Solar Powered, Multi-seated, Internetted Computer System

Final Report

December 3rd, 2008

Sponsored By:

In Cooperation With:

Michigan State University University of Dar es Salaam

ECE 480 - Design Team #2 - Fall 2008Management Jakub Mazur

Web Josh WongDocument Ben Kershner

Presentation/Lab Eric Tarkleson

Executive Summary

With the increasing proliferation of affordable, reliable personal computers

into the marketplace, there is a great demand to develop affordable personal

computers for remote and underdeveloped areas. Before deploying a computer

system into such harsh conditions several obstacles must be overcome, including

source of electricity, telecommunications, and the savannah climate. The Lenovo

Corporation has tasked this team to develop a solar-powered computer workstation

that can accommodate up to eight users. The solution must be robust enough to

withstand the harsh environment with as little technical maintenance as possible,

yet still be affordable for rural schools.

A bank of solar panels charges a small battery bank using a commercially

available charge controller. A custom engineered battery management system

monitors voltages and currents from the solar panels and the battery to calculate

system data. The system also monitors case temperatures to insure everything is

operating within a safe range. Should the battery become discharged or

temperatures rise above the safe limits the system will automatically shut itself

down. All power data is logged to the computer and stored for system optimization.

A small LCD panel displays pertinent system information

A single computer can connect up to 8 monitors, keyboards and mice. Each

terminal allows independent simultaneous logons. The operating system is Linux

based and uses only free and open source software (hereinafter referred to as

FOSS).

Since this project has three vastly different, but equally important main tasks

that needed to be researched, tested, and built this report is split into three main

sections. First is solar power system design, second is power management, and third

is Multi seat hardware and software. Each section will address the research, design

issues, testing, and conclusions that were found. The last section will deal with

system integration and project findings and conclusions. Since we did not deal with

the telecommunications issues these will not be addressed in this report.

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Acknowledgement

We would like to thank our sponsor, Lenovo, for their help in making this

project a success. We also would like to thank our team members in the

Telecommunications department as well as the faculty and students working with

us at the University of Dar Es Salaam, Tanzania.

Also we would like to thank LEM and Man vs. Machine for their donations

and samples. Their engineers and salespeople were very helpful in guiding us in the

right direction.

This project would not have been possible without the help of our facilitator

Dr. Jian Ren. Also we would like to thank Dr. Goodman for helping keep us on track

and helping us plan our deployment of this project in Tanzania.

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Figure 1 - Power system block diagram.

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Table of Contents

Solar Powered, Multi-seated, Internetted Computer System 1

Executive Summary...................................................................................................................................................2

Acknowledgement......................................................................................................................................................3

Section 1 - Photovoltaic System Design............................................................................................................7

Determining Size of Photovoltaic Panel Array:............................................................................................7

Determining Load Power Consumption:..........................................................................................................7

Determining Solar Insolation Levels:................................................................................................................ 8

Sizing Battery Array.............................................................................................................................................. 11

Wire Sizing and Connections:............................................................................................................................ 12

Maximum Solar Power Output:......................................................................................................................... 13

Inverter to Battery Wiring.................................................................................................................................. 14

DC-AC Inverter.......................................................................................................................................................... 15

Charge Controller.................................................................................................................................................... 16

Conclusion.................................................................................................................................................................. 17

Section 2 - Power Management.........................................................................................................................18

Research...................................................................................................................................................................... 18

Voltage Measurements......................................................................................................................................... 19

Control Board........................................................................................................................................................... 21

Power Management Board................................................................................................................................. 21

Conclusion.................................................................................................................................................................. 22

Section 3 - Multi Seat System Hardware and Software...........................................................................23

Thin Clients................................................................................................................................................................ 27

Multiple-Motherboards.........................................................................................................................................28

Multi-User................................................................................................................................................................... 29

Testing/conclusion................................................................................................................................................. 30

Section 4 - System Integration and Conclusion..........................................................................................31

Integration................................................................................................................................................................. 31

Safety............................................................................................................................................................................ 31

Future Improvements:........................................................................................................................................... 33

Intelligent Monitoring........................................................................................................................................... 34

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Conclusion:................................................................................................................................................................. 36

Appendix 1 – Technical Roles and Responsibilities..................................................................................38

Eric Tarkleson........................................................................................................................................................... 38

Joshua Wong.............................................................................................................................................................. 39

Jakub Mazur.............................................................................................................................................................. 40

Ben Kershner............................................................................................................................................................. 41

Appendix II - Schematics......................................................................................................................................42

Appendix III - Nomenclature..............................................................................................................................44

Appendix IV - References and Recommended Reading..........................................................................45

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Section 1 - Photovoltaic System Design

There are many types of solar systems but most can be categorized into a

variation of the following: A “grid-tie” system where there are no batteries and the

power grid provides back-up power. A hybrid “grid-tie” system where the power

grid provides back-up for the solar panels and batteries act as a backup for the grid.

In cases where there is no access to grid power an “off-grid” system is used, in which

the battery bank stores and provides all the energy for the system without a backup.

Since this is generally the case in under-developed areas this will be the system

discussed here. There are also systems with generators as backups, they are

comparable to “grid-tie” systems and will also be omitted from discussion here.

Determining Size of Photovoltaic Panel Array:

There are several steps involved in sizing the PV array, determining load

power consumption, accounting for losses and dividing by solar insolation levels for

deployment region.

Determining Load Power Consumption:

The first step is to determine how much power the total system load will

draw. Power is measured in Watts:

P = V ∗ I (Joule’s Law)

However, the power rating is more useful when looked at in terms of time,

this is indeed how electric companies charge consumers. For example a 200Watt

light bulb running for 24 hours uses 4.8 KWh.

