Wiring Material: security

Showing posts with label security. Show all posts

Thursday, September 4, 2014

Night security light

Here is a simple schema switches on a light around 2 hours after midnight, the time at which most of the robberies taking place.

This simple schema is build around a CMOS IC 4060 to obtain the required timing. During day time the LDR has low resistance and keeps the pin 12 of the IC1 high, preventing the IC1 from oscillating. When it is dark the LDR resistance becomes high and the pin 12 of IC1 becomes low and the IC starts oscillating, which indicated by the flashing of LED D3.The values of the timing components R1, R2, C4 are so selected that the out put pin3 of IC1 goes high after 8 hours. That means the high output drives the triac to switch on the lamp around 2’O clock. At morning, the LDR resistance drops and the pin 12 of IC1 goes high and stops the oscillation, making the lamp OFF. The switch S1 can be used to manually ON the lamp. The capacitor C2 prevents false triggering.

Notes.

* Assemble the schema on a good quality PCB or common board.
* The LDR can be general purpose LDR.
* The light sensitivity can be adjusted using the preset R6.
* The IC1 must be mounted on an IC holder.

Wednesday, August 27, 2014

Powerful Security Siren

This schema was requested by several correspondents. Its purpose was to obtain more power than the siren schema 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 schema. Pressing on P1, C2 gradually discharges through R8: the schema 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 schema stops oscillating, reaching a stand-by status.

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 schema. * Maximum current drawing at full output is about 200mA.