Elenco's PK-201 Experiment #22: The Voltmeter

This experiment will measure the voltage at the base of each of the two transistors. And, is a circuit that is in a form called the Differential Pair transistor configuration. When the base voltage of each transistor is equal, both LED's will be equal in brightness. If the right LED is brighter, the base voltage of the right transistor is higher than the left transistor and vice-versa. In the video, I demonstrate this by switching between the base voltages of each transistor and measuring them with my multimeter. The variable resistor is used to adjust the voltage at the base of the left transistor, which feeds voltage into the second transistor therefore controlling the voltage across the base of each transistor.

 

 

Circuit

 

Elenco's PK-201 Experiment #21: The One Finger Touch Lamp

This experiment is an improvement of experiment #20. The circuit is completed with one wet finger between two resistors. In addition, to show the basic principle used in touch lamps and touch devices. The lamp does not stay lighted because there is no memory built into the circuit.

 

 

Circuit

 

Elenco's PK-201 Experiment #20: The Two Finger Touch Lamp

This experiment demonstrates that the body can be used to conduct electricity. By using one's body to complete the circuit the transistor is turned on and the LED lights. More over, the experiment show that dye fingers do not conduct as well as wet fingers.

Circuit

Dry

Wet

Elenco's PK-201 Experiment #19: The Darlington

In this experiment, the transistor configuration is called the Darlington configuration, current is amplified twice. All the current flowing through the emitter of the first transistor (left) will flow to the base of the second transistor (right). This means that the current flowing into the base of the left transistor will be amplified twice (once by each transistor), or twice the amount of base current is needed to control the larger current in the circuit turning on the LED. To turn on both transistors the capacitor voltage must exceed 1.4V before the LED will light. And, since the input current to the base is so small, it will take much longer to discharge the capacitor. In the video, I show the voltage at the capacitor. First, when the switch in on, charging. Second, when the switch is off, discharging. In addition, midway through the video, I show the voltage at the collector of the right transistor as voltage is pooling. Last, in the video I short the capacitor to discharge it much faster. The pictures below the video show the voltage at each transistors in the order of base, collector, and emitter. For some reason, at times, Blogger does not let me insert text for all my images.  

 

 

Left Transistor base voltage

Left Transistor collector voltage

Left transistor emitter voltage

Right transistor base voltage

 



Elenco's PK-201 Experiment #18: Very slow Light Bulb

This experiment combines transistor basic principles and what was learned in experiment #8 (capacitor charge/discharge). When the switch is first turned on the current flows through the 100k ohm resistor (controls charge time of capacitor) to charge up the capacitor, the transistor and LED will be off. When the capacitor rises to 0.7V the transistor turns on first and than the LED will turn on. Current will increase as the capacitor voltage rises. When the switch is turned off the capacitor will discharge through the 470 ohm resistor and the transistor base (resistor controls discharge of capacitor), the LED will dim as this discharge current decreases. When the capacitor voltage drops below 0.7V the transistor will turn off.

 

 

 

Elenco's PK-201 Experiment #17: Standard Transistor Biasing Circuit

This experiment uses a variable resistor to show that 0.7V is needed at the transistors base to allow current to flow in the circuit. As the voltage increase the transistor turns on until a larger collector current lights the LED.

 

 

 

Elenco's PK-201 Experiment #16: The Substitue

In this experiment, the NPN transistor base is connected to the collector making the transistor function as a diode. Once 0.7V is applied to the base current flows with only slight resistance and no current gain. Exactly as a diode functions.