P1 is of experimental value. Start with 220 Ohms or so and modify to suit your needs. The transistor is a general purpose kind and is not critical, almost any pnp type will work. L1 is a bell-transformer which is usually already present in the house. If you wish, you could use a battery instead of the bell transformer. Just hookup a 9-volt battery to points “A” and “B” (A=+) the diode (D1) is to protect the circuit from accidental polarity reversal and is optional, but required for use with the bell transformer.

T1 is a General Purpose PNP transistor and probably anything will work. L2 comes out of an old am transistor radio. They look like miniature transformers and are usually colored red or green. You have to fiddle with different transformers as the sound can vary depending on the value. The loudspeaker is a 8 Ohm type and must be larger than 200milli-Watt. I used a 2 Watt type, but anything over 0.2 Watt will do. It really sounds like a bird and when you release the doorbell button the sound slowly fades away. I have used this circuit in my house for over 20 years and even build the “Birdie” for others. Although
an old circuit, the experimentation and the final results still give a punch. Having fun..!

How the Simple Smoke Alarm Works

If no smoke presence around the device, the gap of photo interrupter module is clear and the light from LED falls on the phototransistor through the slot. As a result, the collector of phototransistor is pulled towards ground. This causes reset pin 4 of IC 555 to go low. Accordingly, the timer is reset and hence the alarm does not sound.

However, when smoke is present in the gap of the photo interrupter module, the light beam from LED to the phototransistor is obstructed. As a result, the phototransistor stops conducting and pin 4 (reset) of IC 555 goes high to activate the alarm.

Take a note that this simple smoke alarm must be housed inside an enclosure with holes to allow the smoke to enter the box.

This is a low cost, simple, yet a surprisingly powerful electronic siren powered by just a 9V battery. The circuit may provide the final circuit block module in an alarm circuit using a relay to activate it.

How The Simple Electronic Siren Work

When the switch is pressed C3 charges up through R4 with a time constant of 0.47 seconds. When the switch is released C3 begins a slower discharge through R7 and R3 with a time constant of about 5 seconds. The op amp is set up as a voltage controlled oscillator. The control voltage in this simple electronic siren circuit is the exponential rise and fall in the voltage of C3 as it charges and discharges.

When the output of the oscillator (pin 7) switches low, there is a charge remaining on C1 which holds pin 5 below the switching point. Current through R7 is proportional to the control voltage on C3. This current discharges C1 causing the voltage on pin 5 to rise towards the switching point at a rate proportional to the voltage on C3. When the switching point is reached pin 7 switches high, and initially pulls pin 6 high via C1. This causes the op amp to temporarily turn on hard. But C3 quickly recharges through D2 causing the voltage on pin 5 to fall below the switching point and causing the op amp to switch off again.

The positive pulse output from the op amp puts a fixed amount of charge into C2 slightly raising the potential of pin 6. This causes the potential on pin 6 to rise and assist the sharp switch off of the op amp. Also R5 & C2 delay the rise on pin 6 long enough to get a good output pulse.

The cycle then repeats. However, during the C3 discharge cycle the rate of charge of C1 is lower with each repetition of the oscillator (because the control voltage is lower) and the output frequency is correspondingly lower. During the C3 charge cycle the reverse applies.

The output pulses are buffered by a second op amp then the current is applied to a driver transistor. The output waveform has a low duty cycle, but gives a surprisingly loud sound.

The kit of this simple electronic siren based LM358 is available. Download the PDF version, part list included there…

PDF Manual Simple Siren Circuit Kit

1 file(s) 33.49 KB

Download

Here the circuit design of vibration sensor alarm. Initially, when power switch S1 is flipped to “on” position, power indicator LED1 lights up immediately. IC LM555 (IC1), wired as a simple latch circuit with control input, is powered and R-C components R4 and C5 connected at its reset pin 4 force the latch to standby mode (with inactive low output). The circuit is driven into sleep mode.

As soon as vibration is detected, MOSFET T1 is fired by the positive-going pulse output from the vibration sensing mechanism built around piezo-ceramic wafer and associated components. As a result, control input pins 2 and 6 of IC1 latch are grounded. Output pin 3 of IC1 now goes high. The positive supply from output pin 3 of IC1 is extended to three-tone siren generator UM3561 (IC2) through R5, D1 and R6. Components R6 and ZD1 stabilise the input power supply of IC2 to around 3.3V. Output signals from IC2 are amplified by Darlington-pair transistors T2 and T3 to produce alert tone (police siren sound) via loudspeaker LS1.

Reset switch S1 can be used to switch off the alarm sound by resetting the latch circuit. For safety, use key-lock type switches for S1 and S2. A relay can also be connected at the output socket (SOC1) of the circuit to energise high power beacons, emergency sirens and fence electrification units.

The smart vibration sensor alarm circuit powered with a 9V DC power supply. A compact PP3-/6F22-type alkaline battery can be used to power the circuit.

