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Here is a simple non-contact AC power monitor for home appliances and laboratory equipment that should remain continuously switched-on. A fuse failure or power breakdown in the equipment going unnoticed may cause irreparable loss. The monitor sounds an alarm on detecting power failure to the equipment. The circuit is built around CMOS IC CD4011 utilising only a few components. NAND gates N1 and N2 of the IC are wired as an oscillator that drives a piezobuzzer directly. Resistors R2 and R3 and capacitor C2 are the oscillator components. The amplifier comprising transistors T1 and T2 disables the oscillator when mains power is available. In the standby mode, the base of T1 picks up 50Hz mains hum during the positive half cycles of AC and T1 conducts. Circuit diagram:     Non-Contact Power Monitor circuit diagram    This provides base current to T2 and it also conducts, pulling the collector to ground potential. As the collectors of T1 and T2 are connected to pin 2...

As per manufacturer’s data sheets, a 12V rechargeable lead-acid battery should be operated within 10.1V and 13.8V. When the battery charges higher than 13.8V it is said to be overcharged, and when it discharges below 10.1V it can be deeply discharged. A single event of overcharge or deep discharge can bring down the charge-holding capacity of a battery by 15 to 20 per cent. It is therefore necessary for all concerned to monitor the charge level of their batteries continuously. But, in practice, many of the battery users are unable to do so because of non-availability of reasonably-priced monitoring equipment. The circuit idea presented here will fill this void by providing a circuit for monitoring the charge level of lead-acid batteries continuously. The circuit possesses two vital features: First, it reduces the requirement of human attention by about 85 per cent. Second, it is a highly accurate and sophisticated method. Lead Acid Battery Charge Monitor Circuit Diagram:   The cir...

The PC processor generates very high temperature during its operation which is dissipated by the large heat sink placed above the processor. If the heat sink assembly is not tight with the processor or the cooling fan is not working, PC enters into the Thermal shutdown mode and will not boot up. If the PC is not entering into thermal shutdown, the high temperature can destroy the processor. This simple circuit can be placed inside the PC to monitor the temperature near the processor. It gives warning beeps when the temperature near the heat sink increases abnormally. This helps to shutdown the PC immediately before it enters into Thermal shutdown. The circuit uses a Piezo element (one used in Buzzer) as the heat sensor. The piezo crystals reorient when subjected to heat or mechanical stress and generates about one volt through the Direct piezoelectric property. IC1 is designed as a voltage sensor with both the inputs tied through the capacitor C1.The non inverting input is connected to...

These circuits are intended for remote monitoring of the current consumption on the domestic mains line. The circuit in Fig. I lights the signal lamp upon detecting a mains current consumption of more than 5 mA, and handles currents of several amperes with appropriate diodes fitted in the D, and D2 positions. Transistor Ti is switched on when the drop  across D,-D2 exceeds a certain level. Diodes from  the well-known I N400x series can be used for currents of up to I A, while lN540x types are rated for up to 3 A. Fuse F, should, of course, be dimensioned to suit the particular application. A number of possible transistor types have been stated for use in the Ti position. Should you consider using a type not listed, be sure that it can cope with surges up to 700 V. As long as Ti does not con- duct, the gate of the triac is at mains potential via  C,, protective resistor R2 and diode Da, which  keeps C, charged. When Ti conducts, alternating current can flow through the capacitor, an...

This circuit is used to monitor the battery voltage to display a dual-colored LED status of the battery to. If the LED “green”battery voltage exceeds 11.9 volts. If the yellow LED , battery voltage 11.9 to 11.5 volts. If the LED is “red” If the battery voltage below 11.5 volts. You can of course change the trigger points by the trimmer resistors and / or changing the value of the resistors in the divider. A dual op amp is used as a comparator. The green LED on the board, until the voltage exceeds 11.5 volts. The red LED illuminates when the voltage falls below 11.9 volts to the circuit. Therefore, in the 11.9 to 11.5 volts, both LEDs are on, producing a slightly yellow color. When the voltage falls below 11.5 V, the green LED , and now only the red LED flashes to indicate low voltage. Parts List R1=1K2 R2-3-4=680R R5=15K R6=10K R7-8-9-10=1K IC1=LM324 D1=5V6 /0.5W Zener D2-3-4-5=LED RV1=10K trimmer  Is recommended that multi-shaper for V1 and V2. Muti-trimmer makes it much easi...

Almost all 24V power systems in trucks, 4WDs, RVs, boats, etc, employ two series-connected 12V lead-acid batteries . The charging system can only maintain the sum of the individual battery voltages. If one battery is failing, this circuit will light a LED. Hence impending battery problems can be forecast. The circuit works by detecting a voltage difference between the two series connected 12V batteries. Idle current is low enough to allow the unit to be permanently left across the batteries. Circuit Diagram Parts: R1 = 2.K R2 = 4.7K R3 = 39K R4 = 39K R5 = 1.5K R6 = 1.5K Q1 = BC547 Q2 = BC547 Q3 = BC557 D1 = 3mm Red LED D2 = 3mm GreenLED B1 = DC 12 Volt B2 = DC 12 Volt

Almost all 24V power systems in trucks, 4WDs, RVs, boats, etc, employ two series-connected 12V lead-acid batteries. The charging system can only maintain the sum of the individual battery voltages. If one battery is failing, this circuit will light a LED. Hence impending battery problems can be forecast. The circuit works by detecting a voltage difference between the two series connected 12V batteries. Idle current is low enough to allow the unit to be permanently left across the batteries. Circuit diagram: Battery Equality Monitor Circuit Diagram Parts: R1 = 2.K R2 = 4.7K R3 = 39K R4 = 39K R5 = 1.5K R6 = 1.5K Q1 = BC547 Q2 = BC547 Q3 = BC557 D1 = 3mm Red LED D2 = 3mm GreenLED B1 = DC 12 Volt B2 = DC 12 Volt

