Category: CIRCUITS (page 1 of 2)


In this instructable, I will be teaching the basics of multiplexing 7 segment displays using an Arduino and a couple of shift registers. This project is well suited for displaying numerical information or if you want to control a bunch of LEDs. For beginners, like me, I had no clue on how to tackle this project. But after trial and error and blood, sweat, and tears, I can say that I have a better understanding of multiplexing and how best to implement it on an Arduino.

First off, what is multiplexing? What about Charlieplexing? Any differences?
Actually, they are they same… Charlieplexing just takes multiplexing to a higher level. Both are techniques used to not only reduce the number of microcontroller pins needed, but also to reduce the power requirements substantially. However, at the cost of time and/or brightness.

In multiplexing, an entire digit or row of LEDs are shown at one time. After some time, the whole digit or row is turned off and the next digit/row is turned on, etc… Simple!

However, Charlieplexing is a bit more complicated in that it goes deeper than multiplexing. Instead of turning on a whole digit or row, a single segment or individual LED is turned on/off. After some time, the segment/LED is turned off and the next segment/individual LED is turned on, etc… After cycling through a digit/row, the process repeats with the next digit/row. So, if you’re charlieplexing a 7-segment, you would consume a max of 20mA vs 160mA in multiplexing since only 1 segment is on at a time. The severe downside is that it takes longer to display information and brightness is reduced because the program needs to cycle through all the 7 segments + decimal or each LED first before moving to the next digit or row. You will also notice a slight flicker as you chain more displays/LEDs.

Look above for a comparison on multiplexing and charlieplexing. Notice how charlieplexing requires more time to display a number?

Before you tackle your multiplexing project, you must lay everything out–research as much as you can. Otherwise, you will end up wasting time, money, and pulling your hair out of frustration.



Have you ever needed a 12 volt power supply that can supply maximum 1 amp? But trying to buy one from the store is a little too expensive?

Well, you can make a 12 volt power supply very cheaply and easily!

Step 1: Things that you will need…


Things that you will need to make this power supply is…

  • Piece of protoboard
  • Four 1N4001 diodes
  • LM7812 regulator
  • Transformer that has an output of 14v – 35v AC with an output current between 100mA to 1A, depending how much power you will need.
  • 1000uF – 4700uF capacitor
  • 1uF capacitor
  • Two 100nF capacitors
  • Jumper wires (I used some plain wire as jumper wires)
  • Heatsink (optional)

Step 2: And the tools…

Also you will need the tools to make this power supply…

    • Soldering iron
    • Wire cutters
    • Wire strippers
    • A thing you can cut protoboard tracks.
    • Hot glue (To hold components down and make the power supply physically strong and sturdy.)
    • And some other tools that you might find helpful.

Okay, I think that is about it, lets get to work!

Step 3: Schematic and others…


Picture of Schematic and others...
If you want a 5 volt power supply, just simply replace the LM7812 to a LM7805 regulator.
Datasheet for LM78XX

If you are going to pull out about 1 amp from this power supply, you will need a heatsink for the regulator, otherwise it will generate very high temperatures and possibly burn out…
However, if you are just going to pull out a few hundred milliamps (lower than 500mA) from it, you won’t need a heatsink for the regulator, but it may get a little bit warm.

Also, here’s the schematic…
I also add in an LED to make sure the power supply is working. You can add in an LED if you want.

Step 4: Make it!


Make sure you get good solder joints and no solder bridges, otherwise your power supply won’t work!

Step 5: Test it!


After you had built your power supply, test it with your multimeter to make sure they are no solder bridges.

After you tested it, put it in a plastic box or something to protect you from shocks.
But do not operate the power supply like I did, it is very dangerous because of the mains voltage on the transformer, you or somebody will get badly shocked!

My power supply has 11.73v output, not too bad, I don’t need it to be exactly 12v…

Step 6: Done…



Source : Instructables



One day in 1994, seven world-leading technology companies sat down and created a new standard for connecting computer peripherals. By “one day,” of course I mean, “over the span of several months.” But all technicalities aside, the standard that they laid down became the Universal Serial Bus, or USB for short.

Today, USB is truly a ‘Universal’ standard and you’d be hard-pressed to find an electronic device that doesn’t have a USB port of one kind or another. But how do you know which USB cable will fit your device? Hopefully this buying guide will help you find the cable that you need for your next project.

What Does USB Do?

USB cables replace the huge variety of connectors that used to be standard for computer peripherals: Parallel ports, DB9 Serial, keyboard and mouse ports, joystick and midi ports… Really, it was getting out of hand. USB simplifies the process of installing and replacing hardware by making all communications adhere to a serial standard which takes place on a twisted pair data cable and identifies the device that’s connected. When you add the power and ground connections, you’re left with a simple 4-conductor cable that’s inexpensive to make and easy to stow.

500px-USB_half Continue reading


We had earlier in 2 different posts discussed about a variable power supply using LM 317. But in this post we discuss clearly about the working and designing of the LM 317 power supply in detailed.

Block Diagram

This circuit, like all voltage regulators  must  follow the same general block diagram


Here, we have got an input high voltage AC going into a transformer which usually steps down the high voltage AC from mains to low voltage AC required for our application. The following bridge rectifier and a smoothing capacitor to convert AC voltage into unregulated DC voltage. But this voltage will change according to varying load and input stability. This unregulated DC voltage is fed into a voltage regulator which will keep a constant output voltage and suppresses unregulated voltage ripples. Now this voltage can be fed into our load.

