Basic Electronics Tutorials and Revision

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Basic Electronics Tutorials and Revision

Elenco's PK-201 Experiment #48: This AND That

In the first circuit configurations, the blue wire is the X input and the red wire is the Y input, and the left LED represent the output. The first circuit configuration is called an AND gate. One can see that both X and Y need to have an input (9v) for the gate to open or to light the left-LED. This means that for the AND gate to be open both X and Y need to have an input. The second circuit configuration is called a NAND gate. Here, the input is the same but both LED's represent an output. The NAND gate is a combination of the AND and NOT gates making it an inverse of the AND gate. For the NAND gate to be closed both the X and Y have to have an input (9v). To open the NAND gate, either X and Y or both inputs would need to be disconnected from the input of 9v.

Combinations of AND and OR gates are used to add and multiply numbers together in computers; in addition, to gates as NOT, NOR, and NAND allows computers to represent any input/output pattern one can think of. And by combining these gates with the memory and timing control that a flip-flop circuit provide, computers of today were created. 

AND gate

Both inputs not connected: gate closed

Both inputs connected: gate open

X input connected and Y input disconnected: gate closed

X input disconnected and Y input connected: gate closed

NAND gate

Both inputs connected: gate closed

Both inputs disconnected: gate open

X input connected and Y input disconnected: gate open

X input disconnected and Y input disconnected: gate open

 Truth Tables

Elenco's PK-201 Experiment #47: Neither This NOR That

This is the OR gate circuit, but with added components to make a NOR gate. Here, the blue wire is the X input and the red wire is the Y input. The LED's (right and left) represent the outputs. For the NOR gate to be open, both X and Y have to have no input (9v) -- the right LED is on. If either inputs (X or Y), have an input of 9v then the gate stays closed -- right LED is off.

A third type of gate (not shown) is called a NOT gate or inverter that is just the opposite of its input. So, if the input is low, the output is high. And, if the input is high the output is low.
The combinations of resistors and transistors that create different logic gates such as OR, NOR, and NOT, to name a few, are the basic building blocks for computers.  

X and Y have input right-LED off: gate closed



X has 9v input Y has no input right-LED off: gate closed



X has no input Y has 9v input right-LED off: gate closed



X and Y have no input right-LED on: gate open



Schematic Symboles

 Truth Tables for gates
NOT gate

Elenco's PK-201 Experiment #46: This OR That

This circuit is a digital circuit called an OR gate. The loose wires in the circuit act as inputs, and the LED is the output. The red wire is X input and the Y input is the yellow wire. The LED will be lite if both or either wire is receiving a 9v input. That is why the circuit is called an OR gate if either input is true then the gate opens. Digital circuits are circuits that have only two states, such as high-voltage/low-voltage, on/off, yes/no, and true/false.

X and Y have 9v inputs LED is on

X has 9v input Y has no input LED is on

X has no input Y has 9v input LED is on.

X and Y has no input LED is off.

 Logic Gates Truth Tables

Digital Logic Systems

Elenco's PK-201 Experiment #45: Finger Touch Lamp with Memory

This experiment is a disappointment because it would not work as the work book described. I had to replace the diode for the LED (same circuit as Experiment #44) to get the transistors to flip-flop and have memory. In the video, the blue wire is negative and the red wire is positive. First, I built the circuit with a diode instead of a right LED (how the circuit is described in the book). Next, I show how the circuit reacts to the negative and positive wires. The book stated that applying the positive wire to the off transistor would turn that transistor on. I found that this is not the case. And, I am guessing, but I believe this is because the diode is not passing the current. Second, I replace the diode for the LED and I show how the LED's flip-flop with positive and negative wires. This seems to be closer to what the work book was trying to show. That positive current will switch on the NPN-transistor's and turn off the other NPN-transistor; more over, the transistor would remember that it had been turned on and would stay on. In this sense, the experiment is the opposite of Experiment #44, but at the same time the circuit is the same -- basic multivibrator and bistable switch-- just the experiment is using positive current instead of ground. To conclude, positive current (red wire) will turn on the off transistor just as the on transistor would turn off by ground (blue wire), and have memory of the action. All this is demonstrated in the video; in addition, I included a copy of the experiment from the work book and pictures of the circuit with diode or LED.    

 

Circuit with diode as described in work book.

Circuit with LED functions as described in work book.

Work Book Information

Elenco's PK-201 Experiment #44: The Flip-flop

 This circuit is another variation of the basic multivibrator configuration. This circuit is formally called the bistable switch but is nicknamed the "flip-flop" due to the way it operates. When the lose wire (ground) is touched to the base of the transistor, that transistor is turned off, and the other transistor turns on. One see's that touching the "on" transistor's base turns that transistor and the LED off "flop" and the other transistor and LED turns on "flip". Touching the off transistor's base has no effect (shown in video).

 This circuit is a basic building block for digital computers. This circuit can be thought of as memory because it only changes states when one tells it to. In other words, the circuit remembers that the transistor is on even though the wire is removed from the transistor's base. By combining several of these circuits together allows letters or numbers to be remembered and by combining thousands of these circuits a computer can remember a small book. A typical computer has many thousands of flip-flops, all in integrated circuit form. The operation of this circuit is simple. If NPN-left is on then it will have a low collector voltage. Since this collector voltage also connects to NPN-right's base, NPN-right will be off. But if you ground NPN-left's base then it will turn off and its collector voltage rises, turning on NPN-right. NPN-right will stay on until the transistor is grounded.

 

NPN-Left's Collector "ON"

NPN-Left's Collector "OFF"

Circuit

 

Computer-memory

Elenco's PK-201 Experiment #43: Alarm with Shut-off Timer

Here Experiment #42 and #30 are combined. To set the alarm, the trip wire must be connected and the switch pressed. Activate the alarm by disconnecting the trip wire. The alarm stays on for a few seconds and then goes off. Re-connect the trip wire and press the switch to reset the alarm.

 

 

Circuit