I had a client recently wanted to use USB in his car. He told me that kind of adaptores cost in the stores about 13-15 euro (8-10 USD) the cheap and about 25euro (18USD) the expensive. That was a challenge for me. So i tried myself to do it.
First of all we have to consider what exactly we need to do with a USB as power supply. To charge an MP3, using it as light resource or other genberal power supply of standart 5,1 V DC.
The materials are...
1. A Car lighter adaptor (from 0,50 to 1euro)
2. One 12V lamp or a led and 330Ohm Resistor 1/4Watt (0,02 euro)
3. A USB Sasshi adaptor. (I had one from spare parts) New costs 0,20 euro
4. Two pieces of cable one black 10cm and one red 7cm
5. One resistor 57 Ohm 1 watt (0,01euro)
6. One diode 5V1 (5,1V) (0,01 euro)
7. one Cooler (0,10 euro)
8. Some soldering and a little attention.
Step 1: Lets Work!
First of all we take the Car lighter adapter. All of them have fuse of 3A. We leave like it is.
The Lighter Adapter i got had a trasparent red cover and then i had another idea. To put a small 12 V lamp to define if it's working or not.
The Positive pole is in most cars the central pin.
So we place the small lamp among the negative and the positive pin of the adaptor
Also we Solder the cables in the + and -.
After we close the car lighter. If we power on it shows like this (Image 3)
Step 2: Power Limitation From 12V to 5,1V
The Power limitation can be done with combination of in Diode 5V1 and one resistor 47Ohm 1 watt.
We combine both like in the image. The + Cable (RED) connects is serial mode with re resistor. We prefer 1 watt or more because the resistor gets hot when the circuit works. The cooler covers the Resistor for better results. The diode of 5,1V says to our circuit that more power than 5,1V is not allowed.
For the USB sashi we need only the edge left and edge right cables. We nude out the cables and we cut the rests. Usual the L and R cables are red-black. Now I will use these 2 cables to solder them with the resistor and the diode. The + goes to resistor and the - goes to the light bulb and the diode. So simple...Just beware of power conflicts!!!. Use isolate tape and isolate thermal tubes...are more effective.... If you have any box in small size like one from old flashes or other are ideal to cover the whole project.
So friends that was the project. Easy, Cheap and need
See You All Around