Firstly let us discuss about the need for the smoothing capacitance.As you know  the out put of the bridge rectifier will be as follows


As you can see, although the waveform can be considered to be a DC voltage since the output polarity does not invert itself, the large ripples Continue reading



In a masterful publicity stunt, Amazon CEO Jeff Bezos announced on 60 Minutes — on the night before Cyber Monday — that his company has been working on a drone service that will deliver items under 5 pounds, and within ten miles of an Amazon fulfillment center, in under 30 minutes..

This is definitely exciting, but exactly how much does Amazon have to accomplish between now and Jeff’s launch goal of 2015? Getting the FAA onboard will be hard enough, but what about actually getting shipments out safely, when that time finally comes? Is this even possible, or simply a publicity stunt by the e-commerce giant? They’re definitely not the first to think about doing this. Matternet has been working on bringing drone-supported shipping to areas of the world where roads aren’t common, or structurally sound enough, to handle everyday deliveries. CEO Andreas Raptopoulos talked about his vision at May’s Hardware Innovation Workshop.

If Amazon is really going for it, here are the main challenges and some of my thoughts on how Amazon will handle them:


Probably the easiest to deal with. Amazon says they’re shooting for 30 minute deliveries, which I’m assuming means 30 minutes from take-off to landing, not order to landing. Jeff says they will deliver to within 10 miles of an Amazon Fulfillment Center, which is doable if the octocopter can go at least 20mph. The challenge here is giving them enough battery power to survive the trip to the customer and back home. Carrying that much weight at that speed for up to an hour is going to require some heavy batteries. Continue reading


Build a motion-sensing alarm with a PIR sensor and an Arduino microcontroller.

In this simple project, we’ll build a motion-sensing alarm using a PIR (passive infrared) sensor and an Arduino microcontroller. This is a great way to learn the basics of using digital input (from the sensor) and output (in this case, to a noisy buzzer) on your Arduino.

This alarm is handy for booby traps and practical jokes, and it’s just what you’ll need to detect a zombie invasion! Plus, it’s all built on a breadboard, so no soldering required!

Step #1: Gather your parts.



  • This project requires just a few parts, and because you’re using a solderless breadboard and pre-cut jumper wires, you won’t need any tools at all — except your computer and USB cable to connect the Arduino.

Step #2: Wire the Arduino to the breadboard.

JHRErPeVwx4oQRk6 Continue reading



I bet some of you had the same problem. I was working on this circuit on breadboard and I found out I do not have means to power that circuit. Batteries are too expensive for testing one circuit. In the end I was able to build small power supply that solved my problems.

Many times we can build PSU with small amount of elements. That is the story in this case. I upgraded PSU that already have 12 V output to 9 V with help of linear voltage regulator.

Be careful and cautious while proceeding with any project.

Step 1: Parts and materials.



– low voltage connector
– 2 pins connector
– cooling element with nut and bolt and with isolating foil (foil is optional)
– piece of black and red wire and two pins
– 7809 voltage regulator
– 470 uF capacitor and 100 nF capacitor
– PSU with output between 12 and 16 V Continue reading


Whether it’s an electronic novice or an expert professional, a power supply unit is required by everybody in the field. It is the basic source of power that may be required for various electronic procedures, right from powering intricate electronic circuits to the robust electromechanical devices like motors, relays etc.
A power supply unit is a must for every electrical and electronic work bench and it’s available in a variety of shapes and sizes in the market and also in the form of schematics to us.
These may be built using discrete components like transistors, resistors etc. or incorporating a single chip for the active functions. No matter what the type may be, a power supply unit should incorporate the following features to become a universal and reliable with its nature:
  • It should be fully and continuously variable with its voltage and current outputs.
  • Variable current feature can be taken as an optional feature because it’s not an absolute requirement with a power supply, unless the usage is in the range of critical evaluations.
  • The voltage produced should be perfectly regulated.

IC 317 Power Supply, Simplest Continue reading



Every project needs a power supply. As 3.3volt logic replaces 5volt systems, we’re reaching for the LM317 adjustable voltage regulator , rather than the classic 7805 . We’ve found four different hobbyist-friendly packages for different situations.

A simple voltage divider  (R1,R2) sets the LM317 output between 1.25volts and 37volts; use this handy LM317 calculator  to find resistor values. The regulator does its best to maintain 1.25volts on the adjust pin (ADJ), and converts any excess voltage to heat. Not all packages are the same. Choose a part that can supply enough current for your project, but make sure the package has sufficient heat dissipation properties  to burn off the difference between the input and output voltages.

Voltage regulator

Schematic of LM317 in a typical voltage regulator configuration, including decoupling capacitors to address input noise and output transients.

The LM317 has three pins: Input, output, and adjustment. The device is conceptually an op amp (with a relatively high output current capacity). The inverting input of the amp is the adjustment pin, while the non-inverting input is set by an internal bandgap voltage referencewhich produces a stable reference voltage of 1.25V. Continue reading



think that it is safe to say that most of the people who make (big or small) electronics-projects have a pc or laptop in theire hobbycorner and a lot of projects need 5V for IC’s or microcontrollers. So using power from a USB cable isn’t that farfetched and lets face it: a lot of devices around us use a USB-connection to get their power or to charge their batteries.

