Light-sensitive Alarm Project
Tuesday, May 18, 2010 by sms
The ambit detects a abrupt adumbration falling on the light-sensor and sounds the bleeper back this happens. The ambit will not acknowledge to bit-by-bit changes in accuracy to abstain apocryphal alarms. The bleeper sounds for alone a abbreviate time to anticipate the array active flat. Normal lighting can be used, but the ambit will assignment
best if a axle of ablaze is abiding to abatement on the light-sensor. Breaking this axle will again account the bleeper to sound. The ablaze sensor is an LDR (light-dependant resistor), this has a low attrition in ablaze ablaze and a aerial attrition in dim light.
Light-sensitive Alarm Project
The light-sensitivity of the ambit can be adapted by capricious the 100k preset.
The breadth of beep can be assorted from 0.5 to 10 abnormal application the 1M preset.
Using the 7555 low-power timer ensures that the ambit draws actual little accepted (about 0.5mA) except for the abbreviate times back the bleeper is aural (this uses about 7mA). If the ambit is switched on continuously an acrid PP3 9V array should aftermost about a month, but for best activity (about 6 months) you can use a backpack of 6 AA acrid batteries.
This activity uses an edge-triggered 555 monostable circuit.
Parts Required
resistors: 10k, 47k, 1M ×3
presets: 100k, 1M
capacitors: 0.01µF, 0.1µF, 10µF 25V radial
transistor: BC108 (or equivalent)
7555 low-power timer IC
8-pin DIL atrium for IC
LDR (light-dependant resistor) blazon ORP12
bleeper 9-12V
on/off switch
battery blow for 9V PP3
stripboard 12 rows × 25 holes
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