Search Posts

Build Simple Transistor Circuits

A compilation of important assorted transistor simple circuits
to build has been included here. Many simple transistor configurations like,
rain alarm, delay timer, set reset latch, crystal tester, light sensitive
switch and many more have been discussed in this article.

In this compilation of simple transistor circuits (schematics)
you will come across many small very important transistor configurations,
especially designed and compiled for new budding electronic enthusiasts.

simple circuits to build (schematics) shown below have very useful applications
and are yet easy to build even for new electronic enthusiasts. Let’s begin
discussing them:

DC power supply
A very nice adjustable power supply unit may be built using just a couple of
transistors and a few other passive components. The circuit provides good load
regulation, its maximum current being not more than 500mA, sufficient for most

This circuit is built around just two transistors as the main active
components. The configuration is in the form of a standard Darlington pair,
which increases its current amplification capacity hugely. Rain drops or water
drops falling and bridging the base with the positive supply is enough to
trigger the alarm.

free power supply
For many audio amplifier circuits hum pick-ups can become a big nuisance, even
proper grounding sometimes are unable to rectify this problem. However, a
high-power transistor and a few capacitors when connected as shown can
definitely curb this problem and provide the required hum free and ripple free
power to the entire circuit.

circuit also utilizes a very few components and will faithfully set and reset
the relay and the output load according to the input commands. Pressing the
upper push switch energizes the circuit and the load, whereas it is deactivated
by pressing the lower push button.

Delay Timer
A very simple yet very effective timer circuit can be designed by incorporating
just two transistors and other handful of components. Pressing the push ON
switch instantly charges the 1000uF capacitor and switching ON the transistors
and the relay. Even after releasing the switch the circuit holds on the
position until C1 is completely discharged. The time delay is determined by the
values of R1 and C1. In the present design it’s around 1 minute.

Crystals can be quite unfamiliar components especially with the electronic
novices. The shown circuit is basically a standard Colpitts oscillator
incorporating a crystal to initiate its oscillations. If the connected crystal
is a good one, will be indicated through the illuminated bulb, a faulty crystal
will keep the lamp shut.

Level Warning Indicator
: No more peeping and nervous apprehensions with
overflowing water tanks. This circuit will produce a nice little buzzing sound
well before you tank spills over. Nothing can be as simple as this one.
Keep watching for more of these little
giants, I mean simple circuits to build with huge potentials.

Stability Tester
Pretty confident regarding your hand dexterity? The present circuit can definitely
challenge you. Build this circuit and just try sliding a constricted metal ring
over the positive supply terminal without touching it. A buzzing sound from the
speaker will entitle you with “antsy hands”.

Sensitive Switch
If you are interested to build a low-cost light dependant switch, then this
circuit is just for you. The idea is simple, a presence of light switches OFF
the relay and the connected load, absence of light does exactly the opposite.

Need more explanations or help? Just
keep posting your valuable comments (comments need moderation, may take time to

35 comments on Build Simple Transistor Circuits

    1. I tried to find the formula but couldn't get a specific formula for this circuit, because here we want to find how long it takes for the current inside the capacitor to discharge below 0.6 volts through a given resistor value….I couldn't get the exact formula for calculating this.


    2. Hi in time delay circuit, do you have a circuit, that compose of 4 switch that represents this number of hours? in 1st switch 1-30 mins. 2nd switch 1 min-2 hrs. 3rd switch 1 min-4 hrs. 4th switch 1 min-6 hours.

      actually im planning to make charger that has countdown timer attach with it. thanks so much.

  1. Hello could you please explain the rain sensor circuit using transistors and please explain to me why you have chosen these components please???? im really stuck

    1. The circuit employs transistors configured in Darlington pair arrangement which is highly sensitive to small current triggers.
      The base of the pair receives small leakage currents through the water bridge accumulated in between the sensor metal terminals and this trigger switches the buzzer.

  2. Mr Swagatam, Im interested with the Set-Reset Latch circuit, but is it possible to recreate the same circuit with set and reset function with a 555 timer IC? If so how ? Thanks Mr Swagatam.

  3. Mr. Swagatam, kindly design a rectifier for my motorcycle(kawasaki brutus 135cc)to be able to charge a 12v battery. The input from magneto is more than 50vac. Thank you and more power!!!


  4. Hi, please help. We have our project in school. Our professor asks us to design a transistor together with a relay that allows a motor to rotate clockwise and then , a switch will be press , then will rotate counter-clockwise. Thanks in advance

  5. Thanks Mr. Swagatam. Kindly post it very soon. Our project deadline is due on february 8. Your help is greatly appreciated.

  6. I want to know the way of making a touch sensitive circuit in which led glow when i touch circuit and vice versa

  7. Hello,
    I am interested in building the Rain Alarm for my science project, and I was wondering if you could please elaborate in regards to how to build it. My partner and I will appreciate it immensely.

Leave a Reply

Your email address will not be published. Required fields are marked *