Translate

Monday, December 10, 2012

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



Thursday, December 6, 2012

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
 

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
 
 

Elenco's PK-201 Experiment #42: One-shot

A variation of the astable multivibrator circuit that is called a one-shot multivibrator, because the LED comes on once each time the switch is turned on. The 33k ohm and variable resistor with the 100 microfarad capacitor control how long the LED is on. In the beginning of the video, the LED is on for a few seconds and then goes out. I increase the resistance of the variable resistor and the LED stays on longer.
 
 
Circuit
 

Elenco's PK-201 Experiment #41: Noisy Blinker

Similar circuit configuration as last experiment (Astable Multivibrator). When the switch is turned on, the LED lights and one hears sound from the speaker. Turning the variable resistor and the frequency of the sound changes. The LED appears to be solid bright then dim but is blinking about 500 times a second (due to the small disc capacitors). In the second video, I replace the disc capacitors with the 100 and 10 microfarad capacitors to make the frequency rate much lower.
 
 
Circuit
 

Wednesday, December 5, 2012

Elenco's PK-201 Experiment #40: Blinking Lights

This experiment is a circuit configuration of an oscillator called Astable Multivibrator. In this type of oscillator there is no inductor, the frequency is controlled only by the resistors and capacitors. One of the two transistors is always on, hence one LED is always on. The left transistor (left-LED) is controlled by the 100k ohm resistor and 10 microfarad capacitor. The right transistor (right-LED) is controlled by a 3.3k ohm resistor, variable resistor (0-50k ohm), and 100 microfarad capacitor. If the variable resistor is turned up to 50k ohms, the right LED will stay on longer than the left one. Because the capacitor's discharge time is being manipulated, with the variable resistor.
 
 
Circuit
 

Tuesday, December 4, 2012

Elenco's PK-201 Experiment #39: Fun with Water

This is the same oscillator circuit used in Experiments #36..38; in addition, same resistance principle's of Experiment #7 and #20. This experiment shows how impurities can lower resistance. And that one's body, has a higher resistance to electrons than water or salt water. In each case, the resistance is lowered and the frequency rate increases. To conclude, adding impurities makes it easier for electrons to flow through semiconductors.