Thursday, April 18, 2013

Reflex Tester Circuit

Testing human reaction speed is not only a fun way of spending time, but also allows the drawing of conclusions, for example on the skills of a momentary driver. When the contact closes the power button, the astabil multivibrator built with IC1 produces pulses that are applied to counter IC3. D1 …. D10 LEDs light up sequentially in a chained fast.

Once the person tested acts stop button S2 the astabil multivibrator is blocked, the last ordered with decoder IC4 LED lights next. If frequency of the astabil multivibrator with P1 is adjusted so that the numerator, for example, receives a pulse every 10 seconds, then the reaction time can be read easily. The test can be repeated after drive reset button (S3). Reflex tester circuit absorbs about 120 mA current, supply voltage (5V) must be stabilized. Frequency can be adjusted to the astabil multivibrator with P1 between 10 Hz and 80 Hz.

Reflex Test Circuit Diagram

reflex tester circuit diagram

LASER diode

Laser is of prime importance in Optical memories, Fiber optic communications, Military applications, Surgical procedures, CD players, Printers etc. Various forms of lasers like Gallium Arsenide laser, Helium Neon laser, Carbon dioxide laser etc are used in various applications. CD players use laser technology to read the optically recorded data in the form o fBits and Pits on the CD.

Laser is a narrow beam of Photonsemitted by specially made laser diodes. Laser diode is similar to an ordinary LED, but it generates a beam ofhigh intensity light. A laser is a device in which a number of atoms vibrate to produce a beam of radiation in which all the waves havesingle wavelength and are in Phasewith each other.

Monochromatic Laser

PS2501-1 MAX706CPA MC10131L LXT907PC H11L1 LM1117MPX-3.3 LT1372CS8 MT8816AP MT8952BE MC34063A LM393DT INA2134UA MAX213ECAI LXT915QC MAX232 ISPLSI1032E-70LT
laser beam
Laser light is Monochromatic and can be focused as a pencil beamThe beam of a typical laser has 4×0.6mm widening at a distance of 15 meters. Like an LED, laser diode converts electrical energy into light energy.
laser gun

How it Works?

The most common laser diode generates semiconductor or injection laser. In these lasers, a population of Inversion Electrons is produced by applying a voltage across its p-n junction. Laser beam is then available from the semiconductor region. The p-n junction of laser diode has polished ends so that, theemitted photons reflect back and forth and creates more electron-hole pairs. The photons thus generated will be in phase with the previous photons. This will give a Pencil Beam and all the photons in the beam are Coherent and in phase.
laser emission

Applications of Laser

Laser diodes can be switched on and off at frequencies as high as1GHz, making them ideal in Telecommunication applications. Since laser generates heat on hitting the body tissue, it is an ideal solution to heal sensitive parts like Retina of Eye and brain. Laser can be used topinpointthe lesions so that nearby tissues are not affected as in the case of surgery.
Laser Diode
A Word of Caution
Laser is a high intensity penetrating beam and is extremely dangerouswhen focused on to the Eye. Low cost Laser pointers are now available in the market and some people handle them carelessly and may even give to children to play with.A Laser pointer with output power higher than 5 mW is harmful. Take utmost care while handling laser diodes. Always take precautionary measures while trouble shooting CD players, Laser printers etc.


The easiest way to connect computer peripherals is through a Universal Serial Bus. The USB is a plug-and-play interface between the PC and the peripherals. The advantage of USB is that the device can be plugged in or plugged out without the need of restarting the PC. Here explains the working of USB.
USB is the short form of Universal Serial Bus, a standard port that helps to connect computer peripherals like scanner, printer, digital camera, flash drive and more to the Computer. The USB standard supports the data transfer at the rate of 12 Mbps.
usb flash drive

USB Specification

Two important aspects of USB are itssupport capability and total bandwidth.USB is capable of supporting127 USB devicesand has a totalbandwidth of 12 Mbit per secondwhich is equal to 1.5 MB per second. Working of a 12 Mbit (full speed device) or a 1.5 Mbit (low speed devices) depends on the total bandwidth of the USB.

USB Connections

Each USB device uses the standardA type USB connector to the USB hostor Hub throughA type receptacle. The other end of the USB cable has seriesB connectorwhich is used to plug into theB type receptacle
usb AB connectors
A connectoris used for the upstream connection towards the host andB connectorfor the downward stream to the USB device. When the USB device is connected to the PC, it activates the host to recognize it. The PC detects the USB device and manages a control flow between the USB device and computer. PC also manages the data transfer between the USB device and PC. Once detected, the PC sends data to the USB system software to recognize it which then identify the device and assign an address. Thisaddressis used to detect the particular USB device. The software controls the input and output data between the PC and USB device. If the software fails to assign the address, PC will not detect the USB device.
usb receptacles

USB Cable

The USB cable provides four pathways- twopower conductorsand two twistedsignal conductors.The USB device that uses full speed bandwidth devices must have a twisted pair D and D- conductors. The data is transferred through the D and D- connectors while Vbus and Gnd connectors provide power to the USB device.
usb a pinout

USB Wiring connection

The USB cable has typically four wires to connect the A type connector
Red 5V Pin 1
White D Pin 2
Green D- Pin 3
Black Gnd Pin 4


TheUSB Hubis used to connect many devices to the PC using a single USB connector. The USB Hub can detect the attachment or detachment of devices in each port of the Hub. The Hub also distributes power to all the devices connected to it. Hub also detects low speed and full speed devices.
usb hub
TheUSB Hubhas two components- AHub controllerand aHub repeater. The Hub controller enables the Hub to communicate with the PC for configuration and control of devices attached to it. The Hub repeater has hardware support for reset, suspend and resume signals.

