Powerful Security Siren

This circuit was requested by several correspondents. Its purpose was to obtain more power than the siren circuit already available on this website (One-IC two-tones Siren) and to avoid the use of ICs. A complementary transistor pair (Q2 & Q3) is wired as a high efficiency oscillator, directly driving the loudspeaker. Q1 ensures a full charge of C2 when power is applied to the circuit. Pressing on P1, C2 gradually discharges through R8: the circuit starts oscillating at a low frequency that increases slowly until a high steady tone is reached and kept indefinitely. When P1 is released, the output tone frequency decreases slowly as C2 is charged to the battery positive voltage through R6 and the Base-Emitter junction of Q2. When C2 is fully charged the circuit stops oscillating, reaching a stand-by status.
Circuit Diagram:

Parts:

P1 = SPST Pushbutton Operating Switch
R1 = 1K
R2 = 10K
R3 = 1K
R4 = 220R
R5 = 10K
R6 = 220K
R7 = 22K
R8 = 100K
C1 = 22uF-25V
C2 = 22uF-25V
C3 = 10nF-63V
C4 = 47uF-25V
Q1 = BC557
Q2 = BC557
Q3 = BC337
B1 = 12V Battery
SW1 = SPST Toggle or Slide Main Switch
SPKR = 8 Ohms Loudspeaker

Notes:

• A good sized loudspeaker will ensure a better and powerful output tone.
• As stand-by current drawing is zero, SW1 can be omitted and B1 wired directly to the circuit.
• Maximum current drawing at full output is about 200mA.
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• Electronics Lab Created By Muhammad Irfan
• Electronics Lab Created By Muhammad Irfan

Shadow Detector Alarm

This is also known as Sun up alarm, in this circuit you can set the LDR’s sensitivity by 100k potentiometer, you can set it with any lamp around your room (tube light, bulb, LED etc) by varrying the 100k potentiometer. We can also control the buzzer time by 1M potentiometer  
You can Enhance this project and set the sensitivity of the LDR with a lazer light and keep it on the way of any door circuit at one side and lazer at other side of the door and a then you can make this project to buzz as soon as some one enters in a room 

I personally set this project in my room with sensitivity of tube light and whenever i came in and turn my room’s tube light on

Parts Required: 555 Timer 100k & 1M potentiometers  10k, 1Mx(3), 47k 0.1mF, 0.01mF & 10mF LDR BC337 transistor Beeper/Buzzer 9v Battery Supply

   Circuit Diagram:

Bread board Arrangement:     Strip Board Version:      Electronics Lab Created By Muhammad Irfan Electronics Lab Created By Muhammad Irfan

Heat Sensor

Electronics Lab Created By Muhammad Irfan

Here is a simple circuit which can be used as a heat sensor. In the following circuit diagram thermistor and 100 Ohms resistance is connected in series and makes a potential divider circuit . If thermistor is of N.T.C (Negative temperature Coefficient ) type then after heating the thermistor its resistance decreases so more current flows through the thermistor and 100 Ohms resistance and we get more voltage at junction of thermistor and resistance. Suppose after heating 110 ohms thermistor its resistance value become 90 Ohms.then according to potential divider circuit the voltage across one resistor equals the ratio of that resistor’s value and the sum of resistances times the voltage across the series combination. This concept is so pervasive it has a name: voltage divider. The input-output relationship for this system, found in this particular case by voltage divider, takes the form of a ratio of the output voltage to the input voltage.
This output voltage is applied to a NPN transistor through a resistance. Emitter voltage is maintain at 4.7 volt with a help of Zener diode.This voltage we will use as compare voltage. Transistor conducts when base voltage is greater than emitter voltage. Transistor conducts as it gets more than 4.7 base Voltage and circuit is completed through buzzer and it gives Sound.

Circuit Diagram of Heat Sensor

* please use 220 Ohms thermistor if not available you can use 2pcs 110 ohms thermistor in series. Resistance parallel with zener diode is not necessary.

You may also be interested in Project using Precision Temperature Sensor .

Electronics Lab Created By Muhammad Irfan