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, the LED blinks at a constant rate. This is because the transistor is being turned on and off. This circuit is called an oscillator and it uses a feedback signal. Feedback is when the input signal is based on the output signal. In this case, the collector signal (part of transistor) is feedback to the base (part of transistor) through a coil (part of transformer) and the 100 microfarad capacitor. The rate at which the transistor is turned on and off is called the frequency and is controlled by the resistor, capacitor, and coil in the circuit.
In this experiment, the left LED blinks when the switch is pressed and than the right LED blinks. When one presses the switch, a sudden surge of current (AC) goes through the inductor that magnetically creates a current on the other side of the transformer, lighting the left LED. The current from the battery settles after the initial surge (becomes DC) and the magnetic induction stops because the current is no longer changing, hence no current flows through the LED even though there is current on the battery side of the transformer. When one releases the switch, the sudden drop in current through the transformer magnetically creates a new current on the other side of the transformer, but this time in the opposite direction so the right LED lights instead of the left LED. Again, this current is brief and the LED only blinks. The transformer has many more turns (more inductance) on the LED side than on the battery side; this boosts the voltage to the LED's (though it also lowers the current). If the transformer was in reverse, there would not be enough voltage to turn the LED's on. The transformer is functioning as a magnetic bridge in electronics, since we use magnetism to cross a barrier that electricity cannot cross by itself. Transformers are mainly used for isolating and buffering different circuits from each other.
This experiment uses the same circuit as in experiment #8. But instead of a capacitor, an inductor is used. An inductor passes stable current (DC) and blocks unstable current (AC). In the video, when I turn the switch on, the LED lights then goes out (blinks). Next, I disconnect and reconnect the wire to show that less inductance produces a dimmer (blinking) LED light. Lastly, I introduce a diode into the circuit to stabilize the current (AC to DC). Because the inductor, part of the transformer, is passing the stable current and blocking the unstable current, the LED only blinks when the button is on. When the diode is introduced to the circuit, the circuit loses the AC frequency rate and stabilizes into DC.
This is an experiment to show how to design a circuit immune to a voltage drop (weak battery). In the video, when one LED is lit, the circuit is connected to a modified 4.7 volt supply. When both LED's are lit, the circuit is connected to the 9 volt supply. The LED that lit both times is representing a circuit immune to voltage drops.
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.
