the Pico.

Your Clock Is Online!

Chrono celebrating You kept a password out of your code and asked a time server for the time. You shifted it from UTC to your own time zone. Next, that time goes onto a clock face with moving hands.

Next: Lab 11: An Analog Clock Face