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. 

 



Elenco's PK-201 Experiment #15: The Current Amplifier

In this experiment, the right LED in the collector path is brighter than the left LED in the base path because the base current is amplified by the transistor. In other words, a smaller current is used to control a larger current. The term "amplified" is misleading and does not amplify an electrical current(Go to Figure 4 and read text below). Remember, in experiment #14 the transistor was used as a switch. Here, it is still functioning as a switch, and in this sense the transistor is used as an amplifier. This is called current gain. Current gain by a transistor can vary anywhere from 10 to 1000 depending on the type of transistor. But, battery voltage and circuit resistance will limit the current gain. The circuit resistances, not the transistor itself, are limiting the current and the transistor is said to be saturated. 





Current at base

Current at collector (about 10x base)








Wealth of Information

Transistor Formulas

Current Gain


Thank you University of Virginia for information that helped me come to an understanding of this experiment.





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

 



Elenco's PK-201 Experiment #8: Slow Light Bulb

This experiment demonstrates the charging and discharging of a capacitor. The charge/discharge time is controlled by resistors on either side of the capacitor. These resistors control the flow of electricity going to the capacitor (charge) and from the capacitor (discharge). The discharge is visualised by the LED in the experiment. The slower the LED dims, the larger the resistor is (ohms) that is controlling the discharge from the capacitor. The charge/discharge times are proportional to both the capacitance (amount of voltage a capacitor can hold) and the resistance in the charge/discharge path. In the below videos titles, the numbers followed by K are the charge and discharge resistor values (respectively), and the last number is the capacitor's capacitance in micro farads.

 

 

 

 

 

 

Elenco's PK-201 Experiment #7: Water Detector

This experiment shows that water will conduct electrical current. But, resistance can vary by amount and purity of the water. In the first picture, tap water is used to conduct electrical current. The LED is dimly lit because the water has a high resistance. In the last picture, salt was added to the same water causing the LED to become brightly lit. To conclude, water will conduct electrical current, but pure water has a higher resistance then water with salt dissolved in it.

Fresh Water (Dim LED)

No Water (off LED)

Salt Water (Bright LED)

Water and Electrical Conduction

Elenco's PK-201 Experiment #6: Combined Circuit

In this experiment there are two LED's (Left and Right). The left LED is connected to a 3.3k ohms resister, and, in addition, to a variable resistor (0 to 50k ohms). The left LED is connected only to a 10k ohms resistor. The first picture, shows a lighted left LED and a very dim right LED because most of the current is flowing in the direction of least resistance. The variable resistor is set to 0 ohms, which leaves only a resistance of 3.3k ohms. Where as the right LED has a higher resistance of 10k ohms. The second picture, shows both LED's lighted because the Variable resistor is set to give equal resistance as the right LED (10k ohms) resistance. In the last picture, the right LED is the brightest because the variable resistor is set to the maximum resistance of 50k ohms. Like experiment #5 current is still flowing in multiple paths, but nearly all the current is flowing towards the path of least resistance.  



Current is flowing through left LED

Equal resistance current is divided between both LEDs

Current is flowing through right LED

Further Study:
Questions and Answers on Physics
What is a Parallel Circuit?
 

Elenco's PK-201 Experiment #5: Comparison of Parallel Currents

This experiment is demonstrating that current can move along multiple paths in a circuit. More over, that the current is proportional to the resistance of said circuit.

100k ohm resistor

1k ohm resistor

10k ohm resistor

More Information

Elenco's PK-201 Experiment #4: Parallel Pipes

In general, this experiment shows that the more resistors that are in parallel in a circuit, the lower the total resistance; subsequently, more current will flow through the circuit. The formula and calculations are at the bottom showing the total resistance in each example.

3.2k ohm's

2.5k ohm's

770 ohm's
 

More information
Resistor 

Elenco's PK-201 Experiment #3: Resistors In Series

Resistors in a series add together to increase the total resistance of a circuit. In addition, the larger resistor in that series will control the flow of current in said circuit.

3.3k and 100k ohm resistors = 103.3k ohms

3.3k and 10k ohm resistors = 13.3k ohms

3.3k and 1k ohm resistors = 4.3k ohms

Elenco's PK-201 Experiment #2: The Brightness Control

In this experiment the focus is understanding the Variable Resistor (0 to 50k ohm). A device that has three pins (terminals to run electrical current through) and a dial. The dial is for increasing or decreasing resistance. When the dial is set to a minimum, the resistance is 0 ohms. Turn the dial to maximum then the resistance is set to 50k ohms. In the pictures, the Variable Resistor is wired from the center pin to left pin, center pin to right pin, or left pin to right pin. This means, depending on how the Variable Resistor is wired, that the resistance is measured between two of the three pins (left to center, right to center, or left to right). In the picture left to right, the resistance is between the left and center post. By turning the Variable Resistor to the right, one would increase the resistance hence dimming the light. In the picture right to left, the resistance is from right to center. By turning the resistance to the left, one would increase the resistance hence dimming the light. In the last picture, the resistance is 50k ohms. This is because the wiring is from left post to right post causing a lose of the variable attribute.

High Resistance (Left to Right)

Low Resistance (Left to Right)

High Resistance (Right to Left)

Low Resistance (Right to Left)



Full Resistance (None Variable)

 

 

Info on resistors