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Useful for power lines control, Simple, transformer less circuitry. This circuit, designed on request, has proven to be useful to indicate when the voltage in a power supply line is changing from 120V to 240Vac. It can be used in different circumstances and circuits, mainly when an increase in ac or dc supply voltage needs to be detected. D3 illuminates when the line voltage is approaching 120V and will remain in the on state also at 240V supply. On the other hand, D6 will illuminate only when the line voltage is about 240V and will stay on because the latching action of Q1, Q2 and related components. C1, D1 and D2 provide a low dc voltage in the 4.5V - 6V range in order to allow proper operation of latch circuit and LEDs. 110 and 220V AC LED Voltage Indicator Circuit diagram: 110 and 220V AC LED Voltage Indicator Circuit Diagram Parts: R1__________470R 1/2W Resistor R2__________220K 1/4W Resistor R3,R7_______470R 1/4W Resistors R4__________1K 1/4W Resistor R5__________2K2 1/4W Resis...

Some types of electronic equipment do  not provide any indication that they are  actually on when they are switched on.  This situation can occur when the back-light of a display is switched off. In addition, the otherwise mandatory mains  power  indicator  is  not  required  with  equipment  that  consumes  less  than  10 watts. As a result, you can easily forget  to switch off such equipment. If you want  to know whether equipment is still drawing power from the mains, or if you want  to have an indication that the equipment  is switched on without having to modify the equipment, this circuit provides a solution. One way to detect AC power current and  generate a reasonably constant voltage  independent of the load is to connect a  string of diodes wired in reverse parallel in series with one of the AC supply  leads. Here we selected diodes rated  at 6 A that can handle a non-repetitive  peak current of 200 A. The peak current  rating is important in connection with  switch-on  curr...

Detects clipping in preamp stages, mixers, amplifiers etc., Single LED display - 9V Battery supply unit This circuit was intended to be used as a separate, portable unit, to signal by means of a LED when the output wave form of a particular audio stage is "clipping" i.e. is reaching the onset of its maximum permitted peak-to-peak voltage value before an overload is occurring. This will help the operator in preventing severe, audible distortion to be generated through the audio equipment chain. This unit is particularly useful in signaling overload of the input stages in mixers, PA or musical instruments amplification chains, but is also suited to power amplifiers. A careful setting of Trimmer R5 will allow triggering of the LED with a wide range of peak-to-peak input voltages, in order to suit different requirements. Unfortunately, an oscilloscope and a sine wave frequency generator are required to accurately setup this circuit. Obviously, the unit can be embedded into an e...

This small circuit was developed to monitor the battery in a model hovercraft. The lift in the model is produced by an electric motor driving a fan. To avoid the possibility of discharging the rechargeable battery pack too deeply, the design lights a conspicuous LED mounted on the model when a preset threshold voltage is reached. The circuit only uses a few components, which helps keep the total weight of the model down. The circuit connects to the model only across the two points where the voltage to be monitored can be measured. These also supply power to the circuit. The best place to connect the circuit is not at the battery terminals, but rather at the motor connections. The circuit is suitable for use with nominal battery voltages of 4.8 V to 9.6 V (four to eight 1.2 V cells). For example, if there are six cells in the battery, its nominal terminal voltage will be 7.2 V. A discharge threshold voltage of around 1 V per cell is appropriate, which means that for six cells the thresh...

This Digital Mains Voltage Indicator Circuit diagram project designed by  Pratap Chandra Sahu . Continuous monitoring of the mains voltage is required in many ap-plications such as manual volt-age stabilisers and motor pumps. An ana-logue voltmeter, though cheap, has many disadvantages as it has moving parts and is sensitive to vibrations. The solidstate voltmeter circuit described here indicates the mains voltage with a resolution that is comparable to that of a general-pur-pose analogue voltmeter. The status of the mains voltage is available in the form of an LED bar graph. Presets VR1 through VR16 are used to set the DC voltages corresponding to the 16 voltage levels over the 50-250V range as marked on LED1 through LED16, respectively, in the figure. The LED bar graph is multiplexed from the bottom to the top with the help of ICs CD4067B (16-channel multiplexer) and CD4029B (counter). The counter clocked by NE555 timer-based astable multivibrator generates 4-bit binary ad-dress...

