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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SIMPLE WATER LEVEL INDICATOR

Description This is the circuit diagram of a simple corrosion free water level indicator for home and industries.In fact the the level of any conductive non corrosive liquids can be measured using this circuit.The circuit is based on 5 transistor switches.Each transistor is switched on to drive the corresponding LED , when its base is supplied with current through the water through the electrode probes.
One electrode probe is (F) with 6V AC is placed at the bottom of tank.Next probes are placed step by step above the bottom probe. When water is rising the the base of each transistor gets electrical connection to 6V AC through water and the corresponding probe.Which in turn makes the transistors conduct to glow LED and indicate the level of water.The ends of probes are connected to corresponding points in the circuit as shown in circuit diagram.Insulated Aluminum wires with end insulation removed will do for the probe.Arrange the probes in order on a PVC pipe according to the depth and immerse it in the tank.AC voltage is use to prevent electrolysis at the probes.So this setup will last really long.I guarantee at least a 2 years of maintenance free operation.That’s what I got and is still going.

Components
T1 – T5 BC 548 or 2N2222 Transistors
R1-R5 2.2K 1/4 W Resistors
R6-R10 22K 1/4 W Resistors
D1 – D5 LED’s ( color your choice)
Notes
Use a transformer with 6V 500 mA output for power supply.Do not use a rectifier! we need pure AC. Use good quality insulated Aluminum wire for probes.If Aluminum wires are not available try Steel or Tin.Copper is the worst.Try the circuit first on a bread board and if not working properly, make adjustments with the resistance values .This is often needed because conductivity of water changes slightly from place to place.
Circuit Diagram and Sensor Arrangement

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SIMPLE LIE DETECTOR

Simple Lie Detector
Here's a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It is not as sophisticated as the ones the professionals use, but it works. It works by measuring skin resistance, which goes down when you lie.


CIRCUIT DIAGRAM :

Details of Parts
Here are the details of the specific parts you will needPart Total Qty. Description Substitutions
R1 33K 1/4W Resistor R2 5K Pot R3 1.5K 1/4W Resistor C1 1uF 16V Electrolytic Capacitor Q1 2N3565 NPN Transistor M1 0-1 mA Analog Meter MISC 1 Case, Wire, Electrodes (See Nots)Notes1. The electrodes can be alligator clips (although they can be painful), electrode pads (like the type they use in the hospital), or just wires and tape. 2. To use the circuit, attach the electrodes to the back of the subjects hand, about 1 inch apart. Then, adjust the meter for a reading of 0. Ask the questions. You know the subject is lying when the meter changes.

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HI-FI DX BASS CIRCUIT

Description.

Here is the circuit diagram of a passive DX bass circuit that can be used with almost all audio amplifiers.

comments on the circuit : The circuit that I have designed is a passive one but you can make it an active one by adding a pre amp at the output. The first stage acts as a main tone stage. It balances the bass and the treble. The 0.01 cap is for high frequency while the 0.22uF cap is for low frequency. The second stage is for sound compression. the caps works the same as at the first stage only that they are there to start the sound compression that is received from the input stage. The 2.2k resistor delays the sound thereby multiplying the compression. The 10k variable resistor is there used to tune the compression depending on the frequency of the speaker. If you are using 4 to 6 inches hi-fi speakers, I advise you to keep the 10k variable resistor at 0 ohm. The circuit is not copyrighted and you can change it to suit your requirement. All I ask is to be posting the updates of the circuit design on the site.

Circuit diagram.

Circuit diagram.

Notes.

• Assemble the circuit on a good quality PCB.
• This circuit does not require a power supply.
• POT R6 is for volume control.
• Switch S1 can be a slide switch and it is the DX Bass switch.

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FM PHONE TRANSMITTER

This project provides the schematic and the parts list needed to construct a FM Phone Transmitter. This device attaches in series to one of your phone lines. When there is a signal on the line (that is, when you pick up the handset) the circuit will transmit the conversation a short distance. In particular it will radiate from the phone line itself. It is a passive device - there is no battery. It uses the signal on the phone line for power. No aerial is needed - it feeds back the RF signal into the phone line which radiates it in the FM band. The frequency of transmission may be adjusted by the trimcap. Note that some countries may ban any electronic device which attaches to the telephone. It is the responsibility of the constructor to check the legal requirements for the operation of this FM Phone Transmitter and to obey them.