USB Flash Drive

The most commonly used USB device is theFlash drivethe commonly called Pen drive. It is a mass storage device capable of functioning like a hard disk of computer
inside usb flash drive

Infrared Repeater System circuit

This infrared repeater system is used to extend the range of an infrared transmitter used at an audio or video equipment at 10 m. The original signal is captured by the infrared receiver (figure 1), amplified and delivered to the IR transmitter (figure 2) through a coaxial cable.Its is possible to control an audio system located in the living room from the dining room so it can be used as an infrared remote repeater.

Although in fig. 1 it is used the BPW34 IR diode you can get good results with BP104. The performances of the IR receiver built on the PCB shown in figure 3 were much better than on a Veroboard.
The receiver consumes a strong current dependent of the digital code used by the remote system and it is between 30 mA and 100 mA.
The power supply lines for T1 and T2 must be kept as short as possible.

Infrared Repeater’s Receiver Circuit Diagram

PCF8576CT OPA541AP PCI1420PDV RTL8139D OPA2130UA PCM1720E SP232ECN OP37GS OPA2134PA OPA2650U infrared repeater receiver circuit diagram
The range of the transmitter depends to some extent by the room in which it is used but under normal conditions should be about 10 meters.
The output signal frequencies may be between 5 kHz and 200 kHz. Special attention should be given to avoid optical reactions between the receiver and transmitter.

IR Repeater’s Transmitter Circuit Schematic

ir repeater transmitter circuit schematic
Infrared Repeater PCB Layout

Wednesday, April 17, 2013

Battery Monitor Circuit

Here is a simple Battery Monitor circuit for a quick check of 12 voltLead-Acid Battery. Battery charge should be constantly monitored to increase the life of the battery.Overchargeas well asunder chargewill reduce the battery life. The terminal voltage of the Lead Acid battery should be with in the range of 12.5 to 13.5 volts. If the battery voltage reduces below 10 volts for long period, battery will not accept any charging current. Similarly if the terminal voltage exceeds above 14 volts, battery will be destroyed.

The circuit is aZener controlled transistor switchlighting three LEDs Red, Green and Yellow to show battery states likeLow, Normal and High.When the battery voltage is less than 11 volts, Zener diodes ZD1 and ZD2 cease to conduct and Red LED only lights indicating low battery condition. If the voltage is between 12 volt and 14 volts, Zener diode ZD1 forward bias and T1 conducts. The Green LED connected to the collector of T1 lights indicating normal voltage. If the battery voltage exceeds 15 volts, Zener diode ZD2 also conducts and T2 forward bias. This lights Yellow LED indicating over charge. Thus the following indications can be obtained

Battery Monitor Circuit Diagram

battery monitor circuit diagram

Solar Charger Circuit

Here is a solar charger circuit that is used to charge Lead Acid or Ni-Cd batteries using the solar energy power. The circuit harvests solar energy to charge a 6 volt 4.5 Ah rechargeable battery for various applications. The charger has Voltage and Current regulation and Over voltage cut off facilities.

Solar Charger Circuit Diagram

The circuit uses a 12 volt solar panel and a variable voltage regulator IC LM 317. The solar panel consists of solar cells each rated at 1.2 volts. 12 volt DC is available from the panel to charge the battery. Charging current passes through D1 to the voltage regulator IC LM 317. By adjusting its Adjust pin, output voltage and current can be regulated.
VR is placed between the adjust pin and ground to provide an output voltage of 9 volts to the battery. Resistor R3 Restrict the charging current and diode D2 prevents discharge of current from the battery. Transistor T1 and Zener diode ZD act as a cut off switch when the battery is full. Normally T1 is off and battery gets charging current.
When the terminal voltage of the battery rises above 6.8 volts, Zener conducts and provides base current to T1. It then turns on grounding the output of LM 317 to stop charging.

UM3561 Siren Generator Design

 UM3561 is an excellentROM ICthat can generate Multi siren tones simulating Police siren, Ambulance siren, Fire brigade siren and Machine gun sound. This 8 pin low power IC can work down to 2.4 volts.
The UM 3561 is a low cost siren generator designed for use in toy applications. The IC has an inbuilt oscillator and tone selection pins. It is easy to make a siren generator with only a few external components. Only one external resistor and a speaker driver transistor are sufficient to make a simple siren generator.
IRF830 LT1361CS8 MAX843ISA LP2951CM LM2903 LT1399CS INA132U MAX3241CAI EPF10K30RC208-3 EPM7032AETI44-7

Inside the UM3561
Inside the IC, there is an oscillator circuit and the frequency of oscillations is controlled by the external resistor connected to OSC 1(Pin 7) and OSC2 (Pin 8). A 220 K resistor will give satisfactory results. The oscillations thus generated will be then transferred to a control circuit which function based on the tone selection through the connections of SEL 1 (Pin 6) and SEL2 (Pin 1) . The control circuit passes the signal to an address counter and then to the ROM. The tone pulses thus generated will be available from the output pin 3. Since the sound is weak, an amplifier is necessary to get loud sound. A single NPN transistor will amplify the sound.
Pin Assignment
Pin 1 Tone Sel.2
Pin 2 Gnd
Pin 3 Output
Pin 4 NC- Used for testing purpose
Pin 5 3V
Pin 6 Tone Sel .1
Pin 7 Osc 1
Pin 8 Osc 2
Tone Selection
By changing the pin connections of Sel.1 (Pin6) and Sel. 2(Pin 1) it is easy to change the siren tones.
Sel 1Sel 2Tone
Pin 6 Pin 1

NC NC Police siren
3V NC Fire Engine sound
Gnd NC Ambulance Siren
NC 3V Machine Gun sound

UM3651 Siren Generator Circuit Diagram