Although you may well be the proud owner of the very latest NiCd battery charger, you may still come across the odd 'incompatible' battery, for example, one having a rare voltage or requiring a much higher charging current than can be supplied by your off-the-shelf charger. In these cases, many of you will resort to an adjustable mains adaptor (say, a 500-mA type) because that is probably the cheapest way of providing the direct voltage required to charge the battery. Not fast and not very efficient, this 'rustic' charging system works, although subject to the following restrictions: Circuit diagram: Battery-Charging Indicator Circuit Diagram You should have some idea of the charging current. In case you use an adaptor which is adjustable but of the unregulated, low output current type, you can adjust the current by adjusting the output voltage. You have to know if the current actually flows through the battery. A current-detecting indicator is therefore much to be pref...

The second example below uses a LDR (light dependent resistor) to indicate some desired light level. The LDR has a large dynimic range and varies in resistance from less than 100 ohms on a cloudy day to over a megohm in total darkness. A 2K pot was used to adjust the window range for usual room light conditions. This setup might also be used to indicate sunrise/sunset conditions. Light Level Indicator  Circuit Diagram

Remote Audio Level Indicator Circuit Diagram. The normal level-indicator circuits which are available in the market require connections to be made to the output of the player, which may not be easily accessible. The audio level indicator circuit described here removes this restriction as it may be placed close to the player’s speakers and yet the desired effect can be realized. Remote Audio Level Indicator Circuit Diagram : Remote Audio Level Indicator Circuit Diagram As shown in the circuit, signals are picked up by the condenser microphone, which get further amplified by the noninverting amplifier built around one of the four op-amps of LM324. The remaining three, along with four op-amps of the second LM324, are used as seven comparators to work as the level detector, giving seven output levels through seven coloured LEDs.  The sensitivity of the audio level indicator circuit may be improved by varying the 220k potentiometer. If a fine adjustment is desired, a 4.7-kilohm potent...

Mechanical deficiencies that affect the reproduction of sound in a stereo amplifier is probably what you are thinking, armpit all the problems have been overcome. And actually bigger role than we know. True, the effect is so small that only a few of us who record it, or divert it to other things. Most of such shortcomings can be traced back toto the stereo volume control ,maybe two in the no -stepresistance . As a result, the volume difference arises between the two channels and can usually be in balance again by the regulator balance. If you intend to define these differences precisely, stereo balance these indicators can fulfill your purpose. Stereo Balance Indicator circuit Quite simply, this circuit by connecting the output terminal and the right channel loudspeaker left channel of the amplifier and feed the same signal, should sinusoid (or cues mono) to the second input channel amplifier. If then the signals at both terminals tarafnya exact same loudspeakers, meters (zero in the m...

Continuous monitoring of the mains voltage is required in many applications such as manual voltage stabilisers and motor pumps. An analogue voltmeter, though cheap, has many disadvantages as it has moving parts and is sensitive to vibrations. The solidstate voltmeter circuit described here indicates the mains voltage with a resolution that is comparable to that of a general-purpose analogue voltmeter. The status of the mains voltage is available in the form of an LED bar graph. Presets VR1 through VR16 are used to set the DC voltages corresponding to the 16 voltage levels over the 50-250V range as marked on LED1 through LED16, respectively, in the figure. The LED bar graph is multiplexed from the bottom to the top with the help of ICs CD4067B (16-channel multiplexer) and CD4029B (counter). The counter clocked by NE555 timer-based astable multivibrator generates 4-bit binary address for multiplexer-demultiplexer pair of CD4067B and CD4514B. The voltage from the wipers of presets are mul...

