Hacks and Mods: VFD Talking Alarm Clock

Are you having a hard time waking your hubby from sleeping? And when you leave the house for work, are you in doubt that he has not gotten out of bed? One thing that
will stop your worries is to use this clock that does not just tell
红包扫雷苹果下载地址 time but also “swears”.

This is an All-in-one alarm clock. It shows an alphanumeric
character, it has a calendar, temperature, and a light sensor to control
its brightness. You can plug it on to your power source or use a
battery. Although this is cool, It’s not ok being around kids. We don’t
红包扫雷苹果下载地址 want young kids to learn to swear or say bad things, right?

Simple Darkness Activated Alarm

Most darkness activated
alarms employ opamps and some logic ICs. Here, a less expensive approach
is shown based on the eternal 555, this time in monostable
multivibrator mode. Components R2 and C1 represent a one-second network.
When the LDR (light dependent resistor) is in
the dark, its resistance is high, pulling pin 2 of the 555 to ground.
This triggers the monostable and the (active!) 6-volt piezo buzzer will
sound. Preset P1 is adjusted depending on ambient light levels. The
circuit may be fitted on a wall in your home. Assuming P1 has been set
for the existing ambient light level, the shadow cast by anybody
红包扫雷苹果下载地址 entering the room or hallway will trigger the alarm.

Simple Darkness Activated Alarm Circuit

Simple Darkness Activated Alarm Circuit Diagram

红包扫雷苹果下载地址author: myo min – copyright: elektor july-august 2004

Drinking Water Alarm

The State Jal Boards
supply water for limited duration in a day. Time of water supply is
decided by the management and the public does not know the same. In such
a situation, this water alarm circuit will save the people from long
wait as it will inform them as soon as the water supply starts. At the
heart of this circuit is a small water sensor. For fabricating this
water sensor, you need two foils—an aluminium foil and a plastic foil.
You can assemble the sensor by rolling aluminium and plastic foils in
the shape of a concentric cylinder. Connect one end of the insulated
flexible wire on the aluminium foil and the other end to resistor R2.
Now mount this sensor inside the water tap such that water can flow
through it uninterrupted. To complete the circuit, connect another wire
from the junction of pins 2 and 6 of IC1 to the water pipeline or the
红包扫雷苹果下载地址 water tap itself. The working of the circuit is simple.

Timer 555 is wired as an astable multivibrator. The multivibrator
will work only when water flows through the water tap and completes the
circuit connection. It oscillates at about 1 kHz. The output of the
timer at pin 3 is connected to loudspeaker LS1 via capacitor C3. As soon
as water starts flowing through the tap, the speaker starts sounding,
which indicates resumption of water supply. It remains ‘on’ until you
switch off the circuit with switch S1 or remove the sensor from the tap.
The circuit works off a 9V battery supply. Assemble the circuit on any
general-purpose PCB and house in a suitable
cabinet. The water sensor is inserted into the water tap. Connect the
lead coming out from the junction of 555 pins 2 and 6 to the body of the
water tap. Use on/off switch S1 to power the circuit with the 9V PP3

Speed Alarm For Cars

In normal suburban
driving you pass through so many different speed zones that it can be a
nuisance having to switch speed settings. The speed display can also be a
distraction. This circuit eliminates the display and the need for speed
selection. Each time you exceed a particular speed setting (eg, 40km/h,
50km/h, etc), a piezo buzzer will beep. Speed pulses are fed to the
base of Q1 and the resulting waveform at its collector is fed via an RC
network to the input of an LM2917 frequency-to-voltage converter, IC1.
The resulting voltage is fed to three comparators (IC2d-IC2b) which have
the reference voltages at their inverting inputs set by 10-turn
trimpots VR1, VR2 & VR3. The output of each comparator is applied
via another RC network to the gate of an SCR. The anodes of the three SCR红包扫雷苹果下载地址s are commoned connected to the inverting input of the remaining comparator, IC2a.

Circuit diagram:

Speed Alarm Circuit

Speed Alarm Circuit Diagram

Its non-inverting input is set to +2.3V by trimpot VR4. In use, once
you exceed the speed setting for a particular comparator, its
associated SCR briefly conducts to pull pin 2
of IC2a low and a short beep is emitted by the piezo buzzer. Then, as
you exceed the next speed setting, another beep will be heard. The idea
is make each speed setting a few km/h higher than actual so that if you
are driving at the correct speed in a given zone, the buzzer will not
sound. But as you increase speed, the buzzer will beep once as you
exceed the speed setting for each zone. In this way, there is no need to
continually switch speed settings as you drive through different zones
and you can choose to ignore beeps that are not “illegal”.

author: col edwards – copyright: silicon chip electronics magazine

Overheat Detector Alarm/Switch

At the heart of this
circuit is a precision integrated temperature sensor type LM35 (IC1),
which provides an accurately linear and directly proportional output in
mV, over the zero to +155 degrees C temperature range. The LM35 develops
an output voltage of 10 mV/K change in measured temperature. Designed
to draw a minimal current of its own, the LM35 has very low self heating
in still air. Here the output of the LM35 is applied to the
non-inverting input of a comparator wired around a CA3130 opamp (IC2). A
voltage divider network R3-P1 sets the threshold voltage, at the
inverting input of the opamp. The threshold voltage determines the
adjustable temperature trip level at which the circuit is activated.