 About USB-connectors and power

3 Continue reading


A well designed and variable power supply for electronics hobbyists and DIY’ers is a must, you don’t want to spend a huge amount of money in batteries [On the long run]. A variable power supply can come in handy for testing and powering  any project you are building. The mentioned power supply ranges from 1.25V – 37V @ 1.5A using the famous LM317 voltage regulator. LM317T is a very famous IC and easily available in the market comes with 3 pins, supporting input voltage is from 3 volt to 40 volt DC and delivers a stable output between 1.25 volt to 37 volt DC.


Whether you are watching it on television or searching for it on Pinterest, chances are you have admired a few Do It Yourself (DIY) projects recently. Have you taken it a step further and actually completed a DIY project? There are three key reasons why the trend of DIY projects is so popular.


The first reason that people want to try a DIY project is usually because it sounds like fun. You learn a new skill and the end result will be just what you are looking for. Since Halloween is just around the corner you may be thinking: “Should I go searching for the perfect costume or should I try to design and sew it myself?” Not everyone would have an interest and natural ability in making their own costume so learning to sew would seem like fun. Chances are you are artistic and enjoy ways to tangibly express that creativity. Now imagine taking it one step further and Continue reading



Touch screens are so ubiquitous that physical keyboards are becoming a thing of the past, at least for mobile devices. Now imagine if the capability of touch spread from the display to the entire device, allowing control by gently pressing on any part of the phone, or even making any household item into a touch-sensitive interface with your computer.

Anything solid vibrates a specific way when it’s hit physically with another object or with sound waves. The characteristic is called resonance. For example, when you tap on a crystal glass, it vibrates at a certain frequency, producing a ring. If you hit it with sound waves — for example, the ambient background noise in a room — it vibrates at a different frequency. Grip the glass while it rings, and the sound stops. Continue reading


For a device created to save lives, the household smoke detector sure takes a lot of heat for being annoying: the false alarms when the cookies get burned, the incessant beeping when the battery needs changing and all those times standing on wobbly chairs while trying to find minuscule buttons.

dnews-files-2013-10-nest-smoke-alarm-gallery-670-jpg Continue reading


As your embedded project grows in scope and complexity, power consumption becomes an ever more apparent issue. As power consumption increases, components like linear voltage regulators can heat up during normal operation. Some heat is okay, however when things get too hot, the performance of the linear regulator suffers.

How much is too much?

A good rule of thumb for voltage regulators is if the outer case becomes uncomfortable to the touch, then the part needs to have an efficient way to transfer the heat to another medium. A good way to do this is to add a heat sink as shown below.

breadboard Continue reading



This is a quick how-to explaining everything you need to get started using your Flexiforce Pressure Sensor.  This example uses the 25lb version, but the concepts learned apply to all the Flex sensors.



Necessary hardware to follow this guide:

  • Arduino UNO or other Arduino compatible board
  • Flexiforce Pressure Sensor
  • Breadboard
  • M/M Jumper Wires
  • 1 MegaOhm Resistor  Continue reading


Capacitors Galore

Capacitors are one of the most common elements found in electronics, and they come in a variety of shapes, sizes, and values. There are also many different methods to manufacture a capacitor. As a result, capacitors have a wide array of properties that make some capacitor types better for specific situations. I would like to take three of the most common capacitors – ceramic, electrolytic, and tantalum – and examine their abilities to handle reverse and over-voltage situations. Note: several capacitors were harmed in the making of this post.


Ceramic Capacitors

The most common capacitor is the multi-layer ceramic capacitor (MLCC). These are found on almost every piece of electronics, often in small, surface-mount variants. Ceramic capacitors are produced from alternating laye Continue reading


Power factor is a measure of how effectively you are using electricity. Various types of power are at work to provide us with electrical energy. Here is what each one is doing.

Working Power – the “true” or “real” power used in all electrical appliances to perform the work of heating, lighting, motion, etc. We express this as kW or kilowatts. Common types of resistive loads are electric heating and lighting.

An inductive load, like a motor, compressor or ballast, also requires Reactive Power to generate and sustain a magnetic field in order to operate. We call this non-working power kVAR’s, or kilovolt-amperes-reactive.

Every home and business has both resistive and inductive loads. The ratio between these two types of loads becomes important as you add more inductive equipment. Working power and reactive power make up Apparent Power, which is called kVA, kilovolt-amperes. We determine apparent power using the formula, kVA2 = kV*A.

Going one step further, Power Factor (PF) is the ratio of working power to apparent power, or the formula PF = kW / kVA. A high PF benefits both the customer and utility, while a low PF indicates poor utilization of electrical power.  Continue reading


Radio-Frequency Identification (RFID) is technology that allows machines to identify an object without touching it, even without a clear line of sight. Furthermore, this technology can be used to identify several objects simultaneously. RFID can be found everywhere these days – anything from your cat to your car contains RFID technology. This post will cover how RFID works, some practical uses, and maybe even some example code for reading RFID data.



What is RFID?

