Building an Electromagnetic Pendulum Clock

An electromagnetic pendulum clock uses a pendulum as its mechanical timebase and a magnet-and-coil system to replace the energy normally supplied by a clock escapement. A sensor detects each swing, a timer or microcontroller schedules a short pulse, and a transistor switches current through the coil. The goal is not maximum magnetic force: it is a small, repeatable impulse delivered at the correct phase of every swing.

This project combines careful construction with basic electronics. Build and stabilize the pendulum first, then add sensing, electromagnetic drive, and finally the clock display.

#	Preview	Product	Price
1		Youngtown Pendulum Clock Movement Replacement Kit with Pendulum 9/10" Shaft	$15.99	Buy on Amazon
2		Youngtown Pendulum Clock Movement Replacement Kit with Pendulum 4/5" Shaft	$12.98	Buy on Amazon
3		Mavdecll DIY Metal Pendulum Wall Clock, 3D Puzzle Mechanical Model	$206.26	Buy on Amazon
4		Abong Laser-Cut Mechanical Wooden Pendulum Clock - 3D Clock Puzzle Model Kit - DIY Wooden Clock Kit	$50.00	Buy on Amazon
5		12888 Westminster Chime Pendulum Clock Mechanism Replacement Kit, 23.5mm	$29.99	Buy on Amazon

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How the clock works

The essential system is:

pendulum → position sensor → timing circuit → MOSFET → coil
    ↓                                             ↑
    └──────────── magnet attached to pendulum ────┘

A permanent magnet is attached to the pendulum. A stationary coil attracts or repels it briefly as it passes. The pulse replaces the small amount of energy lost to air resistance and pivot friction.

This differs from a conventional pendulum clock, where a mechanical escapement transfers energy from a weight or spring. It also differs from a quartz clock: in a genuine pendulum-regulated design, the pendulum is the oscillator rather than a decorative moving part driven by an electronic one-second timer. A microcontroller may count the pendulum crossings and operate a display, but it should not silently replace the pendulum as the timebase.

#1 Best Overall

Youngtown Pendulum Clock Movement Replacement Kit with Pendulum 9/10" Shaft

• Good for repairing, replacing or making a clock.
• Young town manufactures the 12888 series in various models,Please check the dimensions of this movement prior to purchase to verify the dimensions.
• Pendulum type STEP movement, suitable for 9 - 13 mm (9/25 - 1/2 inches) thickness clock panel;Total shaft length: 23 mm ( 9/10 inches), thread length: 15.4 mm ( 3/5 inch).Max Pendulum Swing: 26°;Max Pendulum Weight: 40g ; Max Pendulum Length: 35cm.
• Pendulum type STEP movement, suitable for 9 - 13 mm (9/25 - 1/2 inches) thickness clock panel;Total shaft length: 23 mm ( 9/10 inches), thread length: 15.4 mm ( 3/5 inch).Max Pendulum Swing: 26°;Max Pendulum Weight: 40g ; Max Pendulum Length: 35cm.
• This clock doesn't contain hook, they can't hang directly; If the handle is too long, you can snip them as you want according to the size of the clock panel.

$15.99

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An Arduino-based project documented by Hackaday used the coil to sense the pendulum, applied energy selectively, and converted the motion through a ratchet and gear train. Its reported every-third-pass drive strategy is specific to that design, not a universal rule.

Pendulum length and timekeeping

For a small-amplitude simple pendulum:

T ≈ 2π√(L/g)

Here, T is the complete back-and-forth period, L is the distance from the pivot to the pendulum’s center of mass, and g is gravitational acceleration.

A traditional “seconds pendulum” has an approximately two-second full period and crosses its centerline once per second. The effective length ends at the center of mass, not simply at the bottom of the rod, so a heavy bob and rod mass must be included in the real adjustment.

A longer pendulum swings more slowly and makes fine rate changes easier to observe, but it needs a tall, rigid frame and is more exposed to air currents, temperature-driven expansion, and accidental contact. A short tabletop pendulum is easier to build and enclose; a long pendulum is more visually satisfying but mechanically less forgiving.

Mechanical construction

Build the oscillator first

1. Construct a rigid wood, aluminum, acrylic, or printed frame that cannot twist or rock.
2. Install a low-friction pivot, such as a flexure, knife edge, jeweled bearing, miniature bearing, or polished pin.
3. Fit a light, straight rod and a dense bob with fine vertical adjustment.
4. Measure pivot-to-center-of-mass length.
5. Confirm that the pendulum swings in one plane without lateral movement.
6. Run it unpowered and time 20–50 crossings or several complete cycles.

