How does a Quartz Watch Works?

  

    Time is the leader of the universe. It describes everything. This time, makes us to know our universe better. From the big bang theory to Einstein’s relativity and to all scientific researches depends upon time. Such a time, now rest in our walls and wrist, as clocks and watches. Clocks and watches are ingenious pieces of invention. Without knowing the time we will not know when we are starting and where we are ending. So such a device marks a remarkable place in our life.

    There are various types of clocks and watches used in human history, namely, gravity clocks (pendulum clocks), mechanical watches, automatic watches, quartz watches, digital watches, and smart watches. Except for the pendulum, mechanical, automatic watches and all other watches share the common principle of working. Only the output displayed will be varied. We will take an overview of everything and take a deep look over the quartz watches which are widely used nowadays.

    Over the past, pendulum clocks were very popular. Its timings were also mostly accurate. These clocks use the power of gravity to move the gears. The gravity pushes the weight downwards which is connected to the escapement wheel controlled by the pendulum. Through the process of the escapement wheel, the second-hand moves. The pendulum is either moved by the gravity of the weight or through magnetic power (in the case of an electromagnetic pendulum) or through quartz power. In the case of quartz power, there is no need for a pendulum. But it is now designed in such a way as a decorative element. The mechanical and the automatic watches use a winding spring that rotates several gears sets by unwinding. When unwinded the spring must be winded again to run. Mechanical watches spring must be wounded manually, to make it run for certain days. So after a certain number of days, it must be manually winded again by us. While automatic watches springs are wounded automatically by the rotation of the rotor inside the watch. It is due to the kinetic energy of the movement of the watch. Automatic watches can also be wounded manually.

Mechanical Watch

    When coming to the quartz watches the situation becomes different. There is no spring or not so many gears and components. Quartz watch purely depends upon the electrical signals in turning up a motor to move the second's hand. We can differentiate the quartz between mechanical and automatic watches by the movement of the second's hand. In the mechanical and automatic watches, the second's hand moves through smoothly as the spring delivers the power continuously by unwinding. But in the case of quartz watches, the stepper motor moves step by step, which gives the second's hand a gap for every movement. But modern quartz watches also deliver smooth sweeping second’s hand by increasing the pulsing rate to the motor and by changing the gear appearance. We’ll see about the pulsing rate later in this article.

    As we know, that all the watches have 3 sticks for representing the time. One is the second's hand, the next one is the minute's hand and the other one is the hour's hand. If the second's hand makes one 360° rotation (60 seconds) the minute's hand moves one minute, and if the minute's hand moves 360° rotation (60 minutes), the hour's hand moves by one hour. The main target is to move the second's hand at a certain speed, which makes the minute's and hour's hand to move at a correct pace. In quartz watches, this is made to done by a series combination of gears, electromagnets, and quartz material, which makes the name quartz watch. Let’s now see the operation of the quartz watch by understanding the pulsing rate. Here I had attached a sample video of the operation of the Quartz clock, 

    Quartz is a piezoelectric material, which is a kind of material that produces an electric voltage at the output, when mechanical stress is given at the input. Similarly, when an input voltage is given at the input, a mechanical stress in the form of vibration is given at the output. It is basically a transducer that converts one form of quantity into another form. In clocks, this vibration is produced by an incoming battery voltage (electrical stress to mechanical stress). This vibration is made at a certain frequency, such that the generated alternate voltage (mechanical stress to electrical stress) is given to a microchip which is coated with epoxy in the PCB board and stored in it. 

 

Quartz Crystal

    

Microchip

    This microchip is the storage of many circuitries, among which the flip flops are the important ones. When the generated frequency of 32,768 Hz from the quartz material is given to the chain of flip flops it gets ON and OFF at a certain pattern that the last flip flop sends an output signal (pulsing) for every one second. The frequency should be exactly 32,768 Hz or 2^15 Hz. This number should be exact, as humans could not hear sounds above 20,000Hz. But dogs, cats, and other animals can hear this frequency. Also, 2 is the first power to generate a minimum frequency that is greater than 20000Hz. Other powers generate very high frequency which requires more power. Even if we generate higher frequency or lower frequency, the last flip flop produces a one-second flip or flop (ON or OFF) only at the 32,768 Hz. Only the switching speed varies in a higher frequency range. So the power of 2 is chosen due to the ON and OFF logic of flip flop.   

