Electronics Circuits for the Evil Genius lessons #9 and #10 cover the operation of both the NPN and PNP transistors. Specifically speaking the NPN-2N3904 and the PNP-2N3906. The lessons demonstrate how each transistor type reacts when voltage is applied to the base of the transistor.
The demonstration circuit for lesson #9 reveals how the voltage held in a capacitor is used to power the transistor and subsequently allow the LED to turn on.
Moreover, the base of the transistor requires less power than the load required for the LED; through observation you determine that the capacitor drains the stored voltage very slowly. Further circuit analysis indicates that the capacitor in the circuit is the sole power source for the transistor, and it is the transistor that ultimately provides power to the LED.
Pressing the pushbutton plunger allows the voltage and current to flow through the circuit from the main source. However, when the pushbutton is open, the current and voltage is cutoff resulting in no voltage being sent to the base of the transistor.
I decided to have a little fun and developed a simulated SPICE circuit prior to breadboarding. The video here shows the simulation in progress.
The circuit for lesson #10 demonstrates how the NPN and PNP transistors differ in operation. Once the capacitor is fully charged, voltage is applied to the base of the transistor causing an interruption in current flow. When applying the battery to the circuit the first thing you notice is that the LED is immediately handling a voltage load – the result of a lack of voltage pressure at the base of the transistor.
The valve of the transistor is open, allowing current to flow from the emitter onward to the collector. Once the plunger of the pushbutton is pressed, voltage is instantly sent to the base of the transistor, closing its internal valve. This blocks the flow of current and causes the capacitor to charge.
However, once the pushbutton is released, the voltage from the capacitor applies pressure on the base of the transistor, closing the valve and restricting current flow from the emitter to the collector.
Next up is lesson #11 which demonstrates the capabilities of the phototransistor, using both the clear and darkened glass versions of the component.
This lesson is quite interesting as you develop a combination circuit in which have there is an input, processor, and output component.The objective here is to observe how each input component affects the processing component (light spectrum dependent). This circuit however requires that the experiment be conducted away from sunlight. You will also need to print out a disc provided by the text to properly complete the experiment.
The overall purpose is to see how fast or slow the processing component is affected when the (input) light source is blocked. The inputs used are a yellow LED and the clear IR phototransistor. The processors use are an LDR and the dark IR phototransistor.
Up next is the first of two main projects for this section. Putting it all together.
Looking forward to it.