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Digital Watch

Digital Watch

Put the power of time into your watch. Let’s code up a real digital watch for your micro:bit!

Duration: ~20 minutes

Make the time variables

We need to make some variables to keep track of the time and for a few other things.

  • Go into Basic in the toolbox and pull an on start on to the workspace.
  • Ok, in Variables click on Make a Variable. Name the variable as hours. Drag out a set to block and change the name with the dropdown to hours. Place the variable into the on start block.
  • Repeat this 4 more times to make variables named minutes, time, adjust, and ampm.
  • Now, for the set to block for time, go to Text and drag a " " in and replace the 0.
  • For the ampm variable, change the 0 there to a false from the Logic catagory.

Display the time, kind of

So, let’s try showing the time on the display. We aren’t keeping time yet but we’ll just see if we can make our watch show something.

  • Get in the Input catagory and pull out an on shake. We’ll have our watch show the time when it’s shaken.
  • Get another set to and put it into the on shake. Change the name to time.
  • Replace the 0 with a join from Text. Get another join and put it into the second slot of the first join you pulled out.
  • Change the " " in the first join to the hours variable. Change the text in the first slot of the second join to ":". And, change the last slot in the second join to the minutes variable.
  • Finally, stick in a show string below the set to. Switch the text inside to the variable time.
  • Download the code to you micro:bit and give it a shake. Did you see the time of “0:0” go by on the LEDs?

Set the time with buttons

There has to be a way to set the time on your watch. We’ll use the buttons to set the current time. One button is for setting the hours and another button is for the minutes.

Set the hours

Let’s make a way to set the hours for the watch.

In Input, find an on button pressed an put it somewhere on the workspace. Get an if then else block from Logic and put it in the on button pressed. From the same Logic category, get a 0 < 0 and relpace the false condition with it. Change the left 0 in the condtion to the hours variable. Change 0 on the right to 23. This limits our hour count to 23 hours. In the then section, put a change by there. Select the hours variable name from the dropdown. In the else section, put a set to there. Select the hours variable name from the dropdown and leave the 0.

Set the minutes

Setting minutes is almost the same as setting hours but with just a few changes.

To make things easy, right click on on button pressed block and select the Duplicate option in the menu. This makes a copy of the original block. In the new on button pressed, change the button to B. Change every variable name from hours to minutes. Change the 23 in the if condition to 59. This is the limit of minutes we count.

Select 24 hour or 12 hour time

Time is shown in either 24 hour or 12 hour format. We’ll use one more button to choose which format to show. Using the 12 hour format adds an ‘AM’ or ‘PM’ at the end.

  1. In Input, get an on button pressed an put it on the workspace. Change the button to A+B.
  2. Grab a set to, put it in the block and change the variable to ampm. Put a not from Logic in where the 0 is.
  3. Pick up a ampm from Variables and connect it on the right of the not. This switches our 24 hour format to 12 hour and back.

Make the timer tick

A watch really has three parts: the display, settings, and timer. We need a way to make the minutes and hours count up at the right time. Let’s code the timer.

In Basic, get a forever loop out to the workspace. Also in Basic, take out a pause an put it into the loop. Change the time from 100 to 60000. The time is in milliseconds so we want to count each minute every 60000 milliseconds. Below the pause, put a if then else block. Change the condition in the if to use a 0 < 0. Replace the 0 on the left with the minutes variable. Change the 0 on the right to 59. Put a change by into the then. Change the variable to minutes. Get a set to and put it in the else. Again, change the variable to minutes.

Keep on coding…

Now, take another if then else and put it just below the set to inside the first else. In the second if, put in a 0 < 0 as the condition. Replace the left 0 with the hours variable. Change the right 0 to 23. We count hours up to 23 until we go back to 0 (midnight). Put a change by into the second then. Change the variable to hours. Get a set to and put it in the second else. Again, change the variable to hours. Ok, the timer’s ready to tick.

Shake and show…the time!

We’re going back to the display code we made earlier. We’ll now make it show the real time! This step is going to be busy but we’ll get it done.

First, we have to code an adjustment for the hours number when we’re using the 12 hour format.

  1. Find the on shake block we coded earlier. Pull out and drag to the trash the blocks inside. We’re starting fresh.
  2. Pull out a set to an put it inside the on shake. Change the variable to adjust. Change the 0 on the right to the hours variable.
  3. Get a if then and put it under the set to. Replace the condition with the ampm variable.
  4. Grab a if then else and put it in the then part of the first if then. Change the condition to 0 < 0. Replace the 0 on the left with the hours variable. Change the 0 on the right to 12. Switch the < to a >.
  5. Go get another set to and put it in the then of the second if then else. Change the variable to adjust. In Math take a 0 - 0 and replace the 0 in the set to. Change the 0 on the left to the hours variable and the 0 on the right to 12.
  6. Take one more if then and put it in the else. Change its condition to 0 = 0. Put the hours variable in place of the 0 on the left.
  7. Inside this last if then place a set to. Change the variable name to adjust and set the value to 12.

Keep on coding…

Now, we have to join up the hours and minutes to make text that will display on the watch.

  1. At the bottom of the on shake, insert a set to. Change the variable name to time. Connect it to a join from Text.
  2. Make 3 copies of this last set to using the Duplicate option in the menu when you right click on the block. Put the copies underneath each other so that all 4 are stacked together.
  3. In the first set to, replace the second "" in the join with the adjust variable.
  4. With the second copy, change the first "" in the join to the variable time. Change the second string in the join to ":".
  5. In the third copy, change the first "" in the join to the variable time. Change the second string in the join to division operator from Math. Set the left 0 to the minutes variable and the right 0 to 10.
  6. In the fourth copy, change the first "" in the join to the variable time. Change the second string in the join to a remainder of in Math. Set the left 0 to the minutes variable and the right 0 to 10.

Keep on coding…

Ok, we’re getting close to finishing now. Here we need to add the ‘AM’ or ‘PM’ if we are in 12 hour format. Then, finally, display the complete time string.

  1. Put an if then block at the end of the on shake. Replace the true condition with the variable ampm.
  2. Insert a if then else into this if then. Use a 0 < 0 as the condition. Change the left 0 to the hours variable. Change the right 0 to 11. Switch the < to a >.
  3. Place a set to in the then. Change the variable to time and attach a join. Make the first part of the join be the variable time and the second part to the text "PM".
  4. Do the exact same thing as in the last step but put the set to block in the else underneath. Make the second part of the join be "AM" this time.
  5. Finally, at the very bottom of on shake, go get a show string from Basic and put it there. Change the string "Hello!" to the time variable.

Link: https://makecode.microbit.org/_XAtJ8kUTwTpY

Complete!

Wow, so awesome! You’ve got your watch coded and ready to try. Go press the Download button and put your code on the micro:bit. When you shake it, it shows the current time.

Right now, it’s showing 24 hour format: hours go from 0 to 23 and back to 0. Press the A+B buttons together to change to 12 hour format: hours go from 12 to 12 with 1 through 11 in between. It has either "AM" or "PM" at the end.

To set it to the current time, you use the A and B buttons. The A button moves the current hour up by one each time it’s pressed. The B button moves the minutes up by one every time it’s pressed.

Now that you can tell time on your micro:bit who knows what you will accomplish next. Only, time will tell!