Making a USB-socket in a car with our own hands
To begin with, let’s find out what this concept means – a USB-socket? Nothing special in essence: USB-port on the car dashboard, equipped with power line, but with unused data transfer line, which is, roughly speaking, a universal interface for powering all sorts of USB-devices from small to large, and most importantly – for charging anything and everything that can be charged by USB: phones, photo / video equipment, mp3-players, etc.
By the way, for something that by default is not charged by USB, but only from a socket, you can always solder the appropriate cable for charging from USB to the specific device, just know the pinout – in general, it is not difficult.
So, let’s get down to the business of an old idea… First, let’s deal with the pinout of the USB-connector.
As you can see from the first picture you took from the search engine it’s pretty straightforward! So we need to use 1 and 4 pins of the plug. 1 pin should have stabilized 5 volt and 4 should be switched to ground. Where can we get stabilized 5 volts in the car?
For this we need a linear voltage regulator LM7805 and a couple of capacitors to it, namely two low-capacity ceramic capacitors to the input and output of the regulator for smoothing high frequency interference and preferably – electrolytic capacitor not very high capacity at the input to smooth low frequency interference, which in the car onboard network – not uncommon.
As you can see from the picture, the stabilizer is a three-legged radio component with input, output and mass. Assemble the whole thing and put an electrolyte on the input.
Basically we could stop here, but Vlad found a circuit for charging a currently popular mp3 player called I-Pod somewhere on the net. As it turned out, Apple products are a little more capricious and require special conditions, namely: raising the voltage on the USB Data pins (2 and 3) to 2V, which will be the charging control signal for the I-Pod.
This is implemented by connecting these two legs to stabilized 5V through resistors of certain ratings. Fewer words, the circuit will say much more, more concisely and faster:
Actually, at the beginning of the path we had (so far apart from each other) the following:
– LM7805 linear voltage regulator; – 0.1 uF ceramic capacitor – x2; – 470 uF electrolytic capacitor, 16V; – 75Kohm resistor – x2; – 51Kohm resistor (closest to 49.9) – x2; – double USB interface; – a piece of aluminum plate to use as a radiator for the stabilizer, which tends to get very hot during operation; – a piece of heat shrink of needed diameter.
Vlad, of course, wanted to solder everything neatly on a small etched board using SMD-radio parts, but a natural laziness and a sort of simplicity of the company prevailed, and we did everything on a hinged assembly, and then pulled it all into shrinkwrap.
Maybe not particularly neat… But who is going to mess around in the depths of my panel?!
I placed the connectors near the diagnostic, almost under the ashtray, a little to the right – there it is not conspicuous, but at the same time easily accessible. And you can connect two devices at once, and the cables can be divided in different directions as you want.
Building a universal, machine USB charger (try number one)
Hello Habra gentlemen and Habra ladies! I think some of you know the situation: “Car, traffic jam, N-th hour driving. Communicator with a running navigator beeping about the end of the charge for the 3rd time, despite the fact that all the time connected to the charge. And you, as evil, have absolutely no sense of direction in this part of town.” Next, I’ll talk about how to have a moderately direct hands, a small set of tools and some money to build a universal (suitable for charging at rated current, both Apple and all other devices), USB car charger for your gadgets.
WARNING: Lots of pics, a little work, no LUT and no happy ending (not yet).
Author, what’s the point of all this?
Some time ago I got the situation described in the prologue. Chinese usb-double, absolutely shamelessly let my smartphone run out of battery while navigating, out of the declared 500mA it gave out about 350mA on both sockets. I must say I was very angry. But never mind, I was a fool myself, I decided and the same day, in the evening, I ordered on eBay car charger for 2A, which has rested in the bowels of the Chinese-Israeli mail. By happy coincidence I found a step down DC-DC converter board with output current up to 3A and I decided to use it to build a universal and reliable car charger.
A little about chargers. Most of the chargers on the market I would divide into four types: 1. Apple-engineered ones with a little bit of charging trickery. 2. Conventional – aimed at most gadgets, which only need to be shorted DATA+ and DATA- to consume the nominal charging current (the one stated on your gadget’s charger). 3. The dumb ones that have DATA+ and DATA- hanging in the air. Due to this, your device decides that it is a USB hub or computer and does not consume more than 500 mA, which negatively affects the rate of charge or in the absence of it at all under load. 4. The tricky %%!$&e – since they have a microcontroller installed inside that
tells the device something from the category of what the notorious hero of Kipling told the animals – “We are one blood, you and I”, verifies the originality of the charging. For all other devices they are chargers of the third type.
The last two options, for obvious reasons, I consider not interesting and even harmful, so let’s focus on the first two. Since our charger should be able to charge both apple and all other gadgets, we will use two USB outputs, one will be oriented to the Apple – devices, the second for all others. I should only mention that if you by mistake connect your gadget to a USB socket which is not intended for it, nothing bad will happen, just it will take the same notorious 500mA. So, the goal is: “With a little hand work to get a universal charger for the car.”
What we need
1.First, let’s deal with the charging current, usually it is 1A for smartphones and about 2 Amps for tablets (by the way my Nexus 7, for some reason from his own charger does not take more than 1.2A). Total to charge an average tablet and smartphone at the same time we need a current of 3A. So the DC-DC converter which I have in my possession will do. I must admit that the converter for 4A or 5A would be better for these purposes, in order that the current would be enough for 2 tablets, but a compact and inexpensive solutions have not found, and also the time was running out. Therefore, I used what was: Input voltage: 4-35V. Output voltage: 1.23-30V (controllable by potentiometer). Maximum output current: 3A. Type: Step Down Buck converter.
