Temperature warning indicator circuit

The circuit is a low temperature regulator, supervisor, warns us about global warming. Temperature control is done by the thermistor TH1, which is a negative factor. The resistance varies between 10KO at 25 ° C and about 1KO at 94 ° C. The trimmer TR1 regulate the exact temperature at which the Q1-2, connected as a Darlington, lead me, making the relay K1 to close and IZ, sound.


The alarm is activated when the temperature is greater than the default. The thermistor should be located away from the rest of the circuit, so as not to risk from the heat. The power circuit is battery 9V, but if it is mounted in a fixed position, then we can supply with a constant voltage power supply. The relay contacts can be connected load which we, as a bulb, another circuit, etc. It can also add an LED, if we are to sign and visual stimulation.


The adjustment is done by immersing the thermistor TH1, in the water which we know the temperature (contacts should be well insulated so we do not have short circuit) and adjusting the trimmer until the circuit is excited. The cable connecting the circuit with the TH1 must be shielded.

Temperature warning indicator circuit

 

Part List
R1= 820 ohm
R2-3= 1Kohm
C1= 220uF 16V
TR1= 2.2Kohm Trimmer D1= 5.6V 0.5W Zener
D2-3= 1N4148
Q1-2= BC550C
TH1= Thermistor 10Kohm at 25° C
K1= 6V 200 ohm Relay
BZ1= Buzzer
S1= 1×2 Switch
BATT= Battery 9V or external supply

Application
 
This circuit is designed not only setting a detection of high temperatures, but can also be changed to be set on the detection of low temperatures in some areas. It can be used for refrigeration, walk-in refrigerator or freezer and other environments that are sensitive to temperature. Some integrated circuits high-temperature alarm modules will be used in motor vehicles to the profession in which the temperature element senses a temperature very dangerous in the interior of a motor vehicle, and encourages the employment sensor detects the presence or determine the absence of an occupant. In the absence of the inhabitants, the sensor is that after a period during which an audible alarm is activated to provide the attention to the motor vehicle in the presence of an occupant. This type of alarm can be reset with a key.
Take a temperature alarm can be advantages such as protection of valuable equipment by high temperature, low temperature, high humidity or sometimes provided. Other programs of high temperature can be used to protect against loss of or against the air conditioning system for heating off. Instead, the program for low-temperature failure of the heating system be used to prevent frozen pipes. The alarm can also reduce downtime, get a phone call and the notification of a possible power failure or failure before damage occurs in one unit

Simplest Transformerless LED Drivers

In this post we learn regarding three interesting transformerless power supply circuits for illuminating LEDs from mains that uses minimum number of components


Circuit 1

A capacitor must be having a rating of more than 200V and should be having dialectic of metallize polyester or poly poplin.

A resistor 1K is employed to limit the in rush current the resistor should be having the wattage value of more than 1Watt.

A diode is connected in anti-parallel to the LED. This diode limits the reverse voltage across the LED. The diode also provides the path for the negative half cycle as the LED is connected to a AC power source.

This particular circuit behaves like a constant current source of 15 to 20mA depending on LED voltage bias and supply line stability with a nominal 60Hz power supply frequency. The circuit 2 is an improvisation over circuit 1 and it enables to glow two LED’s at a time. This gives a color benefit also.

Putting two switches to the series part of individual LEDs can enable the viewer to have three colors.

In this transformerless circuit using the above formula the current can be manipulated by changing the capacitor value. Power LEDs can also be driven directly from AC power source.

Circuit2

The third circuit employs a zener diode of 5.6 V/1W. The zener diode serves dual purpose. Firstly it acts as a bias of the negative half of circuit like the diodes employed in circuit 1 and 2. Secondly, it acts as a voltage regulator for the LED driver circuit.

This circuit provides 5 Volts steady output with a 30mA current pumping facility. The 1000uF capacitor acts as a ripple suppressor and it allows a moderate ripple of 6% that is 300mV in this case. Employing the third circuit the use can expect better life of the LED. The current limiting capacitor used is 1.5uF at 200Volts.

The capacitor supplies the current to the driver as well it biases the zener to remain active during operation.

Please note that while using any LED it's datasheet should be studied beforehand. In general natural white LEDs, cool white LEDs, warm white LEDs all have a nominal bias voltage of 3.5V DC. But the activation starts at 2 to 2.4V DC.

The highest efficiency of the LED is achieved at 3.5V DC. Optimization of power supply is the highest priority in any LED driver circuit.

Circuit 3

If a constant voltage supply is provided it is to be notes that the power supply must have minimum ripple content.

The peak of the ripple shall also effect the performance of the LED so far as the junction temperature of the wafer is concerned. However a constant current source is a safest power supply alternative for a LED. A constant current source can achieved in many ways.

A variable power supply that is regulated by a current loop is the general trend. A capacitor in series is obviously the most economic constant current source so far as AC power supply is concerned.

Any fluctuation in the input power might result into the change in the current value,for this purpose,a regulator like 5.6 V zener is a safe practice.

While connecting the LED to the regulator circuit the power capacity of the regulator is to be kept in the mind along with the power requirement of the specific LED.

How to build Decibel Meter

The post explains a very handy little decibel meter circuit which may be built by any new hobbyist at home.

Description

Decibel (dB) is a unit of sound pressure. In this particular circuit three LEDs or lamps are employed to indicate the pressure of a available audio input. When the three lights are ON, the audio level would be 4x. When two lights are ON it would be 2x and when one light ON it would be x. the circuit is built around a quad OP-AMP LM324.

