Computer Engineering Projects I by qza17959

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									    Computer Engineering Projects I
Remote Visual Surveillance Vehicle: (RVSV)
      Independent Learning Project
           Manoj Bhambwani
                  5/5/04
Project Description:

        The Remote Visual Surveillance Vehicle (RVSV) is a radio-controlled vehicle
that provides the user at a PC with visual feedback. The user controls the vehicle’s
direction and the camera positioning through an Internet interface The RVSV provides
the visual feedback using an camera which is mounted to the vehicle. The camera
transmits the video data to router or access point which supplies it to the user through an
Internet connection.

Project Subsystems:

        The subsystem described in this report is the power subsystem. Since the RVSV is
completely wireless, power consumption is a major concern. All the power must be
provided using batteries and therefore the systems on the vehicle must be designed to
perform under a range of voltages and consume less power. In this report different battery
types will be explored, and methods of designing low-power devices will also be
investigated.
        The next major subsystem in this project is the communications system. The
communications system consists of the serial interface between the PC, and radio control
signals to the vehicle and the camera positioning system. This topic is covered by my
partner, Tameka Thomas. In my partner’s report, the RS-232 interface to the PC, radio
control, and all other signal processing will be covered in detail.

Operational Specifications/Issues:

        The operational lifetime of the RVSV is expected to be at least 2 hours of
continuous use before having to replace any of the batteries in the system. This appears to
be a simple task, however this presents a major problem. The block diagram below
(Figure 1.1) shows the different subsystems in the RVSV that need to be powered. Note
that each one of these can consist of multiple smaller components which also need
power.
Figure 1.1:




         Now that each subsystem needing power is defined, the next step is to determine
what voltages each one needs and how much current they each draw as a whole.
The transmitter subsystem already must be physically connected to the PC so providing
power here is not as much of a problem. It can use the same power as the PC (assuming
that the PC is using 120VAC line). The same goes for the wireless router. The vehicle
system, however, must be battery operated. As shown in the block diagram, the vehicle
system consists of three subsystems each requiring battery power. First is the physical
vehicle subsystem, since this vehicle is a pre-made device it will already have its power
requirements satisfied by the batteries it was designed for. In this case, it will be 3 AA
alkaline batteries. What is not known however is whether these batteries can power the
vehicle through 2 hours of continuous use. This question will have to be answered
through experimentation which will be covered later in this report. Next is the camera
subsystem, this consists solely of the internet camera. This camera, even though wireless,
was not designed for batteries and uses a 5V,2.5A wall adapter as the power supply. This
presents one of the most outstanding power issues in this project. The actual power
demands must be determined (technical specifications show 900mA) and a battery power
supply must be created to meet these demands. Also, the voltage tolerances of the camera
must also be determined as the voltage of the batteries will drop slightly as the batteries
are used. Experiments must be performed to determine these characteristics in order to
proceed with the design. The need for a likely large battery pack also presents another
issue. Since, the RVSV is designed to be a surveillance vehicle it is desired that the
battery packs be hidden away within the chassis of the vehicle. This presents a space
issue if a large battery pack is needed. Also, batteries add weight to the vehicle thus
reducing its speed or even preventing it from moving at all. The last subsystems here is
the camera positioning subsystem. This subsystem consists of a micro controller and a
DC motor, and it is responsible for moving the camera 360°. This presents another power
issue as the micro controller will need about 5V as will the DC motor. A even more
important issue, however, is the current draw of the DC motor which can go up to a
couple amperes.
         All of these issues can be separated into three categories: current, voltage, and
space. These categories must be weighed against each other to find the optimal solution
to providing power to all of the vehicles subsystems. The power supply, in this case
battery or battery pack, must be able to withstand the current demands of the subsystem
for at least 2 hours. The voltage tolerances of each subsystem must be determined and/or
designed to be low voltage and tolerant of changes in voltage. The battery (pack) must be
as small as possible in order to fit inside the chassis of the vehicle. The next section will
now investigate possible solutions to the problems stated.

Power Options:

          The first possible solution to the problems stated above is to explore different
battery types. There are four major types of batteries which are available to the average
consumer, Alkaline, Nickel Metal Hydride (NiMh), Nickel Cadmium(NiCd), Lithium.
The most common of these is the Alkaline battery. Alkaline batteries are the most
popular and are used in many devices, however they are not rechargeable. Nickel
Cadmium(NiCd) batteries are commonly used rechargeable batteries. Nickel Metal
Hydride(NiMh) is a new type of rechargeable battery which offers better performance
than NiCd. Lithium batteries are available in non-rechargeable and rechargeable types
(Lithium-ion). The rechargeable Lithium batteries are commonly used in cell phones and
other such devices. Each of these battery types will be compared to determine which is
more suitable for use with this project. Also, the availability and cost of each battery type
will be analyzed as the end-user will have to replace the batteries when they wear out.
          First, the common alkaline battery will be analyzed. Alkaline as said before are
the most common of these batteries. They mostly used in everyday consumer electronics
such as, alarm clocks, cd players, and cameras. The reason for this is that alkaline
batteries are very economical. They offer solid performance and are fairly inexpensive.
Alkaline batteries also come in many different shapes and size. The most common shapes
are the cylindrical AAA, AA, C, and D type batteries. All of these cylindrical batteries
provide about 1.5V.The other common alkaline battery is the rectangular 9V battery,
however this battery is merely made up of six 1.5V batteries in series. This report will
focus on the cylindrical type of batteries as these are the most common. Alkaline batteries
are made up of maganese dioxide and zinc conductors within a alkaline electrolyte. These
chemicals provide the chemical reaction necessary to produce the voltage. A fresh
cylindrical alkaline battery usually has an open circuit voltage of 1 .58V. When a load is
applied to a battery its voltage gradually decreases depending on the amount of current
being drawn. The graph below shows the number of service hours vs. the discharge rate
of a Energizer AA battery. This battery’s rated capacity is 2850mAh at a cutoff voltage
of 0.8V, but as you can see the more current drawn from the battery the shorter it will
last. It is also noted that this graph is nonlinear in the higher currents and demonstrates
that the test current must be taken in to consideration when reviewing battery ratings. In
this case the test current for the rating was 25mA which is around the linear area of the
curve.
Graph 1.1




