My $15 12v Automotive 7-port USB hub

**colin** · 08-22-2009, 10:32 PM

With all the talk around here regarding automotive USB hubs and all that, I decided to take everyone's advice and build one. Here's how it came out:

As you can see, there are 7 ports and it clips right into the radio harness to grab power, ign, and ground. Tomorrow I'm going to hot glue it all so that it's a bit more sturdy and add some terminals so I can use the output from my IGN relay.

**meddler** · 08-22-2009, 10:38 PM

good work. I look forward to some more info about this.

**Punky** · 08-22-2009, 10:58 PM

Looks sweet!
curious why you chose to use the radio harness instead of just having +/-/ign, seems less flexible to me.

**colin** · 08-23-2009, 01:21 AM

I made it for me. Its simplest for me to get an IGN line from the radio harness and tomorrow I'm going to put some terminals at the top so I can access the IGN line and send it out to my amps. That and all my USB devices are up front so it just works out best.

I basically just ran the IGN from the harness into a relay that switches the battery when the car is on. Then that goes out to terminals for later and also into a DC-DC regulator. That puts out 5v at 3A for the USB hub. Stuffed that in an old project box and bam all set

**Punky** · 08-24-2009, 02:58 AM

don't mind me asking, what's in the box?

**colin** · 08-24-2009, 02:45 PM

Exactly what everyone said to use.

Inside the box is a relay, a DC-DC step-down converter, and the USB hub. A little soldering here and there and I have a high-power IGN circuit and a 12v USB hub with 7 ports

**rockyct** · 08-25-2009, 01:06 AM

Originally Posted by colin

Exactly what everyone said to use.

Inside the box is a relay, a DC-DC step-down converter, and the USB hub. A little soldering here and there and I have a high-power IGN circuit and a 12v USB hub with 7 ports

Where did you get the step down converter? Also, I'm assuming the way you wired it (relay off the ign wire?), the hub isn't powered when the car is off.

**2k1Toaster** · 08-25-2009, 02:14 AM

did you just do step down, or did you do buck-boost? Did you integrate a microcontroller for startup/shutdown delay or simple relay on/off with the car activation?

Have you taken the lifespan of the relay and the induction of the coils into effect on sensitive USB lines?

**Punky** · 08-25-2009, 12:27 PM

Buck boost is definitely the way to go here, it'll give you a much wider voltage range and would make it more car suitable. I don't think he used a ucontroller from the sound of it, and plus its probably add unnecessary complication if he did.

personally, i always used the extra usb header ports on my motherboard (most have 4 to 6 + 4 USB header) because i just want to avoid usb hub altogether.

Originally Posted by 2k1Toaster

did you just do step down, or did you do buck-boost? Did you integrate a microcontroller for startup/shutdown delay or simple relay on/off with the car activation?

Have you taken the lifespan of the relay and the induction of the coils into effect on sensitive USB lines?

**colin** · 08-27-2009, 12:13 PM

Guys, this is seeming way too complex. It's a simple hub. I used a Step Down DC/DC converter. I believe it is based off a buck circuit. Input voltage ranges from 4 - 25v and the output can range from 1 - 10v or 1.22 - 6.70v depending on the precision. It has 3A maximum output at 5v. At a full 3A, the efficiency is 90% whereas at about 1A it's 93%.

Yes, I have considered the "sensitive USB lines" and they are fine. The relay is an old one I had lying around since I bought so many of them. They have a very long lifespan if powered properly.

Yes, the hub loses power when the car is shut off. Remember this was just for me and that's the features I would like since I've had so many problems with my car starting nicely. I was posting this to show that it CAN be done.

No, there is no microcontroller. Although I am proficient in microchips, I did not see any need to add such complexity to this otherwise simple use! You need a relay, a power converter, and a hub. Shutdown controllers are for the computer. If you want this thing to shut off when your PC shuts off, then use the 12v line on your molex connector as the IGN line for the circuit. It will turn on when your PC turns on, and turn off when your PC turns off, the whole time using power from the car.

Any more questions? I just wanted to show that it can easily be done for much less than the $85 that MP3Car wants for a similar product. If, like me, you don't need those extra crazy features, this will be perfect.