Tracing the history of education system in Kenya, one would quickly admit that instead of climbing up the dungeon we are busy digging deep!
The current state of events speak for itself. The recent research shows that class six pupils are brighter than their teachers. That indeed is very shocking! Besides, to nail this fact on the cross, the earlier research had it that primary teachers score as little as 19% in class 8 Mathematics and English exams. Wonders will never cease. Furthermore, the current fierce battle between the KNUT and the government as per whether lower classes should be taught in mother-tongue for those hailing from rural areas, and the equivalent city characters be taught in Kiswahili. This is very ridiculous! Just to give one of the greatest challenge that await the innocent pupils; as much as the so called 'government' and KNUT...have the audacity to decide for them, I wonder whether they take in consideration that people keep on changing their residential areas year in year out. Maybe because of transfer issues, war-torn regions, search for greener pastures among those you think of. For instance, a class 3 whose parents have moved from rural area to Nairobi all of a sudden beginning to learn in a different scenario, it doesn't pay oh. The Kenyan child should have no restrictions whatsoever to schooling in any region or place, not at all on the basis of language which takes us back to 'Egypt'-tribalism. How many pupils are benefiting from the laptop project?
The exam cheating witnessed over years in the KCSE is another thorn in the flesh. The 'Big Fish' obviously having an upper hand over the small ones. Such a shame! With exam oriented teaching in high school whereby only one exam, KCSE exams, determining the fate of a student whether eligible to join institutions of higher learning, it really waters down the credibility of the measure. This can be a topic for a whole month.
The nightmares seen in the universities, colleges and the likes is another horror movie! Most students do not attend lectures, they do exams and well their transcripts are full of A's but have very little if not nothing to offer to the corporate world. These institutions have become money makers with little concern on the impact they have in the lives of their don't care clients. It's such a sorry state yet we live with it.
DIY POWER BANK.
Packet students can use during the workshop, and then take home with them in addition to their solar. It would be good to introduce more basic concepts like voltage and current with the LED circuit before doing something more complicated like the solar. Some amount of basic knowledge would be helpful.
This is meant to be a follow-up to the basics of electronics. Not really complicated, but not intuitive for beginners either.
Things to go in packet:
- How it works
- Explain voltage, current (water metaphors?), resistance
- Power, charging battery, etc.
- USBs and how they work (D-, D+, 5v, gnd)
- Voltage divider explanation
- Capacitor and reason for its use
- Schematic
- Layout on Board
- Picture of completed board
- Color-code things, make it easy for people to see where things go
- Instructions on how to use it
- Approx. charge time
- Try not to leave it in the rain
- Turn off panel, batteries, charging instructions
- Take it back to Twende if breaks
- RECYCLE THE AA BATTERIES WHEN THEY DIE (directions to a place in Arusha that can recycle)
- Basic soldering techniques? Maybe separate packet we can steal from online.
- Promote Twende… encourage people to come to the workshop and tinker
- List of external resources… websites, videos, books, places to get electrical supplies for tinkering in Arusha
****Scroll down to see draft***
Build Your Own Solar Charger
You will need:
- 1 x 150k Ω resistor
- 1 x 100k Ω resistor
- 1 x 220 μF capacitor
- Female Solder USB
- Perforated Prototyping Board
- 4 x AA Batteries
- 1 x Solar Panel (2W at 6V)*
- 1 x Switch
- Soldering Iron
- 1 x Project Box
Overview:
This is a circuit diagram of our solar charger. Circuit diagrams are a way of representing the electrical connections in a system. Think of each of the black lines as a wire, connecting the ends of each components together. We will be walking through the circuit diagram step-by-step and explaining each component.
Batteries - Rechargeable batteries are the heart of your solar charger. They provide the power necessary to charge the phone or device you connect to the charger. The chemicals within a battery allows them to store an electrical charge. Think of rechargeable batteries as pools of water, that can drain water until it is empty, and then be filled up again. Normal alkaline batteries slowly release the charge stored in the chemicals, providing current to the circuit until the charge in the chemicals runs out. Rechargeable batteries are special because this process can be reversed. After the batteries are drained, by putting a current across a rechargeable battery you can restore the charge. This allows you to drain a battery, and recharge it many times. Unfortunately, many of the chemicals in rechargeable batteries are harmful to the environment. After a rechargeable battery stops working, it is important to dispose of it properly by taking it to a recycling facility. 
Solar Panel - Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.
PV cells also all have one or more electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.
