Movement: Release Candidate 2

Sensor Watch: Instructions for the Stock Firmware

Before you Begin

Your Sensor Watch board shipped with a build of Movement, the community firmware for Sensor Watch, preinstalled. While you can build versions of the Movement firmware with any list of watch faces in any order, the version that is preinstalled comes with the following watch faces in the following order:

  1. Simple Clock
  2. World Clock
  3. Sunrise/Sunset
  4. Moon Phase
  5. Temperature
  6. Settings
  7. Time Set

You will navigate through the watch faces in Movement by pressing the Mode button on your Sensor Watch. The Mode button will always advance from the current watch face to the next watch face in the list. When you press Mode while on the last watch face, Time Set, it will wrap around and return to the first watch face.

Most watch faces will remain on screen indefinitely; if you leave Sensor Watch on the World Clock, it will stay there until you press Mode to advance to another watch face. However: the Time Set and Settings faces will “time out” after 60 seconds. When this timeout happens, Sensor Watch will automatically return to the first watch face in the list.

Finally: Sensor Watch enters a low energy sleep mode after one hour of inactivity. This reduces the update frequency from one update per second to one update per minute to save power. Most watch faces will replace the seconds display with a small “tick tock” animation to indicate that they have entered sleep mode. To wake Sensor Watch from sleep mode, you must press the Alarm button. Neither the Mode nor the Light button will wake the watch from this mode.

Simple Clock

The Simple Clock watch face echoes the classic time and date display of the stock F-91W. It displays the day of the week and day of the month on the top line, along with the current time on the bottom line. Pressing the Light button illuminates the LED so that you can read the display in the dark. Holding the Light button keeps the LED on while the button is held.

If you soldered the buzzer connector to your Sensor Watch board, you may also toggle the Hourly Chime feature by pressing and holding the Alarm button. When you release the Alarm button, the Signal indicator will turn on, indicating that the hourly chime is enabled.

The Simple Clock face also incorporates a low battery warning: this watch face will display the LAP indicator when it detects that the battery voltage is low. This does not mean that power failure is imminent, but it does mean that your battery has only about 5% of its original capacity remaining and you should start thinking about a replacement. The battery is a CR2016 coin cell.

World Clock

The World Clock watch face is similar to the Simple Clock face: it displays the day of the month at the top right, and the time in the bottom row. Instead of displaying the day of the week at the top left, you can use the two alphanumeric characters there to title the time zone you wish to display. This requires that you customize the World Clock display:

While on the World Clock face, press and hold the Alarm button to enter customization mode. The first character on the top row will begin to blink. Use the Alarm button to advance through the letters of the alphabet. Then use the Light button to advance to the second character. Again: use Alarm to select a letter, and press Light to move to time zone selection. Finally, use the Alarm button to cycle through the available time zones; then press Light one last time to return to the main display mode.

Note that not all characters are available in position 2; this is a limitation of the F-91W LCD.


When you first see this watch face, it will display “No Loc”, or No Location. This is because your latitude and longitude are required to calculate sunrise and sunset. When on this screen, you can set your location in a similar way to the World Clock screen.

Press and hold Alarm to enter location setting mode. The top line will read “LA” (Latitude), and the bottom line “+ 0000”. The large digits are the whole number part of the latitude, and the smaller digits (in the seconds place) are the fractional part. Enter your latitude and longitude (“LO”) by pressing the Alarm button to change the sign or advance the digits, and the Light button to move to the next character; for example, a latitude of 40.73° N would be “+ 4073”, and a longitude of 73.94° W would be “–07394”.

Once you have set your latitude and longitude, the Sunrise/Sunset face will display the next sunrise or sunset on the bottom row, and the day of that sunrise or sunset at the top right.

A short press on the Alarm button will advance to the following sunrise or sunset: for example, on Monday afternoon, it will display Monday evening’s sunset, but a short press on the Alarm button will display Tuesday morning’s sunrise.

