NeoPixel Clock: Seconds

Part of the Projects section of Coddy's Arduino journey. Lesson 21 of 24.

The last project is a clock with no numbers: a ring of 12 NeoPixels, like the 12 hours on a clock face, with each hand a coloured light. Pixel 0 is at the top, at 12 o'clock, and the numbers go round clockwise. Two buttons will set the time.

First the seconds hand. A minute has 60 seconds and the ring has 12 pixels, so the hand moves one pixel every 5 seconds.

seconds % 60 counts 0 to 59 and then starts again at 0, like the seconds on a clock. Whole-number division by 5 turns 0 to 59 into 0 to 11:

unsigned long seconds = millis() / 1000;
int secondPixel = (seconds % 60) / 5;

On each pass of loop(), draw the ring from scratch: ring.clear(), set the hand's pixel, ring.show(). Without the clear, old positions stay lit and the ring fills up. Ten redraws a second are plenty, so the starter ends with delay(100).

Challenge

Medium

The ring is on pin 6. Draw the seconds hand:

work out the seconds since power-on with millis() / 1000
the hand's pixel is (seconds % 60) / 5
clear the ring, light that pixel blue with ring.Color(0, 0, 255), and show it

Keep the delay(100). Press Run and watch the hand go round, then Check.

Try it yourself

#include <Adafruit_NeoPixel.h>

const int ringPin = 6;
const int pixelCount = 12;
Adafruit_NeoPixel ring(pixelCount, ringPin, NEO_GRB + NEO_KHZ800);

void setup() {
  ring.begin();
}

void loop() {
  // work out where the seconds hand is, and draw it in blue

  delay(100);  // redraw ten times a second
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

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