Tuesday week 2

We started off by introducing the transistor, an electronic switch. The circuit i constructed applied voltage to the base of an NPN transistor, which switched it on, passing the voltage from collector to emitter and turned on the LED.We then replaced the Base resistor with two wires and held them in our fingers. We saw that as we varied the voltage going to the base by squeezing tighter, the LED grew brighter. A transistor amplifies any change in voltage applied to the base and applies it to the emitter as a change in current!

After that, I constructed a basic logic probe. The concept for the basic one is that when the probe is disconnected, the LED is dim, when it recieves a HIGH logic signal (~5v) it goes bright, and when it recieves a LOW (0v) it goes off. This is my basic logic probe receiving a high signal:
After i did that, I spent the rest of the evening working on building the advanced version. The difference is that it uses 2 LED's. When the probe is unconnected, both stay dim. When it receives a high signal, the green LED illuminates, and if it's low, the red LED lights. The circuit uses an NPN and PNP transistor, one for each signal type. The hardest part was choosing the correct value of resistor to match the gain of the transistors and get the correct brightness on the LEDs. The prototype on the breadboard, and the completed perfboard.