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Electronics Manufacturing – M528

Assignment 1.


Eco friendly watches and their components.


Introduction

Some of the best electronic devices are those that are used by everyone without them even realising that they are there, and timekeeping has been an important aspect of human existence since it was realised that tasks may take a finite amount of time to be accomplished. For these reasons watches have been used in varying forms for many years, an example of an early timing device is Stone Henge. There are many components involved in building a watch, and in recent years this has become much more complicated with the invention of the eco watch.

Originally watches were powered by varying methods, such as weights that stored the energy or the winding of the watch in order to provide the mechanical parts with a continuous power (Howstuffworks, 2007, How quartz watches work). This provides sufficient power for the mechanical parts for short periods of time, as little as one day to a month, which can be a problem if the watch or clock is not regularly wound. This can cause the timepiece to loose time, which is undesirable in a piece of machinery designed for accuracy.

More recently batteries have been used in order to power the quartz oscillating crystal, which is used to regulate the mechanical parts in order to accurately keep the time. Batteries also power various other types of mechanical components and electronic devices such as microprocessors and motors. The problem with this is that the battery will at some point need replacing, and the modern batteries typically last for only five to fifteen years. The other problem is that the disposal of the batteries can also harm the environment, and to be recycled properly it is very expensive to do.

One of the solutions to this problem is the invention of eco watches (Europa Star, 2007, Battery-less watches), this is where the watch is powered by heat, movement or light. These readily available sources of energy are converted to electricity which can be stored by either capacitors or rechargeable batteries. Although this still has the problem of the batteries that may need to be disposed of when the watch is destroyed, this happens less often as the battery is continuously being charged. These eco watches are typically expected to last for a hundred or more years, with the most likely reason of failure due to mechanical failure or the rechargeable battery becoming degraded.

The watch has thus become a mixture of mechanical parts and electronic components working in harmony to keep the correct time. Only the electronic components shall be analysed, however the mechanical aspects of the timepiece are essential for displaying the time. The electronic components of an eco watch are used for gathering energy from external sources, converting it into electricity, storing the collected energy, using the collected energy to power a microprocessor that is in turn used to regulate the quartz oscillating crystal which is used to accurately measure time. The picture below which is sourced from Citizen Watches (2007, How eco-drive works). shows the process of collecting and storing the energy, where the energy is gathered form sunlight.

Solar Watch

The solar cell

It is clear to see from the diagram above that the first stage of this process is to gather the sunlight and convert it from photon energy into electronic energy. The solar panel is often located just under the display panel, which is made out of a material that the sunlight can penetrate. Energex (n.d., Photovoltaic energy) explain that the solar panel or photovoltaic panel consists of many cells, which are made of materials such as silicon. The individual cell is designed with a positive and negative layer to create an electronic field similar to that in a battery. As the photons from the sunlight are absorbed into the cell, their energy causes electrons in the material to become free. The free electrons move to the bottom of the cell and exit through a connecting wire that the electrons flow down. This flow of electrons is the electricity that can be stored by the battery, which will in turn power the watch.

This technology, although not extremely efficient, produces sufficient power for the watch. This technology tends to only be susceptible to area’s where the light source is dim, however this is countered by a long battery life when the battery is fully charged, typically being around 6 months to 2 years. The major benefit of solar technology compared to other eco watch technologies is that the watch does not have to be worn regularly to continue to work effectively, which is extremely useful for household clocks. Another advantage of this technology is that it can be powered by almost any type of light, such as a light bulb, and not just that of light produced by the sun. Below is an image which shows a solar cell used to collect energy from light and convert it into electricity, this image was sourced from Wikipedia (2007, Solar cell).

Solar Cell

Below are some slides from the site Energex (n.d., Photovoltaic energy) that explain how a solar panel such as the one shown above converts light energy into electricity.