FM Phone Transmitter Schematic

FM Phone Transmitter Circuit Description

The circuit is a radio frequency (RF) oscillator that operates around 93 MHz (93 million cycles per second). Power for the circuit is derived from the full wave diode bridge. C1, C8, L3 & T1 forms the FM oscillator.

Every Tx needs an oscillator to generate the Radio Frequency (RF) carrier waves. L1, C6, T2 forms the power amplifier. Audio from the telephone

lines is coupled through R3 & C2 into the base of T1 to modulate the oscillator. This is done by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. R1 & C4 act as a low pass filter.

C3 is a high frequency shunt. L2 is call a RFC (radio frequency shunt.) It decouples the power and audio from the transmitter amplifier circuit. This type of circuit usually should be calibrated. The resonant frequency of the L1-C6 amplifier circuit should be adjusted to match the resonent oscillator frequency of C1, C9-L3. However, in practice, we think you will find that the unit operates perfectly OK as it is constructed without the need to calibrate anything. If you want to try calibration you will need a frequency meter, a CRO or just trial and error.

Calibrate by moving the coils of L1 further apart. With C1 at 27p you will find that the it tunes into the FM band in the 86 - 95 MHz area. With C1 at 22p the band is raised to about 90-95mhz (depending in the coil spacing.) If you want to move this tunable area still higher to over 100MHz range then replace C1 by a 15pF or 10pF capacitor. This assumes that the on-hook voltage is about the standard 48V. If the on-hook voltage of an extension phone network is lower, say about 39V, C1 will have to be lower in the 15p to 10p range to be in the commercial FM band in this case.

Note that you should not hold the printed circuit board physically in your hands if you try to do any calibration. Your own body capicitance when you touch it is more than enough to change the oscillation frequency of the whole unit.

You can experiment the FM Phone Transmitter to get greater transmission range away from the phone line by adding an aerial (about 150 cm of 26 gauge wire) to the collector of T2.

FM Phone Transmitter Assembly Instructions

The ZTX320 has a flat and a curved side. Match these two sides with the flat and curved sides as shown on the overlay for T2. Also note these points when assembling this project:

1) Two of the three coils have enamel insulation lacquer on them. This must be physically removed from both ends of the coil before it can be soldered. Now during the manufacture of these coils they have been solder dipped to remove this lacquer. But check each leg to see that this is the case.

2) Spread out the turns in the L3 coil about 1 mm apart. The coils should not touch.

3) A solder connection (or tap) is required from the top of the first turn in the L3 coil to the pad next to the coil. Solder a piece of wire to the top of the first turn as shown on the overlay. Then solder the other end to the pad immediately next to the L3 coil.

4) The cathodes of all diodes point to the top of the PCB.

5) Attach 3" of wire with an alligator clip on the end to the pads between the diodes marked - 'TO LINE' No aerial is needed. The phone line itself acts as a sufficient aerial. To make the Kit small, resistors & diodes stand on their ends. The kit attaches to ONE of the two phone lines going to your phone. Either of the two lines will do. In most of the world this is the green or red wire. In the UK it is one of the wires attached to the terminals 2 or 5. Cut the phone line. Attach one alligator clip to one cut end and the other alligator clip to the other cut end. Take your phone off the hook and turn on an FM radio at about 93 MHz. It should be very easy to tune into the transmission. Take a portable FM receiver outside and follow the phone line.

FM Phone Transmitter Parts List

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3V FM TRANSMITTER

This project provides the schematic and the parts list needed to construct a 3V FM Transmitter

. This FM transmitter is about the simplest and most basic transmitter to build and have a useful transmitting range. It is surprisingly powerful despite its small component count and 3V operating voltage. It will easily penetrate over three floors of an apartment building and go over 300 meters in the open air.