Stepper Motor

    Thus the output signal from the last flip flop is given to a stepper motor, which rotates the gear assembly according to it. The stepper motor is present with an electromagnet and a permanent magnet that repels each other at an interval of one second. As we saw before, that the last flip flop ON or OFF (flips or flops) per second, can be said in the power of 2 as 2^0; which is 1. So the first flip flop must be at the position of 2^15. Thus there is a combination of 15 flip flops in the microchip with each switching speed varies. The property of the flip flop is, that it stays in a position whether ON or OFF, till the signal cuts off. Now let’s understand the working in the chain of flip flops with a neat diagrammatic representation.

 

Square Wave Signal

   

    Now as the first signal comes IN and switches to “OFF”, the first flip flop flips to the “ON” position. And again when the next “OFF” signal comes, the flip flop flops to the “OFF” position. When the output of the first flop is taken and given to the second flip flop, the switching speed decreases. This is due to the reason that the second flip flop switches “ON” or “OFF”, only when the first flop turns “OFF”. So the switching frequency decreases. In a progression of 15 flip flops, the switching frequency decreases for each flip flop. If the first flip flop switches “ON” 32,768 times per second, then the last flop turns “ON” once per second; which is the desired pulsing rate for moving the second-hand gear. 

Operation of Flip Flop

Different time intervals of Flip Flop

    In the case of digital watches, the output of the quartz power is given to drive an LCD display. Now let’s look through the dissection of a quartz clock and take over the ingenious mechanism of the alignment of the gears and accessories.

Note: For clear understanding and identification each gear is coated with different colors

    Here we can see the output of a quartz clock which consists of many gears of various sizes.  So all those PCB boards, quartz material, stepper motor, electromagnet's job is to make the second's hand gear to rotate at a one-second pace. The remaining all gears rotation depends upon another gear rotation.

Full Setup of Quartz Clock

   

Second's hand gear

   Now as the stepper motor rotates the first yellow gear, it turns the biggest orange gear directly which is connected to the second's hand. As the orange gear rotates, it rotates the blue gear, which rotates the gear assembly present under the top layer. Now the blue gear rotates the minute's hand gear which is connected to the minute's hand; such that for every rotation of the second’s hand gear, the minute's hand gear rotates at a single minute pace. 

   

Minute's hand gear

    

    

    

    

    Now the minute's hand rotation is passed through the violet gear, which you can observe from the below picture.  This gear rotates the hour's hand gear every single hour pace for every single rotation of the minute's hand gear.

   

    In the case of the alarm quartz clock, there will be an addition of two more gears; an alarm-hand, and a speaker to sound. Now as you can see in the picture, whenever the holes in the alarm gear match with the holes in the hour gear, the alarm turns “ON”. In other words, as we set the alarm (for example 4’O clock) the alarm gear holes are set at one place. Now when the time runs, the hour's hand holes, match with the holes in the alarm gear, which releases the small gear to set, and makes the connection with the plate and the PCB board, to sound the speaker.

    

    The important thing that needs to be considered in making clocks and watches is the error rating. All the timepieces have errors. Pendulum and mechanical watches have more errors than quartz watches. So the main objective in making watches is to minimize the error rating. Quartz watches make a smaller error of 2 seconds every year. These errors are negligible in daily life purposes. But for important applications like location determination, guiding space shuttles and satellites; precise timing is required without any errors. For that purpose, atomic clocks are used. Atomic clocks have microseconds of errors for thousands of centuries.

    But even though atomic clocks have the lowest error rating, it too uses the quartz material for the frequency generation. So the frequency may vary sometimes. Thus caesium atoms are used for keeping the frequency steady. If the frequency generation varies by the quartz crystal, the caesium atoms move to a higher energy state which is detected by a detector, and the crystal is made to vibrate at a steady frequency by applying more or less power to the crystal. By this procedure, we can achieve a stable error-free timing for centuries.