USB LED Lamp circuit.

USB LED Lamp circuit.

USB Lamp Circuit Description. Here is a simple USB powered lamp that can be used to light your desktop during power failures. The circuit operates from the 5 Volt available from the USB port.The 5V from the USB port is passed through current limiting resistor R2 and transistor Q1. The base of transistor Q1 is grounded via R1 which provides a constant bias voltage for Q1 together with D2.The diode D1 prevents the reverse flow of current from battery.C1 is used as a noise filter.Two white LED’s are used here for the lamp, you can also use a 2 V torch bulb instead of LED’s. LED D3  indicates connection with USB port.

• USB port is only able to provide up to 100 mA current.So don’t overload the circuit with more no of LED’s.
• Before wiring the circuit confirm the positive and ground leads of USB by a multimeter.
• Switch S1 can be used to turn on the lamp.

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MOBILE INCOMING CALL INDICATOR

Description. This circuit can be used to escape from the nuisance of mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated. When a call is coming to the mobile phone, the transmitter inside it becomes activated. The  frequency of the transmitter is around 900MHz.The  coil L1 picks up these oscillations by induction and feds it to the base of Q1. This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at  its output pin (pin 3) to blink. The blinking of the LED is the indication of incoming call.

Notes. 

• The coil L1 can be made by making 150 turns of 36 SWG enameled copper wire on a 5mm dia plastic former.Or you can purchase a 10 uH coil from shop if available.
• The circuit can be powered from a 6V battery.
• Assemble the circuit on a good quality PCB.
• C1 & C3 are to be polyester  capacitors.
• The electrolytic capacitor C2 must be rated 10V.

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Infrared intrusion barrier

Description.

Here is the circuit diagram of an infrared intrusion detector. Whenever a trespasser cuts the invisible infrared beam an alarm sound will be raised. The arrangement consists of a receiver circuit and a transmitter circuit.

The transmitter circuit is based on two TLC555 ICs (IC1 and IC2). The first 555 (IC1) is wired as an astable multivibrator operating at 300Hz.The second 555(IC2) is also wired as an astable multivibrator operating at 36 KHz which can be adjusted by using POT R4.The output of IC1 is given to the reset pin of IC2. So the output of IC2 will be a burst of 36 KHz pulses modulated by a 300Hz signal. In simple words, the output will be a burst of 36KHz pulses with a spacing of 3mS in time. This signal is fed to the base of Q1 which drives the IR LED to transmit the waveform.

The receiver stage is based on a TSOP1836 (IC1) IR receiver and a TLC555C timer IC1. When the IR signal is falling on the TSOP1836, its output will be low and this prevents the TLC555C from oscillating. This is because the output of TSOP1836 is connected to the reset pin of TLC555C and this makes the reset pin low as long there is IR waveform falling on the receiver .When the IR waveform is cut by a passing intruder, output of IC1 goes high and makes the IC2 to start oscillation. The piezo buzzer connected at the output of IC2 sound to indicate the intrusion.

Circuit diagram (Transmitter and Receiver).

Notes.

• Transmitter and receiver can be powered from 5V DC.
• TLC555 ICs must be mounted on holders.
• Adjust POT R4 to get exactly 36KHz.The TSOP1836 responds only to 36KHz IR signals. So this part is very important.
• Transmitter and receiver must be assembled on two different PCBs.

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INFRARED MOTIN DETECTOR

Description.

Here is the circuit diagram of an infrared motion detector that can be used to sense intrusions.Infra red rays reflected from a static object will be in one phase, and the rays reflected from a moving object will be in another phase.The circuit uses this principle to sense the motion.

The IC1 (NE 555) is wired as an astable multivibrator .The IR diode connected at the output of this IC produces infrared beams of frequency 5Khz.These beams are picked by the photo transistor Q1 .At normal condition ie; when there is no intrusion the output pin (7) of IC2 will be low.When there is an intrusion the phase of the reflected waveforms has a difference in phase and this phase difference will be picked by the IC2.Now the pin 7 of the IC 2 goes high to indicate the intrusion.An LED or a buzzer can be connected at the output of the IC to indicate the intrusion.

Circuit diagram with Parts list.

Notes.

• Comparators IC2a and IC2b are belonging to the same IC2 (LM1458).So the power supply is shown connected only once.No problem.
• When there is disturbance in the air or vehicles passing nearby,the circuit may get false triggered.
• POT R5 can be used for sensitivity adjustment.

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12v&5v combo power supply

Description.

This is a simple approach to obtain a 12V and 5V DC power supply using a single circuit. The circuit uses two ICs 7812(IC1) and 7805 (IC2) for obtaining the required voltages. The AC mains voltage will be stepped down by the transformer T1, rectified by bridge B1 and filtered by capacitor C1 to obtain a steady DC level .The IC1 regulates this voltage to obtain a steady 12V DC. The output of the IC1 will be regulated by the IC2 to obtain a steady 5V DC at its output. In this way both 12V and 5V DC are obtained.