Overheat Detector Alarm/Switch Circuit

Overheat Detector Alarm/Switch Circuit Diagram

When the measured temperature exceeds the user-defined level, the
comparator pulls its output High to approx. 2.2 V causing transistor T1
to be forward biased instantly. T2 is also switched on, supplying the
oscillator circuit around IC3 with sufficient voltage to start working.
The 555 set up in astable mode directly drives active piezoelectric
buzzer Bz1 to raise a loud alert. Components R7, R8 and C4 determine the
on/off rhythm of the sounder. A transistor based relay driver may be
driven off the emitter of T1 (TP1). Similarly, replacing the piezo
sounder with a suitable relay allows switching of high-power flashers,
红包扫雷苹果下载地址 sirens or horns working on the AC mains supply.

author: t. k. hareendran – copyright: elektor electronics 2007

Mains Failure Alarm

This circuit was
designed to produce an audible alarm when the mains power is
interrupted. Such an alarm is essential for anyone whose livelihood
depends on keeping perishable foodstuffs in cold storage. The circuit is
powered by a 12-V mains adapter. LED D5 will
light when the mains voltage is present. When the mains voltage
disappears, so does the +12 V supply voltage, leaving the voltage
regulator IC1 and relay driver T1-T2 without power. The relay driver, by
the way, is an energy-saving type, reducing the coil current to about
50% after a few seconds. Its operation and circuit dimensioning are
discussed in the article ‘Relay Coil Energy Saver’. The value of the
capacitor at the output of voltage regulator IC1 clearly points to a
红包扫雷苹果下载地址 different use than the usual noise suppression.

Circuit diagram:

Mains Failure Alarm Circuit

Mains Failure Alarm Circuit Diagram

When the mains power disappears, Re1 is de-energized and the 0.22 F
Gold-cap used in position C4 provides supply current to IC2. When the
mains voltage is present, C4 is charged up to about 5.5 volts with IC1
acting as a 100-mA current limit and D10 preventing current flowing back
into the regulator output when the mains voltage is gone. According to
the Goldcap manufacturer, current limiting is not necessary during
charging but it is included here for the security’s sake. The CMOS
555 is configured in astable multivibrator mode here to save power, and
so enable the audible alarm to sound as long as possible. Resistors R5
and R6 define a short ‘on’ time of just 10 ms. That is, however,
sufficient to get a loud warning from the active buzzer. In case the
pulses are too short, increase the value of R5 (at the expense of a
higher average current drawn from the Goldcap).

LDR & LED Pair Smoke Detector and Alarm by LM1801

Smoke detectors are
generally used in advanced alarm systems. Most of this professional
devices use gas-detectors, ionization rooms or radioactive elements as
sensors. In this circuit we are not using any of this complicated
components. Instead of these, we are using two LDRs and one LED.LM1801
special-purpose IC ,which is designed especially for smoke detectors,
provides us building this circuit by using the minimum number of
components. It includes one internal zener supply, two reference voltage
outputs, one voltage comparator, fixing diodes and one 500mA output

Circuit is connected to the mains directly. D1 rectifies the
alternating source and R7 reduces it to the level that the circuit can
operate with. C2 capacitor stabilizes the voltage and zener inside the
IC regulates it. Two identical LDR红包扫雷苹果下载地址s are connected in bridge type so this connection prevents the circuit from temperature changes and ageing effects.

R13 LDR and LED must be placed such a way that smoke particles reduce the light drop on LDR and change its resistance. On the other hand R12 LDR and LED must be placed adjacent and no air circulation occurs. Best way to do it, place R12 and LED in a separate box. So smoke won’t effect R12 and its resistance will remain same.

When the comparator detects the voltage difference between two LDRs
it triggers Th1 transistor and as a result, alarm starts. P1 is the
calibration potentiometer. Hp1 is an alarm sound generator. Circuit
includes one extra alarm output to drive external alarm system.

Photodiode Alarm

This Photodiode based
Alarm can be used to give a warning alarm when someone passes through a
protected area. The circuit is kept standby through a laser beam or IR
beam focused on to the Photodiode. When the beam path breaks, alarm will
be triggered. The circuit uses a PN Photodiode in the reverse bias mode
to detect light intensity. In the presence of Laser / IR rays, the
Photodiode conducts and provides base bias to T1.

The NPN transistor T1 conducts and takes
the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable
oscillator using the components R3, VR1 and C3. The Astable operates
only when its resent pin becomes high. When the Laser / IR beam breaks,
current thorough the Photodiode ceases and T1 turns off. The collector
voltage of T1 then goes high and enables IC1. The output pulses from IC1
drives the speaker and alarm tone will be generated.

Photo Diode Alarm Circuit

Photo-Diode Alarm Circuit

IR Transmitter Circuit

IR Transmitter Circuit

A simple IR transmitter circuit is given which uses Continuous IR
rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.

