Schematics LPG Gas Leakage Alarm Circuit PCB

Circuit

All of us aware of the danger while handling the LPG gas cylinders which uses in the kitchen or in the motor vehicles. LPG gas is supplied in pressurized steel cylinders. When the gas leakes from a cylinder, it it flows along floor and tends to settle down in low spots of the room, because the LPG is heavier than air. If not properly exhausted, this can cause, fire or suffocation.

Fig. 1: Circuit for gas leakage alarm

Fig. 2: Pin details of gas
sensor module

Here is an electronic circuit that detects LPG presence and alert the user through LED and speaker alarm. The circuit is based on the 555 timer IC which is available easily. A 9V battery can be used to operate this equipment and the zenar diode used cover the supply to 5V dc. This drives the LPG gas sensor module SEN-1327 from RhydoLABZ. This is an active high device, which means the output goes high when the gas level exceeds a minimum level in the vicinity.

The Gas detector is sensitive to propane, butane, isobutene, LPG and natural gas as per the data sheet. It can also be used to detect combustible gas  mainly methane. 

Threshold LPG concentration : 1000  ppm

The multivibrator basically works as a tone generator which is triggered by the high output of the gas sensor module. The pitch of the tone can be changed by varying preset VR1. Use a suitable heat-sink for transistor SL100.

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Schematics Smoke Alarm Using 555 PCB

Circuit

The smoke alarm circuit presented here is based on the readily available photon-coupled interrupter module and timer IC NE555. The photo interrupter module is used as the smoke detector, while timer 555 is wired in astable configuration as an AF oscillator for sounding alarm via a loudspeaker.

Circuit diagram of  Smoke Alarm Using 555: Click on image to enlarge

In the absence of any smoke, the gap of photo interrupter module is clear and the light from LED falls on the phototransistor through the slot. As a result, the collector of phototransistor is pulled towards ground. This causes reset pin 4 of IC 555 to go low. Accordingly, the timer is reset and hence the alarm does not sound.

However, when smoke is present in the gap of the photo interrupter module, the light beam from LED to the phototransistor is obstructed. As a result, the phototransistor stops conducting and pin 4 (reset) of IC 555 goes high to activate the alarm.

Note: The unit must be housed inside an enclosure with holes to allow entry of smoke.

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Schematics Frequency Variation Using 555 PCB

Circuit

A novel method of frequency variation using 555

Electronic hobbyists are very much familiar with  the functioning of timer 555 in astable mode of operation. Traditionally, if at all there was a need to keep the duty factor constant and change the frequency continuously, the method was to use a variable capacitor, rated in picofarads. But in that case, changing the frequency in tens of hertz range would become tedious. On the other hand, sacrificing duty factor, change of frequency can be done by changing the values of R1 or R2. 

Both of the above-mentioned problems can be overcome simply by using a variable resistor, as shown in the circuit diagram. Surprisingly, increase of resistance results in increase of frequency, instead of decrease. When the value of variable resistor is zero, frequency is given by

                                                           f=1.44/(R1+2R2)C1

Now, when the value of variable resistor VR1 is increased, the frequency increases from the value of ‘f ’ as determined from above formula (with VR1=0). The circuit has been practically verified with two different values of timing capacitor C1 and the results obtained are tabulated in Table I.

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Schematics Rotation Sensor Circuit Using 555 PCB

Circuit The picture shows the circuit diagram of a rotation sensor that can turn on a device like motor or buzzer while the circuit assembly rotates. The circuit is based on basic 555 timer operation.

Circuit Diagram of  Rotation Sensor Circuit Using 555 : Right Click >> View Image to view full size

• When the circuit rotates, the switch will trigger the circuit.
• The transistor SL100 will activate the relay.

Note:
The circuit is not tested:-

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Schematics Electronic Harmonium Using 555 PCB

Circuit

Here's the circuit diagram of a simple electronic harmonium that can produce all the seven notes. As timer IC 555 based design, the circuit is very simple to assemble and use. It only requires single 555 IC, one or two capacitors and some resistors.

Circuit Diagram of Electronic Keyboard Using 555: Right Click >> View Image to view full size

In this circuit, the NE555 IC works in astable operation. When ever the voltage at pin no.2 exceeds the voltage at pin no.6, theres will ble a high output and vice versa.. So a capacitor c2 is included to charge or discharge automatically to flip and flop the output.

