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You can use this laser-based intruder alarm conveniently at the entrance of a hall or any other similar location to protect the same from unauthorised access as and when desired. Its range can be extended further to protect the perimeter of a  building from unauthorised intrusion by using a cascade arrangement of multiple alarms. The circuit consists of a transmitter and a receiver. Circuit diagram : Fig. 1: Transmitter circuit Diagram The transmitter circuit (shown in  Fig. 1) is nothing but a laser diode (LD1) driven by a 9V PP3 battery. The  output of IC1 is regulated 5V as long as  its input remains equal to or more than  7.5V, thus ensuring a constant drive  current for the laser diode. The battery (Batt1) is connected to the circuit  through switch S1. The laser diode (LD1) can be  replaced with a laser pointer (torch)  emitting red laser beam. The laser  pointer itself can be used as a transmitter. The pointer has in-built series  resistance, on/off switch and battery. Ci...

What i am making here is a USB lock with smartcard key. The idea is that a phonecard reader made with a PIC micro will be able to store a number of different phonecards into memory. Whenever one of these cards is inserted into the slot, it will activate a 4-ports USB On/Off switch. If the card is removed, the USB ports will be de-activated. [ ]

panStamp is an open source project created for the enthusiasts that love measuring and controlling things wirelessly. panStamps are small wireless boards specially designed to fit in low-power applications, simple to program and simple to work with. With panStamps, you can measure almost everything by simply connecting your panStamp to the sensors, placing a battery and sending wireless data from the first moment. panStamps are suitable for any kind of project needing remote control and low-power wireless transmissions, including home automation, energy metering, weather monitoring and robot control. If you are one of these three things: a hobbyist, a professional or an end-user, you will find that panStamps provide extreme flexibility and power when creating custom wireless networks. [ ]

Although a simple crystal oscillator may be built from one comparator of an LT1720/LT1721, this will suffer from a number of inherent shortcomings and design problems. Although the LT1720/LT1721 will give the correct logic output when one input is outside the common mode range, additional delays may occur when it is so operated, opening the possibility of spurious operating modes. Therefore, the DC bias voltages at the inputs have to be set near the center of the LT1720/LT1721’s common mode range and a resistor is required to attenuate the feedback to the non-inverting input. Unfortunately, although the output duty cycle for this circuit is roughly 50%, it is affected by resistor tolerances and, to a lesser extent, by comparator offsets and timings. If a 50% duty cycle is required, the circuit shown here creates a pair of complementary outputs with a forced 50% duty cycle. Crystals are narrow-band elements, so the feedback to the non-inverting input is a filtered analogue version of the...

Long time ago I came across this page http://tobe.nimio.info/project/moodlamp, where Toon Beerten created a Moodlamp using a PIC16F628 µC. I remember that back then I didn’t have much knowledge on µC’s programming, so the first thing I did was to buy a Arduino board, and since that time I have been learning a lot and making many different projects with it…[ ]     Time has passed, I’ve built the breadboard prototype, then the first version, using only one layer (which is a good version if you want to etch your own PCB). Always wanted to make the project public as an Open Hardware, but due my lack of time, I never did, until I arrive in Genova. I then decided to make a second version of the board, two layers, the ability to program the µC without removing it from the socket (for programing you will need an Arduino, FTDI or USB-to-serial cable) and some available pins for those who want’s to add more features to the board, like a temperature sensor or another kind of sensor. Her...

This is a very Low Distortion Wien Bridge Based Oscillator Circuit Diagram Project .This complex oscillator circuit uses a photocell and common-mode-suppression circuitry to achieve distortion of 0.0003%. This oscillator circuit replaces the lamp in the traditional Wien bridge with an electronic equivalent.  Very Low Distortion Wien Bridge Based Oscillator Circuit Diagram 

One tool that I’ve been missing at my lab at home is function generator. They tend to be a bit expensive, so I haven’t bought one. I thought this might be a good opportunity to try and make one myself. I found a pretty common DDS (direct digital synthesis) chip, called AD9833. Then just strap a USB-enabled AVR micro there and maybe some analog electronics. This board doesn’t do any of the special analog magic to allow for variable amplitude or offset for the signal. The output is fixed to 0-4v. I’m planning to make another completely analog board for adjusting amplitude and offset.