200Watts ∗ 24hrs = 4800 Watt-Hours or 4.8 KWh

A list of all devices connected to the system should be made with their

appropriate power draw available from specifications sheets or better yet, actual

measurements.

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Component Power (Watts)

Lenovo S10 (Idle) 91

Lenovo S10 (Full Processor + Hard

Drive)

116.76

Lenovo S10 (30% Duty Cycle) 98.73

Satellite Router (Idle) 53.8

Satellite Router (Busy) 72.5

Est. Typ. Satellite (30% Duty Cycle) 59.41

17” LCD Screen x 4 (20*4) = 80

Total 238.14 Watts

Figure 2 - Power measurements on 11/11/2008. Note: Headsets, Keyboards & Mice are

currently not included in calculations because the team is not in possession of them and their

power consumption should be minimal.

Since these devices are designed to plug into AC power, a DC-AC power

inverter is needed. The power inverter ideally operates at 90% efficiency. Therefore

the maximum inverter draw from batteries is:

238 Watts / 0.90 = 264.60 Watts

This system power draw is then multiplied by the amount of hours per day

that it will operate.

264.60 Watts ∗ 8hrs/day = 2116.80 Watt Hrs/day

To compensate for system losses during battery charge/discharge cycles the

total system power consumption is multiplied by a 20% compensation factor

(Sunwize).

2115.52 Watt Hrs/day ∗ 1.2 = 2540.16 Watt Hrs/day

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Determining Solar Insolation Levels:

In order to determine a good approximation of how much power the PV

panels will output, solar insolation levels need to be considered. Solar insolation is

the amount of incoming solar radiation incident on a surface, for PV applications the

surface of interest is the earth’s surface. The values of solar insolation are commonly

expressed in kWh/m2/day, which is the amount of solar energy that strikes a

square meter of the earth's surface in a single day. This is commonly referred to as a

“Sun-Hour-Day”. The amount of insolation received at the surface of the Earth is

controlled by the angle of the sun, the state of the atmosphere, altitude, and

geographic location.

Figure 3 - World insulation levels.

This map divides the world into six solar performance regions based on

winter peak sun hours.

It is important to keep this in mind when designing the system because as

seen below in Figure 4, during the winter you have a much smaller ‘Solar Window’.

Worst case scenarios should be calculated as it is better to have extra energy in the

summer than not enough in the winter. Therefore the “Sun-Hour-Day” values for

December (since December days are shortest) are generally used.

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Figure 4 - Sun path chart.

Solar Insolation Levels for Arusha, the prototype deployment area, are seen

below in Figure 5.

The compensated total power consumption per day value calculated above is

then divided by the solar insolation values for given deployment region to

determine minimum PV panel array power output requirement:

2540.16 Watt Hrs/day / 5.5 = 461.84 Watts

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Figure 5 - Hankins.

Sizing Battery Array

Nearly all large rechargeable batteries in common use are Lead-Acid type,

although there are three variations, flooded, gelled electrolyte (“Gell Cells”) and

absorbed glass matt (“AGM”). Flooded is the oldest and cheapest technology used

but can be dangerous, in case of a malfunction acid can spill. Gell Cells contain acid

that has been "gelled" by the addition of Silica Gel, turning the acid into a solid mass,

therefore even if the battery where cracked open, no acid would spill. Gell batteries

need to be charged at a slower rate (capacity / 20) but this is not a concern in the PV

setup as the panels will not be outputting nearly this much current. AGM batteries

are the newest technology and have all the advantages of Gell Cells without the

charging limitations.

All deep cycle batteries are rated in amp-hours. An amp-hour (Amps x Hours)

is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. The accepted

AH rating time period for batteries used in solar electric and backup power systems

is the "20 hour rate". This means that it is discharged down to 10.5 volts over a 20

hour period while the total amp-hours it supplies is measured (Windsun).

The compensated total power consumption per day value is used again to

calculate minimum battery array size.

2540.16 Watt Hrs/12 Volts = 211.68 AmpHrs/day

Number of days of autonomy to support: 1 (8hrs)

211.68 ∗ 1 = 211.68 AmpHrs

“Battery life [deep cycle] is directly related to how deep the battery is cycled

each time. If a battery is discharged to 50% every day, it will last about twice as long

as if it is cycled to 80% DOD [depth of discharge]. If cycled only 10% DOD, it will last

about 5 times as long as one cycled to 50%. Obviously, there are some practical

limitations on this - you don't usually want to have a 5 ton pile of batteries sitting

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there just to reduce the DOD. The most practical number to use is 50% DOD on a

regular basis (Windsun).”

Depth of discharge for battery: 0.5

211.68 / 0.5 = 423.6 AmpHrs

This means that after 8 hrs of use without sun the battery will be discharged to 50%

8 Hrs of autonomy and battery depth of discharge at 0.80 (Half the life-span of 0.50):

264.60 Amp Hrs

6 Hrs of autonomy and battery depth of discharge at 0.50:

264.6 Watts ∗ 6 Hrs = 1587.6 Watt Hrs / day ∗ 1.2 = 1905.12 Watt Hrs / day

1905.12 Watt Hrs/12 Volts = 158.76 AmpHrs

142.8 AmpHrs / 0.5 = 317.52 Amp Hrs

4 Hrs of autonomy and depth of discharge at 0.50:

238 Watts ∗ 4 Hrs = 1058.4 Watt Hrs / day ∗ 1.2 = 1270.08 Watt Hrs / day

1270.08 Watt Hrs / 12 Volts = 105.84 Amp Hrs

105.84 Amp Hrs / 0.5 = 211.68 Amp Hrs

Wire Sizing and Connections:

