A digital watch is personal time measurement device that doesn’t use mechanical gears and needles. Time in digital watch is commonly indicated by LED or LCD panel, which is controlled by an accurate timebase.

LED

Light Emitting Diode (LED) is used in many electronic devices and it works by emitting visible light when a current passes through it. Digital watches use seven LED to represent a number and when all LEDs are activated they will form the number “8″, the so-called “seven-segment” can form any number from 0 to 9.

Its main advantages are:

• A long lifespan of about 100,000 hours or over 10 years without the first sign of failure
• Perfectly suited to low light condition
• Very low-power requirement
• Exceptional resistance to shocks

Most electronic devices require DC (direct current) and if only small amount of power needed, battery is a perfect source of DC. LED watches use a small transformer, a device that stabilizes the input voltage to a value suitable for the operation of the LEDs.

LCD

Liquid crystals reflect different wavelengths of light depend on the orientation of the molecules, which also depend on the temperature variation.

Liquid crystals are used for various types of displays, such as digital watches, calculators, small TVs, laptops and others. LCD screens often use less power than traditional CRT displays.

There are several types of liquid crystals used in organic materials: smectic (layered structure) and nematic (liquid birefringent), each of these phases is characterized by a different arrangement of molecules. We can adjust the optical properties of a liquid crystal by applying a magnetic or electric field that changes the orientation of its molecules. For example, if we apply a weak electric field to certain liquid crystals, we observe a color change of the crystal, which changes from a light shade to a darker hue. Consequently, by applying a small amount of DC from battery to a LCD panel, it is possible to display numbers. With the LCD technology, we can display much more than numbers, displaying alphabets and shapes is much easier in a LCD watch.

Digital watches do not use mechanical gears, in fact numbers in both LED and LCD digital watches are determined by a timebase which uses a 60Hz oscillations generated by a crystal oscillator. One Hz usually represents one second and used to trigger changes on the display.