The voltage and the current provided by the solar panel can be used to produce a current across the batteries and recharge them. Current flows from high voltage potential to low voltage. That is why if you connect a 6V panel across 4.8V batteries, it creates a current across the batteries that recharges them. This is also why we placed a diode (D1) between the solar panel and the batteries. A diode only allows current to flow in one direction. This is important because the voltage across a solar panel will vary a lot depending on the amount of light it is exposed to. If the voltage were to drop below the battery voltage (4.8V), then current could flow out of the battery, draining it and wasting energy. The diode makes sure that the current only ever flows from the panel into the battery, and not the other way.
USB - We use USB cables all the time. Ever wondered how they work? If you cut open a USB cable, you’ll find that it has 4 wires inside of it. Each wire serves a different purpose. The red and black wire are used to power the device that is connected. USBs typically operate on 5V, meaning that the red cable is the +5V wire, and the black cable is ground. This is why the positive USB is connected to the positive battery wire, and the negative battery wire to the ground wire of the USB. The green and white wire are the data connections. This is how your device communicates with your computer when it is plugged in. Small electrical signals are sent along each data wire to and from each device, enabling you to copy photos and files from your phone onto your computer. In a USB connector, there are four pins, one for each wire.
Because all we care about is charging the device, the two power cables should be enough, right? In the past, this was true--- if you connected 5V to the red wire and ground to the black wire, your device would charge. However, most modern devices are programmed to reject a charger if it doesn’t have a data connection. This is why we need to provide 2V to each of the data connections. This gives the phone the go ahead to charge.
The Voltage Divider
So, we need the voltage on each of the data pins to be 2V. But all we have is 5V and ground, how do we get 2V? This is where the voltage divider comes in.
Voltage dividers are very common in electrical circuits and simple to build. All you need is a power source and two resistors. Any time you have resistors connected between a power source and ground, there will be a voltage drop associated with each resistor. With just one resistor, the entire input voltage will drop across the resistor. With two resistors, some percent of the input voltage will drop across the first resistor, and the rest will drop across the second resistor. Accessing the point between the two resistors yields a different voltage than the input voltage.
Vin is the voltage we have, and Vout is the voltage we want. R1 and R2 are the values of the two resistors. The value of Vout is going to depend on the values of R1 and R2, and we can choose the values such that we get the value of Vout we want. The value of the new voltage will depend on the values of the two resistors. If the first resistor is much larger than the second, more of the voltage will drop across it and Vout will be smaller. If the first resistor is much smaller than the second, less of the voltage will drop across it and Vout will be bigger. If the two resistors are the same size, then Vout will be half the original voltage.
The equation used to calculate a voltage is given here:
Vout =R2R1+R2Vin
In our example, Vin= 5V, R1 = 150kΩ
and R2 = 100kΩ This means that
Vout = 150kΩ/(100kΩ +s:) * 5V = ⅖* 5V = 2V
We have reached our target voltage! Hooray!
(side note, might take out. that or elaborate) So you can see that the size of the resistor doesn’t matter too much so long as you get the right ratio. I chose 100kΩs as my second resistor because they are easy to find, plus it is a large value so there will be less power drawn to the data connection. (if elaborate, will explain )
The Capacitor We’ve covered most of the components in our solar USB charger. So what is the capacitor for? You can think of a capacitor like a very, very small battery. Capacitors store and release charge, but much faster and in much smaller amounts. When we first connected the phone to the batteries, we found that the voltage fluctuated a lot. Instead of a steady 5V that the phone needed to charge, the voltage was changing from 4.7 to 5.3 very quickly. In general, capacitors are resistant to quick changes in voltage. By connecting a large capacitor to the power source, we were able to stabilize the voltage. When the voltage goes up, the capacitor stores the charge. When the voltage goes down, the capacitor releases charge. This smooths out the rapid changes we were seeing in the voltage.
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Now that you know how it works, LET’S BUILD IT!
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How to Take Care of your Charger
Now that you have your very own solar USB charger, let’s take good care of it. Here are some tips to make sure your little charger will last a long time.
- To charge the batteries, attach the solar panel to the positive and negative terminal on the project.
- Try to protect the circuit from water and rain.
- Be gentle with the charger. Try not to drop it or jostle it.
- When the batteries expire, make sure you take them to a recycling facility or bring them to Twende.
If your charger breaks or stops working, bring it to Twende. We’ll help you fix it!
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Additional Resources
Did you enjoy this workshop? This is only the beginning. Want to learn more? Have a cool idea you want to build? Come to Twende! You are welcome anytime.
Twende is located in the TASO Nane Nane Grounds, Njiro, Arusha. You can find more information at www.aisetanzania.org or email marko@twende-tanzania.org or call Marko at +255 (0) 762 612 602.
There are hundreds of step-by-step projects you can build here:
Here is an interactive guide to voltage dividers:
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