It may be tuned anywhere in the FM band. Or it may be tuned outside the commercial M band for greater privacy. (Of course this means you must modify your FM radio to be able to receive the transmission or have a broad-band FM receiver.) The output power of this FM transmitter is below the legal limits of many countries (eg, USA and Australia). However, some countries may ban ALL wireless transmissions without a licence. It is the responsibility of the constructor to check the legal requirements for the operation of this kit and to obey them.

The circuit is basically a radio frequency (RF) oscillator that operates around 100 MHz. Audio picked up and amplified by the electret microphone

is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit (the 5 turn coil and the trimcap) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. The tank circuit is connected in a Colpitts oscillator circuit.

The electret microphone: an electret is a permanently charged dielectric. It is made by heating a ceramic material, placing it in a magnetic field then allowing it to cool while still in the magnetic field. It is the electrostatic equivalent of a permanent magnet. In the electret microphone a slice of this material is used as part of the dielectric of a capacitor in which the diaphram of the microphone formsone plate. Sound pressure moves one of its plates. The movement of the plate changes the capacitance. The electret capacitor is connected to an FET amplifier. These microphones are small, have excellent sensitivity, a wide frequency response and a very low cost.

First amplification stage: this is a standard self-biasing common emitter amplifier. The 22nF capacitor isolates the microphone from the base voltage of the transistor and only allows alternating current (AC) signals to pass.

The tank (LC) circuit: every FM transmitter needs an oscillator to generate the radio Frequency (RF) carrier waves. The tank (LC) circuit, the BC547 and the feedback 5pF capacitor are the oscillator in the Cadre. An input signal is not needed to sustain the oscillation. The feedback signal makes the base-emitter current of the transistor vary at the resonant frequency. This causes the emitter-collector current to vary at the same frequency. This signal fed to the aerial and radiated as radio waves. The 27pF coupling capacitor on the aerial is to minimise the effect of the aerial capacitance on the LC circuit. The name 'tank' circuit comes from the ability of the LC circuit to store energy for oscillations. In a pure LC circuit (one with no resistance) energy cannot be lost. (In an AC network only the resistive elements will dissipate electrical energy. The purely reactive elements, the C and the L simply store energy to be returned to the system later.) Note that the tank circuit does not oscillate just by having a DC potential put across it. Positive feedback must be provided. (Look up Hartley and Colpitts oscillators in a reference book for more details.)

ASSEMBLY INSTRUCTION

Components may be added to the PCB in any order. Note that the electret microphone should be inserted with the pin connected to the metal case connected to the negative rail (that is, to the ground or zero voltage side of the circuit). The coil should be about 3mm in diameter and 5 turns. The wire is tinned copper wire, 0.61 mm in diameter. After the coil in soldered into place spread the coils apart about 0.5 to 1mm so that they are not touching. (The spacing in not critical since tuning of the Tx will be done by the trim capacitor. It is quite possible, but not as convenient, to use a fixed value capacitor in place of the trimcapacitor - say 47pF - and to vary the Tx frequency by simply adjusting the spacing of the coils. That is by varying L of the LC circuit rather than C.) Adding and removing the batteries acts as a switch.Connect a half or quarter wavelength antenna (length of wire) to the aerial point. At an FM frequency of 100 MHz these lengths are 150 cm and 75 cm respectively.

CIRCUIT CALIBRATION

Place the transmitter about 10 feet from a FM radio. Set the radio to somewhere about 89 - 90 MHz. Walk back to the FM transmitter and turn it on. Spread the winding of the coil apart by approximately 1mm from each other. No coil winding should be touching another winding. Use a small screw driver to tune the trim cap. Remove the screwdriver from the trim screw after every adjustment so the LC circuit is not affected by stray capicitance. Or use a plastic screwdriver. If you have difficulty finding the transmitting frequency then have a second person tune up and down the FM dial after every adjustment. One full turn of the trim cap will cover its full range of capacitance from 6pF to 45pF. The normal FM band tunes in over about one tenth of the full range of the tuning cap.