CIRCUIT DIAGRAM OF OP AMP BASED MONOSTABLE MULTIVIBRATOR (741 IC) MONOSTABLE MULTIVIBRATOR USING OP AMP 741 Monostable multivibrator is also called as One Shot Multivibrator. It has a Stable State and a Quasi-Stable State. The circuit remains in stable state until a triggering signal is applied to its input. After getting the triggering signal the output transit from stable to Quasi-stable state and return back after a time period. So a Single Pulse is generated for single Trigger. Consider the instant at which the output Vo=+Vsat. At that time diode D1 damps the Capacitor voltage, Vc at 0.7V. Feedback voltage is +βVsat at Non-Inverting terminal. When the negative trigger is applied, the potential at Non-Inverting terminal becomes less than 0.7v the output switches to -Vsat, which makes the diode more negative than -βVsat. Comparator switches back to +Vsat. The Capacitor C starts charging to +Vsat through R until Vc reaches 0.7v and C becomes damped to 0.7v. The pulse width is given by...

            It is becoming increasingly difficult for users to interact with the slew of portable gadgets they carry, especially in the area of text entry. Although miniature displays and keyboards make some portable devices, such as cell phones and PDAs, amazingly small, users’ hands do not shrink accordingly.             To solve this problem, we proposed a Virtual Keyboard. This device will replace a physical keypad with a customizable keyboard printed on a standard A4 size paper whose “keystrokes” are read and translated to real input. This virtual keyboard can be placed on any flat surface, such as desktops, airplane tray tables, kitchen counters, etc. and can theoretically be interfaced with any computing device that requires text entry. This would eliminate the need to carry anything around and also prevent any chance of mechanical damage to the keypad in harsh environments if a simple lamin...

Here i am presenting you a Fingerprint based security system using r303a module . By using this you can secure a room, office, lockers or any private areas. The basic principle used in this project is Biometric Authentication, it refers to the identification of humans by their physical or behavioural characteristics. The physical biometric authentication involves FINGERPRINT VOICE FACE IRIS Here we are using fingerprint as the identification factor, for that a fingerprint module R303 is used. it is a low cost, high performance, easily available one and can be able to store upto 120 fingerprint images in its memory. We can also interface it with a computer by means of max232 level converter. The fingerprint module R303 can be divided into two sections Read More.....

MOSFET based amplifiers as we all know are outstanding with their sound qualities and they can easilly beat the performance of other counterparts based on power transistors or linear ICs. However amplifiers based on mosfets are not always easy to design or make. Moreover after assembling a prototype, testing to perfection always remains an issue with new electronic hobbyists. You might have come across many hi-fi complex mosfet amplifier designs, but might have not dared making it just because of the above reasons. The simple mosfet amplifier circuit diagram is super simple to build and yet will provide you with a crystal clear 100 watts of raw music power that all the listeners will cherish for a long time. The idea was developed a long time ago by the Hitachi researchers and still it remains one of the favorite designs of all time considering the involved simplicity against quality. Looking at the figure we can understand the circuit with the following points: The involved simplicity...

This universal battery charger is based on LM317 and has an adjustable regulated output voltage and also has an adjustable constant-current charging circuit that makes it suitable to use for charging most NiCad batteries and some other types of batteries . This LM317 universal battery charger can charge a single cell or a number of series-connected cells up to a maximum voltage of 18 V. This universal battery charger circuit use just some common electronic components like LM317 regulator , operational amplifier and some 2n3055 power transistors .2n3055 power transistors Q1 and Q2 are connected as series regulators to control the battery charger's out¬put voltage and charge-current rate. The LM317 used as an adjustable voltage regulator supplies the drive signal to the bases of power transistors Q1 and Q2. By turning the potentiometer R9 the output-voltage level will be modified. A current-sampling resistor, R8 (a 0.1-fi, 5-W unit), connected between the negative output lead and cir...

This is the simple Ic 555 Based 10 Note Sound Synthesizer Circuit Diagram. As shown, three ICs are used to produce the sounds. ICl is a 555 timer that generates clock pulses. It is configured as an astable multivibrator. The frequency of the clock pulses is set by trim: mer potentiometer PI. These clock pulses are coupled to the input of IC3 (a 4017 CMOS Johnson counter) on its clock input pin 14.   Ic 555 Based 10 Note Sound Synthesizer Circuit Diagram Each clock pulse causes IC3 to shift a high to each of its output pins in sequence. A trimmer resistor, which can be adjusted to set a different frequency for each note, is connected to each of IC3`s output pins. One side of each of the trimmers is connected to pin 5 (the control voltage pin) of IC2. IC2, another 555 timer IC, creates the tone; the overall pitch of the tone can be varied by P2.  As the output sequences from the 4017, that tone, which is changed in frequency by each output shift is applied to a small speake...