Alarms of all kinds, electronic circuits, page 3

Alarm Circuits Page 3
Alarms: #-C D-G H-O P-R S T-U V-Z
Last Updated on: Monday, October 03, 2011 06:07 PM

Circuits Designed by Dave Johnson, P.E.

Human Traffic Footstep Alarm
This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps. At has an adjustable sensitivity. (added 12/04)

Low Voltage 120vac Power Line Alarm
This circuit will turn on a beeper when the line voltage drops below 100 volt AC.

MACHINE POWER LOSS BEEPER
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.

MICRO POWER OVER-TEMPERATURE ALARM
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.

Motion Alarm Using Piezoelectric Device
An inexpensive piezoelectric device is used as a motion sensing device for this motion alarm. This circuit will activate a beeper whenever the circuit is moved. It could be used as an earthquake alarm. (added 7/06)

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

Head Light Alarm - "Never forget to turn off your head light ever again! Most newer cars already have this feature built-in but there are still lots of cars out there without it..... [Tony van Roon's circuit]

Highway Alert Signal Lamp - (electronic Circuit / Schematic added 10/04)

Hijack Alarm - There are two alarms here, be sure to scroll down. The first circuit was 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,.... [Circuit designed by Ron J]

Home Security Project - (diagram added 6/03)

How To Measure the Switching Voltage And Hysteresis Of A CMOS Gate - Manufacturing tolerances mean that the switching characteristics of Cmos ICs vary from one batch to the next. This page provides two small circuits....[Circuit design by Ron J.]

Human Traffic Footstep Alarm - This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps. At has an adjustable sensitivity. …. [Designed by David A. Johnson]

Infrared beam barrier/ proximity sensor - his circuit can be used as an Infrared beam barrier as well as a proximity detector. The circuit uses the very popular Sharp IR module. The pin nos. shown in the circuit are for the Sharp module only. For other modules please refer to their respective datasheets.... [Radioland.nt.au]

Intruder Radio Alert System - (electronic Circuit / Schematic added 10/04)

Keypad Controlled Switch No. 2 - This is a simplified version of the 4-Digit Keypad Controlled Switch. I have modified the design to reduce the complexity of the circuit, and the number of components required. As a result, the code is somewhat less secure. However, there should be lots of situations where it will still be adequate.... [Ron J.'s circuit]

Knock Alarm (Sunil Kumar) - This circuit (Fig. 1), used in conjunction with a thin piezoelectric plate, senses the vibration generated on knocking a surface (such as a door or a table) to activate the alarm. It uses readilyavailable, low-cost components and can also be used to safeguard motor vehicles....(electronic Circuit / Schematic added 10/04)

Light-Sensitive Alarm - The circuit detects a sudden shadow falling on a light-sensor and sounds a bleeper for a short time (adjustable). 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.... [Designed by John Hewes]

Loop Sensor - Many security systems use a closed loop of wires and switches arranged so that whenever a door or window is opened, the loop will be broken and the alarm will sound. An obvious problem is that someone can tamper with the system, short out the loop, and later on, come back and burglarize the premises....

Low Power RFID Transponder - For some time railroad companies have been wrestling with the problem of tracking rail cars. This has traditionally required manual log entry of identification numbers displayed on the cars as they pass through the switching yard….(diagram added 7/03)

Low Voltage 120vac Power Line Alarm - This circuit will turn on a beeper when the line voltage drops below 100 volt AC.... [Designed by David A. Johnson]

Low Voltage Alarm - NE555 Low Voltage Battery Disconnect Circuit… [design by Arron Cake]

Luggage Security System - (electronic Circuit / Schematic added 10/04)

Machine Power Loss Beeper - 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. …. [Designed by David A. Johnson]

Melody generator for greeting cards - his tiny circuit comprising of a single 3 terminal IC UM66 can be built small enough to be placed inside a greeting card and operated off a single 3V flat button cell.
There is not much to the circuit. The UM66 is connected to its suppl…. [Radioland.nt.au]

Micro Power Over-Temperature Alarm - 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. …. [Designed by David A. Johnson]