RFID is a sort of umbrella term used to describe technology that uses radio waves to communicate. Generally, the data stored is in the form of a serial number. Many RFID tags, contain a 32-bit hexadecimal number. At its heart, the RFID card contains an antenna attached to a microchip. When the chip is properly powered, it transmits the serial number through the antenna, which is then read and decoded. Continue reading


Limiting current into an LED is very important. An LED behaves very differently to a resistor in circuit. Resistors behave linearly according to Ohm’s law: V = IR. For example, increase the voltage across a resistor, the current will increase proportionally, as long as the resistor’s value stays the same. Simple enough. LEDs do not behave in this way. They behave as a diode with a characteristic I-V curve that is different than a resistor.

For example, there is a specification for diodes called the characteristic (or recommended) forward voltage (usually between 1.5-4V for LEDs). You must reach the characteristic forward voltage to turn ‘on’ the diode or LED, but as you exceed the characteristic forward voltage, the LED’s resistance quickly drops off. Therefore, the LED will begin to draw a bunch of current and in some cases, burn out. A resistor is used in series with the LED to keep the current at a specific level called the characteristic (or recommended) forward current.

image1 Continue reading


Microcontrollers are a ton of fun. Once I got hooked, there was no

turning back. Initially playing with sensors and LCDs, I quickly discovered the limits to what a microcontroller could control. A microcontroller’s GPIO (general purpose input/output) pins cannot handle higher power requirements. An LED was easy enough, but large power items such as light bulbs, toaster ovens, and blenders required more sneaky circuitry. Something sneaky called a relay:



In this tutorial we will discuss a small relay board to control the power to a normal AC outlet using 5VDC control.

All the usual warnings apply: Main voltage (120VAC or 220VAC) can kill you. This project, done incorrectly, could certainly burn down your house. Do not work on or solder to any part of a project while it is plugged into the wall – just unplug it!

You can get the Eagle files for the control board here. The control board is composed of a relay along with a NPN transistor and LED. Continue reading


More and more these days, I am meeting people who have built complex, impressive, and clever electronic projects, and, when I ask, I’m surprised to find out that they have no formal engineering or technical education. Now, I’m not surprised because I don’t believe that electronics can’t be learned outside of a university, a good deal of my job is to try to teachelectronics outside a university. I’m surprised because, more often than not, this impressive project will include a design element, component, or concept that I doubt I ever would have been exposed to had I not attended college. How do people learn a complex subject, like say, fourth-order filters, on their own time? I am always blown away by the fact that people have mastered concepts, on their own, that I had never even heard of, let alone attempted to study, before I had the dreadful feeling of finding out that it was one of my required college courses.

Where are these people getting this information?! How did they manage to find such a (sometimes) very dry subject and keep themselves engaged long enough to master it? I ask these questions because I’m jealous. I’m jealous of artists and designers that were exposed to this field at a young age. I’m especially jealous of those lucky people who manage to find just the right book, or mentor, or resource to teach them and keep them engaged in a subject that, in college, I paid a boatload of money for someone to teach me. Continue reading



Why use a relay with an Arduino board?

Individual applications will vary, but in short – a relay allows our relatively low voltage Arduino to easily control higher power circuits. A relay accomplishes this by using the 5V outputted from an Arduino pin to energize an electromagnet which in turn closes an internal, physical switch attached to the aforementioned higher power circuit. You can actually hear the switch *click* closed on even small relays – just like the big ones on street corners used for traffic signals. Continue reading


relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.


htsybluxcykpudib Continue reading




At the end of this instructable you will be able to detect your car as it approaches the wall inside your garage, signalling you that the car is inside far enough so you can close the door.
Most car sensors will use a microprocessor to help calculate the distance of an approaching car when entering the garage.

The main component and the challenge was to use a 555 timer as the driving “brains” of the project. So here we go: Continue reading




Lets now start of with a new series – “Hobby DIY Electronics” which contains small projects to start for beginners, robotics and much more. Enjoy the series of upcoming posts and do leave your experiences and messages in the comments section below.




Making Bibberbeests with kids is a HUGE success at schools, parties and festivals

Now what is more fun than a Bibberbeest? A remote controlled bibberbeest, using a standard audio/video RC?
So what I needed was a receiver circuit for a standard TV RC that can switch on and off a Bibberbeest’s motor, working on 3 Volts max.

At first I was tempted to go the microcontroller way, But in my eternal search to keep things simple, I eventually decided to use a hardware-only circuit: Just eight parts on a 2,5 x 4 cm board (1″ x 1,5″).
After some trial and error I used this IR toggle switch diagram (with slight mods) around a 555 timer chip by member BIC, which works quite well.

Step 1: Tools and materials

F6LAMNYHKVKM5UV.LARGE Continue reading


Recently I wanted to replace a rechargeable battery pack from a RC car. I tried getting a rechargeable battery pack similar to the original one but that didn’t last even half the period the original one had lasted. So I had to find out an economical way of getting batteries replaced.

Instead of taking a chance on another unreliable replacement battery pack, I decided to look inside the existing one. The plastic shell consists of two parts held together with transparent tape that is easily removed with a razor blade. Inside, there are three industrial tabbed cells of the same length and diameter of consumer AAA cells, without the bump on the positive terminal.


