WATER SEEPAGE ALARM

Posted by The Past day on Monday, November 30, 2009 | 0 Comments |

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.

More Detail discovercircuits.com

DOORKNOB ALARM

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Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms. A metal chain attached to a box holding the electronics is placed around the inside doorknob of a wood door. Anyone grabbing the knob from the outside is detected by the electrical capacitance change that occurs from the human hand contact between the knob and the box.


lmost all of the commercial devices sold use a more expensive and power consuming radio frequency circuit approach to detect the capacitance change. But, a very inexpensive and micro power technique can also work.
This circuit schematic should dramatically reduce the cost of the device and allows it to operate for many years from one set of batteries.

MACHINE POWER LOSS BEEPER

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For some medical equipment it is important for an operator when power is lost to the machine.
The beeper is powered from a 9v battery and requires the machine to have a power switch with a third set of contacts.

More Detail Please see discovercircuits.com

POWER REMINDER BEEPER

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This circuit produces a short beep once each minute. It is powered directly off the 120vac power line to remind you that a device connected to the circuit is turned on.


It is simple enough to be packaged inside a small plastic box. It might be ideal for computers, printers or some test equipment that shouldn't be left on all night.

MICRO POWER OVER-TEMPERATURE ALARM

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The circuit is powered for years by a single 3 volt lithium battery. It sounds an alarm when the temperature exceeds a certain point. With some minor changes the circuit could also be configured for an under temperature (freeze) alarm.
The circuit uses a cheap but accurate thermistor as the temperature sensor.
More Detail
http://www.discovercircuits.com/PDF-FILES/overtemp.pdf