# Hamilton's Early Digital Watch with LED Display

> Hamilton's 1972 patent for a digital watch that uses electronic circuits and light-emitting diodes (LEDs) to show time, instead of gears and hands, powered by a rechargeable battery.

- **Patent:** US 3672155
- **Original title:** Solid state watch
- **Owner:** Hamilton Watch Co
- **Granted:** 1972
- **Status:** Public domain (expired)
- **Times cited:** 118
- **Field:** consumer_electronics, semiconductors, software

## What it does

This patent describes a digital watch with no moving parts for telling time. It uses a crystal-controlled oscillator to create precise timing signals. These signals are then processed by an integrated circuit that divides the frequency and drives light-emitting diodes (LEDs). The LEDs form a digital display, showing hours, minutes, and seconds in base-ten numbers. A key feature is a 'demand switch' that only turns on the LEDs when pressed, saving battery power. Another innovation is an ambient light sensor that adjusts the brightness of the LEDs based on surrounding light conditions. The whole system is powered by a rechargeable battery.

## What it does NOT cover

- Watches that use mechanical gears and hands to display time.
- Watches that use analog displays instead of digital numbers.
- Watches that do not have a crystal-controlled oscillator for timing.
- Watches that do not use light-emitting diodes for display.
- Watches where the display is always on without a demand switch.
- Watches that do not adjust display brightness based on ambient light.

## The clever bit

The invention cleverly combined a stable crystal oscillator with integrated circuits and an LED display, all managed by a 'demand' system and ambient light control, to create a completely solid-state, power-efficient digital watch.

## Real-world examples

1. Hamilton Pulsar (1972)

## Why it matters

This patent represents an early step towards modern digital watches and electronic timekeeping. The Hamilton Pulsar, based on this technology, was one of the first digital wristwatches available to consumers, marking a significant shift from traditional mechanical watches.

## Frequently asked questions

### What does Hamilton's Early Digital Watch with LED Display cover?

Hamilton's 1972 patent for a digital watch that uses electronic circuits and light-emitting diodes (LEDs) to show time, instead of gears and hands, powered by a rechargeable battery.

### Who owns patent US 3672155?

Hamilton Watch Co owns this patent, granted in 1972.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 3672155 cited by?

This patent has been cited by 118 later patents that build on its ideas.

### What problem does this patent solve?

This patent represents an early step towards modern digital watches and electronic timekeeping. The Hamilton Pulsar, based on this technology, was one of the first digital wristwatches available to consumers, marking a significant shift from traditional mechanical watches.

### What does this patent NOT cover?

Watches that use mechanical gears and hands to display time.

**Full plain-English explainer:** https://patentbrief.org/patent/us/3672155/digital-watch-pulsar

**Original patent:** https://patents.google.com/patent/US3672155

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


## Related patents

Semantically similar inventions in the PatentBrief corpus:

- [How Texas Instruments Invented the Handheld Electronic Calculator](https://patentbrief.org/patent/us/3819921/barcode-upc-scanner) — This 1972 patent describes the architecture for the first truly portable, battery-powered electronic calculator that could fit in a pocket.
- [How Liquid Crystal Displays (LCDs) Were Invented](https://patentbrief.org/patent/us/3322485/lcd-liquid-crystal-display) — This 1962 patent describes the first practical way to use organic liquid crystals to create a display that scatters light when an electric current is applied.
- [The First Digital Camera's Core Technology](https://patentbrief.org/patent/us/4131919/digital-camera-electronic-still) — Kodak's 1978 patent on the fundamental technology for capturing, processing, and storing digital images using a CCD sensor and magnetic tape.
- [How Jack Kilby Invented the First Integrated Circuit](https://patentbrief.org/patent/us/3138743/kilby-monolithic-integrated-circuit) — Texas Instruments' 1959 patent for the first integrated circuit, which combined transistors and resistors on a single piece of semiconductor material.
- [The Invention of the Junction Transistor](https://patentbrief.org/patent/us/2569347/junction-transistor) — William Shockley's 1951 patent for the junction transistor, the fundamental building block of all modern digital electronics.