If you made a mistake while entering your location, or if you simply wish to change your location, you can re-enter location setting mode with another long press on the Alarm button.

Moon Phase

The Moon Phase face is similar to the Sunrise/Sunset face: it displays the current phase of the moon, along with the day of the month and a graphical representation of the moon on the top row.

This graphical representation is a bit abstract. The segments that turn on represent the shape of the moon, waxing from the bottom right and waning at the top left. A small crescent at the bottom right will grow into a larger crescent, then add lines in the center for a quarter and half moon. All segments are on during a full moon. Then gradually the segments at the bottom right will turn off, until all that remains is a small waning crescent at the top left.

All segments turn off during a new moon.

On this screen you may press the Alarm button repeatedly to move forward in time: the day of the month at the top right will advance by one day for each button press, and both the text and the graphical representation will display the moon phase for that day. Try pressing the Alarm button 27 times now, just to visualize what the moon will look like over the next month.


This watch face displays the current temperature in degrees Celsius. When the watch is on your wrist, your body heat interferes with an ambient temperature reading, but if you set it on a bedside table, strap it to your bike handlebars or place it outside of your tent while camping, this watch face can act as a digital thermometer for displaying ambient conditions.

The temperature sensor watch face automatically samples the temperature once every five seconds, and it illuminates the Signal indicator just before taking a reading.

Pressing the Alarm button toggles the unit display from Celsius to Fahrenheit.


The Settings watch face allows you to configure various options on your Sensor Watch. Like all other screens, you advance the field you’re setting with the Light button, and advance its value with the Alarm button. The Settings screen labels each setting with a two-letter code on the top row; the following list describes each setting and their options:

CL - Clock mode. This setting allows you to select a 12-or 24-hour clock display. All watch faces that support displaying the time will respect this setting; for example, both Simple Clock, World Clock and Sunrise/Sunset will display the time in 24 hour format if the 24 hour clock is selected here.

BT - Button tone. This setting is only relevant if you installed the buzzer connector, and it toggles the beep when changing modes. If Y, the buzzer will sound a tone when Mode is pressed. Change to N to make the Mode button silent.

TO - Timeout. Sets the time until screens that time out (like Settings and Time Set) snap back to the first screen. 60 seconds is a good default for the stock firmware, but if you choose a custom firmware with faces that you’d like to keep on screen for longer, you can set that here.

LE - Low Energy mode. Sets the time until the watch enters its low energy sleep mode. Options range from 1 hour to 7 days, or Never. The more often Sensor Watch goes to sleep, the longer its battery will last — but you will lose the seconds indicator while it is asleep. This setting allows you to make a tradeoff between the device’s responsiveness and its longevity.

LT - Light. This setting has three screens:

On the last two screens, the LED remains on so that you can see the effect of mixing the two LED colors. On the Special Edition boards, you’ll have red, blue and a variety of shades of pink and purple to experiment with!

Time Set

The Time Set watch face allows you to set the time on Sensor Watch. Use the Light button to advance through the field you are setting, and the Alarm button to change the value in that field. The fields are, in order: Hour, Minute, Second, Year, Month, Day and Time Zone.

For features like World Clock and Sunrise/Sunset to work correctly, you must set the time to your local time, and the time zone to your local time zone. This allows Sensor Watch to correctly offset the time. This also means that when daylight savings time starts or ends, you must update both the time and the time zone on this screen.

Before you Go

You are not limited to the stock Movement firmware! You can load a custom build of Movement on to Sensor Watch by plugging the bare circuit board into USB and double tapping the tiny “Reset” button on the back of the board. When you do this, the blue LED will begin to pulse, and a drive called “WATCHBOOT” will appear on your computer. You can drag firmware in the UF2 format onto this drive, and this new firmware will replace the existing firmware on the watch.

Check out for more information about Movement, and for some custom builds tailored to individual use cases.

Original F-91W SVG is © 2020 Alexis Philip, and is used here under the terms of the MIT license.