Introduction: A Bidirectional Logic Level Converter (for I2C)
When working with sensors and microcontroller or arduino's, you'll need a level converter as a lot of sensors are designed for 3,3V and most microcontrollers will be 5V.
I know that they can be bought cheaply at sparkfun and others but when you only want to buy one converter you might pay more for the shipping than for the actual thing. And besides that, it is a simple thing to make.
You only need two bss138 mosfets, four 10k resistors, two sets of male headerpins and a pcb or a piece of veroboard.
Step 1: The Circuit.
There is not much to tell about te construction of this circuit. Connect the gates directly to 3,3V, the sources via a 10K resistor to 3,3V and the drains via a 10K resistor to 5V.
Then make yourself a nice PCB-layout or find yourself a small piece of leftover veroboard and head to the next step.
Step 2: Soldering and Hook Up
Solder everything together. There are only 8 components so it shouldn't take long before you can add it to your breadboard.
I added a picture with the connections on it. The sda and scl could be swichted aslong as you switch them on the other side too.