So it is best to adjust it in steps of 5 to 10 degrees at each turn. So tuning takes a little patience but is not difficult. The reason that there must be at least 10 ft. separation between the radio and the FM transmitter is that the FM transmitter emits harmonics; it does not only emit on one frequency but on several different frequencies close to each other. You should have little difficulty in finding the Tx frequency when you follow this procedure.

LEARNING EXPERIENCE

It should already be clear from the above circuit description that there is a surprising amount of electronics which may be learnt from this deceptively simple kit. Here is a list of some advanced topics in electronics which can be demonstrated or have their beginnings in this project:

Class C amplifiers; FM transmission; VHF antennas; positive and negative feedback; stray capacitance; crystal-locked oscillators; signal attenuation The simple halfwave antenna used in the project is not the most efficient. Greater efficiency may be gained by connecting a dipole antenna using 50 ohm coaxial cable. Connect one lead to the Antenna point and the other to the earth line.

You may experiment using 6V or 9V with the circuit to see how this increases the range of the transmitter. The sensitivity may be increased by lowering the 22K resistor to 10K. Try it and see. Note that this FM transmitter is not suitable for use on your body, for example, in your pocket. This is because it is affected by external capacitance and the transmitting frequency drifts depending how close you are to it. Stray capacitance is automatically incorporated into the capacitance of the tank circuit which will shift the transmitting frequency.

FM TRANSMITTER PARTS LIST

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HVAC THEMOSTAT

Introduction To HVAC Thermostat

HVAC thermostat has been one of the common device used in residential and industrial buildings to control the temperature of a space be it a warehouse, a room, a hall or an office. This thermostat project will focus on the heating control of a space that uses electric heater as its source of heating. It basically consists of a comparator that controls the ON and OFF of the electric heater

based on the sensor temperature.

The control of the fan speed is usually hardwired with two speed or three speed motors and is incorporated into the thermostat. The temperature range of this thermostat is from 5 Celcius to 30 Celcius with a tolerance of approximately 3 degree Celcius. Hence, only non critical tolerance control of temperature control such as a room can be used.

Circuit Description

The circuit diagram

shows the configuration of the HVAC thermostat. The LM358 Op Amp is used as a comparator to sense the inputs of the reference voltage (PIN 3) and room temperature (PIN 2). The thermistor used is a NTC (negative temperature coefficient) type where its resistance will drop when the temperature increases and vice versa. It has a resistance of 20K ohm at 25 degree Celcius. When the room temperature drops, the thermistor resistance will go up and hence the output of the operational amplifier

will be low. This cause the relay to turn OFF and the heater will conduct until the temperature of the room rises again.






The circuit is calibrated using variable resistor VR1. Set the lever of the slide potentiometer or rotary potentiometer VR2 to 25 Celcius location. Place the thermistor at a space where the temperature is at 25 Celcius. By varying VR1, set the resistance at the position between the ON and OFF of the relay. Use a suitable contact relay rating according to the load of the heater.

Parts List

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DATA ACQUISITION SYSTEM

Assembly
Please read all these instructions through once
before starting assembly. First note that 4
components are mounted underneath the double
sided, plated through PCB. The overlay shows these
components but they are mounted
UNDERNEATH the board on the copper side of
the PCB. The 4 components are C7 C8 R5 & R2.
C7, the 10uF tantalum capacitor must be pushed
over on its side so that the total height from the
surface of the PCB is under 5mm (otherwise it will
not fit inside the case.) The ceramic capacitor, C8,
also needs to be pushed over a little. The 1/8W
resistors will be under 5mm above the board.
All the other components are on the top of the PCB
as normal. Again the tantalum capacitor must be
pushed over to be under 5mm high. Make sure to
identify C6, the 103 monoblok capacitor and get it
in the right position. Make sure also that the two 10
pin IC’s are soldered in the right positions. U2 is the
MAX186. Note the orientation of the 1N4148
diode. The 78L05 must be mounted flush on the
PCB so it is not above 5mm. The resistor networks
can be either way around.
Make sure that the two DB25 connectors are
correct: J1 is male, J2 is female. Use one half of the case as a jig to hold the connectors & the PCB
before you solder any lugs. If you do not do this
then you run the risk that a connector will be skew
on the PCB & not fit properly into the case at both
ends.
The extra male DB25 connector & case are
provided for the power supply & inputs as
described in the documentation.
COMPONENTS KIT
0.1 104 monoblok .........C1 C2 C3 C5 .......... 4
0.01uF 103 monoblok ...C6 ........................... 1
1/8W 5% resistor
1K brown black red .....R5 ........................... 1
10K brown black orange R2 ......................... 1
10R brown black black .R1 ........................... 1
1N4148 diode ...............D1 ........................... 1
4.7uF/16V tantalum .......C4 ........................... 1
10uF/16V tantalum ........C7 ........................... 1
4K7 resistor network .....R3 R4 ...................... 2
74HCT373 ...................U1 ........................... 1
78L05 ...........................Q1 ........................... 1
220pF capacitor ............C8 ........................... 1
MAX186 ......................U2 ........................... 1
K118 PCB ..................................................... 1
D shell snap set ............................................... 1set
Male 25 pin PCB connector ......................... 2
Female 25 pin PCB connector ........................ 1
DB25 shell case .............................................. 1