Quiz-type game shows are increasingly becoming popular on tale vision these days. In such games, fastest finger first indicators (FFFIs) are used to test the player’s reaction time. The player’s designated number is dis played with an audio alarm when the player presses his entry button. The circuit presented here determines as to which of the four contestants first pressed the button and locks out the remaining three entries. Simultaneously, an audio alarm and the correct decimal number display of the corresponding contestant are activated. Circuit Diagram: Fastest Finger First Indicator Circuit Diagram When a contestant presses his switch, the corresponding output of latch IC2 (7475) changes its logic state from 1 to 0. The combinational circuitry comprising dual 4-input NAND gates of IC3 (7420) locks out subsequent entries by producing the appropriate latch-disable signal. Priority encoder IC4 (74147) encodes the active-low input condition into the cor responding binary coded de...

Simple, two-wire, remote monitoring unit, Three-LED level display, 9V battery powered The whole project was developed on a friend's request. Its purpose was to remotely monitor the water-level in a metal tank located in the attic by means of a very simple control unit placed in the kitchen, some floors below. Mains requirements were: No separate supply for the remote circuit Main and remote units connected by a thin two-wire cable Simple LED display for the main unit Battery operation to avoid problems related to mains supply and water proximity As the circuit was battery operated a low current consumption was obviously welcomed The very small remote unit is placed near the tank and measures the water level in three ranges by means of two steel rods. Each range will cover one third of the tank capacity: Almost empty - signaled by means of a red LED (D3) in the control unit display About half-level - signaled by means of a yellow LED (D2) in the control unit display Almost full - ...

Signals when an on-circuit battery is exhausted 5V to 12V operating voltage A Battery-status Indicator circuit can be useful, mainly to monitor portable Test-gear instruments and similar devices. LED D1 flashes to attire the user's attention, signaling that the circuit is running, so it will not be left on by mistake. The circuit generates about two LED flashes per second, but the mean current drawing will be about 200µA. Transistors Q1 and Q2 are wired as an uncommon complementary astable multivibrator: both are off 99% of the time, saturating only when the LED illuminates, thus contributing to keep very low current consumption.  Flashing-LED Battery-status Indicator Circuit diagram : Flashing-LED Battery-status Indicator Circuit Diagram The circuit will work with battery supply voltages in the 5 - 12V range and the LED flashing can be stopped at the desired battery voltage (comprised in the 4.8 - 9V value) by adjusting Trimmer R4. This range can be modified by changing R3 and/o...

T his t sink in high power circuits. In this temperature indicator, diode voltage drop in ambient temperature is used as reference level. Temperature is measured by a transistor mounted on a radiator or near power transistor controlled.T1 temperature sensor and voltage to the base - emitter is compared, through potentiometer P1, with the common point of reference in its D1 and R1. Transistor remains blocked as long as temperature remains below a certain level, which is set to P1. Base-emitter voltage of transistor will decrease by about 2mV for a temperature increase of about 1 ° C. When the emitter voltage of transistor voltage falls below the cursor P1, the transistor will go into conduction and D2 will light.The values of R1 and R2 are voltage dependence of Ub and relationships can be calculated: R1 = [(Ub - 0.6) / 5] k, R2 = [(Ub - 1.5) / 15] k

Here is a simple scheme for adding a blown fuse indicator to your existing power supply circuit. This is done by just adding a resistor and LED to the existing circuit. The LED and resistor are connected in series and this combination is connected in parallel to the existing fuse. When the fuse is intact, it offers a low resistance and so the voltage drop across it will be not sufficient enough to glow the LED. When the fuse is blown off, it is equivalent to infinite resistance and so the entire power supply will drop across the resistor LED series combination and makes the LED glow. The resistance R1 is used to limit the current through LED. Blown Fuse Indicator Circuit Diagram   The component values of other components are not given in the diagram because it depends on your specific power supply requirements. Any way for a conventional 12V power supply the component values are as follows: 1N4007 for D1,D2,D3 and D4; 230V primary,12V secondary ,2A step-down transformer for T1, 2A ...

While repairing or installing electrical machines in a building, the AC mains power supply is switched off from the mains electrical switchboard installed outside the building. There is a chance that someone who is not aware of the same may switch on the mains from outside. This poses a great danger for the technician working inside. Hence, an indicator like the one described here, which can be plugged into a nearby mains wall socket, might prove very useful for the technician. This circuit can also be useful for people who are living in a place where there is frequent mains power cut. Circuit and working The circuit diagram of the light and sound indicator for the mains power supply is shown Fig. 1. The circuit is built around capacitors C1 and C2, resistors R1 and R2, diode D1, zener diode ZD1, LED1 and a piezo buzzer (PZ1). Resistor R1 and capacitor C1 are used for reducing the voltage and limiting the current. Diode D1 is a rectifier. C2 is used as a filtering capacitor. Zener diod...

Some types of electronic equipment do  not provide any indication that they are  actually on when they are switched on.  This situation can occur when the back-light of a display is switched off. In addition, the otherwise mandatory mains  power  indicator  is  not  required  with  equipment  that  consumes  less  than  10 watts. As a result, you can easily forget  to switch off such equipment. If you want  to know whether equipment is still drawing power from the mains, or if you want  to have an indication that the equipment  is switched on without having to modify the equipment, this circuit provides a solution.  One way to detect AC power current and  generate a reasonably constant voltage  independent of the load is to connect a  string of diodes wired in reverse parallel in series with one of the AC supply  leads. Here we selected diodes rated  at 6 A that ...

This is an Indicator Balance Stereo Sound Circuit Diagram , that is, it causes the two channels are to the same output level. This circuit eliminates the problems that may occur during recording and playback sound . It is connected to the output terminal of the speakers in the right channel and the left channel of the amplifier . To make the adjustment has to be zero in the middle of the window , however , if the signal level on the left channel is higher than that measured dO right channel will divert to the left ( or right if the opposite occurs ) . Indicator Balance Stereo Sound Circuit Diagram  

Quiz-type game shows are increasingly becoming popular on tale vision these days. In such games, fastest finger first indicators (FFFIs) are used to test the player’s reaction time. The player’s designated number is dis played with an audio alarm when the player presses his entry button. The circuit presented here determines as to which of the four contestants first pressed the button and locks out the remaining three entries. Simultaneously, an audio alarm and the correct decimal number display of the corresponding contestant are activated.  Fastest Finger First Indicator Circuit Diagram:   Fastest Finger First Indicator Circuit Diagram   When a contestant presses his switch, the corresponding output of latch IC2 (7475) changes its logic state from 1 to 0. The combinational circuitry comprising dual 4-input NAND gates of IC3 (7420) locks out subsequent entries by producing the appropriate latch-disable signal. Priority encoder IC4 (74147) encodes the active-low input c...

On most FM tuners, the stereo indicator lights upon detection of the 19-kHz pilot tone. However, this doesn`t mean that the program is actually stereophonic, since the pilot tone is often transmitted with mono programs also. A similar situation exists on stereo amplifiers, where the stereo LED is simply controlled from the mono/stereo switch. The LED-based stereo indicator described here lights only when a true stereo signal is fed to the inputs. Differential amplifier Al raises the difference between the L and R input signals. When these are equal, the output of Al remains at the same potential as the output of A2, which forms a virtual ground rail at half the supply voltage. When Al detects a difference between the L and Rinput signals, it supplies a positive or negative voltage with respect to the virtual ground rail, and so causes C3 to be charged via Dl or C4 via D2. Comparator A3/A4 switches on the LED driver via OR circuit D3/D4. The input signal level should not be less than 10...