Elenco's PK-201 Experiment #14: The Electronic Switch

In this experiment, the transistor (2N3904 NPN Bipolar Junction Transistor) is acting as a switch. In the first picture there exists a closed circuit between the battery, 1k ohm resistor, LED, and transistor, but the LED is not lighted therefore current is not flowing. This is because the transistor is open and functioning as an electronic switch. When the on/off switch is turned on, current is applied to the base of the transistor closing the electronic switch (transistor) completes the circuit, which allows current to flow in the circuit. In the pictures below, I take voltage reading before and after turning the switch on. The first two pictures are at the collector. Notice the voltage before and after the switch is turned on or off. The next two at the positive side of the LED. The following two at the base. When the switch is turned on, 0.78 volts is needed to release the voltage between the collector and emitter. And the last two, the emitter. Note: all the readings are in volts except the last one. That is in millivolt because there is always a voltage drop across the NPN emitter. 

 

Very good visual for the NPN transistor



Switch is OFF Voltage is collected at the Collector 

Switch is ON Voltage is passing to the LED

Voltage at Diode with switch OFF.



Voltage at Diode when switch is ON.

 

 General information on transistors

The NPN Transistor

 



Super Stereo Ear MK136 by Velleman

The Super Stereo Ear is a stereo amplifier that will boost sound up to 50 times. The gadget has volume control via a potentiometer, on/off switch, two microphones, and one IC NE5532 for stereo tone control.

 

 

 

NE5532 Technical data

Elenco's PK-201 Experiment #13: One-way Light Bulbs

In this experiment, Diodes made of Gallium Arsenide are used or more commonly called LEDs. A turn-on voltage of about 1.5V is needed to pass current through these LEDs, but this voltage can vary depending on the type of LED. This current is so high that light is generated as it passes through the LED. In the video demonstration, the red LED lights up and slowly dims as the 100 microfarad capacitor is charged up. The second, blue LED does not light because it is wired in reverse-biased. Then the second wire (ground) is used to light the blue LED, which dims as the capacitor is discharged. The red LED does not light because it is wired in reverse-biased and not passing current. 

 

LEDs
Technical LED Color Chart
 

Elenco's Pk-201 Experiment #12: One-way Current

This experiment demonstrates that a Diode and a LED will only pass current in a one-way direction. A diode's turn-on voltage is 0.7V. In the first picture, the Diode and LED are wired correctly and the circuit works. In the following two pictures, the Diode or LED is wired incorrectly and the circuit does not work. 

 

Diode wired correct

Diode wired wrong

LED wired wrong

What is a diode.

Elenco's PK-201 Experiment #11: Make Your Own Battery

In this experiment, a 100 microfarad capacitor is charged by a battery (red wire) then discharged. A LED is used to show the discharge of electricity. The capacitor is storing the electric charge between metal plates which could be used elsewhere at a later time. However, this is not as efficient as a battery.

 

 

 

Elenco's PK-201 Experiment #10: Large Dominates Small -- Capacitors in Parallel

In this experiment, capacitors in parallel add together for a total circuit capacitance. Here I am using a 100 microfarad and 10 microfarad capacitors in parallel, which add to a total of 110 microfarad of capacitance.

 

 

Elenco's PK-201 Experiment #9: Small Dominates Large -- Capacitors in Series

In this experiment, capacitors in a series combine to make a smaller circuit capacitance. Here I am using two capacitors (100 and 10 microfarads) in series. Below the video is the formula for calculating capacitance for two or more capacitors in a series.

 

 

Good Study Aid