Photovoltaic Panel

Photovoltaic Electric Field

Absorbed Photons

Other forms of energy collection

Other forms of energy collection include heat and kinetic. Heat collection is relatively new, and was only used in a commercial watch in 1998, and an article on this technology is displayed by Trends in Japan (1999, One hot timepiece). As it is a new technology producing a watch that works correctly is expensive. The latest model of 1999 retailed for 2,609 dollars (Trends in Japan, 1999, One hot timepiece), however it is expected that prices will reduce as more research is done in this area. The product is susceptible if it is not worn for a period of time, or if the ambient temperature is similar to that of the wrist of the person wearing the wristwatch. This would cause the battery not to charge, and in the long term would stop the watch from working, which is why the battery is designed to power the watch for 10 months when fully charged. The watch also has a conservation mode which is used to extend the battery life when not in use by stopping the hands from moving if the battery has not received charge for a specified length of time, which is controlled by a microprocessor.

The principle behind heat powered watches is that devised by a German physicist called Thomas Johann Seebeck in the 1800’s, and is thus called the Seebeck effect (Trends in Japan, 1999, One hot timepiece). The principle is that if two different types of metal are joined together in the shape of a ring, and if the two different junctions differ in temperature then electrons will flow from the warmer side to the cooler side, forming a generator. The material used to generate the power in an eco watch is two different types of semiconductors. It is believed that this type of watch power source may eventually exceed the efficiency provided by light power in the future, but this will require more research and development.

It is Kinetic energy (wiseGEEK, 2007, What are kinetic watches?) that is far more promising for wrist watches at the moment, as the amount of natural movement involved is sufficient for keeping it in an operating condition. This means that they tend to be better candidates for a ‘battery less’ method of power storage (Europa Star, 2007, Battery-less watches), however it is still possible to use both heat and light powered watches with ‘battery less’ technology. This type of power source is susceptible if it is not worn for a period of time, which is a susceptibility that is not shared by solar powered watches. Another disadvantage is the fact that the generation of energy by this method requires moving parts, which are susceptible to damage due to general wear and tear. The image below sourced from SEIKO (2006, General information on SEIKO watches) shows the kinetic generator and capacitor storage.

Kinetic Generator And Storage

The principle behind kinetic watches is the same as that of electricity production in power stations (wiseGEEK, 2007, What are kinetic watches?). The movement involved in the user’s daily activities causes a weighted device with a magnet attached to rotate. This rotation is surrounded by coiled wire, and as the magnet moves it induces and electric current in the wire, which is in turn used to charge the power storage device or battery. This type of power production is called a ‘micro generator’.

For household clocks that do not move regularly or have a person attached to them generating heat it seems that solar power is the most sustainable and effective way of powering them, unless the desire arises to carry a grandfather clock into work on a daily basis!

The electricity store or battery

The battery is the next electronic component in the chain. Most watches use lithium ion batteries, however capacitors can also be used. For solar powered watches lithium ion batteries are usually the main choice (Europa Star, 2007, Light-powered watches). This is because lithium ion batteries can be made in varying shapes and sizes, so as to efficiently fill available space (Wikipedia, 2007, Lithium ion battery). This is a good trait to have as watches have a limited amount of space due to their size. Other advantages include the fact that lithium ion batteries are lighter than other battery types, such as capacitors. It is very useful to have a light battery, especially in a wristwatch, as if the watch was too heavy then it would loose its appeal due to the effort involved in carrying such a heavy device. The batteries also have a high open circuit voltage, do not suffer from the memory effect (an effect that causes the battery to hold less charge), and have a low self discharge rate. All of these qualities make the lithium ion battery appealing to the manufacturers of watches.