FOR SOFTWARE VISIT www.electronickits.com/kit/complete/data/ck2000.htm

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5 BAND GRAPHIC EQUALIZER

This circuit uses a single chip, IC BA3812L for realizing a 5 band graphic equalizer for use in hi-fi audio systems.The BA3812L is a five-point graphic equalizer that has all the required functions integrated onto one IC. The IC is comprised of the five tone control circuits and input and output buffer amplifiers. The BA3812L features low distortion, low noise, and wide dynamic range, and is an ideal choice for Hi-Fi stereo applica-tions. It also has a wide operating voltage range (3.5V to 16V), which means that it can be adapted for use with most types of stereo equipment.

The five center frequencies are independently set using external capacitors, and as the output stage buffer amplifier and tone control section are independent circuits, fine control over a part of the frequency bandwidth is possible, By using two BA3812Ls, it is possible to construct a 10-point graphic equalizer. The amount of boost and cut can be set by external components.

The recommended power supply is 8V, but the circuit should work for a supply of 9V also. The maximum voltage limit is 16V.

The circuit given in the diagram operates around the five frequency bands:

100Hz
300Hz
1kHz
3kHz
10kHz

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DIGITAL VOLUME CONTROLLER

This circuit could be used for replacing your manual volume control in a stereo amplifier. In this circuit, push-to-on switch S1 controls the forward (volume increase) operation of both channels while a similar switch S2 controls reverse (volume decrease) operation of both channels.

A readily available IC from Dallas semiconductor, DS1669 is used here.

FEATURES:

Replaces mechanical variable resistors
Electronic interface provided for digital as well as manual control
Wide differential input voltage range between 4.5 and 8 volts
Wiper position is maintained in the absence of power
Low-cost alternative to mechanical controls
Applications include volume, tone, contrast,brightness, and dimmer control

The circuit is extremely simple and compact requiring very few external components.

The power supply can vary from 4.5V to 8V.

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2 TRANSISTOR FM VOICE TRANSMITTER

Warning:

Take care with transmitter circuits. It is illegal in most countries to operate radio transmitters without a license. Although only low power this circuit may be tuned to operate over the range 87-108MHz with a range of 20 or 30 metres.

Notes:

I have used a pair of BC548 transistors in this circuit. Although not strictly RF transistors, they still give good results. I have used an ECM Mic insert from Maplin Electronics, order code FS43W. It is a two terminal ECM, but ordinary dynamic mic inserts can also be used, simply omit the front 10k resistor. The coil L1 was again from Maplin, part no. UF68Y and consists of 7 turns on a quarter inch plastic former with a tuning slug. The tuning slug is adjusted to tune the transmitter. Actual range on my prototype tuned from 70MHz to around 120MHz. The aerial is a few inches of wire. Lengths of wire greater than 2 feet may damp oscillations and not allow the circuit to work. Although RF circuits are best constructed on a PCB, you can get away with veroboard, keep all leads short, and break tracks at appropriate points.