Mini Alarms - This is a selection of small self-contained alarm circuits. They have a very low standby current; and are suitable for battery operation…. [Circuit designed by Ron J]

Miniature Loop Alarm - (Circuit design added 8/03)

Modular Burglar Alarm (Ron J) - This circuit features automatic Exit and Entry delays and a timed Bell Cut-off. It has provision for both normally-closed and normally-open contacts, and a 24-hour Personal Attack/Tamper zone. It is connected permanently to the 12-volt supply and its operation is "enabled" by opening SW1l....(electronic schematic added 8/02) [Circuit designed by Ron J]

Monitor alarm and indicator display multiple deviation boundaries - 22-April-10 Issue of EDN-Design Ideas Use a microcontroller and its ADCs to indicate process errors. [Design Idea by William Grill, Riverhead Systems, Lenexa, KS]

Motion Alarm - Using a piezoelectric device, this circuit will activate a beeper whenever the circuit is moved. It could be used as an earthquake alarm. …. [Designed by David A. Johnson]

Motion Alarm Using Piezoelectric Device - An inexpensive piezoelectric device is used as a motion sensing device for this motion alarm. This circuit will activate a beeper whenever the circuit is moved. It could be used as an earthquake alarm. (added 7/06) …. [Designed by David A. Johnson]

Motion Shadow Alarm - The hobby circuit below works quite well in typical indoor room lighting. I would not recommend its use in direct sunlight. Two small PIN photodiodes positioned about one inch apart form a shadow detector. With no shadow cast on the devices, both devices produce nearly identical current levels. The current is converted to a voltage with a load resistor in parallel with the photodiode. One resistor is adjustable so the two voltages can be carefully balanced under uniform lighting. When a hand or an arm is moved over the sensors, casting a shadow, …. [Hobby Corner Circuit by Dave Johnson]

Motorcycle Alarm - Any number of normally open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc....(Circuit design added 8/03)

Motorcycle Alarm #3 - This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can immobilize the bike, flash the lights etc..(electronic design added 6/07)

Motorcycle Alarm #4 - This is a simple easy to build transistor based motorcycle alarm. It's designed to work at 12-volts. But if you change the relay for one with a 6-volt coil it'll protect your "Classic Bike". The standby current is virtually zero so it won't drain your battery. (added 10/05)

Motorcycle Alarm No.3 - This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can immobilize the bike, flash the lights etc.... [Ron J]

Motorcycle Alarms Numbers 5 & 6 - 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 designed by Ron J. (added 10/05)

Motorcyle Alarm 2 - This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can immobilize the bike, flash the lights etc. Ron has used my Asymmetric Timer as the basis for his design....(added 01/2010) [Circuit designed by Ron J.]

N/O: N/C 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)

Novel Buzzer - (diagram added 6/03)

One Time Only Alarm - This alarm is designed to sound its Siren only once. That is - when the alarm is activated - the Siren will sound for a preset length of time. Then it will switch off and remain off. The alarm will not re-activate.The basic circuit has a single zone with independently adjustable Exit and Entry delays....(added 01/2010) [Circuit designed Ron J.]

One-Time-Only Burglar Alarm - When this alarm is activated its Siren will sound once, for up to 20-minutes. Then it will switch off and remain off. The basic circuit has a single zone with independently adjustable Exit and Entry delays. This will be adequate in many situations. However,....(Circuit design added 05/08)

Open-door alarm prevents accidental defrosts - 1-Feb-07 Issue of EDN Circuit helps save a lab freezer or temperature chamber's contents.... [Design Idea by Tom Lyons Fisher, Juniata College, Huntingdon, PA; Edited by Brad Thompson and Fran Granville]

Oscillating output improves system security - 6-Feb-03 Issue of EDN Many electronic-control systems have digital outputs that use transistors. One method of improving the security in these outputs is to use an oscillating signal to represent a logic-high state instead of a fixed voltage level (Figure 1]. This type of signal, a dynamic variable, can drive the circuit shown in Figure 2.... [Design Idea by Jorge Marcos and Ana Gómez, University of Vigo, Vigo, Spain]

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