Introduction: 5 Cool Projects With a General Transistor

About: So basically i am a crazy person, who loves to think the most odd way ever possible,who makes what he thinks and also let other also make those . Check out my crazy projects if you like do follow me :D

Basically i love to do projects that are microcontroller related.But recently one of my friend from ethiopia said that he wanted to do something that does not includes a microcontroller or arduino but still its worth making in a weekend and also in a small budget.So the idea came why not make a collection of 5 such projects that you can make with a universal transistor.

Why transistor ???

Basically ever since i started electronics . i knew i can find a transistor surely anywhere and also the cost was also less (1.50 rupees) 0.02$ /piece
U can also get 100 pc pack at 1$.

So what is actually a transistor ?

A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems.

Transistor are of two type

  • BJT(Bipolar junction transistor )
  • FET(Field effect transistor )

We are gonna use a bc547 .BC547 is an NPN bi-polar junction transistor.

BC547 is mainly used for amplification and switching purposes.

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Step 1: Transistor Tester

Working with transistor will need you to test transistor.

some time even you will salvage transistor and u want to know whether they work or not .
well this can be done by this circuit .


This is basically a high gain amplifier
with feedback that causes the LED to flash at a rate determined by the 10u and 330k resistor. Remove one of the transistors and insert the unknown transistor. When it is NPN with the pins as shown in the photo, the LED will flash. To turn the unit off, remove one of the transistors.

Step 2: Mains Finder

What about a Main Line Detector ??

One More cool thing or gadget is a main line finder .
It comes handy when u are drilling in wall


This circuit is so sensitive it will detect "mains hum."
Simply move it across any wall and it will detect where the mains cable is located. It has a gain of about 200 x 200 x 200 = 8,000,000 and will also detect static electricity and the presence of your hand without any direct contact. You will be amazed what it detects! There is static electricity EVERYWHERE! The input of this circuit is classified as very high impedance.

Step 3: Lie Detector

Is your friend lying behind to you ??

Time to test it with the lie detector circuit.


This circuit detects the resistance between your
fingers to produce an oscillation. The detectionpoints will detect resistances as high as 300k and as the resistance decreases, the frequency increases. Separate the two touch pads and attach them to the back of each hand. As the subject feels nervous, he will sweat and change the frequency of the circuit. The photos show the circuit built on PC boards with separate touch pads.

Step 4: Ticking Bomb

Wanna scare your friend ??

How about making a fake bomb ticking sound . Damm that gonna scare them badly.Try this ticking bomb circuit.


This circuit produces a sound similar to a loud clicking clock. The
frequency of the tick is adjusted by the 220k pot. The circuit starts by charging the 2u2 and when 0.65v is on the base of the NPN transistor, it starts to turn on. This turns on the BC 557 and the voltage on the collector rises. This pushes the small charge on the 2u2 into the base of the BC547 to turn it on more. This continues when the negative end of the 2u2 is above 0.65v and now the electro starts to charge in the opposite direction until both transistors are fully turned on. The BC 547 receives less current into the base and it starts to turn off. Both transistors turn off very quickly and the cycle starts again.

Step 5:

Always wanted a cheap touch switch ??

Here it is the cheapest circuit to make a touch switch.


This circuit detects the skin resistance of a finger to deliver a very small current to the super-alpha pair
of transistors to turn the circuit ON. The output of the "super transistor" turns on the BC 557 transistor. The voltage on the top of the globe is passed to the front of the circuit via the 4M7 to take the place of your finger and the circuit remains ON. To turn the circuit OFF, a finger on the OFF pads will activate the first transistor and this will rob the "super transistor" of voltage and the circuit will turn OFF.