Another important consideration for the system is the electrical wiring. All

wiring needs to safely accommodate the amount of current draw of the system with

an acceptable amount of losses. In a DC system losses quickly become an issue. This

is especially a concern PV systems as they can only handle a small voltage drop as

there must be enough potential to charge the battery array, and of course it is good

practice to keep energy loss sourced from the sun to a minimum. Generally a 3%

drop between PV array and batteries is acceptable. Also, “any type of connection

bigger than AWG 10 should have a proper compression connector, with appropriate

joint compound and preparation. This does require special tools and dies. Otherwise

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you are running the risk of burning up your connections if you get any kind of heavy

current flowing. (SolarForum)”

Losses associated with transmission of DC power:

CM = (22.2 ∗ A ∗ D)/VD

CM = Circular Mills In Copper

A = current in amps

D = one-way cable distance in feet

VD = Voltage Drop

22.2 = Constant for Copper

For wiring from the PV panels to charge controller the maximum PV short

circuit current specification (from PV data sheet) is used.

Maximum Solar Power Output:

24 Volt Systems:

Configuration Max Current Out (Amps)

6 x PW080 3 x (5.14A-ISC) = 15.42

3 x ST-165 20.63

4 x KY125 20.83

Figure 6

12 Volt Systems:

Configuration Max Current Out (Amps)

6 x 80 Watt 6*(5.14A-ISC) = 30.84

3 x PW165 41.25

Figure 7

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Using the loss equation above the following result was obtained for the

selected system:

Distance: 50ft

Voltage Drop: 0.72

Current: 15.42 Amps

Circular Mills: 23772.5

AWG: 6

Inverter to Battery Wiring

For current level estimates from the battery to inverter maximum power

draw levels are used although this distance is generally short and maximum

available wire gauge is recommended. This is also due to the fact that the system

will encounter surge currents as various components are ‘turned on’. Since the

system used as an example here is not continuously running and is to be turned off

every night and back on in the morning this was a serious issue that needed to be

tested. (Refer to Figure 9).

Maximum Power Draw:

Component Power (Watts)

Lenovo S10 (Full Processor + Hard Drive) 116.76

Satellite Router (Busty) 72.5

17” LCD Screen x 4 (20 ∗ 4) = 80

Total 270 Watts

Figure 8

Assuming the inverter that will be sourced in deployment area is operating at

90% efficiency:

270 Watts = 300 Watts x 90%

Maximum current draw in 12 Volt system = 300 Watts / 12 Volts = 25 Amps

Maximum current draw in 24 Volt system = 300 Watts / 24 Volts = 12.5 Amps

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Power-Up DC Current Draw

-5

0

5

10

15

20

25

30

35

1 1570 3139 4708 6277 7846 9415 10984 12553 14122 15691 17260 18829 20398 21967 23536 25105 26674 28243 29812 31381

Samples

Cur

rent

(Am

ps)

Figure 9

Figure 9 shows DC current draw as measured during power-up of Lenovo

S10 Workstation (custom configuration) and L193p Monitor. Although the system is

only drawing 5 amps while running the surge current spikes are clearly visible. This

is indeed one of the reasons why proper electrical connections are crucial.

DC-AC Inverter

Since the computer and monitors are designed to plug into AC power and

accessory plugs for phone charging are a project specification an inverter is

necessary. There are two types of inverters, pure sine wave and modified sine. Most

devices will work from modified sine, this is what common uninterrupted power

supplies provide and what was selected for this system. It is important to make sure

that the inverter is rated to provide enough power for everything running off of it.

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Charge Controller

The charge controller chosen for this system is the Outback Power FlexMax

60. This decision was based on versatility, efficiency, robustness, and availability in

deployment area. The Outback can accept a wide range of voltage inputs as well as

various battery arrays, this was important for this specific system as ultimately

whatever solar panels are in stock at the time of deployment in the region will be

used.

Note, the efficiency curves (Figure 10 and Figure 11) are for the Flexmax80,

they are identical to the Flexmax60 other than the fact that the FX60 does not accept

85 and 100V.

The highlighted area on the graph represents the highest efficiency while

charging a 12V battery array. The charge controller is operating at about 95.5%

efficiency with an input Voltage between 17-34V. Typically a 12V PV panel's Voltage

at Peak Power is around 17 Volts.

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Figure 10 - Outback charge controller.

The highlighted area in this graph represents the optimum efficiency if the system

where charging a 24V battery array. The charge controller is operating at about

98% efficiency with an input Voltage around 34V. Two 12V panels in series will

typically have 34 Volt equivalent Voltage at peak power.

In an ideal setup the FlexMax 60 would operate at 98.1% efficiency with an

input of 68V while charging a battery array at 48V. This would be the case with the

optimum PV panel chosen in section 1, the Kaneka G-EA060 as the VPM is 67Volts.

Conclusion

Designing an off grid photovoltaic system involves many steps and although

the math is simple all calculations should be double checked. If the calculations for

one component are off chances are the whole system will not work, every stage

relies on the previous one. Designing the system for worst case scenarios is good

practice, it is better to have extra energy than not enough. All safety precautions

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Figure 11 - Outback charge controller.

should be followed especially on electrical connections that have a possibility of

carrying a lot of current. Breaker boxes before and after battery connections for

easy power disconnect should be implemented. These breakers should be rated for

DC voltages.

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Section 2 - Power Management

The core of the power management system is the data-gathering module. The

module uses a PIC microcontroller to measure voltages, currents and temperatures

and send the results to the computer via USB.

