New fire alarm circuit

This system prevents users from fire. It depends on the smoke, which consists of a fire.

When the smoke takes the bulb and LDR, the amount of light falling LDR decreases.

This causes the resistance LDR increases, and voltage transistor base pulled high which makes the provision of COB (chip on board) will be completed. Different ears available in the market to create different sounds.
COB select depends on the user. Signal generated by COB supplemented by audio amplifier.

Under this system, audio power amplifier is connected to some IC TDA 2002. Sensitivity of the system depends on the distance between the lamp and LDR, and create a pre-VR1. This may be a lamp and LDR at an appropriate distance, you can toggle between pre-VR1, to obtain optimal sensitivity.
ON / OFF switch is proposed to contain the system or outside.

DEW sensor circuit

Dew (condensed moisture) ad- versely affects the normal per- formance of sensitive electronic devices.A low-cost circuit described here can be used to switch off any gadget automatically in case of excessive humidity.At the heart of the circuit is an inexpensive (resistor type) dew sensor element.

Although dew sensor elements are widely used in video cassette players and recorders, these may not be easily available in local market. However, the same can be procured from authorised service centres of reputed companies. The author used the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No: 6808-08-04, reference no. 336) in his prototype. In practice, it is observed that all dew sensors available for video application possess the same electrical characteristics irrespective of their physical shape/size, and hence are interchangeable and can be used in this project. The circuit is basically a switching type circuit made with the help of a popular dual op-amp IC LM358N which is configured here as a comparator.

(Note that only one half of the IC is used here.) Under normal conditions, resistance of the dew sensor is low (1 kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal. The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit.

When humidity exceeds 80 per cent, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This pushes up the output of IC1 to a high level. As a consequence, the LED inside the opto-coupler is energised.

At the same time LED1 provides a visual indication. The opto-coupler can be suitably interfaced to any electronic device for switching purpose. Circuit comprising diode D2, resistors R5 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit. This simple arrangement obviates the requirement for a bulky and expensive step-down transformer.

air flow detector circuit

Parts List

R1  100 Ohm 1/4W Resistor
R2  470 Ohm 1/4W Resistor
R3  10k 1/4W Resistor
R4  100K 1/4W Resistor
R5  1K 1/4W Resistor
C1  47uF Electrolytic Capacitor
U1  78L05 Voltage Regulator
U2  LM339 Op Amp
L1  #47 Incandescent lamp with glass removed (See “Notes”)
D1  LED

Notes:
1. The glass will have to be removed from L1 without breaking the filament. Wrap the glass in masking tape and it in a vise. Slowly crank down until the glass breaks, then remove the bulb and carefully peel back the tape. If the filament has broken, you will need another lamp.

Combination Lock circuit

This circuit is very basic to build. To open a the lock which is connected to the K1 Load. you must press each momentary switch in the correct sequence. The sequence used in this circuit is S1,S2,S3,S4. If any of the other switchs are pressed the circuit will reset and you will need to start over. Depending on how you wire the switchs, you can use any 4 switch combination