This blog will keep to a simple theme of my tinkering with electronic and computer related toys, gadgets, projects and the like. I do hope from time to time there is something for someone to find when they are exploring these things for themselves. From an early age, I was always attracted to electronic gadgets an I continue to enjoy myself with my hobby. Unfortunately with a busy life, time becomes short an I can not indulge myself like in the past.
In this experiment, resistors are used to set the voltage at the base of the transistors. If LED right is bright and LED left is off then the battery being tested is good, otherwise the battery is weak. If the battery being tested is equal to the battery supplying power to the circuit, the right transistor base will have higher voltage and switch on the right LED.
This experiment is used to test 1.5 volt batteries. Like the last experiment, this is a variation of the differential pair transistor configuration. In addition, this experiment uses diodes to reference voltage in the circuit. The experiment functions very simply. If the right LED is bright and the left LED is off, the battery being tested is good. If the left LED remains lighted, the battery is weak. This circuit uses two diodes (the left transistor is being used as a diode) to create a combined voltage reference of 1.1 volts. This voltage is constant at the base of the middle transistor that lights the left LED. If the battery being tested voltage is greater then 1.1 volts, the right transistor will light the right LED, and the battery's voltage will turn off the left LED.
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.
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.
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.
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.
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.
