Alarms and security

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Xenon Strobe
Xenon Strobe
March 1, 2011

This is a very simple strobe circuit which I have not seen anywhere else. My inspiration came from a strobe circuit that was in a school fire alarm buzzer - the kind that has a built-in strobe light on top. [more]

Digital Combination Lock
Digital Combination Lock
December 10, 2010

A multiple input combination loack using CMOS counter IC's. Flexibility and code change is allowed by changing output connections. [more]

Electronic Doorbell with Counter
Electronic Doorbell with Counter
December 10, 2010

This circuit uses a synthesized sound chip from Holtek, the HT-2811. This reproduces the sound of a "ding-dong" chiming doorbell. Additionally, the circuit includes a CMOS 4026 counter display driver IC to count your visitors. [more]

Switch De-Bouncer
Switch De-Bouncer
December 10, 2010

This circuit will remove the transient spikes and contact bounces from a non-latching push button switch. [more]

Frost Alarm
Frost Alarm
December 10, 2010

A simple thermistor triggered switch with adjustable threshold. It triggers with cold temperatures so may be used as a frost alarm or cold temperature switch. [more]

Power Failure Alarm
Power Failure Alarm
September 11, 2010

This is a very basic alarm designed to let you know when the electricity supply fails. The alarm is powered from a battery which uses no current consumption at all in standby, a battery should therefore last its full shelf life. [more]

3 Zone Duress Alarm
3 Zone Duress Alarm
September 11, 2010

This is a 3 zone alarm for use in high risk areas or possible duress situations. Typical examples being banking or betting booths. The alarm consists of 3 normally open push button switches which can be hidden or in plain view. Once pressed the alarm... [more]

Two-Zone Intruder Alarm
Two-Zone Intruder Alarm
September 11, 2010

This is a two-zone alarm - with automatic exit, entry and siren cut-off timers. It can be triggered by the usual types of normally-closed input devices - such as magnetic reed contacts - foil tape - PIRs etc [more]

6 Zone Alarm
6 Zone Alarm
September 11, 2010

This alarm system has 6 independent zones, 1 timed entry/exit zone, a 7 segment LED display and a test or walkthrough facility. Suitable for a small office or home environment, it can also be adapted to use a combination lock or keypad to set and... [more]

Hijack Alarm No. 3
Hijack Alarm No. 3
September 9, 2010

this circuit was designed primarily 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... [more]

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