Almost all 24V power systems in trucks, 4WDs, RVs, boats, etc, employ two series-connected 12V lead-acid batteries. The charging system can only maintain the sum of the individual battery voltages. If one battery is failing, this circuit will light a LED. Hence impending battery problems can be forecast. The circuit works by detecting a voltage difference between the two series connected 12V batteries. Idle current is low enough to allow the unit to be permanently left across the batteries.  . Battery Equality Monitor Circuit diagram: . Battery Equality Monitor Circuit Diagram Parts: R1 = 2.K R2 = 4.7K R3 = 39K R4 = 39K R5 = 1.5K R6 = 1.5K Q1 = BC547 Q2 = BC547 Q3 = BC557 D1 = 3mm Red LED D2 = 3mm GreenLED B1 = DC 12 Volt B2 = DC 12 Volt

The idea for this project may have come to me in a flash of inspiration, and its a very simple way to check if a fuse has blown without removing it from its holder. Simple Fuse Monitor Indicator Circuit Diagram :   The simplicity of this circuit uses just two components, but with just one resistor and an LED this circuit gives visual indication of when a fuse has blown. LED1 is normally off, being "short circuited " by the fuse, F1. Should the inevitable "big-bang" happen in your workshop then LED1 will illuminate and led you know all about it! Please note that the LED will only illumininatet under fault conditions, i.e. with a short circuit or shunt on the load. In this case the current is reduced to a safe level by R1.

Battery Level Monitor Circuit This simple circuit can monitor the charging process in 12 Volt Lead Acid battery or Tubular battery. The status of LED indicates whether the battery is accepting charge or not. It also indicates the full charge condition. Battery Level Monitor Circuit Diagram The circuit can be incorporated in any battery charger like 6 volt, 9 volt, 12 volt etc. The only change needed is replacement of the Zener ZD with appropriate value. That is for 6 volt charger , use 6.1 volt Zener and for 9 volt charger it should be 9.1 volt Zener. The circuit is based on the switching of two NPN transistors (BC547) to drive the corresponding LED. Zener diode ZD is connected to the base of T1 so as to switch on T1 when the Zener conducts. This happens only when the battery voltage is above 12 volts. Green LED lights when the battery voltage is normal or battery attains full charge. Resistor R1 and Preset VR adjust the base bias of T1 for smooth switching. When T1 conducts, base of T...

The circuit was designed to provide distribution, extension and splitting of personal computer video output to two or more monitors. Super Video Graphics Array (SVGA) – defined in 1989 as a set of graphic standards that supports 800 X 400 resolution or 480,000 pixels with support for 256 colors or a palette of 16 million colors. Pixel – short for picture element, is the smallest point or single item of information in a graphic image and the basic unit of programmable color on a computer image or computer display. 2N3906 – a common PNP BJT transistor intended for medium voltage, lower current and power, which can operate at moderately high speeds, used for general purpose switching and low-power amplifying applications. The circuit may also be called as video port expander, multiple monitor, PC video splitter, LCD Y splitter, etc. It provides the same high resolution image to several monitors using a single PC. Each line of the SVGA card of the analog output stage of PC contains 75 ohm ...

Description This simple circuit enables you to listen to your heartbeat, for instance, while you are exercising. The transducer used for detecting the pulse is an electret microphone, X1 in the diagram. The model used has two (polarized) terminals. As usual with this type of microphone, it functions via a series resistor, R1. The potential drop across this resistor is applied to op amp IC1a via C1. The amplification of the op amp is set to between ´40 and ´1000 with preset P1. Network R4-C3 in the feedback loop of IC1a is a low-pass filter with a cut-off frequency of 34 Hz. Higher frequencies are not needed for the present application. A pulse rate of 180* is equivalent to a frequency of 3 Hz. So as to cater for a wide range of pulse rates, the cut-off frequency is made just over 11 times as high as that representing the highest pulse rate. Operational amplifier IC1c, in conjunction with push-pull am-plifier T1-T2, creates a headphone amplifier, whose output resistance is equivalent to...

The idea for this project may have come to me in a flash of inspiration, and its a very simple way to check if a fuse has blown without removing it from its holder. The simplicity of this circuit uses just two components, but with just one resistor and an LED this circuit gives visual indication of when a fuse has blown. LED1 is normally off, being "short circuited " by the fuse, F1. Circuit diagram:  Fuse Monitor Circuit Diagram Should the inevitable "big-bang" happen in your workshop then LED1 will illuminate and led you know all about it! Please note that the LED will only illuminate under fault conditions, i.e. with a short circuit or shunt on the load. In this case the current is reduced to a safe level by R1. Author: Andy Collinson - Copyright: Zen

Circuit Diagram  Description   If you feel that somebody is tampering with your telephone line you might find this little circuit useful. It detects if there is another telephone connected to the line, if there is a short or an open line. Sound and a flashing light will tell you which is the current situation. The speaker is practically cut out during a normal conversation thus preserving privacy, only the LED will flash occasionally. The circuit does not require any battery and takes the supply from the telephone line itself. The transistors used are wired in a reversed biased fashion thus behaving as oscillators. You might try the 2N2222A as an alternative (not tested). This monitor is, of course, suitable only for analogue lines. Watch the polarity of the input line: the circuit will not be damaged by a polarity reversal but it will not operate correctly.  Author : smartkit Source http://www.electronics-lab.com/