USB chargers are one of the most popular things to build here on Instructables. However countless people have been disappointed to find out that after all of their hard work, their iPods just sit there and do nothing, despite receiving 5V.
Recently my USB car charger died. I thought it'd be great if I could just install USB ports into the center console, and I totally did too. But the iPod wouldn't charge, so I scoured the internet looking for an answer. I found out what I needed to do was put resistors onto the data lines, but nobody agreed on what resistors or even how to hook them up. Finally I just ripped apart my broken USB charger to see how they did it.
Recently my USB car charger died. I thought it'd be great if I could just install USB ports into the center console, and I totally did too. But the iPod wouldn't charge, so I scoured the internet looking for an answer. I found out what I needed to do was put resistors onto the data lines, but nobody agreed on what resistors or even how to hook them up. Finally I just ripped apart my broken USB charger to see how they did it.
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Signing UpStep 1: Schematics
First off I should mention that this is supplemental Instructable to the countless others that show you how to build a USB charger. I am assuming you've already made something that can supply 5 volts DC. I assume no responsibility for how this jives with your 5V power supply or the USB devices you connect to it. All I really know for certain is it works perfectly with my 4G iPod, my Energizer USB-powered battery charger, and my cellphone.
OK, here we go.
The values of the resistors in the schematic below can be approximate. Those are just the values I measured from the resistors on my dead car charger. You could also hook up different valued resistors in series to dial in the exact ohms (22K + 22K = 44K, perfect for R2.) Also, 1/8W resistors will work just fine.
Once you build the circuit, test it. You should get around 2.7 volts out of D- and 2V out of D+. This may seem scary high but it's in the USB spec for signaling a USB 2.0 connection. This is how the iPod knows it's OK to draw the power it needs to charge.
OK, here we go.
The values of the resistors in the schematic below can be approximate. Those are just the values I measured from the resistors on my dead car charger. You could also hook up different valued resistors in series to dial in the exact ohms (22K + 22K = 44K, perfect for R2.) Also, 1/8W resistors will work just fine.
Once you build the circuit, test it. You should get around 2.7 volts out of D- and 2V out of D+. This may seem scary high but it's in the USB spec for signaling a USB 2.0 connection. This is how the iPod knows it's OK to draw the power it needs to charge.
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Why would you want the phone to charge at 1A. If you force that much current into the phone you may damage something. FYI, the USB spec only calls for an output of 5V @ .5A. So less then .5A is all that is needed to charge the device. Also keep in mind the 7805 outputs 5V and has 1A of current available that doesn't mean your device will pull that much amperage.
- R1= 22K Ohms
- R2= 26K Ohms (1x 22K resistor and 1x 4K resistor in series)
- R3= 15K Ohms
When i first connected everything on my breadboard for testing the voltages came out wrong. So i flipped the resistors, putting both R1s on the Positive side and R2 and R3 coming off the Ground Lead. After checking the voltages across D+ and D- everything looked good so i plugged in my 2nd and 5th Gen iPod Touches and they where charging.
Thanks again for the info about the voltages on the data lines needed to enable charging.
Here is my schematic:
Would an inductor be a wise thing to include to help filter out the starter-motor's noise? And if so, are there things that need to be considered when choosing an inductor? Size? Core type? I don't want to inadvertently make a resonator circuit and do not (yet) have the mathematical knowledge to make an informed decision.
Also as other posters have stated, there seems to be a very wide range of what resistance is required in order for this to work. Pleasantly surprised everything went off without a hitch my first attempt, a fantastic instructable. My only recommendation would be to change one of the R1's in the schematics to a R4, especially since the third picture shows a R4.
IMHO, R4 should become "R5" and the R1 which is paired with R3 in the left hand voltage divider branch should be changed to R4 to make this circuit more understandable for those with less experience in electronics so you end up with an R1/R2 voltage divider on the right and an R3/R4 voltage divider on the left of the two voltage "divider diamond".
fry other phones or devices
However, I have a question. Since the - and + power lines meet (right?) because both R1's, R2, and R3 touch, would you then need a diode on one (or both?) power lines to prevent power flowing back to the batteries?
Is this circuit all that is required? Or is it a more complex chip as others have stated?
43k = yellow orange orange then gold or silver
74.9k approx 75k = violet green orange then gold or silver
43k = yellow orange orange then gold or silver
74.9k approx 75k = violet green orange then gold or silver
the 5v and 0 pins are still used to do all off the charging to the device
the data lines just tell the ipod it can charge (most likely so you can only plug it into a apple charger)
the data lines just need a set voltage. it consumes a very small amount off amps and none off that goose into charging the ipod