Such a circuit is very useful in cases when we need two DC voltages for the operation of a circuit. By varying the type number of the IC1 and IC2, various combinations of output voltages can be obtained. If 7806 is used for IC2, we will get 6V instead of 5V.Same way if 7809 is used for IC1 we get 9V instead of 12V.

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a good quality PCB or common board.
• The transformer T1 can be a 230V primary, 15V secondary, 1A step-down transformer.
• The fuse F1 can be of 1A.
• The switch S1 can be a SPST ON/OFF switch.
• The LED D1 acts as a power ON indicator.
• If 1A bridge B1 is not available, make one using four 1N4007 diodes.
• 78XX series ICs can deliver only up to 1A output current.

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MAINS OPERATED LED CIRCUIT

This is a modified version of the circuit Super bright LED Night Light published here.

This is the circuit of a well tried and reliable 230 Volt AC mains operated 24 LEDs (super bright 50mA LEDs). While practically compare the brightness between this circuit and 11watts tube, the LED light is much better. The layout is made in such a way, you get uniform illumination. A photograph of the cicuit is also given in this post.

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FREQUENCY TO VOLTAGE CONVERTER

Description.
LM331 is basically a precision voltage to frequency converter from National Semiconductors. The IC has a hand full of applications like analog to digital conversion, long term integration, voltage to frequency conversion, frequency to voltage conversion. Wide dynamic range and excellent linearity makes the IC well suitable for the applications mentioned above.
Here the LM331 is wired as a frequency to voltage converter which converts the input frequency into a proportional voltage which is extremely linear to the input frequency. The frequency to voltage conversion is attained by differentiating the input frequency using capacitor C3 and resistor R7 and feeding the resultant pulse train to the pin6 (threshold) of the IC. The negative going edge of the resultant pulse train at pin6 makes the built-in comparator circuit to trigger the timer circuit. At any instant, the current flowing out of the current output pin (pin 6) will be proportional to the input frequency and value of the timing components (R1 and C1). As a result a voltage (Vout) proportional to the input frequency (Fin) will be available across the load resistor R4.

Circuit diagram.

Notes.

• The circuit can be assembled on a vero board.
• I used 15V DC as the supply voltage (+Vs) while testing the circuit.
• The LM331 can be operated from anything between 5 to 30V DC.
• The value of R3 depends on the supply voltage and the equation is R3= (Vs – 2V)/ (2mA).
• According to the equation, for Vs = 15V, R3=68K.
• The output voltage depends on the equation, Vout = ((R4)/(R5+R6))*R1C1*2.09V*Fin.
• POT R6 can be used for calibrating the circuit.

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LIGHT TO FREQUENCY CONVERTER

Introduction.

Here is the circuit diagram of a effective light to frequency converter circuit that can be used for variety of applications such as light intensity measurement,fun etc.

The circuit is based on TLC555, the CMOS version of famous timer IC NE 555. A photo diode is used for sensing the ligt intensity.The timer IC is wired in astable mode.The leakage current of the reverse biased photo diode is proportional to the light intensity falling on it.This leakage current charges the capacitance C1.When the capacitor voltage reaches 2/3 of the supply voltage the out put (pin 3) goes low.As a result the capacitor discharges through photo diode .When the capacitor voltage reaches 1/3 the supply voltage the out put (pin 3) of IC goes high.This cycling continues and we get a frequency at pin 3 proportional to the light intensity falling on the photo diode.

Circuit Diagram & Parts List.

Notes.

• With the given components the frequency varies from 1KHZ @ complete darkness to 24 Khz @ bright sunlight.The frequency range can be changed by using different values for C1.
• Use any general purpose photo diode for D1.

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CABLE TV AMPLIFIER

Description.
This is a very simple cable TV amplifier using two transistors. This amplifier circuit is most suitable for cable TV systems using 75 Ohm coaxial cables and works fine up to 150MHz. Transistor T1 performs the job of amplification. Up to 20dB gain can be expected from the circuit.T2 is wired as an emitter follower to increase current gain.

Circuit diagram.

can be assembled on a Vero board.

Use 12V DC for powering the circuit.

Type no of the transistors are not very critical.

Any medium power NPN RF transistors can be used in place of T1 and T2.

This is just an elementary circuit. Do not compare it with high quality Cable TV amplifiers available in the market.

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plant moisture level monitor

Description.

Here is a simple circuit that will give a visual indication when the soil water level inside your flower pot goes low below a certain limit.

The U1C and associated components are wired as an oscillator producing a 2KHz square wave. This square wave is given to one gate input of U1D via a variable potential divider former by R1 and R2.When the resistance across the probes A and B are low that is when soil moisture level is high, the C2 will divert the square wave to ground. The output of U1D will be high. The U1 A inverts this high state to low and so the IC U1B is blocked from producing oscillations. The LED will remain OFF. When there is no moisture across the probes, the C2 cannot bypass the 2KHz signal to the ground and it appears at the gate input of U1D.The output of U1D goes low, and it is inverted to high by U1A.The oscillator wired around U1B is activated and it starts oscillating. These oscillations are amplified by Q1 to drive the LED and LED starts pulsating as an indication of low moisture. Since square wave is used there won’t be any oxidation on the probes. The resistor R7 limits the current through LED and ensures a longer battery life.

