We talked about transistors and how they can only pass a limited amount of current because of their gain. We first built a circuit which uses a small transistor with low gain to turn on a incandescent 12v bulb. The light is unable to fully illuminate because of the limit of the small transistor. If we use a single larger transistor, the PICAXE is unable to provide enough current to fully "turn on" the transistor. The dimly lit bulb:
We can use the small transistor to power the base of the larger transistor. This is the result:
As you can see, much more current gets to the bulb. However, this dual transistor arrangement is commonly used, so we can use an already manufactured transistor called a darlington transistor which is the same thing in a single transistor package.
I used this transistor along with the PIC to control the motors on my fish.
After that I looked at the PWM capabilities of the pic and then serial interfacing with the computer. I wrote a program that allows the computer key presses to send data to the pic which would return the data to the screen. This required building a circuit that could switch between program mode and serial interface mode:
To do that I just have to move the white serial wire between pins on the breadboard. I went home and programmed the pic to turn on and off an LED with a keystroke. And slept.
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