THE Simplest IPod / IPad / IPhone Charger Circuit




Posted in TechnologyElectronics

Introduction: THE Simplest IPod / IPad / IPhone Charger Circuit

About: Just getting into the microcontroller craze. I used to do this sort of thing building circuits for 8 bit microprocessors back in the early 80s, so this is kind of like reliving a bit of my childhood. Back th...

Ok, so you have some parts hanging around, and maybe tried to make something to charge up your iPhone or iPod/iPad but nothing seems to work right. You keep getting that message saying that Charging Is Not Supported With This Device - or some such similar message.
Well, this is my super simple solution to this all too common issue.

The idea here is put some rechargeables in a project box, or get a battery case or a  sealed lead acid rechargeable or whatever - the circuit is the key.

Build it into a flashlight, AM/FM Radio / ghetto blaster, or other battery operated device that you might take camping or anywhere you may not have a power source.

The circuit itself is where the genius is. To my knowledge, NOBODY else has made the circuit this way.

The video of the final product I made is below. I decided not to edit out the initial OOPS where I didn't quite get the switch fully flipped...LOL. Stuff happens!

Step 1: Parts List:

5 resistors of the same value.
We don't really care much what value they are. Put away your calculator - we don't need it.
I have tried from about 100 ohms to about 5K and they all work, as long as all 5 are the same value.
Using 5 resistors means no calculations of ratios, and chances are, the last time you bought an assorted pack of resistors, there was a value you didn't use - or if you bought 100 of some value of resistor, chances are, there's leftovers.
This reduces cost, as we don't have to buy them if we already have them.
Also, if you are buying new resistors, you don't have to get 2 different values.
It's cheaper to get one value, as you usually have to buy a minimum quantity anyway.

A 5V DC power supply. 
If you want to use a battery pack, then we are going to also need a 5V regulator.
A small amount of wire, solder, and soldering skill
A female USB type A socket.
A scrap piece of perfboard

Step 2: The Hookup

Later I am going to discuss an even easier way to do this...but for now...
Connect all the resistors in series.

connect one end to the GND of the USB, and the other to the 5V.

Connect the junction between resistor 2 and resistor 3 (counting from GND) to both the D+ and D- of the USB.

That's it. If you put 5V into the USB, your apple or other device will now see it as a valid charger.

If your source is a battery, you will need to put it through a 5V regulator first, and put the output from the regulator to the 5V on the USB plug.

If you want, you can put separate inputs for 5V and 6+V (the 5V input bypassing the regulator).

Step 3: That's IT - Except, We Can Make It Simpler Still

OK, that's it. 
I made a quick and dirty one to prove the concept, and it worked on my iPod and an iPad I have in for repairs.
I didn't have a 7805, so I used a 5V 1117 SMT regulator.
This lets me charge or run a USB device portably off a battery pack (rechargeable or otherwise).
Better yet, mount it to a 9V battery clip! 
Going out to the woods for the whole weekend? Get a 6V lantern battery or Sealed Lead Acid rechargeable.
I actually built this into a $5.00 6V flashlight. You have to take the flashlight anyways, may as well make it all 1 device!
You'll have power for everything you need most all weekend long! Similar devices start around $100 and go up from there, and don't last nearly as long.
JUST REMEMBER TO SWITCH IT OFF OR UNCLIP THE BATTERY PACK WHEN NOT IN USE - There will ALWAYS be SOME current flow because of the resistors across the power supply and/or the regulator. Higher value resistors = less current drain when idle. 5KΩ each works well.

Don't forget that you WILL get that error message about not being able to charge off your source once your batteries or source voltage drop below a certain point!

But guess what? We can make it EVEN SIMPLER!!!

Remove the 5 resistors, and put in an adjustable potentiometer (a trim pot).

Step 4: The Simplest Version

Remove the 5 resistors, and put in an adjustable potentiometer (a trim pot).

Put either end of the trim pot across the USB Power (5V and GND) and trim it until the wiper (center) voltage is 2V.
Connect the wiper of the trim pot to the D+ and D- of the USB connector.

That's it. That's as simple as we can make it!

If you have a 5V source, putting this trim pot on the connector will allow charging the device.
If your source is more than 5V, you will require a regulator, just as before.

Above is the basic schematic and examples of adjustable trim pots.

Have fun charging or running your favorite devices from your favourite alternate sources!
Just remember that 5V regulators produce more and more heat, the more your source is above 5V
I usually don't recommend going above 9V (12V with a GOOD heat sink) into the regulator.

Also don't forget that you WILL get that error message about not being able to charge off your source once your batteries or source voltage drop below a certain point!



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    Well, it actually happened. Cell almost dead, and POOF - the power went out.
    Knowing where the flashlight is when the power goes out makes it easy to know where your charger source is! It's always great when what you thought was a good idea gets real world validation!

    What about the capacitors that the 7805 needs?

    5 replies

    Not necessary when using a DC source.

    I have never found the capacitors to be necessary. Back in the 80's when I first was using these regulators, the capacitors were not ever even mentioned.

    Without it, there will be stability issues. In a production item, we've had occasional assembly issues and with specific circuit behaviours, we could easily point to a regulator capacitor issue, which turned out repeatedly to be poor solder joints. For a few pennies, I'd highly recommend adding these.

    You cannot say there WILL be stability problems.
    There MAY be stability problems - and I have never run into any thus far.
    Yes, it's good practice to put in external caps, but the device itself is designed with all the components it NEEDS internally to operate properly under most conditions.
    If you are worried about it, use a RECOM 7805 replacement device. It's more efficient and does not require these components outside of the device.
    When using a DC source, a cap on the input side is redundant, and the cap on the output only serves to provide additional stability with rapidly changing loads (of which a cell phone is not one)

    I am not saying DON'T use them - add them if you wish - but for this application, they simply aren't needed.