Circuit diagram with Parts list.

Notes.

• Power the circuit from a 3V battery.
• Two metal wires 10 cm long and 5cm apart driven into the soil will do the job for probes.
• The probes are to be connected at the terminals A and B shown in circuit.
• Capacitors C1 and C2 must be polyester type.
• The IC U1 is a quad two input Schmitt NAND IC 4093.
• The sensitivity can be adjusted by varying the preset R2.
• Mount the IC on a holder.

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watch dog for telephones

Watch-Dog for Telephones
Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap/misuse indications. Quite often they do not offer guaranteed protection against unauthor-ised operation. A very simple and uni- que circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described here. This little circuit keeps continuous watch over the telephone lines and sounds an alarm in case of any misuse. In addition it transmits a loud tone through the telephone lines to prevent further misuse. When switch S1 is turned on, the normal (on-hook) telephone line voltage at the output of bridge-rectifier diodes D1 to D4 is approximately 48 volts, which being well above the break-down voltage of zener diode D5, the diode conducts. As a result transistor T2 gets forward biased. This effectively grounds the base of transistor T1 which is thus cut off and the remaining circuit does not get any power supply. In this state, only a small (negligible) current is taken by the circuit, which will not affect the telephone line condition. However, when handset of any telephone connected to the telephone lines is lifted (off-hook), line voltage suddenly drops to about 10 volts. As a result, transistor T2 is switched off and transistor T1 gets forward biased via resistor R1. Now, the astablemultivibrator built around timer IC1 starts oscillating and the speaker starts sounding. Output of the astable multivibrator is also connected to the base of transistor T1 through capacitor C5. As a result, only a loud (and irritating) tone is heard in the ear-piece of the unauthorised telephone instrument. This circuit can be constructed on a veroboard using easily available low-cost components and it can be connected to any telephone line without the fear of malfunctioning. No extra power supply is required as it draws power from the telephone line for operation. Note: Please disconnect the gadget when you are yourself using the telephone as it cannot distinguish between authorised and unautho- rised operation

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anemometer

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circuit to generate surround sounds

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SESMIC SENSOR

Here is a simple sensor which can detect the seismic vibrations caused by a person or large animal walking nearby. A representative application for the sensor is a deer repellent for the vegetable garden. When a deer steps near the sensor a loud buzzer or beeper sounds for a few seconds startling the would-be vegetable thief away. The sensor also makes an effective intruder detector to catch trespassers as soon as they step on the property!
Deer Repellent/ Seismic Sensor :

The unit is designed to consume minute amounts of power to provide many months of unattended protection (practically set by the battery shelf life). The seismic sensor is built from an ordinary 2 inch speaker by gluing a mass to the speaker cone to lower its resonance frequency. A lid from a baby food jar with a little extra weight glued to the inside will work fine.
The CA3094 I.C. is an unusual op-amp consisting of a programmable transconductance amplifier connected to a darlington transistor. In this circuit the darlington is combined with a pnp transistor to form a monostable timer which determines how long the buzzer sounds. When the ground shakes, the vibration sensing speaker generates a small voltage which is amplified causing the voltage on pin 1 to go high. The darlington in the IC and the 2N4403 turn on with regenerative feedback provided by the diode. The 2N4401 turns on, powering the buzzer until the monostable resets. The circuit may be used to activate a variety of devices including a relay to control line voltage devices, a transmitter to telemeter an alarm from a remote location, a battery- powered walkway light, or even one of those battery powered squirt guns! The output transistor may be replaced with a power darlington transistor for directly controlling higher current loads. The circuit may be built into ordinary plumbing PVC pipe or practically any weatherproof enclosure. A larger detection area may be accomplished by burying a long pole or PVC pipe just below the surface of the ground with the seismic sensor located above the pole. Vibrations will readily travel down the pole whenever a footstep occurs anywhere along its length. The seismic sensor may be replaced with other sensors for different applications. A photocell/ resistor divider will sense changes in light level, a microphone will sense fairly low sound levels, and a diode detector will sense a low-level RF field.

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VIDEO ACTIVATED RELAY

This simple circuit from the May 1996 Think Tank column of Popular Electronics activates a relay when it senses a composite video signal. This allows you to use the tuner built into your VCR to turn on and off older TVs that are not equipped with a remote. It can also be used to activate surround sound equipment, turn off the room lights, turn on video game consoles, etc. For such a simple circuit, it is very versatile.

Parts
Part
Total Qty.
Description
Substitutions
R1, R2
2
10K 1/4 W Resistor
R3
1
1K 1/4 W Resistor
R4
1
33K 1/4 W Resistor
C1
1
1uF Electrolytic Capacitor
Q1, Q2, Q3
3
2N2222 NPN Transistor
2N3904 NPN Transistor
D1, D2, D3
4
1N4148 Diode
K1
1
9V Relay
J1
1
RCA Jack
MISC
1
Case, wire, board

Notes
Since you may be using this circuit to switch mains voltage, it should be enclosed in a case.
The circuit will also work with most line level audio, although you may have to adjust the value of R1.

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