In a previous article, I talked about how a bidirectional mosfet level shifter works. I built a 4-channel model.

Now let's see how it actually performed.

Ever wanted to connect 5V logic to 3.3V logic? Annoying, isn't it? The voltages are so close... sometimes, a 5V logic pin even recognizes 3.3V as high. (Tip: don't rely on this as an acceptable solution. Fried chips happen.)

There are a few ways we can deal with this. We can use a buffer chip. We can use resistors or diodes to drop voltage. Blah, blah, blah. Here's the approach I like:

So how does it work? Let's find out after the jump. The basic theory of operation is the opposite of what you usually expect - a high voltage causes the transistor to turn off and not conduct!