Given the identical cell size, it distresses me that the  manufacturer didn’t simply mold a AAA battery holder into the handset. This consumer-friendly feature would have allowed the end user to replace the individual cells using off-the-shelf consumer batteries. The idealist assumes this is a safety feature to prevent errant installation of alkaline cells or mixed chemistries that might catch on fire when recharged from the base. Continue reading


When a vehicle is driven on the highway at night, it is required that light beam should be of high density and should illuminate the road at a distance sufficiently ahead. However, when a vehicle coming in the opposite direction approaches the vehicle with a high-beam headlight, driver of that vehicle will experience a glare, which may blind him. This dazzle effect is one of the major problems faced by a driver in night driving. To avoid this impermanent blindness, a separate filament is usually fitted in the “dual-filament” headlight bulb in a position such that light beam from this second filament is deflected both down and sideways so that the driver of the oncoming car is not blinded. In practice, one mechanical dimmer switch is used by the driver to manually select high (bright) or low (dim) headlight beam. However, this is an awkward task for the driver especially during peak traffics.



Our project “Adaptive Lighting System for Automobiles” is a smart solution for safe and convenient night driving without the intense dazzling effect and aftermaths. Adaptive Lighting System for Automobiles needs no manual Continue reading


This simple, wearable circuit uses an operational amplifier (or “op-amp”) chip to convert sound into light. An LM324 op-amp and a transistor boost input from a mini condenser microphone to light a series of LEDs. Watch it blink to the beat of your favorite music.


Components Required

  • Battery, 9V (1)
  • Solder, lead-free (1)
  • Battery snap, 9V (1)
  • Hookup wire, 22 gauge, multiple colors (1)
  • PC board, grid style, with 371 holes (1)
  • Resistor assortment, 500 piece (1)
  • Transistor, NPN, 2N4401 (1)
  • Microphone condenser element (1
  • Capacitor, 0.1 µF ceramic (100 nF, capacitor code 104) (1)
  • Capacitor, 1.0µF non-polarized electrolytic (capacitor code 105) (1)
  • Op-Amp chip, Quad, LM324 (1)
  • LED 5mm (1)

Step #1: Gather the parts


  • The electret microphone element is polarized, so be careful not to reverse the connections. The ground leg is the one with the 3 silver traces running to the case (second photo).
  • To identify resistor values from their color codes, you can use this online calculator.
  • The LM324 chip has four op-amps, but this circuit only requires two of them. Continue reading




LDR-based automatic lights  flicker due to the change in light  intensity at dawn and dusk.  So compact fluorescent lamps (CFLs)  are unsuitable in such circuits as flickering may damage the electronic  circuits within these lamps. The circuit  described here can solve the problem  and switch on the lamp instantly when  the light intensity decreases below a  preset level. The circuit uses popular timer IC  NE555 (IC1) as a Schmitt trigger to give  the bistable action.

The set and reset  functions of the comparators within  the NE555 are used to give the instantaneous action. The upper threshold  comparator of IC1 trips at 2/3Vcc,  while the lower trigger comparator  trips at 1/3Vcc. The inputs of both the threshold comparator and the trigger  comparator of NE555 (pins 6 and 2) are tied together and connected to the  voltage divider formed by LDR1 and  VR1. The voltage across LDR1 depends  on the light intensity. Continue reading




Some of the mosquito repellents available in the market use a toxic liquid to generate poisonous vapours in order to repel mosquitoes out of the room. Due to the continuous release of poisonous vapours into the room, after midnight the natural balance of the air composition for good health reaches or exceeds the critical level. Mostly, these vapours attack the brain through lungs and exert an anesthetic effect on mosquitoes as well as other living beings by small or greater percentage. Long exposure to these toxic vapours may cause neurological or related problems.

Here is a circuit that automatically switches on and off the mosquito repellent after preset time interval, thus controlling the release of toxic vapours into the room. Continue reading



I am a big fan of garage sales, flea markets, and thrift stores. They are great places to find used parts and materials for your next project. But one problem that I often run into is not being able to test battery powered electronics to see if they work. Because there are so many different combinations of batteries that are used in portable electronics, it isn’t really practical to carry around batteries for testing. One device may need 6 AA’s and another may require 4 D’s. So I came up with this simple pocket-sized variable power supply. It can plug into either a 9V battery or a 12V battery pack. You can then adjust the output voltage to match the device that you want to test and attach the output wires to the end terminals on the device’s battery connectors. This lets you power the device long enough to see if it works.


  • 8-Position DIP Switch
  • 220 ohm Resistor
  • 1 µF Capacitor
  • 0.1 µF Capacitor
  • LM317 Adjustable Voltage Regulator
  • 2 x Alligator Clip Wires
  • Perf Board
  • 9V Battery Connector
  • 270 ohm Resistor (preferably 1/8 watt) (7)
  • Soldering Iron and Solder


Step #1: Materials



  • LM317 Adjustable Voltage Regulator, 0.1 µF Capacitor, 1 µF Capacitor, 220 ohm Resistor, 7 x 270 ohm Resistor (preferably 1/8 watt), 8-Position DIP Switch, Perf Board, 9V Battery Connector, 2 x Alligator Clip Wires, Continue reading



It’s easy to build up a “junk box” of items you can use to build projects seen in just about any-thing you can imagine.

