Hot Water Level Indicator

Notes:
Save fuel bills and the economy of the planet with this circuit. SW1 is a normally open press button switch which allows you to view the level of hot water in a hot water tank. When pressed the voltage difference at the junction of the thermistor and preset is compared to the fixed voltage on the op-amps non-inverting input. Depending on the heat of the water in the tank, the thermistors resistance will toggle the op-amp output to swing to almost full voltage supply and light the appropriate LED.

Construction:
Masking tape was used to stick the bead thermistors to the tank. Wires were soldered and insulated at the thermistors ends. A plastic box was used to house the circuit. Battery life will probably be 4 to 5 years depending on how often you use the push switch, SW1.

Sensor Placement:
Thermistors NTC1-4 should be spread evenly over the height of the tank. I placed NTC1 roughly 4 inches from the top of my tank and the others were spaced evenly across the height of the hot water tank. As hot water rises the lowest sensor indicates the fullest height of hot water and should be about 8 to 10 inches from the bottom of the tank.

Calibration:
With a full tank of hot water adjust P1-4 so that all LEDs are lit. As hot water rises, the sensor at the bottom of the tank will be the maximum level of hot water. "Hot" can be translated as 50C to 80C the presets P1-4 allow adjustment of this range.

Parts:

I have used a quad version of the LM324 but any quad opamp can be used or even four single op-amps.
R2-R5 I used 330ohm resistors, but value is not critical. Lower values give brighter LED output.
NTC1-4 The thermistors maximum resistance must roughly equal the resistance of the fixed resistor and preset. As negative temparature coefficient (NTC) thermistors are used, then their resistance decreases for increases in temperature. I used a thermistor from the Maplin Catalogue. Cold resistance was around 300K, hot resistance 15k. Alternative thermistors may be used with different resistance ranges, but the presets P1 to P4 must also be changed as well.

R7-10 series resistance, only required if your thermistors resistance is several ohms at the hottest temperature.
P1 - P4 Chosen to match the resistance of the thermistor when cold.
R1 & R6. These resistors are equal and bias the op-amp inverting input to half the supply voltage. I used 100k.

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Supply Voltage Indicator circuit and explanation

A novel supply voltage monitor which uses a LED to show the status of a power supply.

This simple and slightly odd circuit can clearly show the level of the supply voltage (in a larger device): as long as the indicator has good 12 volts at its input, LED1 gives steady, uninterrupted (for the naked eye) yellow light. If the input voltage falls below 11 V, LED1 will start to blink and the blinking will just get slower and slower if the voltage drops further - giving very clear and intuitive representation of the supplys status. The blinking will stop and LED1 will finally go out at a little below 9 volts. On the other hand, if the input voltage rises to 13 V, LED2 will start to glow, getting at almost full power at 14 V.

The characteristic voltages can be adjusted primarily by adjusting the values of R1 and R4.

The base-emitter diode of T2 basically just stands in for a zener diode. The emitter-collector path of T1 is inversely polarized and if the input voltage is high enough - T1 will cause oscillations and the frequency will be proportional to the input voltage. The relaxation oscillator ceases cycling when the input voltage gets so low that it no longer can cause breakdown along the emitter-collector path.

Not all small NPN transistors show this kind of behavior when inversely polarized in a similar manner, but many do. BC337-40 can start oscillations at a relatively low voltage, other types generally require a volt or two more. If experimenting, be careful not to punch a hole through the device under test: they oscillate at 9-12 V or not at all.
Source:www.zen22142.zen.co.uk

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Fuel Reserve Indicator For Vehicles

Here is a straightforward circuit for monitoring the gasoline stage in vehicles. It offers an audiovisual indication when the gasoline stage drops alarmingly under the reserve degree, helping you to keep away from working out of petrol on the way. Nowadays autos come with a dash-mounted gasoline gauge meter that point outs the fuel degrees on an analogue display. The ‘reserve’ level is indicated with the help of a pink marking in some vehicles, but the needle motion in the path of the crimson marking is additionally complicated and no longer actual. This circuit displays the fuel tank under the reserve stage and warns thru LED indicators and audible beeps when the chance level is drawing near. 

Circuit diagram :

Fuel Reserve Indicator For Vehicles Circuit Diagram

The gas sensor system includes a tank-mounted waft sensor and a current meter (fuel meter), that are connected in sequence. The go with the flow-driven sensor hooked up to an interior rheostat offers excessive resistance when the tank is empty. When the tank is full, the resistance decreases, permitting extra current to cross in the path of the meter to give a higher studying. The gas monitoring circuit works by sensing the voltage model developed across the meter and prompts the beeper when the fuel tank is nearly empty. Its level A is hooked up to the input terminal of the fuel meter and point B is connected to the body of the car. The circuit consists of an op-amp IC CA3140 (IC1), two 555 timer ICs (IC2 and IC3) and decade depender CD4017 (IC4). 

Op-amp IC CA3140 is wired as a voltage comparator. Its inverting input (pin 2) obtains a reference voltage managed thru VR1. The non-inverting enter (pin 3) obtains a variable voltage tapped from the enter terminal of the fuel meter via resistor R1. When the voltage at pin 3 is better han at pin 2, the output of IC1 goes high and the green LED (LED1) glows. This situation is maintained until the voltage at pin three drops beneath that at pin 2. When this occurs, the output of IC1 swings from high to low, sending a low pulse to the set off pin of the monostable (usually held high by using R3) by manner of C1. The monostable set offs and its output goes high for a predetermined time according to the values of R5 and C2. With the given worths, the ‘on’ time will doubtless be around four minutes. 