The end result of this system is similar to the power management utility in

your laptop. Just as with a laptop this is a self contained system that will not have

access to external power some of the time (when there is no sunlight). We feel that

because of the complexity of the multi user computer as well as the photovoltaic

system we needed to design a system that not only watches battery voltage but also

stores and interprets data for intelligent power decisions.

Research

The current sensors used are LEM FHS series

sensors. They are Hall effect sensors which operate by

measuring the electric field produced by the current

carrying wire. The field is proportional to the current.

These current sensors are isolated from the actual power

path and can be turned off to conserve power. Different

models of the sensors are capable of measuring anything from milliamps to over 50

amps. The biggest advantage of these sensors is scalability. A single chip can handle

any range of current by clever PCB board design. We acquired several sample units

from LEM and put them into small project boxes that can be used anywhere. They

attach to the power management system via d-sub cables.

Temperature measurements use a small probe, which outputs a voltage

proportional to the ambient temperature. We chose the national instruments

LM335z. These are Zener diodes with a linear internal voltage drop proportional to

the temperature of the device. Our design allows for up to 4 sensors.

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Because the PIC uses a very small amount of power, it is continuously

operating to ensure system safety. The PIC is connected to a small LCD screen which

displays pertinent information about the condition of the battery and solar panels.

Two buttons mounted beside the screen allow a user to scroll through the

information showing them battery voltage, current, and amp hours remaining. Also

there will be displays for voltage and current from the solar panel. This information

will be used to compute time and percent remaining before system power down.

There are also three status LED's that inform the user of system power, battery

good, or battery low.

The PIC communicates to the computer via USB. This is done using the FTDI

UM232R. This device automatically converts the USB signal to a standard serial

signal. It also registers with the computer as being a serial port. With the

connection, the computer can query the PIC about the status of the battery and can

shut the system down safely when the battery is low. The computer can also query

the PIC to get real time data on the voltages, currents and temperatures. The

information is stored in an XML file and can be easily reprocessed into any file

format for analysis of the data.

Voltage Measurements

Voltage measurements require the addition of a voltage divider into the

circuit because the PIC has a maximum dynamic range of 5 volts. An advantage of

using the PIC to measure voltage is that the value of the resistors in the voltage

divider can be accurately measured and the program can use that information to

improve the accuracy of the voltage measurement.

The built-in 10-bit ADC of the PIC 18F4520 microcontroller is a cheap way to

measure analog voltages. A drawback is that it is limited to measuring only 0-5VDC.

By adding a voltage divider, customizing the software slightly, and using a digital IO

pin as a current sink, we can efficiently and accurately measure much larger

voltages.

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Figure 12 - Voltage divider with selectable current sink.

The 10-bit ADC on the PIC18F4520 is implemented as an RC circuit inside of

the PIC. Because of this, there are certain parameters to be aware of, all of which

have been taken from the PIC18F4520 Datasheet.

By adding a voltage divider to the input pin of the PIC, we are now able to

scale the input voltage. All that is left is the selection of resistor values. Starting with

known values, we can select vout to be 5V, as that is vref+ on the PIC. Also, recalling

from the first section, the nominal input impedance to the PIC is 2.5k , and as such Ωwill be selected for R2. The node labeled vin is the high voltage input to the voltage

divider, and should be selected as the highest voltage desired to be measured. For

this example we will say 50V.

As can easily found by inspection, the formula for a voltage divider is:

vout = vin ∗ (R2 / (R1 + R2))

This gives us a formula, three knowns, and one unknown. Solving for R1:

R1 + R2 = vin ∗ R2 / vout

R1 = R2 ∗ ((vin / vout) – 1)

R1 = 2.5kΩ ∗ ((50V / 5V) – 1)

∴ R1 = 22.5kΩWe can now build our new voltage divider and accurately measure

voltages up to 50V! To convert the ADC result to actual voltage, the following

equation is now used:

van0 = ((VDD ∗ ADC_output) / 1023) ∗ (R2 / (R1 + R2))

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Control Board

This is the schematic and for the control board. It is mounted behind the

control panel and connects directly to the LCD header. There are headers for

connection to the status LEDs as well as the control buttons. A ribbon cable connects

this board to the rest of the circuit

Figure 13 – LCD control board schematic.

Power Management Board

This circuit allows connection of up to 4 current sensors, 4 temperature

probes, and 4 independent voltages. The voltage inputs have a voltage divider

circuit that can be configured to accept voltages for systems running at 12, 24, or 48

volts. A USB connection allows data sharing with the computer.

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Figure 14 - Power system monitor schematic.

Conclusion

Our power management system performs as it was designed to. Each

channel accurately reads a voltage from the sensor and converts the voltage to a

value. The PIC then uses this information and displays this information clearly on

the LCD panel. Both boards are mounted in an enclosure with connectors for each

sensor. The board will be mounted in the main enclosure and will allow a user to

turn of the entire system with the touch of a button. The sturdy PCB design and

construction will stand the test of time. The PCB board also allows for on site

reprogramming if it is deemed necessary.

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Figure 15 - Power system monitor and faceplate.

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Section 3 - Multi Seat System Hardware and Software

The primary goal of this project is to help promote education in developing

countries by providing grade schools with electronic resources. There are a variety

of other groups that have already initiated solutions to this problem. The most

prominent group is the One Laptop Per Child Association (hereinafter referred to as

OLPC), which has created a cheap, durable laptop known as the XO-1. Other groups

such as the Center for Scientific Computing and Free Software (hereinafter referred

to as C3SL) have made significant strides in reusing older computers for schools;

however, both of those programs have some significant drawbacks.