Many of my articles take advantage of found components, often picked out of trash bins. Just because an electronic device has failed at its original task doesn’t mean it can’t perform other tasks. Castoffs can be recovered and the parts repurposed in countless ways.

Recently, my trash-picking adventures turned up a discarded laser printer. I set about finding what wonders were waiting beneath the plastic covers.


My first discovery was the main circuit board. Once I stripped the heat shields off, I found over 50 nonproprietary electronic parts, including capacitors, resistors, voltage regulators, transistors, transformers, coils, and integrated circuits. Jackpot! A couple of boards like this, and you’re on your way to building a backup supply of parts for future projects. A second, smaller PC board also yielded numerous useful components. Continue reading




Click the picture to view the MINI ROVER in action

Ever wanted to explore your house from a pet’s perspective, here’s the Mini Rover Surveillance bot which is going to do exactly that.


Step #1: Strip down the car.


  • Using Scientific Toys’ EZTEC-branded 1:17 scale Chevy Silverado R/C car as a camera platform. This toy is cheap, hacker-friendly, and works astoundingly well for the price.
  • First, detach the truck body shell from the chassis by removing 3 screws: 2 on top, in the truck bed, and 1 from below, between the front wheels.
  • Now, open the electronics compartment by removing 4 screws, as shown, and lifting the plastic cover gently up and off. The floppy wire antenna, which is threaded through a hole in the cover, should slip out the bottom as you do this.

Step #2: Install the chassis standoffs.



  • Position the video camera mounting base on the car’s electronics compartment cover, as shown. Use the base as a template to drill 3 matching 5/32″-diameter holes in the electronics compartment cover.
  • TIP: You may find it easier to operate the drill through the baseplate if you remove the camera mount ball joint at the top of the stem first. Simply turn the wingscrew all the way out and the whole assembly will come off.
  • Turn the electronics compartment cover over, and attach three 10cm standoffs on the top side of the compartment cover using the screws that come with the standoffs. Continue reading




The incandescent lamp provided inside the refrigerators glows whenever we open the door. It suffers from several disadvantages like:

1. Being a single light source, located in the upper corner, light does not spread uniformly. Only upper shelves get good light and the lower shelves are in darkness because of the shadows of food items kept.

2. Ironically, the lamp generates heat in the space which we are trying to cool, thus making the compressor work for longer duration.

3. During power outages, there is no illumination inside the fridge, when it is most needed.

The above problems could be overcome by using a distributed array of LEDs with battery back-up, which provides shadow less light and cool operation.



Fig. 1: Rows of LEDs placed in PVC channels


Fig. 2: Orientation of LEDs and the arrows indicating the direction of light from LEDs

Two columns of six white LEDs in each row (2×6 array of white LEDs) are made using white PVC channels. The length of the channel equals the height of the cooling compartment of the fridge. The LEDs are placed such that each shelf has two LEDs located at the top corner. These channels are placed in the left- and right-hand corners inside the fridge as shown in Fig. 1. Continue reading



This easy-to-build electronic alarm will remind you of an impotant task after a preset time. It is particularly useful for housewives and busy professionals. All you have to do is set the time in minute swith the help of two thumbwheel switches (S3 and S4) and press and release start switch. Precisely after the time set by you is over, there is an audio as well as visual indication to remind you that the time you set has elapsed. The gadget is portable and operates off a 9V battery.

At the heart of this circuit are two counter ICs CD4029 (IC4 and IC5). These are programmable up/down 4bit binary/decade counters belonging to CMOS family of digital integrated circuits. The information present on them is fed to inputs P0 through P3 in parallel. It is loaded into the counter when the PL input is high, independent of the clock pulse input. In this circuit, IC4 and IC5 count in up/down mode when the up/down input is high/low. These have been wired as 4-bit binary counters in countdown mode with B/D input low. The counter advances by one count on every low-to-high transition of the clock pulse. Continue reading

Disposable Drones Take Flight


When we think of drones — nay unmanned aerial vehicles — we typically picture military drones or those ubiquitous quadrotors. However, two new mini-drone designs are taking shape: a paper airplane and a maple seed.

a team of roboticists created both designs to help record atmospheric conditions in the event of a forest fire. The disposable, self-steering drones are essentially sensor modules that can be dropped over a forested area to relay environmental data that could indicate potential for fire.

The first prototype looks exactly like a standard paper airplane, only this one’s made of biodegradable cellulose material. Once deployed from a larger aircraft, the so-called Polyplane drone steers itself using tabs attached to the back of each wing. An onboard control system bends each tab to direct the craft as close as possible to a pre-determined landing area. Because the circuits Continue reading



Here is the circuit of a simple electric window charger. With a couple of minor circuit variations, it can be used as an electric fence charger too. A standard 12V, 7Ah sealed maintenance-free (SMF) UPS battery is required for powering the entire unit.

Any component layout and mounting plan can be used. However, try to keep the output terminals of transformer X1 away from the circuit board. Timer NE555 (IC1) is wired as a free-running oscillator with narrow negative pulse at the output pin 3. The pulse frequency is determined by resistors R2 and R3, preset VR1 and capacitor C3. The amplitude of the output pulse can be varied to some extent by adjusting variable resistor VR1. You can vary the frequency from 100 Hz to 150 Hz.  Continue reading



Long before Fukushima, energy saving was a watchword. Efficient use of energy reduces the number of power stations. The conventional filamentlamps are problematic because of their low efficiency On the other hand, energy-saving CFL lamps too are not without problems due to their mercury content. For this reason, advances in light-intensive white LEDs are welcome. These offer an additional advantage—long life. With proper cooling, LED lamps have a life expectancy 50 times greater than filamentlamps. However, these might Continue reading


The following post describes a simple low battery indicator circuit by using just two inexpensive NPN transistors. The main feature of this circuit is its very low stand by current consumption.


