Build Simple Transistor Circuits

A compilation of important assorted transistor simple circuits to build has been included here.

Simple Transistor Circuits for New Hobbyists

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.

The 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:

Adjustable DC power supply

Adjustable 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 applications.

Rain Alarm circuit


Rain Alarm:

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.

Hum free power supply circuit


Hum 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.

 Set-Reset Latch circuit


Set-Reset Latch:

This 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.

 Simple Delay Timer circuit

Simple 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.

Crystal Tester circuit

Crystal Tester:

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.


water level indicator circuit

Water 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.

 Hand Stability Tester circuit


Hand 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”.

Light Sensitive Switch circuit

Light 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 appear).


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8 thoughts on “Build Simple Transistor Circuits”

  1. Hello
    first of all thank you for the great efforts . i want to make printed circuit that have one application of transistor i don't want it to be not so simple and not so hard i am thinking about a circuit have (transistors -dc motor – leds – resistors ….) but i don't know how to ? can you help me applying my idea and if you have better idea that would also be great
    thanks in advance

  2. 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.

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