Water Alarm Circuit >>

Have you ever seen the stairs to one of the upper stories in your house turn into a waterfall? Or maybe you’ve come home to find your aquarium fish trying to swim across the carpet? For your sake, we hope not, because the consequences are usually fairly dramatic. With a handful of electronic components, you can at least ensure that you will be warned before you have to put on your waders. It’s better to prevent water problems than to have to correct them. But no how many precautions you take, an occasional leak can still happen.

A burst water supply hose for the washing machine, a bath tap that someone forgot to turn off, a broken aquarium wall, or a leaking boiler or central heating tank – anything is possible. In such cases, it’s nice to be warned as quickly as possible, for example by an acoustic water alarm. Then you can at least limit the damage. If you’re handy with a soldering iron and know the difference between an IC and a PC, you’ll no doubt enjoy building the electronic water alarm described here.

The circuit takes advantage of the fact that ‘normal’ water is always slightly contaminated, even if only slightly, and thus conducts electricity to a certain extent. It is built around an popular IC from the somewhat antiquated 4000-series logic family: the 4093. This IC contains four inverted-output AND gates (NAND gates) with Schmitt-trigger inputs. If water is detected between the probes, it emits an intermittent and rather irritating beeping tone.

 

Laser Alarm Circuits >>

This circuit may be a optical device alarm just like the one we tend to see in varied movies. It uses a optical device pointer beam to secure your valuables and property. primarily, once the beam gets interrupted by someone, animal or object, the resistance of a photodiode can increase associated an alarm are going to be activated. The optical device and therefore the receiver will be fitted in same box, sharing a standard power offer. because the receiver attracts but ten mA on the average, you’ll before long notice that the optical device is that the most current hungry device! Mirrors area unit accustomed direct the beam in no matter setup you need. samples of a passage and {an area unita|a neighborhood|a district|a region|a locality|a vicinity|a part|a section} protected by the alarm are shown within the diagram.

Alarm Translator Mini Circuits

This circuit, fenced in a very tiny plastic box, will be placed into a bag or purse. alittle magnet is placed near the reed switch and connected to the hand or the garments of the person carrying the bag by means that of a small twine. If the bag is snatched dead, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts periodical and therefore the speaker system emits a loud alarm sound. A complementary transistor-pair is wired as a high potency generator, directly driving alittle speaker system. Low part-count and 3V battery provide enable a really compact construction.

Parts:

R1 = 330K
R2 = 100R
C1 = 10nF-63V
C2 = 100uF-25V
Q1 = BC547
Q2 = BC327
B1 = 3V Battery or Two AA Cells in Series
SW1 = Read Switch & Small Magnet
SPKR = 8R Loudspeaker (See Notes)

Speed Alarm Circuit 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 SCRs are commoned connected to the inverting input of the remaining comparator, IC2a.

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".Electronics Circuit Application

Author: Col Edwards - Copyright: Silicon Chip Electronics Magazine

IC Using Two-Tone Siren Circuits

This circuit is intended for children fun, and can be installed on bicycles, battery powered cars and motorcycles, but also on models and various games and toys. With SW1 positioned as shown in the circuit diagram, the typical dual-tone sound of Police or Fire-brigade cars is generated, by the oscillation of IC1A and IC1B gates. With SW1 set to the other position, the old siren sound increasing in frequency and then slowly decreasing is reproduced, by pushing on P1 that starts oscillation in IC1C and IC1D.

The loudspeaker, driven by Q1, should be of reasonable dimensions and well encased, in order to obtain a more realistic and louder output. Tone and period of the sound oscillations can be varied by changing the values of C1, C2, C5, C6 and/or associated resistors. No power switch is required: leave SW1 in the low position (old-type siren) and the circuit consumption will be negligible.