We can also make a low battery indicator circuit using a 741 IC and a 555 IC, which are no doubt outstanding with their abilities of detecting and indicating low battery voltage thresholds.

However the following post relates yet another similar circuit which is much cheaper and employs just a couple of NPN transistors for producing the required low battery indications.

The main advantage of the proposed two transistor low battery indicator circuit is its very low current consumption compared to the IC counterparts which consume relatively higher currents. A IC 555 would consume around 5mA, a IC741 around 3 mA, while the present circuit would just consume around 1.5mA current.

Thus the present circuit becomes more efficient especially in cases where Continue reading


Most of us are more comfortable with 1, 2, 3, 4… rather than 001, 010, 011, 100. We mean to say that we will need a decimal coded output in many cases rather than a raw binary output. We have many counter ICs available but most of them produce binary data as an output. We will again need to process that output by using decoders or any other circuitry to make it usable for our application in most of the cases.

Let us now introduce you a new IC named IC 4017. It is a CMOS decade counter cum decoder circuit which can work out of the box for most of our low range counting applications. It can count from zero to ten and its outputs are decoded. This saves a lot of board space and time required to build our circuits when our application demands using a counter followed by a decoder IC. This IC also simplifies the design and makes debugging easy.

Pin-Diagram-of-4520 Continue reading



Here is an art project for you to try out. In this article we shall learn the design and working of the circuit Circling LEDs. In this, we have eight LEDs which glow one after the other to form a circling effect. My intention in publishing this circuit is not just to make some art work with electronics but also to illustrate the working principle and circuit design using IC 555 in astable mode, 4017 counter and to explain the related concepts.

IC4017 Circuit Schematic:

circling-LEDs Continue reading


passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors.

Different Types Of PIR Sensors :

  • Multi-Fresnel lens type of PIR
  • PIR motion detector housing with cylindrical faceted window. The animation highlights individual facets, each of which is a Fresnel lens, focusing light on the sensor element underneath.

  • PIR front cover only (electronics removed), with point light source behind, to show individual lenses.

  • PIR with front cover removed, showing location of pyroelectric sensor (green arrow).

Operating principles

All objects with a temperature above absolute zero emit heat energy in the form of optical radiation (light). Usually this light is invisible to the human eye because body temperature radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose. Continue reading


The sensors could be utilized as a part of measuring the radiation temperature without any contact. For different radiation temperature ranges various filters are available. An infrared (IR) sensor is an electronic device that radiates or locates infrared radiation to sense some part of its surroundings. They are undetectable to human eyes.


An infrared sensor could be considered a Polaroid that briefly recalls how an area’s infrared radiation shows up. It is very regular for an infrared sensor to be coordinated into movement indicators like those utilized as a feature of private or business security systems. An IR sensor is shown in figure; basically it has two terminals positive and negative. These sensors are undetectable to human eyes. Continue reading


Famous among the DIY electronics community for their single-board microcontroller, Arduino recently launched a new wheeled robot at the 2013 Bay Area Maker Faire.

Designed with Complubot, a four-time Robocup Junior champion in robotic soccer, the Arduino Robot, with its self-contained platform, will allow tinkerers of all stripes to explore their robotic whims with endless hours of interactive play and experimentation.

As the first official Arduino on wheels, the hockey puck-shaped robot includes two processors, one on each of its two boards: the motor board, which obviously controls the wheel motors, and a control board, which reads sensors and makes decisions on operations.

Essentially, the top and bottom surfaces of the robot are full Arduino boards that are programmable with the Aduino IDE software.

“Programming the robot is similar to the process with the Arduino Leonardo” microcontroller. “Both processors have built-in USB communication, eliminating the need for a secondary processor. This allows the Robot to appear to a connected computer as a virtual (CDC) serial / COM port.”

Every element of the platform — the hardware, software and documentation — is open-source and available like all other Arduino products. This allows users to modify the software and build unique hardware on top of it, making the platform perfect for novices and more seasoned roboticists to build interactive machines of their own design.

Credit: Arduino


LED are known to have a very wide range of applications in the lighting field and are also known to have very high efficiency and longer life when compared to CFL and incandescent bulbs, here we discuss a few interesting application of LED’s.

Here are two night lamp circuits using LEDs. One could be used as a night-vision clock and the other as a TV lamp. Both the circuits are AC operated and consume very little power. These are also protected against mains fluctuations. The night-vision lamp uses twelve LEDs arranged in the circular pattern of a wall clock, while the TV lamp uses 24 LEDs in prism format.

Fig. 1: Night-vision clock circuit

Source : Electronics For You
Fig.1 shows the circuit of night-vision clock. Capacitor C1 (0.22µF) reduces the Continue reading


This is a really innovative way to increase the efficiency in harnessing the Solar energy. Research suggests that if we are able to harness solar energy to a 90-100%  then using the energy harnessed in one day, we can run about one million cars powered by solar, but theoretically we are harnessing less than 10%.