One final point, don't hold the circuit in your hand and try to speak. Body capacitance is equivalent to a 200pF capacitor shunted to earth, damping all oscillations

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CONTROL ELECTRICAL APPLIANCES USING PC

Here is a circuit for using the printer port of a PC, for control application using software and some interface hardware. The interface circuit along with the given software can be used with the printer port of any PC for controlling up to eight equipment .
The interface circuit shown in the figure is drawn for only one device, being controlled by D0 bit at pin 2 of the 25-pin parallel port. Identical circuits for the remaining data bits D1 through D7 (available at pins 3 through 9) have to be similarly wired. The use of opto-coupler ensures complete isolation of the PC from the relay driver circuitry.
Lots of ways to control the hardware can be implemented using software. In C/C++ one can use the outportb(portno,value) function where portno is the parallel port address (usually 378hex for LPT1) and 'value' is the data that is to be sent to the port. For a value=0 all the outputs (D0-D7) are off. For value=1 D0 is ON, value=2 D1 is ON, value=4, D2 is ON and so on. eg. If value=29(decimal) = 00011101(binary) ->D0,D2,D3,D4 are ON and the rest are OFF.


FOR SOFTWARE VISIT www.electronic-circuits-diagrams.com

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LIGHT BARRIER DETECTOR

This simple circuit using a single transistor turns ON the relay when light falls on the LDR. The potentiometer is adjusted for the required sensitivity. The power supply is 6V. Be careful about the impedance of the relay. Its impedance should not be less that 60ohm. Its working can be explained as follows: With the light falling on the LDR,its resistance is low and the transistor is saturated and turns the relay ON. When light is obstructed, the LDRs resistance becomes very high. The potentiometer shorts the transistors base to ground and it is cut off. Hence the relay is OFF.

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OPTOCAL TOGGLE SWITCH

Using dual flip-flop IC CD4027 employ a 555 based monostable circuit to supply input clock pulses. The circuit described here obviates this requirement. One of the two flip-flops within IC CD4027 itself acts as square wave shaper

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TV REMOTE CONTROL BLOCKER

Just point this small device at the TV and the remote gets jammed . The circuit is self explanatory . 555 is wired as an astable multivibrator for a frequency of nearly 38 kHz. This is the frequency at which most of the modern TVs receive the IR beam . The transistor acts as a current source supplying roughly 25mA to the infra red LEDs. To increase the range of the circuit simply decrease the value of the 180 ohm resistor to not less than 100 ohm.

It is required to adjust the 10K potentiometer while pointing the device at your TV to block the IR rays from the remote. This can be done by trial and error until the remote no longer responds.

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500W LOW COST 12V TO 220V INVERTER

Attention: This Circuit is using high voltage that is lethal. Please take appropriate precautions

Using this circuit you can convert the 12V dc in to the 220V Ac. In this circuit 4047 is use to generate the square wave of 50hz and amplify the current and then amplify the voltage by using the step transformer.

How to calculate transformer rating

The basic formula is P=VI and between input output of the transformer we have Power input = Power output
For example if we want a 220W output at 220V then we need 1A at the output. Then at the input we must have at least 18.3V at 12V because: 12V*18.3 = 220v*1
So you have to wind the step up transformer 12v to 220v but input winding must be capable to bear 20A.

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VGA TO TV SCART CIRCUIT

Description:

This is a circuit converter from VGA in TV SCART connection. Basically it is a circuit that accepts the signals from the exit of card VGA, him it then changes in combination RGB+composite sync and it leads to fastener SCART. The elements of picture from her exit card VGA, RED, BLUE and GREEN are already ready, bring right tendency the 0.the 7 vpp and right resistance of 75W for direct connection with fastener SCART, for depiction in the TV. What should it changes it is the right combination the horizontal and vertical synchronization signals from the VGA in a complex signal that will be led to the entry VIDEO in pin SCART. This transformation him they undertake electronic elements of circuit.