This is the circuit diagram of 70W OCL power amplifier with output power of 70 watts single channel. It uses power transistor TIP2955 and TIP3055 as main component. The power supply used for this amplifier is a symmetrical / dual polarity power supply with output voltage 25V – 32V. This amplifier dan be used to drive the 4-16 Ohms loudspeaker. For stereo sound system application, you need to make two similar circuit and use 5A transformer for power supply.

What is OCL Amplifier?

An OCL amplifier (output capacitor-less amplifier) is any audio amplifier with direct-coupled capacitorless output. Typically, OCL amplifiers can be any of several amplifier classes, and typically have a push-pull output stage (wikipedia).

Advantages of OCL amplifiers over capacitor-coupled amplifiers include:

1. Avoiding the cost and bulk of an output capacitor
2. better immunity to motorboat oscillation
3. larger output power at very low frequencies and DC

I wish you luck with this 70W OCL power amplifier project.

Initially, when the water level is below the L1 strip, supplying electrical oscillation frequency is not transferred to the diode D1. Thus the low output and LED1 does not light. Also, because the base voltage of the transistor T1 is low, it is in a state of cut-off and the collector voltage is high, which enables to produce melody IC1 (UM66) and the alarm is sounded.

When the water is just touching the L1 level detector strip, the oscillation frequency of the supply transferred to the diode D1. This straightening supply voltage and positive DC voltage developing capacitor C1, which is lit LED1. At the same time the base voltage of the transistor T1 becomes high, which makes forward bias and collector voltage falls to near ground potential. Disabling IC1 (UM66) and the alarm is inhibited.

Depending on the quantity of water present in the tank, which shows the level of the corresponding LED lights up. It thus showing medium level of water in the tank with a bar-chart style.

When the water in the tank just touching the highest level detector lines L12, DC voltage developed in capacitor C2. This makes it possible to produce a melody IC1 (UM66) and the alarm sounds again.

Here is the simple and low cost light alarm circuit built using timer IC 555 as the sound generator and a LDR to sense the environment light. This alarm is activated when the light beam on the LDR photocell is interrupted (You can use the light of a flashlight bulb which will make you a source for remain on, this may be 3 volts, no matter whether AC or DC).

Components List:

Capacitor:
C1: .1 uF

Resistor:
R1: 100K (potensiometer)
R2: 1K
R3: 47K
R4: 100K
R5. 27 ohm
R6: 220 ohm

Semiconductor:
IC1: 555
TR1: 2N3055, C1060 or C1226
D1: 1N4002

Others:
Speaker 8 or 16 ohms
1 LDR / photocell

When the LDR / photocell is receiving light, has low resistance, thus blocking the positive voltage that gives R4 to terminal 4 of IC 555, maintaining multivibrator off and the speaker does not sound when the photocell stops receiving light, its resistance increases in fraction seconds, which makes it reaches the above positive voltage to the terminal, which activates the alarm.

Circuit Note: The LDR should not receive another light than that which serves to activated.

This is the circuit diagram of car audio system anti theft security which can be effectively used to protect and secure your expensive car audio system from stealing. This simple circuit designed based on popular CMOS NAND chip CD4093,.

When the circuit is switched on via switch S1, the indicator LED1 will glow and the circuit state will be in the standby mode. LED inside optocoupler IC1 is lit as the cathode terminal is connected through the car audio (amplifier) body. As a result, the output at pin 3 of gate N1 goes low and disables the rest of the circuit.

Whenever an attempt is made to remove the car audio from its mounting by cutting its connecting wires, the optocoupler immediately turns off, as its LED cathode terminal is hanging. As a result, the oscillator circuit built around gates N2 and N3 is activated and it manages the “on” / “off” timings of the relay via transistor T2. (Relay contacts can be used to energize an emergency beeper, indicator, car horns, etc, if desired.)

Change the values of capacitor C2 to get different “on” / “off” timings for relay RL1 to be “On” / “Off”. With 100uF we get about 5 seconds as “on” and 5 seconds as “off” time. You may make your own experiments as needed.

Gate N4, with its associated components, forms a self-testing circuit. Normally, both of its inputs are in “high” state. However, when one switches off the ignition key, the supply to the car audio is also disconnected. Thus the output of gate N4 jumps to a “high” state and it provides a differentiated short pulse to forward bias transistor T1 for a short duration. (The combination of capacitor C1 and resistor R5 serves as the differentiating circuit.)

As a result, the buzzer in the collector terminal of T1 beeps to announce for a short duration that the safety circuit is intact. This period of “on” ring can be varied by changing the values ??of the capacitor C1 and / or resistor R5.

After construction, fix the LED and buzzer in dashboard as per your requirement and hide switch S1 in a in a convenient place. Then connect lead A to the body of car stereo (not to the body of vehicle) and lead B to its positive lead terminal. Take power supply for the circuit from the car battery directly.

Warning: This design is meant for car audios with negative ground only.

This is the electronic circuit diagram of aquarium temperature probe capable to monitor the temperature of water and indicate the rise in temperature through audio-visual indicators. This circuit uses diode 1N34 as the temperature sensing probe. The resistance of the diode will be vary depends on the temperature in its vicinity.

