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Three Flashing LED Doorbells - These circuits combine a buzzer with one or more
LED displays. When the push switch is operated - the buzzer will sound and the LEDs
will flash. When the switch is released - the buzzer will stop - but the LEDs will go
on flashing for another 30 seconds or so. |
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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. ….(designed by David A. Johnson) |
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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) |
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Tiny 2-zone alarm - Since I travel a lot during summer, I decided to build a
really small alarm that could easily fit inside a pocket. However, I also demanded
reliable operation, simple construction and very low power consumption. I started with
CMOS logic gates, but was soon forced to abandon the concept after a few unsuccessful
(and far too complicated) takes.... (circuit design added 08/08/08) |
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Tiny Two Zone Alarm - (electronic circuit added 1/03) |
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Touch Activated Alarm (Tony van Roon) - (schematic / circuit added 10/02) |
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Transistor Based Motorcycle Alarm - This circuit features a timed output and
automatic reset. It can be operated manually using a key-switch or a hidden switch. By
adding an external relay, it will set itself automatically - and/or immobilize the
machine - every time you turn-off the ignition. It's easily adapted for a 6-volt
system - so it will protect your "Classic Bike". (circuit design added 08/08/08) |
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Travel Touch Alarm - The Travel Touch Alarm can be used to provide a audible
alarm when someone touches the door knob or handle of your hotel room. The door
knob or handle must be made of metal for the circuit to work. The main chip in the
circuit is a 555 timer ….(added 08/08/08) |
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Two CMOS Based Vehicle Anti-Hijack Alarms - The first circuit is designed for the
situation where a hijacker forces the driver from the vehicle. If a door is opened
while the ignition is switched on - the circuit will trip. After a few minutes delay -
when the thief is at a safe distance - the alarm will sound and the engine will fail.
The second circuit is a modification of the first - offering enhanced protection in
many more situations. (circuit design added 08/08/08) |
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Two Simple Relay Based Motorcycle Alarms - These are two - easy to build -
relay-based alarms. You can use them to protect your motorcycle - but they have many
more applications. If you use relays with 6-volt coils - they'll protect your "Classic
Bike". Both alarms are very small. The completed boards occupy about half a cubic-inch
- 8 cc. The standby current is zero - so they won't drain your battery. (circuit
design added 05/08) |
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Ultrasonic Alarm (1) - This alarm equipment transmits a ultrasonic and receives
the ultrasonic which is reflected at the obstacle and gives the alarm in the case
which set within the distance. The distance which can be set is from about 40 cm to 10
m. For example, when setting to the 5 m distance, it doesn't detect a reflection from
more than 5 m distance. However, the alarm can be given when there is a reflected
wave….(added 05/08) |
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Ultrasonic Alarm (2) - This alarm device transmits the ultrasonic and it confirms
a reflected wave from the obstacle. If there is object within the set distance, it
doesn't give the alarm. When there is no object within the set distance, it gives the
alarm. The distance which can be set is from about 40 cm to 5-6 m. For example, when
making a setting distance 5 m, it gives the alarm when the reflected wave from 40 cm
to 5 m passes away. ….(added 05/08) |
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Ultrasonic Remote Control and Alarm - (circuit added 7/02) |
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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. ….(designed by David A. Johnson) |
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Using the MAXQ3210 in a Light-Beam Alarm System - Maxim App Note 4153 --
2/26/2008 -- (app note add 5/08) |