The output of IC2 is used to power the astable circuit together with timer 555 (IC3) by implys of diode D2. Oscillations of IC3 are controlled with the help of R6, R7, VR2 and C4. With the given worths, the ‘on’ and ‘off’ time periods are 27 and 18 2nds, respectively. The pulses from IC3 are given to the clock enter (pin 14) of decade depender CD4017 (IC4) and its outputs go excessive one by way of one. When the circuit is swaped on, LED1 and LED2 glow in case your vehicle has adequate petrol within the tank. 

When the gasoline goes below the reserve stage, the output of IC1 goes low, LED1 flips off and a terrible set offing pulse is received at pin 2 of IC2. The output of IC2 goes excessive for round 4 minutes and all via this time frame, clock pin 14 of IC4 obtains the clock pulse (low to high) from the output of IC3. For the first clock pulse, Q0 output of IC4 goes high and the fairway LED (LED2) glows for round 50 2nds. On receiving the 2nd clock pulse, Q1 goes excessive to illuminate the yellow LED (LED3) and sound the buzzer for round forty five 2ds. This audio-visual sign warns you that the vehicle is working out of gasoline. On receiving the 0.33 clock pulse, LED3 and the buzzer go off. There is a niche of around two-and-a-half minutes before Q5 output goes excessive.

By the time Q5 goes excessive and the red LED (LED4) glows, 4 minutes elapse and the ability provide to IC3 is bring to an end. The output state at Q5 will no longer exchange except a low-to-high clock input is obtaind at its pin 14. Thus LED4 will glow constantly together with the beep. The continuous glowing of the pink LED (LED4) and the beep from the buzzer indicate that the car will run out of fuel very shortly. Q6 output of IC4 is related to its reset pin 15 via diode D3. This means that after ‘on’ state of Q5, the count will at all times begin from Q0. Capacitor C5 presents power-on reset to IC4 when switch S1 is closed. The output of IC1 can additionally be related to reset pin of IC4 by means of diode D1 (1N4148). So when your car is refueled above the reserve stage, LED2 glows to point that the tank has enough gas.

IC5 presents regulated 12V DC for right kind functioning of the circuit even when the battery is charged to greater than 12V. The circuit can be assembled on a perforated board. Adjust VR1 till the voltage at pin 2 of IC1 drops to 1.5V. When level A is hooked up to the fuel meter (fuel gauge) terminal that goes to the gasoline sensor, inexperienced LEDs (LED1 and LED2) glow to indicate the traditional gasoline degree. VR2 may additionally be varied to set the ‘on’ time frame of IC3 at round 20 2ds. Enclose the circuit in a small case and mount on the dashboard the use of adhesive tape. The circuit works most effective in automobiles with poor grounding of the physique.

Author : D. Mohan Kumar

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LM3914 battery level indicator

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 voltage itself.

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Telephone In Use Indicator

This circuit will illuminate a LED if one of your telephones is in use. It should work in all countries (Including UK) that have a standing line voltage above 48 Volts DC. Please note that it is illegal to make a physical permanent connection to your telephone line in some countries (this includes the UK and Ireland). If building this circuit it is advisable to use a plugin cord so that the unit can be unplugged should a fault occur. If in doubt consult either your telephone or cable operator.

If all extension phones are on-hook and the line voltage is around 48 V, Q1 will conduct thus effectively shorting the gate of Q2 to its source, so it will be off and the LED will be disabled. Lifting the handset of any phone on the line causes the line voltage to drop to 5-15 V. The gate voltage of Q1, equal to some 6% of the line voltage, will then be too low and Q1 will be turned off. So Q2s gate is now biased at approximately 1/2 of the line voltage, Q2 turns on and the LED indicates that the line is in use. The circuit itself is practically invisible to the other telephone devices using the same line. LED1 must be low-current and its current-limiting resistor must be 2k2 or more. The other components ideal values may vary slightly, depending on the local telephone line parameters. The circuit is powered off the telephone line. If other types of MOSFETs are used, the 500k trimmer can be adjusted to ensure that Q1 is biased fully on while the line is not in use (LED1 off), and vice versa.

Telephone In-Use Indicator Circuit diagram

 

If Q2 is not a BS108 but some other 200 V MOSFET with a higher G-S threshold voltage, it might be necessary to increase the value of the lower (or decrease the value of the upper) one of the two resistors connected to the gate of Q2. Plain (bipolar junction) transistors can be used instead and the circuit also works fine. But the resistor values are then much lower - letting ten times more microamps of current pass through while the line is not in use, and even this MOSFET design still could not meet formal minimum on-hook DC resistance specifications. Both prototypes PCBs were 4x1 cm. The current-limiting resistor for LED1 is 2k2 in both cases. DO NOT ground any of the leads or conducting surfaces in this circuit. A more reliable design would also include some kind of over-voltage protection etc.

Warning:

In their normal course of operation, telephone lines can deliver life-threatening voltages! Do not attempt to build any of the circuits/projects unless you have the expertise, skill and concentration that will help you avoid an injury. There are also legal aspects and consequences of connecting things to telephone lines, which vary from country to country. Keep away from telephone lines during a lightning storm!

Source:  http://www.ecircuitslab.com/2011/07/telephone-in-use-indicator.html

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