Group 5 Spr-Sum 2011
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- Batteries Carbon Zinc
- Memory Effect
- Self-discharge (months)
- Rechargeable Batteries NiCad
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Table 3 – Comparison of the displays Selecting a Display – For the purposes of this project, more information must be conveyed on the waist-mounted display than can be handled by a single 7, 14, or even 16 segment LED display, and so we must choose either an LCD or a series of LEDs. The trouble with the LCD is that it requires the installation of a driver into the microcontroller. For the purposes of simplicity in interfacing with the microcontroller, and for maximum performance in a wide variety of locations, we could choose to use multiple LEDs. However, in order to display enough alphanumeric characters, we would have to purchase many LEDs, and this also requires significant real estate on the circuit board, as well as either using many pins, or forming a complex multiplexing scheme. The saturation of oxygen in blood is a percentage displayed as a decimal. The pulse of a human being is at a maximum of a 3-digit number, and any of the statuses require no more than six letters. However, adding more letters than this enables us to display extra information, such as the patient’s name. The added benefit of using an LCD is the ability to have extra characters, and to have preprogrammed characters available, in exchange for slightly more up-front setup. Chosen Displays – The Newhaven NHD-0216K1Z-FS_RGB_FBW is a LCD with a configurable LED backlight and gray text, requiring a 5V source with a maximum power dissipation of 90mW. The LCD is arranged in two rows of 16 characters, with each character preprogrammed by the existing LCD controller into a 5x8 array of dots. The LCD is controlled by 18 pins, 8 of which are addressing pins, 10 of which are control pins. Please see section 3.3.1 for a more thorough display of the LCD display control. 2.3.2 Power Considerations There are several options for powering the system. The most common type of power used in devices is batteries. The disposable batteries consist of one or more electrochemical cells that convert stored chemical energy into electrical energy. Another option is rechargeable batteries also called storage battery which also consists of a group of one or more electrochemical cells. They are also known because of their secondary cells because their electrochemical reactions are electrically reversible. There are several differences and pros and cons of each pick. Disposable batteries are said to be largely used for powering low voltage devices that are not used often. Disposable batteries (primary batteries) also come with different chemical agents such as Carbon Zinc being one of the most common ones. Carbon Zinc works best in low energy depleting devices. Other chemical agents are Alkaline, Super Alkaline, Air Alkaline, Lithium, Silver Oxide and Zinc Air. One of the most popular batteries is the alkaline which come in all the standard sizes. The alkaline batteries include the flat round type that work well in often-used medium to high energy depleting items. There are also super alkaline batteries that last longer for high used devices which can include medical apparatus and photo equipment. In Table 4, we can see the comparisons of primary source batteries.
Table 4 - Primary Source Batteries The other choice is rechargeable batteries (secondary batteries). Nickel Cadmium (Ni-Cads) is the most commonly purchased rechargeable battery. The con is that the disposal of these batteries is hazardous to the environment because of the toxic metals in them. There are also nickel metal hydrides (NiMH) that have good performance and are less toxic to the environment. Alkaline batteries can replace the disposable batteries normally used, are less costly than the Ni-Cad and hold a longer charge but have a shorter life span than NiMH. Below are five of the main types of rechargeable batteries which are Nickel-Cadmium, Nickel-Metal Hydride, Nickel-Zinc, Lithium Ion and Rechargeable Alkaline Batteries. Typical uses of the main types of rechargeable batteries include: NiCad is used for low-drain applications such as electronics (power tools), toys, cordless and wireless telephone and emergency lighting. NiMH batteries are used in electric vehicles, cordless wireless phones, digital cameras, remote controlled racing toys and others. NiZn is used in high drain applications such as flashlights, outdoor equipment and cameras. Li-ion batteries are easy to manufacture in different shapes and are used in laptops, cell phones, PDAs, camcorders, digital cameras among other devices. Rechargeable Alkaline batteries are used in low drain applications such as CD/MD/MP3 players, toys, electronic games, cameras, flash lights, remote controls. In Table 5, we can see the comparisons of rechargeable secondary source batteries.
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