I used a double USB socket soldered out from an old USB hub.
You can also use a normal USB extension cable socket.
I used a breadboard. For soldering the USB plug to something and build a simple charger circuit for the Apple.
4. Resistors or resistors, whatever you like and a LED. There are 5 in total, 75kOhm, 43kOhm, 2 50kOhm and one 70kOhm. The first 4 are used to build the Apple charging circuit, the 70 ohm I used to limit the current on the LED.
5. Enclosure. I found a Mag-Lite flashlight case in the back of my house. It would have been perfect for a black toothbrush case, but I couldn’t find it.
6. A soldering iron, rosin, solder, wire cutters, a drill and an hour of free time.
Assembling the charger
1. First of all I shorted together the pins DATA+ and DATA- on one of the sockets:
*Excuse me for being abrupt, I got up early and my body wanted to sleep but my brain wanted to continue the experiment.
This will be our socket for non-apple gadgets.
We cut the necessary size of the breadboard, mark and drill holes in it for the feet of the USB socket, checking at the same time that our contact pins match the holes in the board.
3. We insert the socket, fix it and solder to the breadboard. 3. We connect the +5V pins of the first (1) and second (5) socket to each other, in the same way we proceed with the GND pins (4 and 8).
The photo is only for clarification, the contacts are soldered already on the breadboard
4. Solder to the remaining two pins DATA+ and DATA- the following circuit:
We use the USB pinout to keep the polarity:
This is how I did it:
Do not forget to adjust the output voltage, with a screwdriver and voltmeter set 5 – 5.1V.
I decided to add indication to USB power supply circuit. I soldered yellow ice with 70 ohm resistor in parallel to +5V and GND to limit current.
Please to the people with poor soul and all lovers of beauty: “don`t look at the following picture, the soldering is crooked”.
5. Fixing the converter board to our breadboard. I did it with the help of the same resistors, soldering them into the contact holes on the converter board and the breadboard.
6. Soldering the converter outputs to the corresponding inputs on the USB socket. Make sure that the polarity is correct.
7. Take the case, mark and drill holes for mounting our board, mark and cut the place for the USB socket and add holes for ventilation in front of the converter chip.
We bolt the breadboard to the case and get a box like this:
In the car it looks like this:
Next, I decided to test if my devices will really count as being charged by the native charger. And at the same time to measure the currents as well. Power was provided by a 24V 3.3A PSU from an old printer. I measured the current before going to USB.
Looking ahead, all the devices I have recognized the charge. To the USB socket number one (which is designed for different gadgets) I connected: HTC Sensation, HTC Wildfire S, Nokia E72, Nexus 7, Samsung Galaxy ACE2. For the Sensation and Nexus 7 I tested the charging time, starting at 1% and charging to 100%. The smartphone was charged in 1 hour 43 minutes (Anker 1900 mAh battery), I must say that the standard charger takes around 2 hours. The tablet took 3 hours and 33 minutes to charge, half an hour longer than mains charging (I only charged one device at a time).
In order for both Android devices to get the most out of the charger, I had to solder a small adapter (which I connected to apple USB), it is connected to the HTC Sensation.
To the USB socket number two I connected: Ipod Nano, Ipod Touch 4G, Iphone 4S, Ipad 2. Since the Nano is ridiculous to charge with such a thing – it took 200 mA at most, I checked the Touch 4g and iPad. The Ipad took 1 hour and 17 minutes to charge from zero to 100% (along with the IPAD 2). The iPad 2 charged for 4 hours and 46 minutes (one).
As you can see the Iphone 4S happily consumes its rated current.
By the way the iPad 2 surprised me, it was absolutely no stranger to circuit with shorted data pins and consumed exactly the same current as the socket designed for it.
Charging process and conclusions
To begin with I would remind you that all devices which use lithium batteries have a charge controller. It works according to the following diagram:
The graph is averaged and may vary for different devices.
As you can see from the graph, at the beginning of the charging cycle the controller allows charging at the maximum allowable current for your device and gradually reduces the current. The charge level is determined by the voltage, and the controllers also monitor the temperature and shut off charging when the latter is high. The charge controllers may be in the unit itself, in the battery or in the charger (very rare). You can read more about charging lithium cells here.
Actually here we come to the point of why this topic is called: “Attempt number one”. The thing is that the most I could get out of the charger was: 1.77А
Well, the reason, in my opinion, not optimal selection of inductance coil, which in turn does not give Buck-converter to give its maximum current. I thought about replacing it, but I don’t have SMD soldering tools, and I don’t think I will in the near future. It is not a mistake of ebay board designers, it is just a peculiarity of this circuit because it is oriented on different input and output voltages. Under such conditions, it is simply not possible to deliver the maximum current over the entire voltage range.
As a result, I got a device that is capable of charging two smartphones simultaneously or one tablet in a car in a sane amount of time.
Because of the above it was decided to leave the charger as is and build a new one completely by hand, based on a more powerful LM2678 converter which in the future will be able to “feed” two tablets and a smartphone simultaneously (5A output). But about that for next time!
P.S.: 1. The text may contain punctuation, grammar and semantic errors, please report about them in private. 2. Thoughts, ideas, technical corrections and TAG from more experienced comrades – on the contrary, are welcome in the comments. 3. I apologize for possible technical inaccuracies, as I am not engaged in electronics and circuitry until recently. Thank you for your attention. Good luck and never ending optimism to everyone!