555 Alarm Circuit | Electronic Project Circuits

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Door buzzer with 555

This is easy circuit buzzer. It use IC 555, Speaker 25 -80 OHM.

I demolishes a store-room , see old loudspeaker and other equipment a little again. Then born the though builds Door Buzzer by use , IC 555. Perform sound electric bell origin. When press S1 as a result have a voice fair loud. This circuit almost must not do anything. Because divisible Amen! should use 25-80ohm size loudspeakers. will make good sound use force against electricity low work or economize the electricity. You will may use 9V batteries all right sir.

Be the first to comment - What do you think? Posted by admin - May 20, 2007 at 3:21 pm

Categories: Audio diagram, Circuit diagram, home alarm systems Tags: 555 alarm circuit, Alarm systems, door buzzer systems

Light-sensitive Alarm by IC 555

The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms.

The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light.

- The light-sensitivity of the circuit can be adjusted by varying the 100k preset.
- The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset.

Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.

source : http://www.free-electronic-circuits.com