    Thank you very much! This worked amazingly.


    Could you please show us a chart of how to connect the different components if we were to do this for our science project. We don't understand 100% how we connect everything the simplest way including using a heat sink. We have our bread board, heatsink, regulator and will go get a female usb as well as resistors and or a trim pot . could you please let us know exactly what parts we need. We tried to take a car charger apart but can't figure out how to connect it with our solar panel.Thank you so much. From Alexander and Benjamin

    Could i use one resistor that is 9.53 kilohms and one that is 13 kilohms and connect them in series, one end would go to pin one and one end to pin 4 then connect the midpoint to pins 2 and 3. Would this work properly?

    3 replies

    it MIGHT work, but iPhones, iPads and iPods tend to be very particular about the ratio.

    10K and 15K would work, because that puts the midpoint at 2V.

    Your resistors will give about 3.67V

    With a 9.53K youd need a 14.295K with it to make the right ratio.

    I have found a 10k resistor and 15.4k resistor, would this work well or is it still to far off to work properly?

    should be close have to try it.

    Please help me any one ,can we made our own cable (iPad mini)
    Please help me ,I'm unable do it.

    1 reply

    If you're talking about the USB cable itself, that's not what this instructable is about. The cables are about $1 each or less on ebay. Just go buy a cable.

    You can actually reduce the circuit complexity by using 4 resistors of equal value.

    (R1 + R2 ) > R3 > R4 where + represents parallel and > represents series. Run your tap leading from output to ground between R3 and R4.

    Ohms law isn't rocket science ... there are online calculators if you really need one ... ... if you are going to power an iPhone from another battery, you want to waste as little power as possible providing offset voltages to the D- and D+ pins (Pins 2 and 3 respectively)
    I have tested several chargers, including Apple's Stock 5V1 1 Amp charger ... all the chargers appear to use resistors in the range of 40K to 100K ohms to provide one of 2 modes using offset voltages on pins 2 and 3 ... for the 0.5 Amp chargers, both Pins 2 and 3 use an offset voltage of 2.0 Volts (this is what your example circuit above would provide) ... the 1 Amp chargers use offset voltages of 2.7 volts on Pin 2 and 2.0 Volts on Pin 3
    I tested the following resistor combinations for the 2 modes:

    0.5A mode: using 2 standard value resistors hooked in series 33K + 22K ... 33K tied to 5V and the 22K tied to Ground ... can be used to provide 2.0 Volts to both Pins 2 and 3

    1A mode: using 4 standard values resistors: hook 39K + 27K in series to provide 2.0 Volts on Pin 3 and hook 22K + 27K in series to provide 2.7 Volts on Pin 2

    Also built and tested a charger based on the LM2575T 5V 1A regulator (using the application circuit provided in the Texas Instrument datasheet) plus the 1A mode resistors ... what is great about this regulator is it will accept a wide range of input Voltages up to 45V which is perfect for small scale solar applications. Small scale solar panels around 25 Watts can have output voltages reaching into the 30 Volt range. Consider that this regulator circuit can be plugged directly into a range of battery voltages; 9, 12, 24 or directly in to an unregulated Solar panel without having to make any modifications. The 7805 will start to produce a lot of heat beyond 12 V ... the LM2575 hardly gets warm in the midday sun (read max voltage)

    3 replies

    Yup - the idea here was to make it a no-brainer for anyone with surplus resistors.

    Many of us have to buy 10 or 100 resistors of a given value when we only need a few - so the idea here was that basically regardless of the value of your surplus resistors, you could easily make the circuit using 5 of whatever value you had as long as they are all the same value. Thanks for the tip on the regulator, but the coil it requires makes it much less likely to be able to build with parts we already have or can scavenge off another circuit - plus the regulator itself isn't something we are likely to just have handy or on another circuit. The idea was to make it as simply as possible with stuff we already are likely to have.

    Yes the KISS concept should always be a first consideration ... you did state in your replies that the resistance should be higher then lower.

    However, one of your replies indicates that applying a simple 2V0 on both D- and D+ selects the high current mode ... my findings and testing found that 2V0 on both Pins actually selects the low current mode not the high current mode ... I found that Apple and other 1A (high mode) chargers supply 2V7 on pin 2 and 2V0 on pin 3 and 0.5A (low mode) chargers supply 2V0 on both pins

    As far as ashtray part designs go. While I do raid the ashtray or recover certain parts from junked electronics for some things, I am not willing to take chances using "Surplus Parts" especially when it comes to interfacing to pricey tech like an iPhone.

    I live in a fairly rural area, hundreds of miles from any electronics supplier ... yet online suppliers provide me with one business day to my door service with shipping costs of $8 for orders under $200 or free delivery on orders over $200 ... the parts for one LM2575T charger cost me roughly $12 (including the coil and shipping) ... I splurged and bought enough parts for 3 chargers, plus, had 3 prototype PCB boards made for a cost of $95 ... after all the dust settled, this project cost me roughly $44 ($130/3) for each charger; $27/3 parts, $8/3 shipping, $95/3 for a 3 pcbs ... when I lived in a large city with local distributors I never had service this good. Back in the 80's it always seemed parts were stocked elsewhere ... this required either wasting time going to every distributor in town or paying premium prices to get parts shipped in from other locations in a timely manner.

    Back in the 80's, I got everything at Radio Shack...there was no internet to order from...LOL! If Radio Shack didn't have what I needed, they could order it for me. Back then, the parts weren't "expensive" because I had no frame of reference for comparison - parts simply cost whatever they cost, and that was it.