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.

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: 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: 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: 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: 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: 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: 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 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: 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: 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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33 comments

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Anonymous
February 20, 2012 at 7:56 AM delete

in time delay circuit what is the formula in calculating the time?

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February 20, 2012 at 12:24 PM delete

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.

Regards.

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May 18, 2012 at 10:44 AM delete

Please Help to design a Relay circuit.

> Input 0v to ON, 5-12v to OFF the Relay.
> Should not fluctuate at initial start-up.

Thank You.

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May 18, 2012 at 11:56 AM delete

Please explain the whole application and your need elaborately, so that I can design the circuit properly, send it to hitman2008@live.in

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May 19, 2012 at 1:57 AM delete

Thanks for responding. I have sent you a mail.

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Anonymous
July 13, 2012 at 7:22 PM delete

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

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July 15, 2012 at 5:48 PM delete

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.

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July 16, 2012 at 7:22 PM delete

Sir, please post a 12v automatic battery charging circuit with transistors instead of relay.

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July 17, 2012 at 2:41 PM delete

Hello,
Can i use a transistor instead of the relay?
Thank you

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July 17, 2012 at 2:49 PM delete

Forgot to mention that the relay is meant in light sensor circuit.
Thnanks!

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July 17, 2012 at 3:32 PM delete

Hi Raja,
I have already posted a few in this blog, you may search it through the search box.

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July 17, 2012 at 3:51 PM delete

No you will have to use a relay only for sharp and accurate results.

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July 17, 2012 at 6:41 PM delete

And can I use a phototransistor instead of photoresistor?

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July 18, 2012 at 10:04 AM delete

The above circuit is based on an LDR so you cannot use a photo-transistors here.

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Anonymous
August 2, 2012 at 11:16 AM delete

Hi Mr Swagatham, may I know what software do you use for these schematic drawing ? Thanks.

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August 2, 2012 at 7:26 PM delete

Hi ---,

I use Corel Draw for making these schematics.

Regards.

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JR
August 2, 2012 at 8:23 PM delete

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.

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Anonymous
August 2, 2012 at 8:25 PM delete

Thank you Mr Swagatham.

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August 3, 2012 at 1:30 PM delete

Hi JR,

Im not sure actually, I'll try to design it using a 555, if I succeed, i'll surely post it here.

Thanks and Regards.

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Anonymous
August 22, 2012 at 9:03 AM delete

hi swagatham,me too want same circuit 5v=on and 0v=off.can you plz send it to sandy.nani5@gmail

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Anonymous
August 27, 2012 at 6:57 AM delete

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.

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January 7, 2013 at 1:23 PM delete

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!!!

Anonymous

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January 7, 2013 at 2:28 PM delete

Mr. Lorenzo, you will need a to make a bridge rectifier using 4nos of 6A-4 diodes, as explained at the bottom of this article:

http://homemadecircuitsandschematics.blogspot.in/2012/01/how-to-understand-diodes-and-build.html

Make it first, then I'll explain how to connect it to your bike.

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Anonymous
February 1, 2013 at 8:43 PM delete

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

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February 2, 2013 at 7:56 PM delete

Hi, I'll try to post it soon in this blog....

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Anonymous
February 4, 2013 at 12:51 PM delete

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

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February 4, 2013 at 8:19 PM delete

Please check out the following post:

http://homemadecircuitsandschematics.blogspot.in/2013/02/operating-dc-motor-clockwiseanticlockwi.html

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Anonymous
February 5, 2013 at 7:18 PM delete

Thank you very very much ! ! ! :))

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Anonymous
June 4, 2013 at 12:41 PM delete

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

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August 28, 2013 at 4:18 AM delete

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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August 28, 2013 at 1:13 PM delete

Hello, please refer to the following post which explains everything in details:

http://homemadecircuitsandschematics.blogspot.in/2012/01/how-to-build-simple-rain-sensor-circuit.html

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December 27, 2013 at 6:56 PM delete

hi swagatam, can u explain the water level warning indicator circuit.pls sir i am going to do project in my school exhibition

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December 28, 2013 at 12:47 PM delete

Hi Surya,

yo can try the following circuit:

http://homemadecircuitsandschematics.blogspot.in/2012/04/make-this-water-level-indicator-circuit.html

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