Arduino "analog" (analogue!!) clock.

I conceived this daft project a while back, after being given a box of surplus moving coil meters...

An Arduino driving three analogue meter movements to show hours, minutes and seconds.

There are lots of designs on the net, so here's another.

Now, I'd seen several clock designs on the net, whereby the Arduino's PWM signal is used to keep accurate time. I must say, whilst the idea is sound, most of the stuff I got hold of and downloaded didn't work for one reason or another.

The idea goes like this...

We couple the PWM output of a pin to an interrupt. We set the PWM output going with a mark to space ratio of 50%. The PWM frequency is governed by the internal architecture of the ATMEGA328, and is derived by some programmable timers, which divide down the clock frequency of the micro. The clock frequency on "posh" arduino boards is generated by a nice crystal (on not-so-posh boards, it may be a ceramic resonator, not so accurate). 16MHz. So dividing down this 16MHz should give quite a low error. Good news. So all we need to do is set up an interrupt, so that every time it sees a rising edge of our PWM signal, it increments a counter.

I measured the frequency of the PWM signal, and on a crystal clocked board, with a ATMEGA328P at 16MHz, it's 490.36Hz. (Due's/ Mega's etc will vary as the micro/clock frequency is different).


Excellent, so all we need to do is add a second on every time our counter hits 490 (Let's forget about the 0.36, shall we?). It should keep reasonable time.


After running for a day or so, the drift (caused by the 0.36 Hz left over) does become noticeable, but I recon it's no worse than a DS1307 RTC. So, to correct for this drift, I'll add in a 433MHz radio receiver module, and make it updatable from the GPS Master Clock project. Excellent.

So after a bit of tinkering this was born...

I've added three momentary push buttons, which allows the time to be set manually, and a "Cal" button. Once cal is pressed, the PWM output is switched off for 10 seconds, and then set to 100% for 10 seconds. This allows the user to set the zero mechanically on the meters, and the FSD (Full scale deflection) on the meter using the three pots, R7,R9 and R11. All three of my meters require 1mA for FSD, yours may vary, and you can alter the value of R7, R9 and R11 to suit your meters.

Each meter is driven by a small transistor. With my meters needing just 1mA, there's absolutely no reason why I couldn't just eliminate the transistor and drive the meters directly from the output of the micro to ground. I've added them in, just in case I need some more current, or decide to drive them from a higher voltage source than 5V. 

There's two toggle switches too... 

The 24 hour select switch changes the hour display from 0-24 hours to 0-12 (actually 12:00 or 0:00 is 0 on the meter, but it'll make sense in a minute)

The smooth select switch I'm rather pleased with. I started out wanting the seconds meter to move smoothly, rather that "tick" once a second. I coded this, and then thought I'd apply the same to the hours and minutes. This has one very pleasing effect. All the meters are moving smoothly. so the hour meter will read halfway between 1 and 2 when it's 1:30 ... same with the minutes. It also means that FSD on the hours meter occurs at 23:59 (in 24h mode or 11:59 in 12h mode), rather than going straight from 23 to 0 ..... 

Now, one big issue is daylight saving time. My master clock transmits GMT. I've added a routine that detects BST (British Summer Time) and adds an hour on if required. I've blatantly stolen this routine from here, , and modified it because I'm avoiding the time.h library (although I've no reason too!).

So a prototype is created....

Some meters selected, and calibrated ...

... and a clock created!...