If the unpowered pendulum stops quickly, fix friction, side play, pivot movement, or frame flex before adding a coil. Strong electromagnetic drive can disguise poor construction without producing a stable clock.

Rank #2

Youngtown Pendulum Clock Movement Replacement Kit with Pendulum 4/5" Shaft

• Good for repairing, replacing or making a clock.
• Young town manufactures the 12888 series in various models,Please check the dimensions of this movement prior to purchase to verify the dimensions.
• Applicable to cross-stitch,three-dimensional embroidery,craft clock,frameless draw clock,etc.INSTRUCTIONS - Included along with the movements.
• Pendulum type STEP movement,suitable for 4-8 mm ( 5/32 - 5/16 inch ) thickness clock panel,total shaft length is 20mm（4/5 inch）,thread length is 11.7 mm (9/20 inch).Max Pendulum Swing: 26°;Max Pendulum Weight: 40g ; Max Pendulum Length: 35cm.
• Package includes 3 pieces of minute hands,3 pieces of hour hands, 3 second hands ,1 second cap and mounting hardware kits, easy for installation; Simple and elegant design, these replacement parts suit well to different styles of clock frame.

$12.98

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Fit the magnet and coil

Secure a small neodymium disc or cylinder magnet to the bob or lower rod. Mechanically retain it rather than relying only on adhesive. Keep steel screws and brackets away from the magnetic path, center the magnet in the swing plane, and provide enough clearance to prevent collisions.

Mount an air-core or nonmagnetic-former coil on an adjustable bracket. The magnet may pass over, beside, or through the coil. Provide adjustment in at least two axes and begin with an air gap of several millimeters. The coil normally belongs near the bottom of the swing, where velocity is highest, but the correct impulse phase depends on coil geometry, magnet polarity, amplitude, and drive direction.

As a hobby starting point, an overview from Position Is Everything suggests roughly 500–2,000 turns of approximately 30–36 AWG enamel wire and about 20–100 Ω resistance on a 5–12 V supply. Treat these as starting ranges, not specifications. The correct coil depends on the magnet, gap, pulse duration, pendulum mass, and driver.

Coil driver circuit

Use a low-side logic-level N-channel MOSFET:

+V supply
   |
  coil
   |
MOSFET drain
MOSFET source
   |
  GND

Add a gate resistor of approximately 47–220 Ω, a gate pull-down of approximately 47–220 kΩ, a flyback diode or faster clamp across the coil, 100 nF ceramic decoupling near the controller, and a larger electrolytic capacitor near the coil supply.

The coil is inductive, not merely resistive. When current is interrupted, its collapsing magnetic field creates a voltage spike. A conventional diode is the simplest protective option, although it allows current to decay relatively slowly. A diode-plus-Zener clamp, TVS diode, or suitable dedicated inductive-load driver can produce faster turn-off while increasing electrical stress. The general principles are explained in Adafruit’s transistor guide and Texas Instruments’ inductive-load reference material.

Rank #3

Mavdecll DIY Metal Pendulum Wall Clock, 3D Puzzle Mechanical Model

• [Superior Quality]: Precision-crafted from durable stainless steel and aluminum alloy, ensuring long-lasting durability. All parts are accurately marked, cut, and organized for a seamless assembly experience
• [Enjoyable and Engaging]: Spark your imagination with this model's amazing level of detail, allowing you to create your own unique masterpiece. Delight in the hands-on fun and enrich your practical and creative skills through a wonderful DIY experience
• [Ideal for Science & Tech Enthusiasts]: Perfect for intellectual enthusiasts who love science, technology, and creativity, this model embodies the beauty of machines and scientific exploration
• [Authentic Assembly Experience]: Immerse yourself in the world of mechanical manufacturing with this model's faithful reproduction of mechanical structures. Explore the principles and applications of machinery while appreciating
• [Thoughtful Gift]: A perfect present for adults, teens, and hobbyists alike—ideal for birthdays, holidays, or any special event. Surprise science lovers, DIY enthusiasts, or anyone with a passion for mechanical art

$206.26

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Estimate coil current before connecting it:

I ≈ V/R

Never connect an unknown low-resistance coil directly to an Arduino output pin. The microcontroller should operate the MOSFET gate; the MOSFET should carry coil current.