The resistors R2-R16 is desgned to vary the output frequency of the astable multivibrator according to the tone of the note played. The circuit needs 9V pure dc power supply to work properly. Assemble the circuit on a common PCB and enclose within a plastic cabinet.

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Schematics Rain Sound Generator Using NE555 PCB

Circuit

The circuit diagram shows a timer 555 based rain sound generator. The circuit requires a 9V dc power supply and can be fed from a 9V battery.  The loud speaker for producing sound is of 0.5W 8ohm speaker.The circuit will readily generate a rain like sound whenever the circuit fed by a 9V supply.

Circuit Diagram of Rain Sound Generator : Click  to enlarge

The rain generator has two sections one is a UJT relaxation oscillator. This oscillator is build upon the uni junction transistor 2N2646. This oscillator produces a fixed frequency as per the value of C1. This continuously resets the 555 because the UJT oscillator output is connected to the reset pin of the NE555. On the other hand, the 555 IC works itself as a astable multivibrator. This process result in the generation of a rain like sound from the speaker.

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Schematics Car Wiper Control Using 555 PCB

Circuit

In rainy seasons, it is very annoying that wiper of your car wiping instantly all the time. Have you ever think of speed control of the wiper?.There are wiper control modules available on the market but most of them are costly. So here is an automatic wiper control circuit which enables you to control your wiper sweep rates from 1 second to 10 second.

Circuit Diagram of Automatic Wiper Control circuit Using 555 : Click  to enlarge

The heart of this circuit is an astable multivibrator using 555 Ic. We actually change the duty cycle of the square wave to obtain different sweep rates to control the wiper. The output pin 3 of the IC remains high for a time period set by R2. During this time the wiper motor will sweep at rates.

The power supply to this wiper control circuit should be 12V. fit the potentiometer R2 anywhere on the dashboard of your vehicle and control the sweep rates according to the intensity of the rain.

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Schematics Photo Timer Circuit Using 555 PCB

Circuit

Here is a circuit that is become useful for photo studio owners. This 555 timer circuit switch on and off a light (exposure lamp) in a specific time. Basically this is a timer circuit however we connect a relay to the output. The relay used here is a 12V dc relay and operating current is less than 200mA.

Click on the image to enlarge

Assemble the circuit on a common PCB and this circuit only consist of cheap components so you can set up the circuit from the scratch.

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Schematics Touch Control Switch Using 555 PCB

Circuit

Here is the circuit diagram of an automatic touch plate controller using NE555 IC. The circuit turns on a relay when anyone touches the input metal plate for a short period of time. After then it switch off the relay or controlled device automatically. This circuit can be connected to calling bells, Buzzers, small toys etc.

     Circuit Diagram of  touch plate controller using NE555 : Click  to enlarge

We can connect toy motors to this circuit through a SL100 transistor, where we can avoid D1 and D2 Diodes.

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Schematics Burglar Alarm System With High Sensitivity PCB

Circuit

Most standard light sensors that used in ordinary burglar alarm systems requires precise alignment of light beam to deactivate the alarm system during standby mode. However this circuit of burglar alarm is so sensitive that it will detect a moving person at a distance of few meters in pure daylight or under electric lighting.It requires virtually no set up, and may be simply placed within the line-of-sight of almost any light source including ambient daylight or high end fluorescent electric light. The alarm system uses a beep generated from the circuit driven through a buzzer that is high enough to detect the entry of a person inside the fence.

Click on the image to enlarge

This security system uses a op amp comparator 741 with two potential dividers in its inverting and non inverting inputs. (about half of supply voltage). The burglar detector LDR and its controlling preset VR1 from another potential divider to provide a variable input to NIV input pin 3.

Adjust VR1 properly then output of 555 ic will be high because of the LDR effect. Ie when the shadow of a person come across the LDR light path, its light intensity level and the voltage at the non-inverting input of IC1 will drop momentarily.The output of IC1 suddenly becomes low, allowing T1to conduct. This triggers the monostable (IC2) and the alarm sounds.

You can easily set up the circuit in a common PCB and keep Keep LDR1 inside a black tube to increase its sensitivity. On testing with ideal conditions, the alarm system detected a person from a distance of about three meters.

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