Published November 3, 2021 © GPL3+

Gear Clock 2

A 3D printed clock driven by a single stepper motor using gears to separate hours, minutes and seconds.

IntermediateFull instructions provided8 hours872

Things used in this project

Hardware components

Digilent Stepper Motor

28BYJ-48 (5V)

Microchip ATtiny1614 Microprocessor

1N4148 – General Purpose Fast Switching

SOD-323 Package

AO3400 N-Channel MOSFET

SOT-23 Package

Mini USB socket

Surface Mount

0805 Passive Components

4 x 1K OHM, 4 x 10K OHM, 1 x 0.1uF

Hardware

OD3mm L14mm, L22mm, L33mm Metal such as Cu tube or rod; OD4mm ID3mm L6mm Metal such as Al tube for hour hand; M3 t4mm x 6pcs insert nuts such as https://www.aliexpress.com/item/33008141694.html; M3 bolt L8mm 3pcs, L6mm 3pcs; Option: 3mm L50-100mm rod to make it stable.

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

3D Printer (generic)

Soldering iron (generic)

Story

This build replaces the electronics used in the Arduino Gear Clock by Tada3. The Arduino Nano module and ULN2003A stepper motor driver module has been replaced with a ATtiny1614 microprocessor and 4 MOSFETs. All components are surface mount and fit on a board with the same form factor as the Arduino Nano module.

Video

Demo of clock running at 12 times normal speed

3D Printing

There are no changes to the STL files provided by Tada3. You can obtain the files from Thingiverse. Gears that sit on the build plate should be printed on a raft otherwise the first few layers may be bigger than normal due to the heated build plate.

Follow Tada3's instructions and diagrams on how to assemble the clock. You won't need to add the two M3 x 4mm insert nuts for the holder that holds the ULN2003 board that comes with the stepper motor. All the electronics on that board have been replicated on the microprocessor board.

PCB

The Eagle Files have been included should you wish to get the board commercially made or you can make it yourself. I used the Toner method to make mine.

I find it easier to use solder paste rather than use solder from a reel when soldering SMD components.

If your board is single sided, see my Roman Numeral Clock build for the method I use to add pin headers to the copper side of single sided boards.

Processor Board with 4 MOSFETs to drive the stepper motor

Programming

The ATtiny1614 is part of the new breed of ATtiny microprocessors. Unlike the earlier series such as the ATtiny85, the new breed use the RESET pin to program the CPU. To program it you need a UPDI programmer. I made one using a Arduino Nano. You can find complete build instructions at Create Your Own UPDI Programmer. It also contains the instructions for adding the megaTinyCore boards to your IDE.

The USB socket provides power to the clock (5V). The UPDI pin of the ATtiny1614 processor is connected the D+ pin on the USB socket. This allows the programming of the ATtiny1614 using a custom cable. USB Mini plugs are available on eBay or you can cutup an old USB Mini cable.

USB-Mini connector cable for my home-made UPDI programmer

Finishing the clock

I cut the wires from the stepper motor and added a 5 pin female pin header. The PCB should be a tight fit into the holder that originally took the Arduino Nano board.

Views of the finished clock

Conclusion

As a clock, it works but unlike a digital clock with a RTC chip and backup battery, it will stop working when the power is cut. As a project, it was a pleasant and rewarding build. Thanks Tada3 👍👍👍

Schematics

Code

GearClockV2.ino

/**
 * GEAR CLOCK V2
 * 
 * 2021-08-13 Software by Tada3 (https://www.thingiverse.com/thing:4930786)
 * 2021-11-04 John Bradnam (jbrad2089@gmail.com)
 *    - Changed hardware from Arduino Nano to ATtiny1614
 *    - Replaced ULN2003A wih 4 N-Channel MOSFETs
 * 
 * ATTiny1614 Pins mapped to Ardunio Pins
 *
 *             +--------+
 *         VCC + 1   14 + GND
 * (SS)  0 PA4 + 2   13 + PA3 10 (SCK)
 *       1 PA5 + 3   12 + PA2 9  (MISO)
 * (DAC) 2 PA6 + 4   11 + PA1 8  (MOSI)
 *       3 PA7 + 5   10 + PA0 11 (UPDI)
 * (RXD) 4 PB3 + 6    9 + PB0 7  (SCL)
 * (TXD) 5 PB2 + 7    8 + PB1 6  (SDA)
 *             +--------+
 *             
 * BOARD: ATtiny1614/1604/814/804/414/404/214/204
 * Chip: ATtiny1614
 * Clock Speed: 20MHz
 * Programmer: jtag2updi (megaTinyCore)
*/

#include <Stepper.h>

#define IN_1 0 //PA4
#define IN_2 1 //PA5
#define IN_3 2 //PA6
#define IN_4 3 //PA7

const int NUMBER_OF_STEPS =64;
const int RPM =7;
const float GEAR_RATIO = 64;
int csec;

Stepper myStepper(NUMBER_OF_STEPS, IN_1, IN_3, IN_2, IN_4);


//---------------------------------------------------------------------
//Set up clock
void setup() 
{
  myStepper.setSpeed(RPM * GEAR_RATIO / 2.0); // speed for movement
  csec = 0;
}

//---------------------------------------------------------------------
//Main program loop
void loop() 
{ 
  delay(1000-1000/RPM-59);    // delay for 1 min, 1000ms-60000ms/RPM/60-proc.time
  int sStep = (csec % 8 == 0) ? 35 : 34;
  myStepper.step(sStep);  // step for 1 sec, 35x8+34x52=2048
  stopMotor();
  csec = (csec == 59) ? 0 : csec + 1;
}

//---------------------------------------------------------------------
//Stop motor to save power

void stopMotor() 
{
  digitalWrite(IN_1, LOW);
  digitalWrite(IN_2, LOW);
  digitalWrite(IN_3, LOW);
  digitalWrite(IN_4, LOW);
}

Credits

John Bradnam

146 projects • 179 followers

Thanks to Tada3.

Gear Clock 2

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Video

3D Printing

PCB

Programming

Finishing the clock

Conclusion

Custom parts and enclosures

Arduino Gear Clock

Schematics

Schematic

PCB

Eagle Files

Code

GearClockV2.ino

Credits

John Bradnam

Comments

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Gear Clock 2

Gear Clock 2

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Video

3D Printing

PCB

Programming

Finishing the clock

Conclusion

Custom parts and enclosures

Arduino Gear Clock

Schematics

Schematic

PCB

Eagle Files

Code

GearClockV2.ino

Credits

John Bradnam

Comments

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