The primary competitor identified is the OLPC. The OLPC Association is dedicated to

producing low cost laptops and distributing them to low-income areas. There exist

several problems with the program, including the per-deployment cost and

deployment into rural areas. The original intent was to deliver a laptop to every

child for a cost of $100 per device. The program, however, is unable to deliver the

laptop at the $100 target; in fact, the cost to donate a system is almost $200.

Deployments also require a minimum commitment of 100 laptops. This represents a

very significant financial burden, though once deployed, it is difficult to integrate

multiple PCs into a cohesive learning environment, and this takes away from

educating the students. However, the XO-1’s are extremely rugged PCs and do not

depend on any external power sources except to charge the batteries.

C3SL’s solution integrates into school systems better, and was widely

deployed in the Paraná Digital project. This project involved having multiple

terminals running off of a single computer in multiple schools. This program has

been very successful and shows great promise, but there is a critical flaw. The

program is entirely software, and this software was intended to run in a classroom

equipped with basic utilities, such as power and internet connectivity.

Our solution was to integrate the OLPC's ruggedness and the C3SL's novel

software solution into one robust package. The design team preceding ours built a

solar powered computer system that can be deployed in a relatively durable

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building. They assembled a solar panel, battery, and a charge controller into a self

contained solution, such that deployment in a wide variety of climates and locales is

possible, but they were unable to decide on the computer system. Our primary goal

for this project is integrating the solar charging and battery system with a computer

system that is suitable for educating youth, regardless of regional or socio-economic

boundaries.

The requirements for the computer system were fairly simple; four seats, low

power. This could be established very easily with four laptop computers, but there

were design issues that had to be considered. First, the system will be deployed in a

relatively extreme environment. It also will not be running off of mains power, and

will therefore have to be low power. It should also be as cost efficient as possible, i.e.

lowest cost per seat. Four architectures were discussed for the computer system:

laptops, thin clients, multiple-motherboard, and multi-seat.

Laptops Thin Client Multi-User Blade ClientCost Outline: Baseline:

- Router with advanced features ($200)

Baseline:- Server ($500)

Baseline:- Powerful Server ($800)

Baseline:- Server ($500)

Per Seat:- Lenovo IdeaPad S10 Latop ($439)- Mount ($50)

Per Seat:- Diskless Workstation LTSP 1220PXE Thin Client ($285)- Lenovo L197 Monitor ($239)- Keyboard/ Mouse ($30)

Per Seat:- Lenovo L197 Monitor ($239)- Keyboard/ Mouse ($30)- Video card ($30)- Optional Software ($100)

Per Seat:- Small Motherboard with RAM & CPU ($100)- DC-DC Power Supply ($50)- Keyboard/ Mouse ($30)- Lenovo L197 Monitor ($239)

Total Cost: Base: $200 Base: $500 Base: $800 Base: $500Per Seat: $489 Per Seat: $554 Per Seat: $399 Per Seat: $419

Pros: Easy, Reliable, Server- less, Redundant, Low Power Consumption

Easy, Reliable, Stable, Low Power, COTS

Cheap, Lowest Power Consumption, Single Point of Maintenance,

Possibly Cheaper than Thin Client, 100% Lenovo Hardware

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100% Lenovo Hardware

Cons: Small Screens, Defeats Purpose of Designing a New system as Opposed to Donating Laptops, Security Concerns

Relatively Expensive, Lenovo Does not Make a Thin Client

COTS Software is Expensive and Open-Source is Immature, Reliability is Main Concern

Lots of Enclosure Work, Reliability

Figure 16 - System architecture prototypes.

Laptops

Figure 17 - Laptop-type system architecture mockup.

The first prototype was a simple laptop-server setup. Each workstation

would consist of small laptop (a 10” form factor, such as the Lenovo S10). The

laptops would be connected to the Internet either by an Ethernet cable, or even Wi-

Fi. Laptops would be run without being directly connected to AC power; a charging

station would be setup next to the server.

This style of architecture would be very simple to configure. The server and

the laptops would all be off-the-shelf Lenovo products. The workstations would

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have low power consumption, given the fact that the monitor, computer, keyboard,

and mouse are all combined into one device. Should a laptop be damaged, it would

also be very easy to replace, requiring little re-configuration, and no custom

engineering. The laptops, however, would be most susceptible to accidental damage

given that they would be out in the environment, rather than safe inside the case.

Thin Clients

Figure 18 - Thin client-type system architecture mockup.

The thin client architecture is much closer to a traditional desktop user

experience. A thin client is little more than a small form factor motherboard,

processor, and RAM (no HDD necessary) loaded with a special BIOS. The server

does most of the processing and the think client simply helps to shuttle data back

and forth. With this setup, four thin clients are each connected to their own monitor,

keyboard, and mouse. All of the applications and processing tasks are handled on a

central server.

This is another easy solution that uses all commercial off-the-shelf (COTS)

hardware and software. It also has much lower power consumption when compared

to installing four individual desktops, but the power consumption is not as low as

other methods. The key drawback is price. Since Lenovo does not produce a thin

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client, they would have to be purchased at full market price. This brings the total per

seat cost up to around $700.

Multiple-Motherboards

Figure 19 - Blade client-type system architecture mockup.

One method of avoiding this high per seat cost would be to build custom thin

clients, very similar to the blades of a blade server. The team estimates that even

paying market prices, a hand-built thin client could be built for around $100,

compared to the nearly $300 for third-party thin client.

