IC 555 - How it Works

Everything you wanted to know about the IC 555: Pinout details, modes of operations, formulas, solved examples.

50 best Arduino projects for engineering students and students


Best small power inverter circuits from 50 watt to 5000 watts.

Get 220V AC or 120V AC from any lead acid battery rated from 12V to 48V with appropriate Ah rating.

Battery Charger

Automatic Battery charger circuits for all types of batteries.

Constant current, constant voltage, high and low voltage automatic cut-off, Fully adjustable and cutomizable.


Learn how to integrate solar panels with battery chargers and inverters.

Find many windmill generator circuits.

Convert sea, sun, wind into electrical energy.

LED Projects

LED drivers are very popular nowadays.

These items can be built using SMPS or switch mode technology, and also using the crude capacitive power supply.


Here you will find the most advanced and useful Arduino engineering circuit projects with full programming code.

Complete basic programming tutorial.


Best industrial 3 phase based circuits. Controlling lathe machine and timer based machine control.

Sensor and timer based industrial control

Power Supply

Learn how to build power supply circuits from the scratch. You will simple designs using LM338/LM317, to more sophisticated designs using transistors and opamps.

You will also find concepts using only capacitors (without transformers), and a few ferrite based SMPS.

Power Amplifiers

High fidelity amplifier circuits with easy to build instructions.

Transistor and IC based smallest amplifier with outstanding sound quality.

100 watt to 100 watt range with PCB design.

Free Energy

Free energy devices are enticing. Do they really work?

How could the earlier scientists like Tesla, De Palma succeed in making these devices?

Also learn how to design your own free energy motors!

Water Control

Every house and building has an overhead tank, submersible tank.

Sometime both are present. Learn to make simple water level controllers for these tanks.


If you are new to electronics and are looking for small and easy to build mini circuit project, then this page might help you to get many choices.

Over 500 projects, you can find from moderate to most easy circuit ideas which are fully customizable.


Transistor switch circuit


Small Signal Transistor(BJT) and Diode Quick Datasheet

Below are a list of Transistors and diodes marked ‘TUP’ (Transistor, Universal PNP), ‘TUN’ (Transistor, Universal NPN), ‘DUG’ (Diode, Universal Germaniuml or ‘DUS’ (Diode, Universal Silicon).

This indicates that a large group of similar devices can be used, provided they meet the minimum specifications listed in tables 1a and 1b.

universal NPN transistor current and voltage specifications
Universal diode current and voltage specifications
All NPN and PNP transistor small signal type listing
Transistor equivalents, wattage and package specifications

Detailed BJT Datasheet, Pinouts with Complementary Pairs

The following figure shows a vast range of bipolar transistors and their detailed specifications. You can learn about their NPN/PNP polarity, Uceo, Ic, Pmax, hFE, an also regarding equivalent numbers, or complementary pairs.

Datasheet, pinout of all standard  transistors and BJTs
All Power Transistor datasheet, pin details

Bipolar transistors work with four distinctive areas of operation, characterized by BJT junction biases.

Forward-active (or simply active)

The base–emitter junction is forward biased and the base–collector junction is reverse biased. The majority of bipolar transistors are designed to handle the highest common-emitter current gain, βF, in forward-active mode. In such a scenario, the collector–emitter current is roughly proportionate to the base current, but most of the times greater, for small-scale base current changes.

Reverse-active (or inverse-active or inverted)

By reversing the biasing factors of the forward-active region, a bipolar transistor switches into reverse-active form. In this setting, the emitter and collector areas swap their tasks.

Due to the fact that many BJTs are built to enrich current gain in forward-active mode, the βF in opposite form appear to be many times lesser (2–3 times for the standard germanium transistor).

This transistor function is hardly ever applied, typically used just for failsafe situations plus some kinds of bipolar logic. The reverse bias breakdown voltage on the base might be an level of dimension smaller in this region.


Having both junctions forward-biased, a BJT acquires saturation mode and makes it possible for high current conduction through the emitter to the collector (or the other route when it comes to NPN, with negatively charged carriers moving from emitter to collector). This method refers to a logical "on", or a shut-off switch.


In cut-off, biasing situations are reverse of saturation (both junctions reverse biased). There exists hardly any current, that compares to to a logical "off", or an open switch in this mode.

Resistor Color Code

Resistor color code chart

Capacitor Color Codes

Capacitor color code chart

Electronics Tips and Tricks

In the following sections I'll be sharing with you some electronic circuit related tips and tricks, solved through email discussions and other social platforms, here are a few:

PTC Controller Circuit

I've bought a PTC heating element few days back.This PTC heater rating is 12V ac/dc, 200w. Actually sir i haven't understood how to make a power supply driving circuit via DC. I have tried for several times where I have gotten some problems.

When I used transformer (220/12) and directly connected it with heater, I found transformer becomes hot gradually within a moment.

It would be better for me sir, if u could help me by providing some information about its driving circuit, actually I need a DC driver circuit for powering my PTC heater. Sent by Mr. Joydeep.

My Answer:

You can use the IC 555 PWM circuit from this article, and replace the motor with your PTC, it will do the job for you
The pot can be used for controlling its heat output. 

This will prevent your transformer from heating up and enable you to adjust the heat to 80 watts.
Your present transformer is heating because it's not rated at 200 watt, or 200/12 = 16 amps. If you use a 16 amp transformer then it will not heat up.

LED Series Repairing

I have problem with regard to led bulb. In many LED bulb (9watt) we find problem in led series that we can solve by shorting any (damaged) led points. However, this is not a permanent solution, and after some time it damages another adjoining series led. So without adding an smd led, is there any quick way to solve this problem. For example, using an equivalent resistor which will compensate for voltage and current instead of an actual LED? And can we put this resistor on site while repairing an LED string light? Sent by nakum bhikhu


Yes that's easily possible by calculating an equivalent resistor that would take the place of the damaged LED.

You can calculate the resistor value using the following formula:

R = supply voltage - total LED voltage divided by LED current

If there's already an existing resistor then you should minus the above value from the existing value, and use the new value as the replacement resistor for the blown LED.

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