Digital thermometer circuit

admin July 21, 2011 47 Comments
Digital thermometer circuit. CA3162, CA3161 & LM35. A simple digital thermometer circuit with out a micro controller and having a seven segment LED read out is shown here. The circuit is based on three ICs: CA3162, CA3161 and LM35. CA3162 is a monolithic analogue to digital (A/D) converter that has BCD output. The A/D converter inside the IC is a dual slope type with differential inputs. The IC has an internal timing circuitry and hold function. When the hold...
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Water level Controller

admin January 22, 2014 173 Comments
Water level controller circuit Note:- We have developed another water level controller circuit using micro controller AT89S51 from Atmel. If you are interested, read that too :- Water level controller using micro controller Are you familiar with the basics and the different applications of the 555 timer IC. If not, we recommend you 3 books that provide a very good understanding of the IC and its applications. You can check out the reviews and buy the book from our...
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Thermostat using LM56

john August 14, 2009 2 Comments
Description. Here is the schematic of a very simple electronic thermostat using IC LM56. LM56 is a very accurate dual output low power thermostat from National Semiconductors.LM56 has various useful features like internal temperature sensor, two internal voltage comparators, internal voltage reference etc. Two stable temperature trip points (VT1 and VT2) are created by dividing the LM56’s 1.250V internal voltage reference using 3 external resistors (R1, R2 and R3). There are two digital outputs for LM56 .Output1 becomes LOW...
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Power megaphone circuit

admin April 7, 2010 8 Comments
Description. Just about any power transistor can be used in  this megaphone.Its suitable for boats,playing fields etc.the transistors Q1  & Q2 are the HEP-230 type which are easily available in the market.The transistors are parallely connected to handle the required power and speaker matching.The microphone is a carbon type like that used in telephone hand sets.If  a regular carbon mike is used the push-to-talk (PTT) switch can be connected in place of S1 to provide PTT operation.There will be...
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Electronic siren circuit

admin April 7, 2010 5 Comments
Description. This is a compact electronic siren circuit based on three transistors.This circuit is suitable for in corporating with other alarm or siren projects such as burglar alarms, automatic factory sirens etc or a simple push to on alarm. The  electronic siren circuit given here  is  based on a complementary transistor pair consisting of Q2 & Q3 (BC557 & BC 37)  wired as an astable multivibrator oscillator,which directly drives the speaker.The transistor Q1 is used to provide a full charge on...
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Air flow detector circuit.

admin June 1, 2009 142 Comments
Description. This circuit can give a visual indication of the rate of air flow.It can be also used to check whether there is air flow in a given space. The filament of a incandescent bulb is the sensing part of the circuit.When there is no air flow the resistance of the filament will be low.When there is air flow the resistance drops , because the moving air will remove some of the heat generated in the filament.This variations in...
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Magnetic proximity switch.

admin May 3, 2008 16 Comments
Description. Here is the circuit diagram of a magnetic proximity switch that finds a lot of applications in many fields.The circuit is based on a magnetic reed switch(S1) as the proximity sensor. A monostable multivibrator based on NE555 (IC1) and a toggle flip flop based on CD4013 (IC2) does the rest of the circuit. When a magnet is reached in proximity of S1 it closes to give a negative trigger at pin 2 of IC1.The output of IC1 goes...
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Dew sensitive switch

admin March 8, 2012 15 Comments
Description. Here is a simple circuit that can be used to switch ON or OFF a device when the dew present in the surrounding atmosphere crosses a set value. The circuit uses a dew sensitive resistive element and a comparator based on LM 358 to perform the above said operation. At normal condition the resistance of dew sensor element will be low and so the voltage drop across it. So the voltage at the non inverting pin of LM358...
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Humidity tester

jacky March 7, 2012 6 Comments
Description. A variety of humidity tester circuits are available, but this  is a circuit which is as simple as possible. Using only a transistor, LED and few resistors, this circuit can be used to check the humidity level of materials like soil, paper etc. When the humidity in a substance increases the current conducted through  it also increases. This is the working principle. If there is required humidity, the current through R3 will be sufficient to produce a voltage...
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Digital temperature sensor

admin February 16, 2012 29 Comments
Description. Here is a straight forward, yet effective digital temperature controller that can be used with temperature control systems. The circuit uses IC LM 35 (IC3) to as the temperature sensor. The output of LM 35 is given to the IC ADC 0804 (IC4) which converts the analog output of the LM 35 to digital output. The ADC 0804 is a 8 bit ADC. Eight LED’s are connected to the output  of ADC to show the output logic. If...
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