 

 Circuit diagram

Parts List:

R1 = 470K - 1/4W Resistors
R2 = 680K - 1/4W Resistor
R3 = 470K - 1/4W Resistors
R4 = 82K - 1/4W Resistor
R5 = 330K - 1/4W Resistor
R6 = 10K - 1/4W Resistor
R7 = 33K - 1/4W Resistor
R8 = 3.3M - 1/4W Resistor

C1 = 10µF - 25V Electrolytic Capacitors
C2 = 10nF - 63V Polyester Capacitors
C3 = 100nF - 63V Polyester Capacitor
C4 = 100µF - 25V Electrolytic Capacitor
C5 = 10µF - 25V Electrolytic Capacitors
C6 = 10nF - 63V Polyester Capacitors

D1 = 1N4148 - 75V 150mA Diodes
D2 = 1N4148 - 75V 150mA Diodes
D3 = 1N4148 - 75V 150mA Diodes

Q1 = BC337 - 45V 800mA NPN Transistor
P1 = SPST Pushbutton
B1 = 6V Battery (4 AA 1.5V Cells in series)
IC1 = 4093 - Quad 2 input Schmitt NAND Gate IC
SW1 = DPDT Switch
SPKR= 8 Ohm Loudspeaker  Electronics Circuit Application

Night Alert Circuits ..

Idea of this circuit came to me at midnight when my pet dog started barking continuously on sensing a moving shadow, perhaps that of an intruder. Dogs have a night adaptation capability to maximise the sensitivity of vision in low light. They are well adapted to see moving objects rather than stationary ones in darkness. This circuit turns a lamp ‘on’ for a short duration when the dog barks, giving an impression that the occupants have been alerted.

The condenser microphone fitted in the dog’s cage senses barking sound and generates AC signals, which pass through DC blocking capacitor C1 to the base of transistor BC549 (T1). Transistor T1 along with transistor T2 amplifies the sound signals and provides current pulses from the collector of T2.


The input trigger pulse is applied to the collector of transistor T3 and coupled by capacitor C3 to the base of transistor T4 causing T4 to cut off. The collector voltage of transistor T4 forward biases transistor T3 via resistor R8.Transistor T1 conducts and capacitor C3 discharges to keep transistor T4 cut-off. Transistor T4 remains cut-off until capacitor C3 charges enough to enable it to conduct. When transistor T4 conducts, its collector voltage goes low to drive transistor T3 into cut-off state. Resistor R9 and capacitor C3 are timing components. When fully charged, capacitor C3 takes about two minutes to discharge. So when sound is produced in front of the condenser mic, TRiAC1 (BT136) fires and the bulb (B1) glows for about two minutes.

Assembly instruction:

Assemble the circuit on a general-purpose PCB and enclose in a plastic cabinet. Power to the circuit can be derived from a 12V, 500mA step-down transformer with rectifier and smoothing capacitor. Solder the triac ensuring sufficient spacing between the pins to avoid short circuit. Fix the unit in the dog’s cage, with the lamp inside or outside as desired. Connect the microphone to the circuit using a short length of shielded wire. Enclose the microphone in a tube to increase its sensitivity.

Warning:

Since the circuit uses 230V AC, many of its points are at AC mains voltage. it could give you lethal shock if you are not careful. So if you don’t know much about working with line voltages, do not attempt to construct this circuit. EFY will not be responsible for any kind of resulting loss or damage.
Electronics Circuit Application 

Author: D. Mohan Kumar - Copyright: Electronics For You Mag

power buzzer circuits >>

How usually on the average does one ought to decision members of your family daily to inform them that dinner is prepared, it’s time to go away, and therefore the like? The person you wish is typically during a completely different area, like the hobby area or chamber. a strong buzzer within the area, combined with a pushbutton at very cheap of the steps or within the room, might be terribly handy in such things. the guts of this circuit is made by IC1, a TDA2030. This IC has inbuilt thermal protection, therefore it’s not going to quickly quit the ghost. R1 and R2 apply a voltage capable [*fr1] the availability voltage to the and input of the opamp. R3 provides regeneration. Finally, the mix of C2, R4 and trimmer P12 determines the oscillation frequency of the circuit.