Here's the code ... /* Another stupid clock project. (c) A.G.Doswell 2017 License: The MIT License (See full license at the bottom of this file) PWM referenced clock, driving 3 analogue moving coil meters, set up to read hours, minutes and seconds. Has remote 433 MHz receiver for reception of remote time sync signal from master clock project See http://www.andydoz.blogspot.com/ for more information and the circuit diagram. */ int clockInt = 0; // Digital pin 2 is now interrupt 0 int masterClock = 0; // Counts rising edge clock signals int seconds = 0; // Seconds int minutes = 00; // Minutes int hours = 00; // Hours int secondsAnaloguePin = 3; // Output pin for the Seconds driver circuit and meter int minutesAnaloguePin = 5; // As above for minutes... int hoursAnaloguePin = 6; // ... and hours int calPin = 7; // Calibration push button connects here and ground int minAdjustPin = 8; // Minutes adjust button to pin 8.... int hoursAdjustPin = A2; // ... and hours to A2 int twentyFourHourPin = 14; // 24 hour mode selct switch connects to A0 int smoothSelectPin = 15; // Smooth mode select switch connects to A1 int displayHours; // Actual hours displayed, this is to take care of the 24h mode. unsigned long totalSecondsHour; // Used in smooth mode, humber of current seconds in the hour unsigned long totalSecondsMinute; // Used in smooth mode, current seconds in a minute unsigned long smoothSeconds; // Used in Ssmooth mode. Number of clock "ticks" in a minutes worth of seconds. // set up for remote master clock #include <VirtualWire.h> // available from https://www.pjrc.com/teensy/td_libs_VirtualWire.html #include <VirtualWire_Config.h> int rxTX_ID = 1; //rx indicates remotely received data int rxHours; int rxMins; int rxSecs; int rxDay; int rxMonth; int rxYear; char buffer[5]; void setup() { pinMode (secondsAnaloguePin, OUTPUT); pinMode (minutesAnaloguePin, OUTPUT); pinMode (hoursAnaloguePin, OUTPUT); pinMode (calPin, INPUT_PULLUP); // cal switch connected to pin 7. This allows FSD on meters to be set pinMode (minAdjustPin, INPUT_PULLUP); // Minutes adjust switch pinMode (hoursAdjustPin, INPUT_PULLUP); // Hours adjust switch pinMode (twentyFourHourPin, INPUT_PULLUP); // 24 hour clock mode switch pinMode (smoothSelectPin, INPUT_PULLUP); // Smooth select switch attachInterrupt(clockInt, clockCounter, RISING); // clockInt is the interrupt, clockCounter function is called when invoked on a RISING clock edge analogWrite(11, 127); // This starts our PWM 'clock' ticking with a 490 Hz 50% duty cycle vw_set_tx_pin(12); // Even though it's not used, we'll define it. vw_set_rx_pin(13); // RX pin set to pin 13 vw_setup(1200); // Sets virtualwire for a tx rate of 1200 bits per second vw_rx_start(); // Start the receiver } void clockCounter() // Called by interrupt, driven by the PWM { masterClock ++; // With each clock rise add 1 to masterClock count smoothSeconds ++; // Used to develop smooth seconds if (masterClock >= 490) // 490Hz reached { seconds ++; // Add 1 second masterClock = 0; // Reset } return; } void updateClockDisplaySmooth() { totalSecondsMinute = (seconds + (minutes * 60)); //Number of seconds in the current minute totalSecondsHour = ((seconds / 10) + (minutes * 6) + (displayHours * 360)); // Hours as seconds divided by 10, so as not to exceed a 16 bit unsigned integer int x = map(smoothSeconds, 0, 29400, 0, 255); // Map smoothSeconds to 8-bit value analogWrite(3 , x); // Update PWM x = map (totalSecondsMinute, 0, 3600, 0, 255); // Map and update PWM for minutes analogWrite(5, x); if (digitalRead (twentyFourHourPin) == true) { x = map (totalSecondsHour, 0, 8640, 0, 255); // Map and update the PWM for hours, conditionally on 24h mode. } else { x = map (totalSecondsHour, 0, 4320, 0, 255); } analogWrite(6, x); } void updateClockDisplayCoarse() { int x = map(seconds, 0, 59, 0, 255); // Map seconds to 8-bit value and update PWM analogWrite(3 , x); x = map (minutes, 0, 60, 0, 255); // As above for minutes.... analogWrite(5, x); if (digitalRead (twentyFourHourPin) == true) { // ... and hours, conditionally on 24h mode. x = map(displayHours, 0, 24, 0, 255); } else { x = map(displayHours, 0, 12, 0, 255); } analogWrite(6, x); } void remoteClockSet () { // Remotely sets the clock typedef struct rxRemoteData //Defines the received data, this is the same as the TX struct { int rxTX_ID; int rxHours; int