THAT IT FUNCTIONS

This circuit has been drawn in order to it changes regular signals VGA, standard RGB and the complex signal of timing. circuit is simple because signal RGB from the VGA is ready in standard level 0,7 Vpp and in 75W charge. For the signals of timing exists a circuit that changes the horizontal and vertical in complex. The circuit is simple based on a TTL completed with four gates XOR, two resistances and two capacitors. His choice completed TTL it is reasonable because the signals of timing of VGA they are signals TTL. The converter of signals of timing is system that regulates the difference of polarity of signals, so complex signal it is always right. Card VGA uses different polarities in the signals of timing in order to it informs the Monitor anymore analysis it uses. This circuit regulates the changes polarity the signals in least from 200 mSec, that are faster and from the time of regulation of common Monitor VGA. The circuit in order to function need stabilized tendency + 5V (+/- 5%) and current 120mA.

MANUFACTURE

Converter VGA in TV is easy in the manufacture to him it is enough exists a relative experience in the manufactures electronic. The circuit can be manufactured on one small EPOXY board. Remember only to connect also the completed circuit with the catering of 5V (in the drawing it does not appear). The circuit in order to it rightly functions it needs without fail stabilized tendency consequently it should you use also a REGULATOR LM7805. In the entry the 7805 the tendency should be from 9 until 16V so that it accomplishes us it gives the desirable stabilized tendency of 5V in his exit. Tendency from 9 until 16V we can him take also from our computer or from exterior small power supply's socket. From the computer we can we take from the following points: from door RS232, from the parallel door , from the PS2 and finally from a gambling chip of catering by his interior computer. Big attention should be given in him you stick that you will make and in the wiring of circuit, you avoid the chills you stick why the circuit functions in big frequency and sure will be created instabilities in the circuit with result bad quality of picture or even lack timing in the screen of TV. Be careful in order that the soldering is clean and glazing thus you will only be sure that the soldering has become right. For the wiring you are used shielded cables blentaz and ground the thorax of cables in the board's chassis. Good it is manufacture it is placed in a plastic box and it is placed and a connector EURO/scart female for placement in chassis.

MATERIALLY

U1: 74LS86
C1: 22mF
C2: 2,2 mF
R1, r2: 2k2
R3, r4, r5: 2k2
R6, r7, r9: 47k
R8: 120
T1, t2: 2N2222
Cable of connection VGA male 15pin sub D (DE 15)
Output connector 21pin EURO/scart female

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2KM FM TRANSMITTER

Description.
With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The transistor Q1 and Q2 forms a classic high sensitive preamplifier stage. The audio signal to be transmitted is coupled to the base of Q1 through capacitor C2. R1, R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier stage comprising of Q1 and Q2. Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier.C9 and L1 forms the tank circuit which is essential for creating oscillations. Inductor L2 couples the FM signal to the antenna.

Circuit diagram.

Notes.

• Assemble the circuit on a good quality PCB.
• The circuit can be powered from anything between 9 to 24V DC.
• Inductor L3 can be a VK220J type RFC.
• For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter plastic former. On the same core make 2 turns of 1 mm enamelled copper wire close to L3 and that will be L2.
• Frequency can be adjusted by varying C9.
• R9 can be used to adjust the gain.
• For optimum performance, value of C8 must be also adjusted.
• Using a battery for powering the circuit will reduce noise.

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STRAIN GAUGE

A strain gauge is a device that is used to measure the strain that occurs in an object. The device was invented in the year 1938 by Edward E. Simmons and Arthur Ruge. The device is still being used in many electronic circuits mainly as the principle sensing element for sensors like torque sensors, pressure sensors, load cells and so on.

Strain Gauge working

Strain Gauge Working Principle

Although strain gauges are available in many shapes and sizes, the fundamental working of this device is the same. They also vary in both shape and size according to their field of application.

A strain gauge consists of a foil of resistive characteristics, which is safely mounted on a backing material. When a known amount of stress in subjected on the resistive foil, the resistance of the foil changes accordingly. Thus, there is a relation between the change in the resistance and the strain applied. This relation is known by a quantity called gauge factor. The change in the resistance can be calculated with the help of a Wheatstone bridge.

TAKE A LOOK : WHEATSTONE BRIDGE

The strain gauge used is connected to the Wheatstone bridge with the help of an adhesive called cyanocrylate.