The environmental factors including light and temperature affect fish culture. The temperature of water has profound effect because fish cannot breed above or below the critical temperature limits. Temperature between 24?C and 33?C is found to be the best to induce spawning in fishes. This particular temperature range is also necessary for the healthy growth of nursery fish fries (young fishes). Rise of water temperature due to sunlight may adversely affect the fish rearing process.

How the circuit work:

The diode 1N34 sense the temperature of the water in aquarium. Typically, the diode can generate around 600 mV when a potential difference is applied to its terminals. For each degree centigrade rise in temperature, the diode generates 2mV output voltage. That is, at 5C, it is 10 mV, which rises to 70 mV when the temperature is 35?C. This component is exploited in the circuit to sense the temperature variation in aquarium water.

Since the output from the diode sensor is too low, a high-gain inverting DC amplifier is used to amplify the voltage. CA3140 (IC1) is the CMOS version op-amp that can operate down to zero-volt output. The highest output available from IC1 is 2.25V less than the input voltage at pin 7. With resistor R4 and VR2, the variation in diode voltage can be amplified to the required level. Resistor R1 restricts current flow through diode D1 and preset VR1 (1-kilo-ohm) sets the input voltage at pin 3. IC3 (7805) provides regulated 5 volts to the inputs of IC1, so that the input voltage is stable for accurate measurement of temperature.

The output from IC1 is fed to display driver LM3915 (IC2) through preset VR3 (50-kilo-ohm). With careful adjustments, the wiper of VR3 can provide 0-400 millivolts to the input of IC2. The highly sensitive input of IC2 accepts as low as 50 mV if the reference voltage at its pin 7 is adjusted using a variable resistor. To increase the sensitivity of IC2, preset VR4 is connected at one end to ‘reference voltage end’ pin 7 and its wiper is connected to ‘high end’ pin 6 of the internal resistor chain.

When approximately 70 mV is provided to the input of IC2 by adjusting preset VR3, LED1 (green) lights up to indicate that the temperature is approximately 35?C, which is the crossing point. When the input receives 100 mV, LED2 (red) lights up to indicate approximately 50?C. Finally, the buzzer starts beeping if the input receives 130 mV corresponding to a temperature of 65?C.

In short, LEDs and the buzzer remain standby when the temperature of the water is below 35?C (normal). With each step increase of 30 mV in the input (corresponding to 15?C rise in temperature), LEDs and the buzzer become active.

Pin 16 of IC2 is used to drive the piezobuzzer through transistor T1. When pin 16 of IC2 becomes low, T1 conducts to beep the piezobuzzer. Resistor R7 keeps the base of transistor T1 high to avoid false alarm. IC4 provides regulated 9V DC to the circuit.

Build the circuit on a common PCB and mount in a suitable box. Glass signal diode D1 is immersed in water to sense the temperature of water. Its leads should be coated with enamel paint to avoid shorting in water. Alternatively, enclose the diode in a small glass tube or test tube having sufficient internal space to fit the diode. Make the sensor assembly waterproof using wax or other method to ensure there is no short circuit because of the water.

Take care while calibrating and setting the circuit. With 5V DC supply to diode D1 and an ambient temperature of about 35?C, D1 generates around 70 mV. Adjust VR3 until the voltage in its wiper increases to 70 mV, so that the input of IC2 (pin 5) receives 70 mV corresponding to the diode output voltage at 35?C. At this stage, green LED1 should turn on. If it doesn’t, adjust VR4 until LED1 just lights up. Immerse the diode in temperature adjusted hot water (35?C) and adjust VR3 and VR4 until green LED1 lights up. Increase the water temperature to 50?C by adding hot water. Now red LED2 will glow. At this position, the voltage at pin 6 of IC1 will be around 100 mV. When the temperature of water increases further to 65?C, the buzzer starts beeping. After calibration, immerse the diode assembly in the aquarium tank just below the water surface and fix it permanently to avoid floating.

Source: EFY Mag
Good luck

This laptop / notebook protector is powered by a 12V miniature battery used in remote control devices. IC TLO71 (IC1) is used as a voltage comparator with a potential divider comprising R2 and R3 providing half supply voltage at the non-inverting input (pin 3) of IC1. The inverting input receives a higher voltage through a water-activated tilt switch only when the probes in the tilt switch make contact with water.

When someone tries to take the laptop case, the unit takes the vertical position and the tilt switch breaks the electrical contact between the probes Immediately the output of IC1 becomes high and monostable IC2 is triggered. The low output from IC2 triggers the pnp transistor (T1) and the buzzer starts beeping. Construct the circuit as compactly as possible so as to make the unit matchbox size.

Make the tilt switch using a small (2.5cm long and 1cm wide) plastic bottle with two stainless pins as contacts. Fill two-third of the bottle with water such that the contacts never make electrical path when the tilt switch is in vertical position. Make the bottle leak-proof with adhesive or wax. Fix the tilt switch inside the enclosure of the circuit in horizontal position.

Fit the unit inside the laptop case in horizontal position using adhesive. Use a miniature buzzer and a micro switch (S1) to make the?compact gadget with this circuit. Maintain the laptop case in horizontal position and switch on the unit. Your laptop / notebookis now protected from stealing.