Generally, solar panels are stationary and do not follow the movement of the sun. Here is a solar tracker system that tracks the sun’s movement across the sky and tries to maintain the solar panel perpendicular to the sun’s rays, ensuring that the maximum amount of sunlight is incident on the panel throughout the day. The solar tracker starts following the sun right from dawn, throughout the day till evening, and starts all over again from the dawn next day.

Fig. 1: Circuit of solar tracking system

Fig. 1 shows the circuit of the solar tracking system. The solar tracker comprises comparator IC LM339, H-bridge motor driver IC L293D (IC2) and a few discrete components. Light-dependent resistors LDR1 through LDR4 are used as sensors to detect the panel’s position relative to the sun. These provide the signal to motor driver IC2 to move the solar panel in the sun’s direction. LDR1 and LDR2 are fixed at the edges of the solar panel along the X axis, and connected to comparators A1 and A2, respectively. Presets VR1 and VR2 are set to get low comparator output at pins 2 and 1 of comparators A1 and A2, respectively, so as to stop motor M1 when the sun’s rays are perpendicular to the solar panel. 

When LDR2 receives more light than LDR1, it offers lower resistance than LDR1, providing a high input to comparators A1 and A2 at pins 4 and 7, respectively. As a result, output pin 1 of comparator A2 goes high to rotate motor M1 in one direction (say, anti-clockwise) and turn the solar panel.

When LDR1 receives more light than LDR2, it offers lower resistance than LDR2, giving a low input to comparators A1 and A2 at pins 4 and 7, respectively. As the voltage at pin 5 of comparator A1 is now higher than the voltage at its pin 4, its output pin 2 goes high. As a result, motor M1 rotates in the opposite direction (say, clock-wise) and the solar panel turns.

Fig. 2 Proposed assembly for the solar tracking system

Similarly, LDR3 and LDR4 track the sun along Y axis. Fig. 2 shows the proposed assembly for the solar tracking system.


Are you confused on how to give a fresh new life to a broken CFL bulb, read on you’ll get the answer to this question here.

In this post i’m sharing a LED lamp circuit which can be mounted in a broken CFL bulb and can be  converted into a LED based power saving light. This is just a LED lamp circuit that can be operated from the mains voltage. A string of five LED is driven using a capacitive transformerless power supply. In the circuit 0.47uF/400V Polyester capacitor C1 reduces the mains voltage. R3 is a bleeder resistor which drains the stored charge from C1 when the AC input is switched OFF. Resistors R1 and R2 limits the inrush of current when the circuit is switched ON. Diodes D1 to D4 forms a bridge rectifier that rectifies the reduced AC voltage and C2 acts as a filter capacitor. Finally Zener diode D5 provides regulation and the LEDs are driven.

Here are some of the pictures of the LED lamp.



Components used :

  • 120 Ohm 1/2 Watt resistors [2]
  • 470k Ohm 1/4 Watt resistor [1]
  • 0.47uF, 400 V Polyster capacitor
  • IN4007 Diodes [4]
  • 47uF, 25V electrolytic capacitor
  • 16-18V 1W Zener diode [1]
  • Hi power LED’s. [ Here i have used 1W circular LED’s ]


The circuit board arrangement which i have built.


After assembling the Circuit board in the CFL bulb casing.


The LED arrangement on a laminate sheet.


The completely assembled, finished LED light.


My smart LED lamp in action.


Another close view of the illuminating LED’s.


1. Carefully remove the broken glass pieces of the CFL bulb.

2. Open the assembly carefully

3. Remove electronics and discard

4. Assemble the circuit in dot matrix PC or on a 1mm laminate sheet.

5. Cut a round laminate sheet with (scissor)

6. Mark the position of the 5 round holes on the sheet

7. Drill the holes to suit the LEDs to flush fit in the six holes

8. Use a dab of adhesive to keep the LED assembly in position

9. Close the assembly

10. Ensure the internal wiring does not touch each other

11. Now test on 230Volt AC Your nice compact table lamp / puja room lamp / passage lamp is ready for use.

For any queries related to this post, ask your questions in the comments section below.


The 555 is a single-chip version of a commonly used circuit called a multivibrator, which is useful in a wide variety of electronic circuits. The 555 timer chipis probably the most popular integrated circuit ever made.

You can use the 555 chips for basic timing functions, such as turning a light on for a certain length of time, or you can use it to create a warning light that flashes on and off. You can use it to produce musical notes of a particular frequency, or you can use it to control positioning of a servo device.

Here is the arrangement of the eight pins in a standard 555 IC. The 555 comes in an 8-pin DIP package.



7 Continue reading



This video explains another FM Bug, with a higher range of operation.

This FM bug transmitter circuit will let you spy on people. The transmitter can be placed in the desired room and the conversation heard from a place far away just using a regular FM radio set.

The circuit is designed around a single transistor 2N3904 (T1), a custom-made coil (L1), three capacitors (C1 through C3), a trimmer (VC1), two resistors (R1 and R2) and, of course, a condenser microphone (MIC1). The circuit transmits in the frequency range of 88-105 MHz. Transmission range is 100 metres. Continue reading

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