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.

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 a simple and low cost dew sensor circuit that can be used to switch off any gadget automatically in case of excessive humidity. Dew (condensed moisture) adversely affects the normal performance of sensitive electronic devices.

The main part of this circuit is a low cost dew sensor element (resistor type). Although dew sensor elements are widely used in video cassette players and recorders, these may not be easily available in local market. However, the same can be procured from authorised service centres of reputed companies. The author used the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No:6808-08-04, reference no. 336) in his prototype. In practice, it is observed that all dew sensors available for video application possess the same electrical characteristics irrespective of their physical shape/size, and hence are interchangeable and can be used in this project.

This simple and low cost dew sensor circuit is basically a switching type circuit made with the help of a popular dual op-amp IC LM358N which is configured here as a comparator. (Note that only one half of the IC is used here.) Under normal conditions, resistance of the dew sensor is low (1 Kohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal. The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit.

When humidity exceeds 80%, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This will push up the output of IC1 to a high level. As a consequence, the LED inside the optocoupler is energised. At the same time LED1 provides a visual indication. The optocoupler can be used to any electronic device for switching purpose.

This circuit uses a low voltage, low current power supply unit. The diode D1, resistors R8 and R6 and capacitor C1 do the job. This simple power supply module obviates the requirement for a bulky and expensive step down transformer.

This is the simple circuit of proximity infrared detector, proximity sensor based? infrared. The applications of this circuit are the most varied. From placing it in the front door to prevent people stop in front of this circuit, or even placing it in the back and front of the car to warn other drivers when they get too close to the park.

The circuit operation is based on emitting a burst of infrared light signals which bounce off the close object is received by another component. When received the system detects proximity with the LED output is activated (shines).

The integrated circuit is a generator / decoder tones that well meets the needs of this design. Both the photodiode and phototransistor be situated with units suitable approach to improve the range. With simple LED reflectors are available scope of the order of meters. With convex lens can cover distances of five meters. It is convenient to sacrifice some range but placing UV filters and SUNLIGHT which do not let the phototransistor (receiver element) sunlight.

The power of this circuit can be any voltage between 5 and 9 volts.

To drive external circuitry will suffice to replace the LED by an optocoupler, which actuated by means of its internal transistor circuit to be controlled.

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.

All distances mentioned before can vary, depending on infra-red transmitting and receiving LEDs used and are mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device sensitivity.

Simple Explanation:

• The Q1 photo detector picks-up the infrared beam generated by IR LED1 and IR LED2 and reflected by the surface placed in front of it.
• IR LED1, IR LED2 and Q1 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. Q1 picks-up the infra-red beam which generated by IR LED1 and IR LED2, and reflected by the surface placed in front of it.
• If there is a obstacle the IR beam will radiate back to the IR sensor and the 20KHz modulated signal is given to the pin3 of LM567 through photo Darlington transistor, at this point the pin8 of the LM567 is turned to low and also gets locked to detect the 20Khz signal. By this the LM555 is turned low and disabled by this the led will remain lighting and buzzer makes the continuous sound to alert the driver.

Mount this car parking guard circuit at the back bumper and placed at the center. The piezobuzzer and LED indicator should be placed on the dashboard so the driver able to hear the sound alert clearly and can clearly see the indicator LED.

Make the connection to the reverse indicator light and the circuit in parallel and beware of the polarity (not to reserve).

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

Some application may use this circuit such as robot applications, body height measurement, blind shoes, etc.

How the circuit works:

The transmitter emits an ultrasonic signal (40kHz). The 555 timer chip of the transmitter provides the driving 40kHz signal. Every time the reset pin (pin4) of the 555 timer goes high, a resulting signal of 40kHz on pin 3 is used to drive the ultrasonic transducer. Then, the receiver simply listens for the return echo after it bounces off an object. The small echo signal, when detected, is amplified 1000 times using a standard operational amplifier (LM741 op-amp). The signal is then fed into a tone decoder (LM567) set to lock onto a 40kHz signal. The output of the tone decoder is HIGH when no echo is heard and swings LOW when an echo is detected. The output from the tone decoder can now be fed into a microcontroller or some other type of IC to determine when an echo was received. To help minimize false triggering, the output is fed into a voltage comparator set to trigger at the appropriate level. The LED at the output of the comparator acts as a visual indicator when an echo is detected (very useful when debugging). The typical range of this system is from a few inches to 5-6 feet, depending on the quality of the components, shielding, and most important, tuning.

Detailed explanation about this ultrasonic distance detector circuit: visit this page

Or download this documentation:

Kam Leang Robotics - Sonar Ranging System

1 file(s) 37.68 KB

Download Documentation

This is the circuit diagram of 230V automatic night lamp based photo resistor to sensing the light environment. When the condition is dark enough, the one or more lamps will be turned on and when the condition is bright enough, then the lamps will be turned off.

Q1 and Q2 form a trigger device for the SCR, providing short pulses at 100Hz frequency. Pulse duration is set by R2 and C1.

When the light hits? the photo resistor (R1) then it will has very low resistance value, almost shorting C1 and preventing circuit operation. When R1 is in the dark, its resistance value becomes very high thus enabling circuit operation.

Circuit Notes:

• Variable Resistor R3 used for fine setting of operating threshold and R2 value can be raised to 150K maximum.
• Several lamps can be connected in parallel to the circuit, but total power dissipation of the load should not exceed about 300 – 500W.
• PL1 can be omitted and the input mains supply wires connected in parallel to any switch controlling lamps. In this case, if the switch is left open, the circuit will be able to drive the lamps; if the switch is closed, the lamps will illuminate and the circuit will be by-passed.

Parts List:
R1 = Photo resistor (any type)
R2 = 100K 1W Resistor
R3 = 200K 1/2W Trimmer Cermet
R4,R7 = 470R 1/4W Resistors
R5 = 12K 1/4W Resistor
R6 = 1K 1/4W Resistor
C1 = 10nF 63V Polyester Capacitor
D1 = TIC106D 400V 5A SCR
D2-D5 = 1N4007 1000V 1A Diodes
Q1 = BC327 45V 800mA PNP Transistor
Q2 = BC337 45V 800mA NPN Transistor
SK1 = Female Mains socket
PL1 = Male Mains plug & cable

This circuit come from redcircuit.com

Attention! The circuit is directly connected to 230Vac electric mains, then some components in the circuit board are subjected to lethal potential with high risk!. Avoid touching the circuit when plugged and enclose it in a plastic box for security purpose.

This is the circuit diagram of Clap On / Off Switch. The circuit allows you to operate your lighting or any circuit device which use 24V / 3A maximum supply, simply by clapping your hands.?It has a relay output that can be used to turn external devices on/off.? This circuit is good and ideal for disabled or elderly people.

Circuit Features:

• good immunity against surrounding noises
• ‘1-clap’ or ‘2-clap’-mode selection
• ‘2-clap’-mode features built-in safety turn-off timer (approx. 5h)
• output relay ‘pulse’ or ‘toggle’ selection
• microprocessor-controlled
• output relay with LED indicator

Circuit Specifications:

• Supply 12Vdc / 150mA i.e. mains adapter (Order Code 660.446UK)
• Outputs 1 x SPDT Relays
• Output Load 3 Amps @ 24V max.

Notes:

• This circuit available in kit, you can order the kit at quasarelectronics.co.uk, the circuit copyright belongs to them.
• To switch 220V AC, you may try to find suitable relay meet your requirement.