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How to Use the Index This index is arranged alphabetically on each title word. For example, the "Frost Alarm" will be indexed under "A" and also "F". To find a particular circuit use your internet browsers search function. In Netscape Communicator or Internet Explorer press "Ctrl + F" and enter your search text. Pressing F3 takes you to the next match.
A
Alarm Circuits Alarm PSU AM Transmitter Circuit AM Receiver ATL3 Loop Antenna Audio Circuits Audio Level Meter Audio Notch Filter Audio Voice-Over Circuit Audio VU Meter Cold Activated Switch Enhanced Alarm Keypad Frost Alarm Gate Alarm Miniature Loop Alarm Modular Burglar Alarm
Motorcycle Alarm Peak Reading Audio Level Meter Q-Multiplying Loop Antenna Quadraphonic Amplifier Radio Wave Alarm Soft Switching Amplifier with Tone Controls TDA 2030 Amplifier Water Activated Alarm ZN414 Portable AM Receiver 2 Watt Amplifier 15 Watt Amplifier 5 Zone Alarm
B Boosting Regulator Current Buzzer Circuit DC Push Button Motor Control Fuse Blown Indicator Modular Burglar Alarm Nicad Battery Charger 4 Band Double Tuned Preselector
C Cable Tester Cold Activated Switch Combinational Conjuring Trick Conjuring Trick Connection Tester Control and Interfacing Computer Microphone Boosting Regulator Current
4 Band Double Tuned Preselector Audio Line Driver
E ECM Mic Preamplifier Electronic Canary Electromagnetic Field Detector Electronic Siren EMF Probe with Meter Enhanced Alarm Keypad Electronic Metronome Infra Red remote control extender Infra Red Remote Control Extender Mark 2 Version Music and Special Effects Sound Effects Generator
F Field Strength Meter FM Receiver using MPF FM Transmitter Frost Alarm Function Generator Fuse Blown Indicator Audio Notch Filter Electromagnetic Field Detector Simple Field Strength Meter 2 Transistor FM Transmitter
G Gate Alarm Gyrator Circuit Function Generator
Sound Effects Generator
H Hi-Fi Preamplifier High Quality Intercom Hot Water Indicator
I Infra Red remote control extender Infra Red Remote Control Extender Mark 2 Version Infra Red remote control tester Infra Red Switch Insect Repellant Control and Interfacing Doorphone Intercom Fuse Blown Indicator High Quality Intercom Hot Water Indicator Negative Ion Detector Remote Doorbell Indicator 6 Input Mixer
J
K Keypad Circuit Enhanced Alarm Keypad
L LED Torch Light Detection Circuit LM317 Voltage Regulator
Simple Field Strength Meter Speaker Microphone Temperature Monitor 6 Input Mixer 555 Monostable Circuit
N Negative Ion Detector Neon Desklamp Nicad Battery Charger Night Light Audio Notch Filter
O Over Voltage Protection for LM Logic PSU with Over Voltage Protection Sound Operated Switch Square Wave Oscillator
P Peak Reading Audio Level Meter Perimeter Alarm Porch Light Switch Pot Plant Power Power Control Circuits DC Push Button Motor Control Dual Regulated PSU ECM Mic Preamplifier EMF Probe with Meter Hi-Fi Preamplifier Logic Probe Logic PSU with Over Voltage Protection
L200 PSU
MW Preamplifier UHF Preamplier Uninterruptable Power Supply Unregulated PSU ZN414 Portable AM Receiver 4 Band Double Tuned Preselector 12V 30A PSU
Q Quadraphonic Amplifier Quiz Circuit Q-Multiplying Loop Antenna High Quality Intercom
R Radio Wave Alarm Regulated 12v PSU Remote Doorbell Indicator RF Circuits AM Receiver Boosting Regulator Current DC Motor Reversing Circuit Dual Regulated PSU FM Receiver using MPF Infra Red remote control extender Infra Red Remote Control Extender Mark 2 Version Infra Red remote control tester ZN414 Portable AM Receiver ZN414 SW Receiver Variable Voltage Regulator
Connection Tester Soft Switching Amplifier with Tone Controls Surveillance Transmitter Detector Zener Diode Tester 2 Transistor FM Transmitter 2 Transistor Transmitter 4 Band Double Tuned Preselector 4 Transistor Transmitter 5 to 30 minute Timer
U UHF Preamplier Ultrasonic Dog Whistle Uninterruptable Power Supply Universal DC-DC Convertor Unregulated PSU
V Variable PSU Variable Voltage Regulator Voltage Comparator Switch Audio Voice-Over Circuit Logic PSU with Over Voltage Protection
W Water Activated Alarm Water Activated Relay Water Level Alarm Hot Water Indicator Magic Wand Radio Wave Alarm Square Wave Oscillator
Ultrasonic Dog Whistle 2 Watt Amplifier
X
Y
Z Zener Diode Tester ZN414 Portable AM Receiver ZN414 SW Receiver 5 Zone Alarm
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Gate Alarm.