The other main type of energy store is the capacitor. This storage technology is often called a ‘battery less’ storage (Europa Star, 2007, Battery-less watches), as no traditional battery type is used. This is a good technology to include in eco watches as it means that there is no battery that will ever need to be disposed of. Although this type of energy store is economically friendly, it will require the watch the be ‘tuned up’ every 5 to 10 years, and the main capacitor that stores the energy will eventually need to be replaced due to wear. The other main disadvantages of capacitor energy storage are that the amount of energy that can be stored is far less than the amount stored in a lithium ion battery, and the amount of charge required to fully charge the capacitor is far greater than that required by a lithium ion battery. This means that this technology tends to only be used in kinetic watches, where the current produced is much higher than that of solar and heat power. Some manufacturers do use capacitor technology in solar and heat powered eco watches, though the performance tends to be less than that found in kinetic eco watches.

Microchips and circuitry

After this comes various microchip circuits used to regulate the oscillating frequency of the quartz crystal. This helps to maintain the accuracy of the clock. There are many different types of microprocessors that can be used, but they need to be small and accurate. The quartz crystal itself must be maintained at 32,768 Hz (Answers.com, 2007, Quartz clocks), as this frequency is 215 Hz. This means that the electronic circuitry can be simplified to divide down the signal to get the 1 Hz frequency that is used for the one second time base. All that is needed is 15 cascaded ‘divide-by-two’ stages. The reason for 32,678 Hz resonating frequency being used is because of a compromise between the large physical size necessary for a quartz crystal that resonates at low frequencies, and the large current drain that high frequency resonators require from the watch battery.

Due to the introduction of low current consuming microprocessors watches can contain a small embedded micro controller used to count cycles (Answers.com, 2007, Quartz clocks). This ‘embedded computer’ can be used to add extra functionality to the watch, especially in purely digital display watches, where stopwatches and calculators can be added. Digital display watches also use the micro controller to display the correct time by deciding upon the correct segments to light up. The disadvantage of this method of display is that it is ‘power hungry’, and can cause the battery life to be greatly reduced. Also the use of a liquid crystal display or light emitting diodes means that a solar panel cannot be positioned under these sections as the photons would not penetrate through to the solar panel (Wikipedia, 2007, Solar cell). This means that not only is the battery life reduced, but the ability and speed of recharging the battery is also reduced. Although this is a disadvantage when producing an eco watch, the digital display does have several redeeming features. It is generally easier to read the time, especially in reduced light applications and it is easier to add in extra functionality such as stopwatches and calendars.

The oscillating crystal

Quartz crystals are the main timekeeping component as it oscillates (Wikipedia, 2007, Quartz). Quartz it is unaffected by most solvents and remains crystalline at extremely high temperatures. The reason it is used as the oscillating element in watches and timing devices is because when it is compressed it generates a charge on its surface, this effect is called the Piezoelectric effect (Howstuffworks, 2007, How quartz watches work). If a charge is applied to the quartz crystal, the crystal will bend or change its shape slightly. This is the effect that is used to make the crystal oscillate. A charge is applied to the crystal and removed, and the value of the charge determines the frequency at which the crystal will oscillate. This is why when the battery is running low the watch will ‘loose time’, as the frequency will change as the charge being applied to the crystal will be reduced. Quartz has the property of loosing almost no energy, so it only takes a small amount of energy to keep the crystal oscillating. In order to start the crystal oscillating in the first place a charge must be applied and removed, and the resultant electric current must be amplified using transistors and re-applied to the crystal in order to start it oscillating. Below is a picture of a quartz crystal that would be used in order to keep the time in a quartz clock, the image below was sourced from Wikipedia (2007, Quartz).

Quartz Crystal

The output from the oscillating crystal is then converted into pulses, which are suitable to be used and divided down by digital circuits (Howstuffworks, 2007, How quartz watches work). In a quartz watch with hands the divided one second signal is sent to a tiny electronic motor in one second bursts. The motor is connected to various gears and cogs in order to drive the hands on the face of the clock.