Choose the sensor and controller

A Hall sensor is a natural choice when the pendulum already carries a magnet. Use an optical interrupter if the drive field causes false Hall readings. Separating the sensing point from the drive point is often better than making one coil do both jobs: detect a known position, then apply a controlled delay before the impulse.

555 timer

A simple non-programmable design can use a Hall sensor or reed switch, signal conditioning, a 555 monostable, a MOSFET, and the coil. It avoids firmware and is suitable when the clock only needs a fixed pulse. A microcontroller is more convenient for adjustable delay, pulse width, crossing counts, displays, logging, and diagnostics, but introduces software and electrical-noise failure modes.

Microcontroller logic

The controller should detect an edge, reject duplicate triggers, delay the pulse to the calibrated phase, and turn the coil off automatically. Use elapsed-time logic rather than a long blocking delay; see the official Arduino millis() reference.

const byte sensorPin = 2;
const byte coilPin = 9;
const unsigned long lockoutMs = 150;
const unsigned long pulseMs = 30;

volatile bool detected = false;
volatile unsigned long lastEvent = 0;

void sensorISR() {
  unsigned long now = millis();
  if (now - lastEvent >= lockoutMs) {
    lastEvent = now;
    detected = true;
  }
}

void setup() {
  pinMode(sensorPin, INPUT_PULLUP);
  pinMode(coilPin, OUTPUT);
  digitalWrite(coilPin, LOW);
  attachInterrupt(digitalPinToInterrupt(sensorPin), sensorISR, FALLING);
}

void loop() {
  static bool coilOn = false;
  static unsigned long started = 0;

  if (detected && !coilOn) {
    noInterrupts();
    detected = false;
    interrupts();

    // Insert the calibrated phase delay here.
    digitalWrite(coilPin, HIGH);
    started = millis();
    coilOn = true;
  }

  if (coilOn && millis() - started >= pulseMs) {
    digitalWrite(coilPin, LOW);
    coilOn = false;
  }
}

This is an architecture example, not a guaranteed drop-in program. Change the edge, lockout, delay, pulse width, and polarity for the selected sensor and mechanics. Ensure the coil is off during reset and fault conditions.

Rank #4

Abong Laser-Cut Mechanical Wooden Pendulum Clock - 3D Clock Puzzle Model Kit - DIY Wooden Clock Kit

• Craftsmanship: Meticulously designed parts laser cut for accuracy, making it easy to build a handcrafted wooden clock
• Learning Experience: Gain knowledge about the inner workings of a wooden clock, from the pendulum to the minute hand
• Aesthetic Appeal: The comforting sound and mesmerizing movement create a focal point in any room, adding a touch of modern style
• Material: Made of high-quality wood, providing durability and a natural aesthetic
• Customization: Option to personalize the clock with your choice of counterweight material

$50.00

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Bring-up sequence

1. Unpowered pendulum: correct friction, alignment, lateral motion, and frame flex.
2. Sensor only: use an LED, serial log, oscilloscope, or logic analyzer to confirm one clean event per crossing.
3. Coil polarity: apply a very short pulse and verify that it assists rather than opposes the swing.
4. Short drive pulse: start with low energy and increase it gradually.
5. Phase adjustment: move the sensor or add software delay in small increments.
6. Amplitude stabilization: use the smallest pulse that maintains motion.
7. Rate adjustment: raise the bob to speed the clock or lower it to slow the clock.
8. Display integration: add gears, a stepper, or a digital display only after the oscillator is stable.

Change only one variable at a time: pulse width, gap, supply voltage, pulse frequency, or sensor-to-coil delay. If the pendulum stops, reverse polarity or retime the pulse before simply increasing current. A pulse delivered at the wrong phase can brake the pendulum, create unequal left and right swings, or change the clock rate.

Displaying the time

The least disruptive first display is electronic. Count centerline crossings and divide by two when one complete period contains two crossings. This keeps display load away from the oscillator.

A mechanical ratchet and gear train is more authentic but adds friction, backlash, alignment problems, and energy demand. The documented Hackaday build used this approach for seconds, minutes, and hours. A stepper motor can isolate the pendulum from hand and gear loads, while a digital display is simplest but should be described honestly as a pendulum-disciplined electronic clock.

Calibration and accuracy

After the pendulum’s natural period is measured, verify the sensor timing and tune impulse phase. Then adjust the bob in very small increments and compare the clock with a known reference over 12–24 hours. Record temperature, supply voltage, amplitude, and missed or duplicate events.