rxMins; int rxSecs; int rxDay; int rxMonth; int rxYear; }; struct rxRemoteData receivedData; uint8_t rcvdSize = sizeof(receivedData); if (vw_get_message((uint8_t *)&receivedData, &rcvdSize)) // Process message if received { if (receivedData.rxTX_ID == 1) { //Only if the TX_ID=1 do we process the data. int TX_ID = receivedData.rxTX_ID; int rxHours = receivedData.rxHours; int rxMins = receivedData.rxMins; int rxSecs = receivedData.rxSecs; int rxDay = receivedData.rxDay; int rxMonth = receivedData.rxMonth; int rxYear = receivedData.rxYear; if (isBST() == true) { // Is it British Summer Time? rxHours = rxHours + 1; } // Set the clock hours = rxHours; minutes = rxMins; seconds = rxSecs; } } } boolean isBST() // this bit of code blatantly plagarised from http://my-small-projects.blogspot.com/2015/05/arduino-checking-for-british-summer-time.html { int imonth = rxMonth; int iday = rxDay; int hr = rxHours; //January, february, and november are out. if (imonth < 3 || imonth > 10) { return false; } //April to September are in if (imonth > 3 && imonth < 10) { return true; } // find last sun in mar and oct - quickest way I've found to do it // last sunday of march int lastMarSunday = (31 - (5 * rxYear / 4 + 4) % 7); //last sunday of october int lastOctSunday = (31 - (5 * rxYear / 4 + 1) % 7); //In march, we are BST if is the last sunday in the month if (imonth == 3) { if ( iday > lastMarSunday) return true; if ( iday < lastMarSunday) return false; if (hr < 1) return false; return true; } //In October we must be before the last sunday to be bst. //That means the previous sunday must be before the 1st. if (imonth == 10) { if ( iday < lastOctSunday) return true; if ( iday > lastOctSunday) return false; if (hr >= 1) return false; return true; } } void loop() { remoteClockSet (); if (seconds >= 60) { // Put down your knitting grandma, the real timekeeping starts here minutes ++; // Increment minutes by 1 seconds = 0; // Reset the seconds smoothSeconds = 0; } if (minutes >= 60) { hours ++; // Increment hours minutes = 0; // Reset minutes } if (hours >= 24) { hours = 0; } if (digitalRead (twentyFourHourPin) == true) { // If the 24 hour select is true, then set the display hours displayHours = hours; } else { // If 24 hours is not selected, set the hours conditionally set the display hours - 12 if (hours >= 12) { displayHours = hours - 12; } else { displayHours = hours; } } if (digitalRead (smoothSelectPin) == true) { updateClockDisplaySmooth (); } else { updateClockDisplayCoarse (); } if (digitalRead (calPin) == LOW) { // Cal button pressed analogWrite (3, 0); // Sets all meters to 0% to set zero for 10 seconds analogWrite (5, 0); analogWrite (6, 0); delay (10000); analogWrite (3, 255); // Sets all meters to 100% to set FSD for 10 seconds analogWrite (5, 255); analogWrite (6, 255); delay (10000); } if (digitalRead (minAdjustPin) == LOW) { // Minutes adjust switch detachInterrupt (clockInt); // Temporaily stop the clock running seconds = 0; // Zero the seconds, so if the display is set to smooth, it's setting is not confused by the seconds count smoothSeconds = 0; minutes ++; // Increment minutes updateClockDisplayCoarse(); // Update the display as coarse, regardless of switch setting delay (750); attachInterrupt(clockInt, clockCounter, RISING); // Restart clock } if (digitalRead (hoursAdjustPin) == LOW) { // Hours adjust switch detachInterrupt (clockInt); // Temporaily stop the clock running seconds = 0; smoothSeconds = 0; hours ++; // Increment hours int minutesTemp = minutes; // Temporarily store the minutes minutes = 0; // Zero the minutes, just so the hours display is not confused during setting by a high number of minutes, if the display is set to smooth updateClockDisplayCoarse (); // Update the display as coarse, regardless of switch setting delay (750); minutes = minutesTemp; // Restore the correct minutes. attachInterrupt(clockInt, clockCounter, RISING); // Restart clock } } /* Copyright (c) 2017 Andrew Doswell Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute and sublicense copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. Any commercial use is prohibited without prior arrangement. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESerial FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHOR(S) OR COPYRIGHT HOLDER(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */