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The circuit has been designed to provide an alarm with the use of a buzzer when sensing high temperature by using a thermistor. Thermistor – one type of resistor used as temperature-sensing element which demonstrates a large change in resistance proportional to a small change in temperature because of the composition of its semiconductor material. BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment. The temperature can be regulated by the design of this circuit and it can provide a warning scheme in the case of excessive increase in the temperature. The control of the temperature starts from the thermistor TH1 which contains a negative factor. Since this component has resistance proportional to the temperature that it detects, the resistance can be modified wherein a 10K ohm resistance is produced ate 25° C while 1K ohm resistance will be produced at 94° C. to define a specific value of temperature, a trimmer...

Here is a simple full bathtub indicator Circuit Diagram Project. Running a bath can end in a minor domestic disaster if you forget to turn off the taps in time. This indicator activates an active buzzer to provide an audible warning when a given water level is reached. Because the water sensor and the driver circuit for the buzzer are contained on one PC board, the indicator, together with the 9-V battery and the buzzer, can be built into a compact case. Full Bathtub Indicator Circuit Diagram: Obviously, the sensor, which is etched on the PC-board, must not be fitted in case-iron or steel bath, the indicator is secured to it with the aid of a magnet glued onto the case. To prevent scratching the bath, the magnet can be covered in plastic or rubber. If you have a polypropylene bath, the indicator can be stuck to it with blue tack or double-sided adhesive tape. When the water reaches the sensor, the base of T1 is connected to the positive supply line. As a result, T1 and T2 are switched ...

Most water-level indicators for water tanks are based upon the number of LEDs that glow to indicate the corresponding level of water in the container. Here we present a digital version of the water-level indicator.    It uses a 7-segment display to show the water level in numeric form from'0' to '9.' The circuit works off 5V regulated power supply. It is built around priority encoder IC 74HC147 (IC1), BCD-to-7-segment decoder IC CD4511 (IC2), 7-segment display LTS543 (DIS1) and a few discrete components. Due to high input impedance, IC1 senses water in the container from its nine input terminals. The inputs are connected to +5V via 560-kilo-ohm resistors. Numeric Water-Level Indicator Circuit diagram  The ground terminal of the sensor must be kept at the bottom of the container (tank). IC 74HC147 has nine active-low inputs and converts the active input into active-low BCD output. The input L-9 has the highest priority. The outputs of IC1 (A, B, C and D) are fed to IC...

This is the Simple Water-level indicator Circuit Diagram. n this a warning device WD1 is in series with SCR1. When the liquid level causes a conductive path between the probes, the SCR conducts sounding WD1. The warning device may be a Sonalert (TM), a lamp or a buzzer.D1 acts as a transient suppressor. Press SI to reset the circuit. Simple Water-level indicator Circuit Diagram

This arrow led indicator electronic project can be used in some dark places to show the directions . You can use to indicate direction just an illuminated arrow or a flashing light , but is much nicer if the light moves in the correct direction. This arrow led indicator is based on 74HC14 circuit and some LEDs which are used to show the way . For this arrow led indicator we need six series of three LEDs arranged in the shape of arrows and are connected to the outputs . Each time the lit arrows move over by one column so it appears that the arrows run from right to left. Arrow LED Indicator Circuit Diagram If we want to change the speed of the moving light it’s need to change the value of C1 to C3 or R1 to R3 ( a lower value for this components decrease the time of moving lights). If we want a longer arrow we can mount in parallel with existing columns another columns . For power supply we can use batteries or 6V regulated power supply .

Monitors battery voltage, Three-LED Display. Connecting this circuit to the battery of your vehicle, you will always know at a glance the approximate voltage available. An indication of battery voltage is useful to the motorist for monitoring the battery's capacity to deliver current, and as a check on the efficiency of the dynamo or alternator. Threshold voltages of the Leds are set by means of two Zener Diodes (D6 & D10) plus two further Diodes wired in series (D4, D5 and D8, D9 respectively) adding a step of about 1.3V to the nominal Zener voltage. Parts:   R1 = 1k R2 = 100K R3 = 1k R4 = 3.3K R5 = 3.3K R6 = 1k R7 = 3.3K R8 = 3.3K Q1 = BC547 Q2 = BC547 Q3 = BC557 D1 = Red Led D2 = Amber Led D3 = 1N4148 D4 = 1N4148 D5 = 1N4148 D6 = BZX79C10 D7 = Green Led D8 = 1N4148 D9 = 1N4148 D10 = BZX79C12 Notes: Red LED D1 is on when battery voltage is 11.5V or less. This indicates a low battery charge. Amber LED D2 is on when battery voltage is comprised in the 11.5 - 13.5V range. This ...

The circuit below illuminates an LED to indicate unequal charges between two 12 volt lead batteries. It can be used to verify that two batteries are connected in parallel or isolated since the LED will be off when the voltages are equal within a tollerance, or on if the voltage difference is greater than 100 millivolts. Three comparators and three voltage dividers are used to determine battery conditions. Battery Equal Charge Indicator Circuit Diagram The upper left comparator (+) input at pin 5 is set to about 10 volts with battery #1 at 12 volts. The negative input (pin 4) is set to a slightly lower voltage by adding an additional 240 ohms to the voltage divider so that the output of the comparator will be positive when both battery voltages are equal and negative if battery 2 rises above battery 1 by 100 millivolts or more. The voltage at pin 5 is used as a reference for the lower comparator and the negative input of the lower comparator is set to a lower voltage with the addition o...

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     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 Resistor R6_____________330R 1/4W Resistor C1_____________330nF 630V Polyester Capacitor C2_...

The indicator described here is specifically designed for adjusting the dynamic limiter described elsewhere in this edition and checking whether the maximum level of the reference voltage (P1) needs to be modified. Her e we use a 4 -to -16 decoder IC (type 4514) to monitor the state of the four-bit up/down counter in the limiter circuit. This IC can be powered from the ±8 V supply voltages of the limiter. The limiter board has a 6-way connector (K5) that provides access to the four counter outputs and the sup-ply voltages. Connector K1 of the indicator circuit can be connected to K5 on the limiter board.  Indicator for Dynamic Limiter Schematic One output of the 4514 goes high for each unique 4-bit combination on its inputs, while the other outputs remain logic Low. A separate current-limiting resistor is connected in series with each LED. It was not possible to use a common cathode resistor here because most LEDs have a maximum reverse blocking voltage of only 5 V, while the suppl...

This circuit indicates which of three voltages in the range from about about -4V to about +4V - at A, B and C - is the highest by lighting one of three indicator LEDs. Alternatively, it can be wired to indicate the lowest of three voltages or to indicate both the highest and lowest voltages. Op amps IC1a, IC1b & IC1c are wired as comparators, while the three indicator LEDs and their series 1kO current limiting resistors are strung across the op amp outputs to implement the appropriate logic functions. Maximum Minimum Voltage Indicator Circuit diagram: Maximum Minimum Voltage Indicator Circuit Diagram For example, LED A will light only when pin 8 of IC1c is low (ie, A greater B) and pin 7 of IC1b is high (ie, A greater C). Similarly, LED B will light only when pin 8 of IC1c is high (ie, B greater A) and pin 1 of IC1a is low (ie, B greater C). LED C works in similar fashion if the voltage at C is the highest. Note that if all the LEDs and their parallel 1N4148 diodes are reversed, th...

With the aid of an (old) moving coil instrument it is very little effort to make a simple voltmeter that, at a glance, indicates the status of a telephone line. Because the input impedance of this circuit is very high, there is no problem in having it permanently connected to the line, since it only draws a tiny amount of current. The schematic shows that the circuit consists of no more than a series resistor, a bridge rectifier and a moving coil meter. The value of the resistor depends on the sensitivity of the moving coil meter. In his prototypes, the author used old VU meters that require 250µA for full-scale deflection. A resistor value of 390 kΩ appeared to be optimal for these meters. Telephone Line Indicator Circuit Diagram For a 100-µA-instrument, this resistor value will have to be increased to about 680 kΩ. The starting point, when selecting a resistor value is that when the telephone is not in use, the meter should deflect about 2/3rd of full scale. The amount of meter defl...

Here is an add on circuit to your FM radio for precise tuning of stations. Usually an LED indicator is provided in FM radio to see whether the station is tuned or not. But it is difficult to see the precise tuning points since the variation in the LED brightness cannot be detected easily. This circuit solves the problem. Circuit diagram : Precise  FM Tuning Indicator Circuit Diagram The circuit uses the Op Amp IC CA3140 as a differential amplifier to sense the voltage level between the terminals of the tuning LED. The output of IC1 drives two LEDs one Red and one Green to indicate whether the station is precisely tuned or not. If both LEDs remain off, it indicates precise tuning. If anyone LED is on, it indicates that tuning is not precise. If both LEDs remain on, it indicates that there is no signal. First tune the FM receiver in a station having strong signal. The tuning LED will light brilliantly. Then connect point A and B to the soldering points of the tuning LED observing p...

This circuit serves as an ultra-low power replacement for multiple LED on-off indicators. It also has the advantage of being easy to read in full daylight. With the parts shown, it is possible to display four bits of information. The display that I used has three digits and 2 decimal points for a total of 23 segments. Different groupings of segments can be used for the four indicators. I chose to use three squares (shown) and the three lower segments together (not shown) for the four indicators. Many other combinations could be used, one possibility would be to hard-wire numbers or letters out of each of the digits. Other LCD displays could also be used for different effects. Circuit Diagram A part that doesn't exist as far as I know, but should, is a single pixel LCD indicator (2 wire). An LCD manufacturer could probably make a lot of money with such a part. If such a thing exists, I'd love to hear about it. Specifications: Operating Voltage: 3-15V (5V Nominal) DC Operating Cu...

If you want to make a flasher unit for you motorbike then this circuit is just for you. This simple turn signal flasher circuit can be  easily built and installed in any two wheelers for the desired actions. The circuit employs just two 2-pins instead of 3 as found in other flasher circuits. Once installed, the circuit will faithfully flash the side indicator lights whenever the intended function is switched ON. The circuit also incorporates an optional buzzer circuit which can be also included for getting a beeping sound in response to the flashing of the lamps. . Parts List R1, R2, R3 = 10K R4= 33K T1 = D1351, T2 = BC547, T3 = BC557, C1, C2 = 33uF.25V L1 = Buzzer Coil

Battery level indicator circuit is a circuit that is used to measure the battery voltage / battery. The main components of the battery level indicator circuit is an LM3914 IC. LM 3914 on Circuit battery level indicator is a monolithic IC that detects an analog voltage. And drive the 10 LEDs that produce a linear analog display on a given input voltage. IC LM3914 is easy to get in the market and not expensive. IC LM3914 battery level indicator on the circuit is often encountered in a series of peak indicator audio signals in analog audio equipment. Battery level indicator circuit consists of IC LM3914, 10 pieces of LED, and a few resistors. The scheme of  battery level indicator can be seen below. LM3914 battery level indicator In the circuit of the battery level indicator on the supply circuit voltage taken from the battery / batteries through a switch. Didesaimn this circuit will only display the battery level when the switch is pressed. This is intended to save the battery v...

If you want to make a flasher unit for you motorbike then this circuit is just for you. This simple turn signal flasher circuit can be  easily built and installed in any two wheelers for the desired actions. The circuit employs just two 2-pins instead of 3 as found in other flasher circuits. Once installed, the circuit will faithfully flash the side indicator lights whenever the intended function is switched ON. The circuit also incorporates an optional buzzer circuit which can be also included for getting a beeping sound in response to the flashing of the lamps. Parts List R1, R2, R3 = 10K R4= 33K T1 = D1351, T2 = BC547, T3 = BC557, C1, C2 = 33uF.25V L1 = Buzzer Coil

The existence of the peak indicator (Audio Peak Indicator) in an audio device is needed. Audio Peak indicator is a simple circuit to detect the peak level of audio signal. Audio Peak indicator circuit is built with duabuah transistor and LED indicator as peak level detection of audio signals.  The main function of a series of Audio Peak indicator is to determine the occurrence of the peak level of audio signal which is more than +4 dB, equivalent to 1.25 V rms. If the received audio signal Audio Peak Indicator more than +4 dB was the LEDs in series Peak Audio This indicator will light. Audio Peak indicator circuit is mounted on the output audio system. Audio peak indicator Audio Peak Indicator Component List: R1 = 10Kohm R2 = 1.2Kohm R3 = 220Kohm R4 = 4.7Kohm R5 = 4.7Kohm C1 = 47uF 25V C2 = 2.2uF 25V Q1 = BC550C Q2 = BC550C D1 = Red Led

This circuit produces a random "Yes" or "No" with a single button press - indicated by the illumination of a red or green LED. The circuit has two advantages over similar circuits. First, it uses just a single momentary contact pushbutton, so no on-off switch is required. When the pushbutton is pressed, an oscillator comprising the 10nF capacitor and 22kΩ resistor at pins 1 & 2 is almost immediately stopped by FET Q1, which pulls the oscillator's timing capacitor to the positive rail. However, the 220nF capacitor and 470kΩ resistor in the gate circuit of Q1 introduce a tenth of a second's delay, so that about 250 oscillations take place before the clock is stopped. Due to variations in charge on the circuit's capacitors, as well as voltage and temperature variations, and the unpredictability of when the pushbutton will be pressed, randomness is assured. The circuit has a high degree of randomness because it takes advantage of a near-perfect compleme...