The pros are the same as that of the thin client, with the added benefit of

being cheaper and being made totally of Lenovo hardware. The key drawback

though is the packaging. Since these “thin clients” are just a motherboard, they

would need to be put into a proper case, first. This would add to the cost and could

cause lifecycle issues (a poor case would lead to high failure rates of the

motherboard).

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Multi-User

Figure 20 - Multi-user desktop-type system architecture mockup.

The most attractive architecture is the Linux based multi-seat system. It is

implemented by building a central PC with multiple video cards (2-4), multiple

keyboards, and multiple mice. Each workstation consists of a monitor, keyboard,

and mouse plugged directly into the PC (acting as an X window server).

The cost for such a setup is low. Since no thin clients are required, the per-

seat cost consists of only a monitor, keyboard, and mouse. The power requirements

are also lower, given that the CPU and all of its resources are be shared by all of the

users. The system would also respond much quicker than a thin client, without the

LAN bandwidth and latency issues. With significant customization of the operating

system (UNIX based), this architecture was completed using only free, open-source

software.

This is the architecture that has been chosen by the design team. The low

cost and low power requirements make it an ideal solution. Also the server can be

safely mounted inside a case and only the monitors, keyboards, and mice need to be

outside of the case.

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Testing/Conclusion

To test the computer terminals, four accounts were created and each account

attempted to do the following tasks:

Write a document using a word processor

Watch an offline video

Play an educational game

Browse a simple webpage

Browse a rich webpage

Watch an online video.

These tasks represent what a typical student might be doing on a school

computer. Support for advanced programs, such as MatLab, were not tested. Each

station was able to perform the tasks listed, and therefore the computer terminals

are ready to be deployed.

CPU usage Video Audio Comment

Open Office low good n/aBasic document preperation. Simulates multiple students writing a paper

Firefox basic low good n/aBasic web surfing. Simulates multiple students reading static webpages, ie wikipedia

Firefox rich high good goodAdvance web surfing. Simulates multiple students browsing flash enabled websites, ie Youtube

Totem mid good goodVideo/audio player. Simulates multiple students watching an offline video

Gcompris low good goodEducation games. Simulates multiple students playing non accelerated games

Figure 21 - Programs used to test multi-seat system.

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Section 4 - System Integration and Conclusion

Integration

Our final project consists of a new more robust charge controller and a

custom engineered battery management system. New solar panels have been

chosen for our deployment area but due to their similarity to our current

components they were not ordered here. We decided to change our solar panel

array and battery bank from a 12V to a 24V system. This lowers our current

throughout the system which leads to lower losses and smaller wire gauges. We

purchased a 24V inverter to replace our 12V inverter that was left to us from the

previous team.

The final architecture that we chose was the single workstation multi-seat

system. This allows for relatively low power consumption and the lowest cost per

seat of the other architectures we researched. We were successful in having up to 4

independent simultaneous logons from a single desktop computer with multiple

graphics cards. With our current hardware we can easily support up to 8 seats with

only the addition of more graphics cards and accessories.

We were successful in combining our objectives into a complete and

functioning prototype that can and will be deployed in a rural village in Tanzania for

testing. Our finished prototype has 4 user terminals connected to a large case that

will hold the communications equipment, workstation, batteries, charge controller,

and battery management system. This system will be hooked up to a solar panel

array that should provide enough power for the system to function throughout a

normal school day.

Safety

Since we are designing a system that will be deployed in a school with no

preexisting power, and around people without much experience with electrical

equipment we need to take some extra precautions to make sure that the entire

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system is as safe as possible. There will be solar panels that will either be mounted

on poles outside of the building or on the roof so we will have to make sure to

protect these cables because they will carry high currents. The battery bank also

needs extra safety measures because it will have the potential to unleash huge

amounts of current should a short, or other low resistance connection (ie. body)

cross the terminals.

The solar panels will be mounted outside. If we mount them on the roof then

we need to make sure that the cable runs go into the structure through a watertight

seal. Also there will need to be an earth ground installed in case lightning hits the

building. The building itself must be structurally sound enough not only for the solar

panels but also for several people so that installation and maintenance is safe.

If the building is orientated in such a way that the panels can not face the sun

while they are on the roof then they will have to be mounted on a pole outside of the

school building. In this case extra precaution must be used to insure that a person is

unable to access any wire leads because the current can easily kill a person. Also the

cabling will have to be run underground so the wires will have to be enclosed in the

proper type of duct to that they cannot be cut by someone digging in the area. They

also must be completely weatherproof to avoid the wire insulation breaking down

from the elements. One advantage to this setup is that the structure that the panels

hang on can be used as an earth ground for the entire system.

Once inside the building all wiring outside of the case should be in ductwork.

This prevents a person from easily cutting the wires and also prevents animals from

chewing through the insulation. The system case must have a hole that is not sharp

so that the wires cannot fray over time. Also cabling should be secured to the case so

that it cannot easily be pulled out which could cause short circuits or broken

hardware. Any short unintentional short circuits have a large probability of

destroying the expensive equipment nearby or causing a fire.

The battery bank must be carefully installed so as to minimize any possibility

of short circuits. Each battery terminal should have a cover installed so that it is

difficult to touch the electrodes accidently. All batteries should also be secured to

the casing so that they cannot move if the whole case is tipped or moved.

33

There must be circuit breakers at several key points in the system to insure

that if there is a problem the system will cut off power to itself and hopefully save

the equipment from being ruined. There will be a circuit breaker between the solar

panel array and the Charge Controller and also between the Battery Bank and the

Inverter. These will trip if current exceeds expected ratings and will also allow the

system to be manually shut down if the need arises.

