Alarms, page 5


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Alarm Circuits Page 5
Alarms: #-C D-G H-O P-R S-Z
Last Updated on: Friday, August 29, 2008 02:32 PM

Circuits Designed by Dave Johnson, P.E.

Simple Security Wire Loop Alarm: A wire is looped through various objects which are to be monitored. The loop wire is typically an aircraft cable but could also be any insulated stranded wire. The loop is attached to a table or desk. Should the loop be cut, the alarm is sounded.

TIME TO DUST INDICATOR
I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough. I have not yet built and tested this circuit completely but in concept it should work. The circuit draws very low current from a +3v battery and could be housed in a package similar to a small ashtray.

The assembly might be placed in a suitable out of the way area to collect dust. It would alert a maid when it was time to dust the room. The circuit detects dust with an infrared LED that is pulsed so its light shines onto a smooth flat plate. Any dust settling onto the surface is detected by a phototransistor, mounted at a 90 degree angle from the LED. When the dust reaches a particular level, sufficient light is reflected into the phototransistor to change the logic state of the circuit to an alarm condition. The alarm output could be connected to a beeper, a flashing LED or to one of the LED flashing circuits in this hobby circuit section.

UNPLUGGED POWER CORD ALARM
Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries. However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries. So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time. The device was designed to snap onto the outside of a power cord, where it senses the AC electric field emitted. No direct connection to the internal wires of the power cord is needed. I also included a low battery voltage monitor.

WATER SEEPAGE ALARM
This simple circuit sounds a beeper when its electrodes detect water. It is powered by a single 1.5v N cell. A small 1.5v button battery will also work.

Wire Security Loop Alarm
A wire loop is used to protect valuable objects in this alarm circuit. The circuit is powered by a 9v battery. (added 7/06)

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

SCR Based Burglar Alarm: (electronic design added 6/07)

Security Alarm: (electronic circuit added 1/03)

Seismic Alarm: My original "Deer Repellent/ Seismic Sensor" recommended using a speaker with a weight glued to the cone as a vibration sensor (see bottom of page) but it recently occurred to me that the speaker could supply the mass itself. By gluing a standoff to the center of the cone, an inexpensive 2", 8 ohm speaker becomes a vibration sensor with a natural resonance below 100Hz which is quite good. My... (electronic design added (6/07)

Simple Alarm System: (diagram added 6/03)

Simple Door Alarm Circuit: This is a simple - easy to build - alarm circuit. For power - I used a small 9-volt battery. But the circuit itself will work from 5 to 15-volts - just choose a buzzer that's suitable for the voltage...(added 05/07)

Simple Electronic Buzzer: This very simple circuit just uses a couple of resistors, a capacitor and the easily available 555 timer IC. The 555 is setup as an astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on. The frequency can be changed by varying the 10K resistor. (added 10/05)

Simple Fire-Door Alarm Circuit: This is a simple - easy to build - alarm circuit. For power - I used a small 9-volt battery. But the circuit itself will work from 5 to 15-volts - just choose a buzzer that's suitable for the voltage...(added 05/07)

Single Button Lock Provides High Security: 03/04/99 EDN-Design Ideas / (added 11/05) Figure 1 is the block diagram of an easily programmed, single-button combination lock. You operate the lock by using a series of short and long pulses from a momentary switch that masquerades as a doorbell button. The circuit uses inexpensive CMOS logic. The retriggerable timer, T1, locks out entries made after the....

Single Zone Alarm: (diagram added 6/03)

Snore Alarm: The idea behind this snore alarm, is just to rouse the snorer, not the entire household. To wake the sleeper, vibration is used, not an audible alert. The vibration is provided by a small motor housed in a small 35mm film case, which can be placed under the sleepers mattress or pillow. This circuit has a level control and peak display indicator, a variable trigger threshold and trigger indication. (added 10/05)

Speed Limit Alarm: (circuit added 9/04)

Speed-limit Alert: (electronic design added 6/07)

Sun-Up Alarm: The Sun-Up Alarm can be used to provide a audible alarm for when the sun comes up or it can be used in a dark area and detect when a light comes on. It can also be used to detect a light beam, headlights etc. The circuit works as follows. The phototransistor is very sensitive to light. (Any phototransistor will work fine) The sun shining on this device will provide a .... (added 09/05)

Theft Preventer Alarm: This circuit utilizing a 555 timer IC can be used as an alarm system to prevent the theft of your luggage, burglars breaking into your house etc. The alarms goes ON when a thin wire, usually as thin as a hair is broken. The circuit is straightforward. It uses a 555 IC wired as an astable multivibrator to produce a tone of frequency of about 1kHz which .... (added 10/05)

Timed Burglar Alarm: This is a simple but effective alarm circuit which can reset its self after a time that you select. it has normally open and normally closed triggers which make this circuit very practical. This alarm has normally open and normally closed triggers. It's on a 555 timer so the alarm will reset it's self after a certain amount of time. The time is adjustable.... (added 10/05)

Tiny Two Zone Alarm: (electronic circuit added 1/03)

Touch Activated Alarm uoguelph_: (schematic / circuit added 10/02)

Ultrasonic Remote Control and Alarm: (circuit added 7/02)

Wailing Alarm: (schematic / circuit added 10/02)

Water Activated Alarm circuitsdb: The circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, the transistor will have no bias current and be fully off. However...(added 05/07)

Water Activated Alarm: (diagram added 6/03)

Water Activated Alarm: (electronic design added 6/07)

Water Level Alarm: (electronic design added 6/07)

Water Level Alarm: (schematic added 9/02)

Water Level Controller: (electronic Circuit / Schematic added 10/04)

Water Level Indicator with Alarm #2: Here is a simple, versatile circuit which indicates the level of water in a tank. This circuit produces alarm when water level is below the lowest level L1 and also when water just touches the highest level L12. The circuit is .... (added 10/04)

Water Level Indicator with Alarm: This circuit not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full. The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs. When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected.... (added 10/05)

Water-level Alert: Beeper or flashing LED alert. (electronic design added 6/07)

Wire Loop Alarm: (circuit added 7/02)

Alarms: #-C D-G H-O P-R S-Z