The property of the strain gauge not only depends on the electrical conductivity of the conductor, but also in the size and shape of the conductor used. As a matter of fact, the electrical conductivity also depends on the electrical conductance of the foil. This, in turn depends on the material of the conductor. The electrical resistance of the foil changes according to the change in the foil when it is stretched or compressed. The stretching or compressing is considered normal as long as there is no permanent change in the original appearance of the foil. Stretching causes an increase in the resistance from one end to other. Compressing causes a decrease in the resistance from one end of the conductor to another. Basically, the conductor will be a long strip with parallel lines with the condition that a little stress in the path of the orientation of the parallel lines will cause a resultant bigger strain multiplicatively over the effective length of the conductor. Thus a larger resistance change will be obtained.

The force applied to change elongate or shorten the strip can also be calculated with the help of the obtained output resistance.

An ideal strain gauge resistance varies from a few 3 ohms to 3 kilo ohms when it is unstressed. This value will change by a small fraction for the full force range of the gauge. It also depends on the elastic limits of the foil material. If there are forces applied to such an extent that they lose their original shape and size, the strain gauge will no longer be fit to use as a measuring device. So measurement of small fractional changes in the resistance must be taken accurately in order to use the strain gauge as a measuring device.

Applications

The voltage output in accordance to the stress is about a few millivolts. This voltage can be amplified to about 10 volts and can be applied to external data collection systems like recorders or PC data acquisition and analysis systems.

Strain gauges can be used to measure the stress developed in particular machinery and thus is used to mechanical engg. R&D.

The device is used aircraft component testing. Here also the measure of stress is the main issue. For this, strain gauges of very small size are connected to structural members, linkages and so on.

Gauge Factor Equation

The gauge factor of a strain gauge is given be the equation

GF = [∆R/R_G]/E

∆R – Resistance produced by the strain

R_G ­­– Resistance of gauge before application of stress

E – Strain produced

Types of Strain Gauges

This classification is based on the type of bridge circuit that is connected to the strain gauge. There are mainly three types of connections. They are

1. Quarter Bridge Strain Gauge Circuit

As shown in the diagram below, the imbalance is detected by the voltmeter in the center of the bridge circuit. The resistance R2 will be a rheostat and hence adjustable. The value of this resistance is made equal to the strain gauge resistance without the application of any force. The resistances R1 and R3 will have equal values. Thus, according to the Wheatstone bridge principle the entire circuit will be balanced and the net force will be zero. Thus the strain will also be zero. Now provide a compression or tension on the conductor and the circuit will be imbalanced. Thus you will get a reading at the voltmeter. Thus, the strain produced in response to the measured variable (mechanical force), is known as a quarter-bridge circuit.

Quarter bridge strain circuit

2. Half Bridge Strain Gauge Circuit

As shown in the circuit there are two strain gauges connected. If one of them does not respond to the strain produced it becomes a quarter bridge circuit. If both of them respond in such a way that both the strain gauges experience opposite forces it becomes a half bridge strain gauge circuit. By opposite forces, we mean that a compression on the upper strain gauge makes a stretch on the lower strain gauge. This causes both the gauges to make a better response to strain, thus increasing the response of the bridge to the applied force. As both the strain gauges act opposite and proportionally the response to the changes in temperature will be cancelled thus reducing the errors due to it.

Half bridge strain gauge circuit

3. Full Bridge Strain Gauge Circuit

In the case of sensitivity, a half bridge strain circuit is more sensitive than a quarter bridge circuit. The sensitivity can be increased if all the elements of the bridge are active. Such a circuit is called full bridge strain gauge circuit. The circuit is also advantageous in the fact that it can be used to bond the complimentary pairs of strain gauges to the testing specimen. Thus, this is considered to be the best bridge circuit for strain measurement. The circuit is also advantageous because of its linearity. That is, the output voltage is exactly directly proportional to the applied force. But in the case of a half bridge and quarter bridge the output voltage is only approximately proportional to the applied force. Take a look at the circuit diagram given below.

Full bridge strain gauge circuit

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