Following these simple precautions should allow the system to be safe from

prying fingers, weather, animals and equipment failure. Also in the case of a failure

troubleshooting should be easy because if our battery management system is

running it will provide feedback about which components are not working. If a

breaker is reset then it will also provide clues as to which part of the system failed.

Future Improvements:

A major improvement to the efficiency of the system could be accomplished

by using a computer system that is optimized for minimal power consumption yet

within requirements for the ‘Multi-Seat’ setup. The computer used in the prototype

is a Lenovo S10 workstation. This computer is designed to be a state-of-the-art

processing power house, efficiency was near the bottom of requirements during its

design. However, it is the only hardware that Lenovo currently offers that would

support the ‘Multi-Seat’ architecture; therefore it was used in this proof of concept

prototype. After returning from Tanzania the team is traveling to North Carolina to

give a presentation to Lenovo Corporation about requirements and suggestions for

developing a more efficient computer system for use in PV systems. Amongst

specific suggestions of low-power components include using the Intel Atom

processor and lower power hard drives, this will also include a design modification

to their power supply. The power supply is designed to transform and rectify AC

power to DC which is used by the computer. Since power sourced from PV systems

is already DC unnecessary losses can be avoided by using a DC to DC power supply.

Most modern power inverters optimally operate at 90% efficiency; hence

eliminating these conversions from the system cuts losses significantly.

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Although the team used the most efficient PV panels on the market at the

time of deploying the prototype, a close eye should be kept on advancements in PV

technology. Current panels are still very inefficient and expensive. This is an area

that is heavily researched and as advancements develop in this field they will

greatly benefit the system.

Intelligent Monitoring

One of the goals of developing the power monitoring unit is to collect usage

data. This includes computer and telecommunication equipment duty cycles as well

as specific component power consumptions and PV array and battery efficiencies at

measured operating temperatures. Before deployment many factors are estimated,

once experimental data is available the system can be designed within tighter

tolerances. As part of the product life cycle management minor changes can be made

at identified weak links in order to maximize system efficiency.

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36

Item Cost Quantity Total Cost

Miniature Pushbutton 3.40 2 6.80

Metal Binding Posts 5.47 2 10.94

Liquid Tin 31.94 1 31.94

Project Box 6.99 1 6.99

Outback Flexmax60 545.22 1 545.22

PSE-24125A Inverter 350.00 1 350.00

Winford BCF9 Adapter 6.50 2 13.00

LEM 37.20 1 37.20

Calling Card 10.00 1 10.00

Mobile Computer Cabinet 1871.00 1 1871.00

VGA & USB extensions 54.35 1 54.35

i-rocks USB Hub 11.99 4 47.96

SYBA USB Audio Adapter 7.99 4 31.96

Lenovo S10 Workstation 1190.60 1 1190.60

Total: 4207.96

Figure 22 - Team budget.

Conclusion:

This project is special because the driving force behind it is not artificial. The

team members do not care about their grade. They do not care about the outcome of

the design day competition. This team is driven by passion, and the sole thing this

team cares about is the successful deployment of a system that will provide

hundreds of kids living in a world of great hardship with a priceless tool, a tool that

all of us grew up taking for granted. A tool that has the ability of transforming

people, a tool that transforms kids into students, a tool that transforms thoughts

into dreams… this tool is access to information.

We live in the information age. We live in a society where the term “Just

Google it” is used on a daily basis. Where we are two clicks away from the answer to

any question we have. So, what is it that separates us? What makes us different?

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How do we have access to this tool when there are people living in this world that

are deprived of something so fundamental to us? We are no different. We are just

lucky to be born into this society.

This team is fortunate enough to have the ability to give our most prized tool

to hundreds of under-privileged children. Children that go to bed at night and

dream, and we want to let them dream big and turn those dreams into realities.

The team members participated in every aspect of engineering a product and

service from start to finish. The team not only accomplished everything outlined in

their initial project description but everything that was thrown at them along the

way, and what is yet to come.

This December, Michigan State University’s Design Team 2 will deliver the

most priceless present anyone can ever give, this is all that we care about and there

is nothing that can stand in our way.

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Appendix 1 – Technical Roles and Responsibilities

Eric Tarkleson

Eric Tarkleson was this semester’s lab facilitator and

document preparer. He worked with Ben on the

current and voltage monitoring system. Specifically

he researched and acquired and built the current

sensing equipment used in the final prototype.

Eric also worked with the team to decide on casing

options. He chose the final case design that will be

used on design day. Eric worked with Jakub on

designing and manufacturing the faceplate and box

that will house the battery management system. The

end result is a sleek easy to use interface to the system that was custom designed for

monitoring a solar powered computer system.

Almost all of the PCB design was completed by Eric. The final project includes two

small PCB boards. The main board includes a microprocessor controlled data

acquisition system that monitors the various components power usage. It then

sends this data to the computer via USB for datalogging. The second PCB mounts to

the LCD and routes the appropriate signals to the status LEDs as well as the power,

reset and menu buttons.

Testing was performed by the whole team and Eric was no exception. Much testing

needed to be performed to insure that the correct solar panels, battery banks, and

charge controllers were purchased and ready in Africa. Much power testing was

done on both the Lenovo S10 PC and the monitors. This data will be useful in

determining how to streamline the system in the future.

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Joshua Wong

Josh’s primary duties for the semester were to find

and implement a multi-terminal solution. The first

attempt to implement a multi-terminal solution was

installing and testing an LTSP server. LTSP allows

Linux based system to run thin clients which support

PXE booting and uses the x86 instruction set. This

was rejected due to the use of non-lenovo hardware.