A carefully tuned hobby build may achieve useful seconds-per-day performance, but that is not a guaranteed specification. Rate is affected by effective length, rod expansion, temperature, air currents, amplitude, pivot friction, electromagnetic phase, supply voltage, and display load. A quartz or GPS-disciplined reference remains the easier choice when precision matters more than the mechanical experiment.

Best Value

12888 Westminster Chime Pendulum Clock Mechanism Replacement Kit, 23.5mm

• 4 Chime Modes - Mode 1: Ave Maria on the hour, then the hour strikes. Mode 2: Westminster at :15, :30 and :45, plus melody and strikes on the hour. Mode 3: Westminster on the hour, then strikes. Mode 4: hour strikes only, no melody. Volume is adjustable; aim the speaker at an opening, as a solid panel in front of it muffles the sound.
• Fit Check Before You Order - Total shaft 23.5 mm (59/64 in), thread 16 mm (5/8 in). Fits dial panels 11-13 mm (0.43-0.51 in) thick and needs an 8.5-10 mm mounting hole. Hands fit dials 8-14 in. across. Pendulum supplied: 150 mm; the movement drives one up to 35 cm and 40 g. Not for full-size floor clocks.
• Hourly Chime, Overnight Pause - The chimes stop after 9:00 pm and start again at 6:00 am. The pause covers the quarter-hour chimes too, applies to all four modes and cannot be adjusted. To stop the chimes at any time, remove the two AA cells from the chime module; the movement keeps time on its own battery.
• What Is in the Box - 12888 pendulum movement, Westminster chime module, 8-ohm 1 W speaker, 150 mm pendulum with 60 mm bob, 2 sets of hands, two second hands (black 100 mm and red 90 mm, fit either), 2 washers and a hex nut, illustrated manual with video. Batteries are not included: you supply 3 AA, two for the chime module and one for the movement. No dial or case; indoor use only.
• Wrong Strike Count? Press SET - SET adjusts the chime module only; it does not move the hands. The first press sets 6:00 and each press after moves ahead one hour, so 10:00 am takes 5 presses. Count presses, not sounds: presses from 10 pm to 5 am are silent but still count. Chiming at night and skipping the day means a 12-hour offset, so press SET 12 times. If the chime lands minutes early or late, refit the minute hand at exactly 12.

$29.99

Buy on Amazon

Troubleshooting

Debug in this order: mechanics, sensor reliability, pulse polarity and phase, pulse energy, display loading, then environmental drift. Do not use extra coil power to compensate for a flexible frame or defective pivot.

Safety and practical purchasing

Use low-voltage DC for a first build and keep mains wiring out of the project. Secure neodymium magnets, protect fingers from gears and pinch points, and install a physical stop while testing. Build the permanent driver on soldered perfboard or a PCB rather than leaving an inductive load on a breadboard.

Typical sources include Arduino boards, sensor and MOSFET modules from Adafruit or SparkFun, precisely specified components from DigiKey or Mouser, mechanical hardware from McMaster-Carr, and magnets from K&J Magnetics. Pololu is useful for an isolated stepper display. Printed brackets can be prototyped with materials from Prusa or Bambu Lab, but use a more stable material or mechanism for the precision pivot.

Check current stock, regional shipping, sensor voltage, MOSFET ratings, coil resistance, and magnet dimensions before ordering. Component ranges and prices are not universal.

Quick Recap

Bestseller No. 1

Youngtown Pendulum Clock Movement Replacement Kit with Pendulum 9/10" Shaft

Good for repairing, replacing or making a clock.

$15.99

Bestseller No. 2

Youngtown Pendulum Clock Movement Replacement Kit with Pendulum 4/5" Shaft

Good for repairing, replacing or making a clock.

$12.98

Bestseller No. 3

Mavdecll DIY Metal Pendulum Wall Clock, 3D Puzzle Mechanical Model

$206.26

Bestseller No. 4

Abong Laser-Cut Mechanical Wooden Pendulum Clock - 3D Clock Puzzle Model Kit - DIY Wooden Clock Kit

Material: Made of high-quality wood, providing durability and a natural aesthetic; Customization: Option to personalize the clock with your choice of counterweight material

$50.00

Bestseller No. 5

12888 Westminster Chime Pendulum Clock Mechanism Replacement Kit, 23.5mm

$29.99

Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.