By Rev. Thomas Scarborough
Cape Town
Figure 1 represents a cheap and simple Gate Alarm, that is
intended to run off a small universal AC-DC power supply.
IC1a is a fast oscillator, and IC1b a slow oscillator, which are
combined through IC1c to emit a high pip-pip-pip warning
sound when a gate (or window, etc.) is opened. The circuit is
intended not so much to sound like a siren or warning device,
but rather to give the impression: "You have been noticed."
R1 and D1 may be omitted, and the value of R2 perhaps
reduced, to make the Gate Alarm sound more like a warning
device. VR1 adjusts the frequency of the sound emitted.
IC1d is a timer which causes the Gate Alarm to emit some 20
to 30 further pips after the gate has been closed again, before
it falls silent, as if to say: "I'm more clever than a simple on-
off device." Piezo disk S1 may be replaced with a LED if
desired, the LED being wired in series with a 1K resistor.
Figure 2 shows how an ordinary reed switch may be
converted to close (a "normally closed" switch) when the
gate is opened. A continuity tester makes the work easy.
Note that many reed switches are delicate, and therefore
wires which are soldered to the reed switch should not be
flexed at all near the switch. Other types of switches, such as
5 Zone Alarm System
Description This is a complete alarm system with 5 independent zones suitable for a small office or home environment. It uses just 3 CMOS IC's and features a timed entry / exit zone, 4 immediate zones and a panic button. There are indicators for each zone a "system armed" indicator. The schematic is as follows:
Circuit Notes: Each zone uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppresser. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key. At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.
Return to Alarm Circuits
Since this little alarm is intended to be kept in arms reach at all times, there aren't any provisions for automatic shutdown after a certain period of time. The buzzer will sound until you turn the whole circuit off or connect the wire loop back to the jumpers. The same goes for the two LEDs, each indicating its own zone.
Construction is not critical and there aren't any traps for the novice. The two 100n capacitors aren't really necessary, I just included them to make sure that there is no noise interference coming from the long wire loops. For transistors, you can use any NPN general-purpose audio amplifiers/switches (BC 107/108/109, BC 237/238, 2N2222, 2N3904...). Assemble the circuit on perf board. Together with the buzzer and a 9V battery, it should easily fit in a pocket- sized plastic box smaller than a pack of cigarettes. A fresh battery should suffice for weeks of continuous operation.
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Modular Burglar Alarm
RON J Email: [email protected]
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 SW1. By using the expansion modules, you can add as many zones as you require; some or all of which may be the inertia (shock) sensor type. All the green LEDs should be lighting before you open SW1. You then have up to about a minute to leave the building. As you do so, the Buzzer will sound. It should stop sounding when you shut the door behind you. This indicates that the Exit/Entry loop has been successfully restored within the time allowed. When you re-enter the building you have up to about a minute to move SW1 to the off position. If SW1 is not switched off in time, the relay will energise and sound the main bell. It will ring for up to about 40 minutes. But it can be turned off at any time by SW1. The "Instant" zone has no Entry Delay. If you don't want to use N/O switches, leave out R8, C8 and Q2; and fit a link between Led 3 and C7. The 24 Hour PA/Tamper protection is provided by the SCR/Thyristor. If any of the switches in the N/C loop is opened, R11 will trigger the SCR and the bell will ring. In this case the bell has no time limit. Once the loop is closed again, the SCR may be reset by pressing SW2 and temporarily interrupting the current flow. The basic circuit will be satisfactory in many situations. However, it's much easier to