One section of the IC is being used as an amplifier whereas the other three OP-AMPs have been used as voltage comparators.

Here in this case the audio sensor is a standard 8ohm speaker. One side of the speaker is grounded and the other pin of the speaker is connected to the negative pin of a 10μF electrolytic capacitor. The positive pin of the electrolytic capacitor is connected to the base of a switching transistor of high gain. In this case 2N2222 or 2N3904 is recommended.

The first OP-AMP which is used as an amplifier as a trim pot of value 500K connected between output and inverting input. By adjusting this potentiometer the value of the output is adjusted. In the comparator circuit a potential divider circuit is employed in all the inverting input as shown in the circuit. The output of the amplifier is connected to the non-inverting pins of all the three comparators as shown in the circuit. As soon as the audio signal is available, the 10μF capacitor starts getting charged. As the audio level increases the DC voltage at non-inverting comparator input start increasing and the lamp sequentially get turned ON depending on the audio input available and the adjustment of the potentio divider chain. 

 

A dynamic microphone can be employed instead of a speaker but it has been observed in practice that the performance of the speakers as a decibel transducer is often better than that of microphone. However, it is to be noted that the speaker needs, a rigid mounting and the power supply applied to this particular circuit demands noise less filter DC. In fact decibel is a ratio metric term and a logarithmic expression so if a circuit is to be built to discretize the audio level more steps of light sources need to be employed which demands more stages of comparators and ratio metric tuning of the potential dividers employed in the inverter input of the comparators. One number LM324 can offer further four stages and it cost very nominal. However, a calibrated decibel meter should be used while tuning the resistance change of the potential divider in order to design and accurate sub standard decibel meter having bar graph representation.

How to build Fading Red Eyes

Two Light Emitting Diodes slowly light up and fade away due to the circuitry, giving it a feel of blinking red eyes in darkness.
It is the perfect way to set up your own horror show in Halloween. It can also be installed in series for the Christmas tree or during Diwali or a decorative power indicator for the daily appliance.

A 3 volt linear wave is generated at Pin 1 via LM 1458 IC and followed by a transistor which buffers the emission. A 47 K resistance coupled with a 22uF capacitor is joined at Pin2 to limit the frequency to 0.5Hz. The rate can be varied using a 100K pot(potentiometer) replacing the 47K resistor.

Two operational amplifiers govern the circuit. The transitional voltage is produced by the first op-amp which slowly modulates voltage between 3 to 6 volts. The second op-amp supplies alternating voltage of 2 and 7 volts to charge the capacitor and discharge it via constant current.

Two 47K resistors establish a fixed voltage when joined across Pin 3 & 6 to keep the reference voltage constant. One op-amp works as an inverted amplifier connecting a capacitor across Output Pin 1 and Pin 2 which inverts the output. One of the op-amp compares the voltage to regulate the output in Pin 7. The reference voltage needs to be lower than the input at one point and needs to be higher with the reference at the higher end. A 100K resistance provides a positive feedback and controls the switching point via a capacitor that changes the direction of current. The op-amp also changes its directional output. The triangular waveform at Pin 1 is achieved which moves up or down keeping input constant at 4.5 Volts.

The Point when the LEDs go off can be adjusted by altering the resistance value across Pin 3 and grounding Pin 6. Using a 9 Volt Battery will ensure long operational hours.

Please note that LEDs have a narrow viewing angle of 30 degrees and appears brightest if viewed directly from the front or it might loose the desired effect of the eerie feeling it can generate.

Circuit diagram

The circuit here shows a double pair of LEDs that operate intermittently such that while a pair illuminates, the other pair fades out.

Mains Powered White LEDs using Resistor only

Power LEDs have changed the world of illumination. The number of experimentation on the ouput of power LEDs is the highest in the electronic hobby world.


Before going through the intricacies of the luminance of power LEDs we must first know the characteristics of LEDs. A white LED is generally biased at a voltage range of 2.5 to 3.5V DC.


Depending on the wattage of LED, the input current is determined. White LEDs are used for illumination purposes and are available right from 0.1Watt to 3Watts in general, with the same voltage characteristic but different current rating.


Though very simplistic, it is interesting to use the following serially connected white LEDs in a chain.

Here in this circuit 25 LEDs in a series have been considered a safe zone operation. We decide the bias voltage to be 3V DC in each of this rung. The total potential required to bias the LEDs is 25x3= 75V DC.


A bridge rectifier is employed to rectify 120V AC line without any filter circuit being employed. The peak of the rectifier voltage would be 120x 1.414= 169.68 V DC.


To play with the value of R in the first circuit is very simple as R has to create a potential drop of 95V DC with a justified calculation of the current going through it of wattage is very simple to decide.


Now let us consider the second circuit with half watt rectification with single diode only. This circuit is cheaper and at the same time the heat dissipated in the current limiting resistance is much less. This happens as the circuit employs a half wave rectifier and using an anti parallel diode across a LED chain.

The reminiscent energy is flown back, considering the LED series current to be 20mA. Resistance of value 1200 K is adequate to control the current through the LED chain.


This circuit obviously pushes a larger peak current to the LEDs but this will not be harmful to the circuit operation because it lasts only half the cycle.


In this particular case each LED is biased in such a way that it delivers 0.06 watt of power, in total the entire chain is a 1.5 watt power source which probably is sufficient for reading purpose and worth its cost and life.


As the circuit is designed around live mains, user must be cautious of electrical seepage or short circuits and for this an insulated cover properly designed is a strong recommendation.