Disclaimer: Do not make me responsible for any damage to your device/s
This is my first instructable so I hope it helps you to make this project.
Now this is no portable USB LM7805 phone charger, this is meant to be more energy efficient and practical. Why? Well because LM7805 have a forward voltage drop, which means that if you want a fixed 5 volt output, you want (need) your output votage to be at least 2 volts above it, meaning that you'll need 7 volts or more constantly to keep that 5 volt output stable, because anything bellow that will cause your output voltage to drop bellow 5 volts.
Now what can you use to replace the venerable LM7805? You could use a low dropout linear voltage regulator such as the LM2940, for this one you'll need at least 0.5 volts above your output voltage, meaning that (again) you want a 5 volts fixed output you want your input voltage to be at least 5.5 volts or more to ensure a steady 5 volts output.
Or you can go for a switch mode power supply or SMPS for short.
Some of these have the abillity to either step-down the voltage or boost it step it up, the ones I'm using for this instructable do both, they have a maximum input voltage of 11.8 volts a minimum of 2.7 volts, and create a constant 1 amp when stepping down and 500 mA when stepping up, making them ideal for batteries that inicialy have a charge of 9 volts and discharge bellow 5 volts.
In this case I'll wire up the regulators in parallel so I double my output current. 2 amps when stepping down and 1 amp when stepping up.
Great, now I think I've been talking (writing) too much, from now on I hope that you understood the difference between these type of regulators.
Now let's get to the practice.
You'll need these components.
-2 Pololu or similar 5 volts step-up step-down voltage regulators (http://www.pololu.com/catalog/product/2119)
-2 1k Ohm or larger
-1 or 2 female USB connector
-1 1000 uF 25 - 50 volts electrolityc capacitor (optional)
-1 9 volt battery and battery clip
-Male headers (optional)
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Wiring Up the Regulators
As I said before we'll be wiring up the regulators in parallel, thus giving 2 Amps when stepping down and 1 Amp when stepping up, perfect for most electronic devices such as iPhone's, iPod's, iPad's Android and Windows phone devices. And because they are also a step up and step down we can use it with a solar cell to charge devices using sun light, as it starts to get darker the output voltage generated by the cell starts to drop, which might be a problem with linear regulators, but not with these switched power supply.
Now lets begin with the wiring process.
First of all there's the schematic those S7V7F5 are the regulators.
Step 2: Adding the USB Port, Resistors and Capacitor.
Wiring the USB port is very simple, from left to right the first pin is the VCC or 5 volts out, the next one is D- or Data -, nex to it is D+ you guessed it, Data + and finally is ground or your negative. If you don't feel very confident about this go back and take a look at the schematic I'm sure this will help you.
Now what are the resistors for? Some devices like iPod's iPhone's and other need to sense a small voltage across the data pins in order to charge, that's why. Now why 1k Ohm? Well, it's just a random value I picked, you can use different values, 2.2k, 4.7k, 10k, 100k, and so, but first check that the resistor value you choose works before making it permanetly.
Being said that. Where do you wire up the resistors? Well that's quite easy, just put one between VCC and the data pins, that should do the job.
Now let's add some pictures so you get a better idea on how to wire it up.
First add a wire that connects the output of the regulator to the USB VCC pin (the red wire).
Leave two holes on the breadboard at the end of the wires.
Then add a second wire that runs from the Ground of the regulator to the USB ground pin.
Now begin to add the USB port.
Remember the leftmost pin is VCC or you positive output.
Then add the resistors between VCC and the two data pins.
You can add some male header pins to hold in place the USB port (in case you have wired up the USP port as I do).
Finally add the optional capacitor in between the input of the regulator.
Step 3: Connect the Battery and Test It Out!
If you have been following all the instructions congratulations, this is the last step.
At this point before testing it make sure everything is connected right.
To test it connect the battery terminals to the regulators the positive goes to the input of the regulator and the negative or ground of the battery goes to the ground of the regulator.
Finally connect your iPod, iPhone or mobile device and voilà! It should charge your device.
Step 4: The Final Product
If you've done it right it should look like this.
Thanks to all of you for taking a little bit of your time to read this, as I said earlier this is my first instructable and my English isn't very good, so if any of you have a suggestion feel free to write it down in the comment section as well as some questions.
Thank you :)