         Next is the Nickel Cadmium (NiCd) battery. These batteries are common
rechargeable batteries used also for consumer electronics. One can find these types of
batteries in toy remote control cars. These batteries also come in many different sizes and
shapes including the standard cylindrical sizes (AA, C, D, AAA). These batteries are the
cheapest of the rechargeable batteries. NiCd batteries consist of nickel hydroxide and
cadmium electrodes within a potassium hydroxide electrolyte. Oxidation occurs on the
negative electrode which equals the oxidation reduction on the positive electrode. The
battery becomes recharged by applying an external voltage to the battery and thus
reversing the chemical reaction. These batteries have the advantage of being rechargeable
however there are a few drawbacks. First is that these batteries suffer from the memory
effect if not properly used. There are two causes for this memory effect. The first is when
the battery “remembers” the previous discharge and the only will discharge to that point.
The second is caused by crystal growth in the battery which occurs when the battery is
charged before it is fully discharged. These problems can be avoided by fully discharging
the battery before it recharged. The next problem with NiCd batteries is that the have a
smaller capacity. For example, a typical alkaline AA battery has a capacity of about
1000-2000 mAh while a typical NiCd battery only has about 500-1000 mAh. The last
drawback is that the performance of NiCd batteries varies with temperature and also lose
charge at a rate of about 2% per day. While, alkaline batteries can be stored over a year
and are relatively temperature indifferent.

        The next battery type is the Nickel Metal Hydride (NiMh) battery. This battery is
a newer rechargeable that provides better performance over the NiCd battery. The NiMh
battery is constructed the same as the NiCd battery with the exception of metal hydride
instead of cadmium. The NiMh battery has the advantage over the NiCd battery for a
couple reasons. The first is that it does not suffer from the memory effect explained
earlier. The second reason is that NiMh batteries provide a higher capacity than NiCd
batteries. The typical NiCd battery had a capacity of 500mAh – 1000mAh, but the NiMh
has a capacity of much closer to the alkaline batteries ranging 1000 mAh –2000mAh.
These advantages are causing the NiMh battery to quickly replace NiCd batteries.
         Lithium batteries are also available. These batteries are not available in all of the
standard cylindrical sizes (presently only AA). Lithium batteries are mostly used in
cameras because of their capability to provide power surges. These batteries offer the best
performance. They have a flat discharge rate and are fairly temperature tolerant. The
Energizer AA battery has a capacity of about 2900mAh. This does not seem that great
when compared with the rating of the alkaline battery which had a capacity of 2850mAh.
However, the alkaline battery was rated at a drain of 25mA while the lithium was rated at
200mA. There are different types of lithium batteries also the one explained refers to the
non-rechargeable lithium manganese dioxide battery. The rechargeable lithium batteries
are lithium-ion which are commonly used in newer cell phones.
         Of these batteries the best for this project are the alkaline and lithium batteries.
Even though they are not rechargeable they offer very solid performance and are fairly
inexpensive. The lithium battery is preferred over the alkaline simply because it has a
higher maximum discharge rate and has better performance in high drain applications.

Power Saving Solutions:

        In addition to the type of battery used, there are other methods which can be
implemented in order to conserve battery power. One is the implementation of a sleep
mode. If there is no activity for an extended period of time, power to the camera and
other high drain systems can be cut until activity resumes. This will prevent battery
power being wasted while the RVSV sits idle. Also, power does not need to be applied
to the entire system before it establishes a connection with the base PC. Here is another
period in which battery power can be saved. The last suggestion is a circuit solution to
saving battery power. A setup such as the one shown in Figure 1.2 can be used to save
prevent a continuous drain on the battery. Instead the battery charges a capacitor and then
rests until the capacitor discharges. This setup would save some drain on the battery
however, the addition of a circuit with large capacitors take up space.

Figure 1.2:
                  Rbatt

                           Q2
                          NMOS
          +                                       RL
Vbatt                               Ctot
Conclusion:

        Powering the RVSV will be a major issue in the design. Many test and
experiments will have to be done in order to find the tolerances and drain of the camera,
and also to determine the life of the battery under a simulated load. The circuit solution
will definitely be tested and all IC will have to be low-power. I believe that it still can be
done and as long as the proper steps are taken in the early stages of design there should
be no surprises.

								
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