By hinkmond on Nov 29, 2012
Now we're ready to connect the hardware needed to make a static electricity sensor for the Raspberry Pi and use Java code to access it through a GPIO port. First, very carefully bend the NTE312 (or MPF-102) transistor "gate" pin (see the diagram on the back of the package or refer to the pin diagram on the Web). You can see it in the inset photo on the bottom left corner. I bent the leftmost pin of the NTE312 transistor as I held the flat part toward me.
That is going to be your antenna. So, connect one of the jumper wires to the bent pin. I used the dark green jumper wire (looks almost black; coiled at the bottom) in the photo. Then push the other 2 pins of the transistor into your breadboard. Connect one of the pins to Pin # 1 (3.3V) on the GPIO header of your RPi. See the diagram if you need to glance back at it. In the photo, that's the orange jumper wire.
And connect the final unconnected transistor pin to Pin # 22 (GPIO25) on the RPi header. That's the blue jumper wire in my photo. For reference, connect the LED anode (long pin on a common anode LED/short pin on a common cathode LED, check your LED pin diagram) to the same breadboard hole that is connecting to Pin # 22 (same row of holes where the blue wire is connected), and connect the other pin of the LED to GROUND (row of holes that connect to the black wire in the photo).
Test by blowing up a balloon, rubbing it on your hair (or your co-worker's hair, if you are hair-challenged) to statically charge it, and bringing it near your antenna (green wire in the photo). The LED should light up when it's near and go off when you pull it away. If you need more static charge, find a co-worker with really long hair, or rub the balloon on a piece of silk (which is just as good but not as fun).
Next blog post is where we do some Java coding to access this sensor on your RPi. Finally, back to software! Ha!