The second attempt was to implement a multiseat

system by modifying the login manager and the X

windowing system. During the course of searching

for up to date documentation on Xephyr and gdm a new program called MDM was

discovered. MDM provided scripts to do most of the work referred to by the older

documentation. However, the software was immature and several patches were

needed to ensure it functions correctly. Specifically, there were several bugs which

the developers never tested for, including a bug where the program terminates

prematurely.

Josh was able to analyze the codes and fix most of the bugs. The software

required major retooling to be compatible to with the Nvidia drivers. Fortunately

one of the developers uses an Nvidia system and was able to provide valuable

assistance in adapting the existing code to use the Nvidia drivers. Another major

development was discovering how to enable audio devices for the system. Enabling

audio devices system wide required solving a problem where certain programs

would work properly while others failed. This was eventually traced to an issue

where a file was not getting processed correctly. Other tasks included locating a USB

serial interface and helping my teammates develop software for the USB interface.

Overall, most of my tasks involved dealing with software, or interfacing hardware

with software.

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Jakub Mazur

Jakub Mazur was the Project Manager of the team. He

was heavily involved in photovoltaic component

selection including: Determining the size of the PV

array, sizing the battery array, wiring gauge

selection, and the DC-AC inverter selection.

Jakub acted as supply chain manager since there

needed to be a serious amount of logistics to be

taken care of to source parts in Africa and

communicate and assign tasks to the Tanzanian

students. This included plenty of research, keeping

up with emails on a daily basis and making phone calls at 2am to motivate third

parties to do their job. This task turned out to be extremely time consuming and

quite frustrating. The time-difference also played a role in this as often only one

communication per day is possible.

Jakub was also heavily involved in testing stages, he performed load current

measurements using data acquisition hardware and programming in LabView. This

provided critical power consumption data as well as capturing surge current data.

His technical roles also included helping all the other team members with any issues

they where having. He worked with Ben and Eric on the microprocessor power

monitoring circuitry. He also worked with Eric to design and physically build the

faceplate of the power monitoring equipment.

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Ben Kershner

Ben Kershner, the document prep, handled the

collaboration, formatting, and finalization of the team

documentation. He also spent several days researching

the types and prices of solar panels and batteries, and

building a spreadsheet that helped to organize and

analyze this data, so that the team could choose the

most cost efficient parts of the power system.

The majority of Ben’s time was spent designing

and programming the circuitry for the power system

monitor. He built the prototype on a breadboard and

wrote a series of proof-of-concept coding examples to test the various digital and

analog I/O features of the PIC, including a custom LCD driver library to interface the

PIC to a Motorola 44780-type chipset.

Ben’s application note in measuring high DC voltages with the built-in ADC of

the PIC in a power efficient manner was implemented in the final design of power

system monitor.

Ben also wrote the server side code to accompany the power system

monitor. Written in C++, and taking advantage of UNIX system calls, it enables the

server to pull metric data off of the PIC. It then writes this to an XML file, which is

uploaded to an offsite server on a daily basis.

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Appendix II - Schematics

Figure 23 - LCD control board schematic.

Figure 24 - LCD control board layout.

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Figure 25 - Power system monitor schematic.

Figure 26 - Power system monitor layout.

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Appendix III – Gantt Chart

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Appendix IV - Nomenclature

C3SL – Center for Scientific Computing and Free Software. CPU – Central Processing Unit, refers to the main processor chip on a

computer motherboard, not the computer as a whole. COTS – Commercial Off The Shelf, describes hardware or software that may

be purchased rather than designed and built. FOSS - Free and Open Source Software. MPPT – Maximum Power Point Tracker, a style of solar charge controller. multi-seat – A type of system architecture in which many workstations are

built onto a single machine. PIC – The company that produces the microcontroller used, may also refer to

the microcontroller itself. PV – Photo-Voltaic, i.e. solar panel. PXE – Pre-boot eXecution Environment, a manner of booting computers over

the network without a locally installed operating system. OLPC – One Laptop Per Child. OSS – Open Source Software. system architecture – The term used within this document to describe how

the style in which the workstations are deployed. thin client – A client computer that relies on a central server for a majority of

its processing tasks.

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Appendix V - References and Recommended Reading

Hankins, Mark, and Francis Njeru. Solar Electric Systems for Africa : A Guide

for Planning and Installing Solar Electric Systems in Rural Africa. Ed. Timothy

Simalenga. Beverly: Commonwealth Secretariat, 1995. 7-8.

http://www.knowledgehound.com/topics/solar.htm

World Insolation Map: http://www.sunwize.com/info_center/insolmap.htm

Sun path chart: http://www.oksolar.com/images/solar_path_large.jpg

Outback Power Flexmax User Manual:

http://www.outbackpower.com/pdfs/manuals/flexmax.pdf

Wiring Safety Concerns:

http://www.usbr.gov/power/data/fist/fist3_3/vol3-3.pdf

Also, http://www.solarpowerforum.net/forumVB/showthread.php?

t=1890&page=3

** Source: Sunwize PV installation guide as well as other installer personal

experiences

http://www.sunwize.com/catalog/images/design_sunwize_guide.pdf

http://www.windsun.com/Batteries/Battery_FAQ.htm

http://www.windsun.com/Batteries/Battery_FAQ.htm

http://www.nmsu.edu/~tdi/PV=NEC_HTML/pv-nec/pv-nec.html

http://www.nwes.com/Wire%20Loss%20Tables.htm

http://www.egr.msu.edu/classes/ece480/goodman/spring08/group03/

http://www.outbackpower.com/

http://ww1.microchip.com/downloads/en/DeviceDoc/39631E.pdf

http://ww1.microchip.com/downloads/en/devicedoc/C18_Lib_51297d.pdf

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