Gas Leakage Alarm

gas is supplied in pressurized steel cylinders. As this gas is heavier
than air, when it leaks from a cylinder it flows along floor and tends
to settle in low spots such as a basement. This can cause fire or
suffocation if not dealt with. Here is a circuit that detects the
leakage of LPG gas and alerts the user through
audio-visual indications. Fig. 1 shows the circuit of the gas leakage
alarm. The circuit operates off a 9V PP3 battery. Zener diode ZD1 is
used to convert 9V into 5V DC to drive the gas sensor module. The SEN-1327
gas sensor module from RhydoLABZ is used in this circuit. Its output
goes high when the gas level reaches or exceeds certain point. A preset
in the module is used to set the threshold. Interfacing with the sensor
module is done through a 4-pin SIP header. Pin details of the gas sensor module are shown in Fig. 2.

An MQ-6 gas sensor is used in the gas sensor module. As per its
datasheet, it has high sensitivity to propane, butane, isobutene, LPG
and natural gas. The sensor can also be used to detect combustible
gases, especially methane. This circuit has been tested with LPG gas and was found to work satisfactorily. Whenever there is LPG concentration of 1000ppm (parts per million) in the area, the OUT
pin of the sensor module goes high. This signal drives timer IC 555,
which is wired as an astable multivibrator. The multivibrator basically
works as a tone generator. Output pin 3 of IC 555 is connected to LED1
and speaker-driver transistor SL100 through current-limiting resistors
R5 and R4, respectively. LED1 glows and the alarm sounds to alert the
user of gas leakage. The pitch of the tone can be changed by varying
preset VR1. Use a suitable heat-sink for transistor SL100.

Simple Alarm System

The circuit presented
here is a very simple and yet highly effective alarm system for
protecting an object. The circuit requires no special devices and can be
built using components that you will no doubt be able to find in the
junk box. The alarm-triggering element is a simple reed switch. To
generate the alarm signal itself any optical or acoustic device that
operates on 12 V can be used: for example a revolving light, a siren, or
even both. In the quiescent state the reed switch is closed. As soon as
the reed switch opens, the input to IC1.B will go low (previously the
potential divider formed by R2 and R3 held the input at 5.17 V, a logic
红包扫雷苹果下载地址 high level).

A turn-on delay of between 0 and approximately 90 s can be set using
P1, and a turn-off delay of between 0 and approximately 20 s can be set
using P2. When the system is turned on (using S1), the turn-on delay is
activated, giving the user of the system at most 90 s to leave the
object alone before the system goes into the armed state, and the object
is then protected. Once the reed switch opens the turn-off delay of at
most 20 s starts: this allows the rightful owner of the object to turn
the system off before the alarm is triggered. If some unauthorised
person causes the reed switch to open, the alarm will be triggered after
红包扫雷苹果下载地址 the turn-off delay.

Also, even if the reed switch is briefly opened and then closed
again, the alarm will still be triggered. Once the alarm is triggered,
T3 will conduct for about 45 s (because of R8 and C5). The turning off
of the alarm is necessary to avoid the nuisance caused by a permanently
sounding alarm system. The system then returns to the armed state, which
means that the next time the reed switch is opened the alarm will
trigger again. If it is not desired that the duration of the alarm be
limited, for example if a visual indication is used, D5 should not be
fitted. The system can be extended by fitting multiple reed switches in
红包扫雷苹果下载地址 series. As soon as any one is opened, the alarm is triggered.

When S1 is closed C3 charges via P1. Depending on the potentiometer
setting, it takes between 0 and 90 s to reach the input threshold
voltage of IC1.A. The output of IC1.A then goes low and D3 stops
conducting. Assuming the reed switch is closed, the inputs of IC1.B stay
high and the output therefore low. If the reed switch is opened after
the turn-on delay expires the output of the gate will change state and
turn on T1. This ensures that the output of the gate remains high even
after the reed switch is closed again. C4 now starts charging via P2,
reaching the input threshold voltage of IC1.C after between 0 and 20 s,
again according to the potentiometer setting. The output of IC1.C goes
low, and T2 and T3 are turned on – and the siren sounds.

Any Darlington transistor can be used for T3. At the same time, C5
charges via R8, reaching the input threshold of IC1.D in about 45 s.
When the output of IC1.D swings low, it pulls the inputs of IC1.A low
via diode D5: the siren stops and the system returns to the armed state.
If the potentiometers P1 and P2 are replaced by fixed resistors it is
possible to build the circuit small enough to fit in a match-box, without
the need to resort to SMD components. This is
ideal if the circuit is to be used to protect a motorbike. If the alarm
system is to be used in a car, an existing door switch contact can be
used instead of the reed switch. In this case an RC combination needs to
be added to prevent false triggering. Use a 10 µF/25 V electrolytic for
C6, a 100 kΩ resistor for R9 and a 1N4001 for D7. It is again possible
to wire multiple door switch contacts in parallel: as soon as one
红包扫雷苹果下载地址 contact closes, IC1.B will be triggered.