Other mechanical or electronic parts

Mentioned earlier are various cogs, gears and miniature electric motors used to make the ‘hands’ of a watch work correctly (Answers.com, 2007, Quartz clocks). There are also other components such as various sound devices used for alarms, usually in digital watches. Occasionally it has been known for manufacturers to include infra red devices, along with other devices such as on board memory for USB storage. These additional components tend to be used as extra functionality, and tend to be included for novelty or an extra selling point. These additional functions have only become more popular with the advances in various other technologies such as micro electronics.

Next steps

The possible next steps for watches include improvements in existing technologies which can be used to improve efficiency and the ‘life’ of the watch. Other improvements include microscopic machines (Sandia National laboratories, 1998, Microscopic machines may replace quartz crystals) replacing the quartz crystal at the heart of the watch. These microscopic machines are being developed at Sandia National Laboratories, a Department of Energy national security lab. These machines are a microelectromechanical system (MEMS), which is a micron sized machine similar to the size of a pollen grain with moving parts. These miniscule machines can perform the same task as an oscillating crystal, and the integration of mechanical parts onto a silicon chip (which is the basis of this technology) would also allow for other mechanical parts to be reduced in size if not substituted completely. This in turn would allow watch sizes to be smaller, functionality to be increased and battery life to be increased, due to the fact that the smaller electronics are likely to use less electricity. Unlike the quartz crystal, the MEMS are excited electro statically and due to this move in a similar way to a tuning fork. Below is a high powered microscope view of the MEMS, sourced from Sandia National laboratories (1998, Microscopic machines may replace quartz crystals), ten of these would fit on a pin head.

Microelectromechanical System

Summary

In conclusion it seems that solar powered eco watches are the most effective eco watches at this point in time, although it seems that heat powered watches may soon catch up or even overtake one day. However for general use it would depend on the situation in which the watch shall be used, if the watch is likely to be in an area of intense heat and light such as a desert then the solar powered watch would be more effective, as the heat powered watch would probably not produce enough electricity. In cooler, darker climates the heat powered watches may dominate, due to the fact that a light source may not provide sufficient energy. However the solar powered option is the overall more useful as for static clocks it is the only viable method of energy production. Solar power also has the ability to produce more energy than it takes to make them (Wikipedia, 2007, Solar cell) unlike in most, however this is disputed by some researchers that believe that this does not fully take into account waste, inefficiency and other related energy costs.

It also seems that there is little distinguishing the current power storage types, due to the fact that capacitors wear out and have a minimal storage capacity, but do not pollute, however lithium ion batteries have a relatively long battery life and storage capacity, but require large amounts of money to recycle. There is a large room for improvement in the energy storage field, although significant increases to battery life can be obtained from decreasing the amount of electricity that various devices consume.

Most of the component in an eco watch come from or are in part made from silicon (Wikipedia, 2007, Silicon). Silicon is used due to its varying traits and good semiconductor properties. Without silicon it would be impossible to manufacture the modern eco watch. This means that silicon is an integral part to the ongoing production of eco watches.

When it comes to manufacturing most of the eco watches today are produced by large companies such as Citizen, Seiko and Pulsar. Citizen and SMH have concentrated on kinetic watches, whereas Pulsar has concentrated on solar power watches. Seiko has branched into both areas, and is doing extensive research into both fields. All of the mentioned brands tend to spend a large amount of money in the research and design of new technologies in this field, and ways of producing ‘smarter’ and more efficient watches. Once the designs have been completed the building of the watch is outsourced to countries such as China where the labour is cheaper. The finished product is then shipped back to the various companies headquarters that tend to be in countries such as America, Switzerland and Japan, where the product receives the company’s brand. The product is then shipped and distributed all over the world for sale. This is a major point in question in the production of the eco watch, as can a watch that is made in countries with cheep labour forces and then shipped usually half way round the world, which causes massive amounts of pollution in the transportation and mining of the raw materials, truly be environmentally friendly?



Reference list

All information has been sourced from the sites bellow. Some of the sites have been used to check information obtained from other sites, and all the information has been read and referenced when used in the text.