Cell Phone Charger
The Goal
The goal of this project is to design and fabricate a mobile cellphone charger using a voltage source ranging from 6 volts dc to 24 volts dc. It will be able to operate using a 9 volt battery, a 12 or 24 volt car battery and a pack of 8 AA batteries as a power source.
Step one -- find the constraint
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Operate using a 6vcd to 24vdc input
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ability to charge iphone, android, and samsung phones
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charge faster than a normal wall charger
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charge the phones safely
Step two -- do the math
I phones require a voltage to the data pins in order to charge. The data-pin voltage needs about 2vdc input and the data+pin needs about 2.5vdc input to charge at 1.5 amps. A voltage divider circuit can be used to meet this sort of requirement. A voltage divider circuit uses a higher input voltage which produces a lower output voltage. The circuit diagram below is an example of a voltage divider
The equation for this is
vout = vin*R2/ (R1+R2)
Here is what it look like for me
2.0=5*220/(330+220)
2.5=5*100/(100+100)
Which means I needed one 330Ω resistor, one 220Ω resistor, and two 100Ω resistor
Step three -- design a prototype and bill of materials
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x1 7805 voltage regulator
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x1 330Ω resistor
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x1 220Ω resistor
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x2 100Ω resistor (can be any resistance as long as they are the same)
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x1 10 uf capacitor
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x1 smd usb type a female
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x1 pcb switch 3 pin
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x1 9 volt battery connector
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x1 custom made circuit board
Prototype Design
Step four --design the circuit board
When designing a circuit board make sure that none of the traces(wires) are too close to each other or overlapping each other. In this prototype design, if you look carefully, you can see that the 5 volt trace intersects the ground trace.
Step four retry --- design the circuit board
The prototype error was corrected
Final Circuit Board Design
step five
Here is a final product in a 3D printed case
By Palmer Tetley