Line Following Robot Sensor

Category:
This Line Following Robot sensor or surface scanner for robots is a very simple, stamp-sized, short range (5-10mm) Infrared proximity detector wired around a standard reflective opto-sensor CNY70(IC1). In some disciplines, a line following robot or an electronic toy vehicle go along a predrawn black line on a white surface. In such devices, a surface scanner, pointed at the surface is used to align the right track.

IC1 contains an infrared LED and a phototransistor. The LED emit invisible infrared light on the track and the phototransistor works as a receiver. Usually, black colored surface reflects less light than white surface and more current will flow through the phototransistor when it is above a white surface. When a reflection is detected (IR light falls on the phototransistor) a current flows through R2 to ground which generates a voltage drop at the base of T1 to make it conduct. As a result, transistor T2 start conducting and the visual indicator LED(D1) lights up. Capacitor C2 works as a mini buffer.

Line Follower Robot Scanner Schematic
Line Following Robot Sensor

After construction and installation, the scanner needs to be calibrated. Initially set P1 to its mechanical centre position and place the robot above the white portion of the track. Now slowly turn P1 to get a good response from D1. After this, fine tune P1 to reduce false detection caused by external light sources. Also ensure that the LED remains in off condition when the sensor module is on the blackarea. Repeat the process until the correct calibration is achieved.

The red color LED (D1) is only a visual indicator. You can add a suitable (5V) reed relay in parallel with D1-R4 wiring after suitable alterations to brake/stop/redirect the robot. Similarly, the High to low (H-L) transition at the collector of T2 can be used as a signal to control the logic blocks of the robot. Resistor R1 determines the operating current of the IRLED inside IC1. The sensing ability largely depends on the reflective properties of the markings on the track and the strength of the light output from IC1.
Read More »

Acoustic Sensor

Category:
This acoustic sensor was originally developed for an industrial application (monitoring a siren), but will also find many domestic applications. Note that the sensor is designed with safety of operation as the top priority: this means that if it fails then in the worst-case scenario it will not itself generate a false indication that a sound is detected. Also, the sensor connections are protected against polarity reversal and short-circuits.

The supply voltage of 24 V is suitable for industrial use, and the output of the sensor swings over the supply voltage range. The circuit consists of an electret microphone, an amplifier, attenuator, rectifier and a switching stage. MIC1 is supplied with a current of 1 mA by R9. T1 amplifies the signal, decoupled from the supply by C1, to about 1 Vpp. R7 sets the collector current of T1 to a maximum of 0.5 mA. The operating point is set by feedback resistor R8.

Circuit diagram:
Acoustic Sensor circuit schematic

The sensitivity of the circuit can be adjusted using potentiometer P1 so that it does not respond to ambient noise levels. Diodes D1 and D2 recitfy the signal and C4 provides smoothing. As soon as the voltage across C4 rises above 0.5 V, T2 turns on and the LED connected to the collector of the transistor lights. T3 inverts this signal.

If the microphone receives no sound, T3 turns on and the output will be at ground. If a signal is detected, T3 turns off and the output is pulled to +24 V by R4 and R5. In order to allow for an output current of 10 mA, T3’s collector resistor needs to be 2.4 kΩ. If 0.25 W resistors are to be used, then to be on the safe side this should be made up of two 4.7 kΩ resistors wired in parallel. Diode D4 protects the circuit from reverse polarity connection, and D3 protects the output from damage if it is inadvertently connected to the supply.
Read More »

Thermostat by using LM319

Category:
This first circuit is designed by me to replace the mechanical switches used in some thermal Electric I have heaters.The electrical contacts to these mechanical thermal switches are always stoned and “no longer be trusted.”They could easily be welded together, the maintenance of these heating on full. It is definitely not good! Coarse adjustment of the temperature is a trimmer on the track, set to give a nominal range When using the fine adjustment. It is quite difficult in a D-53, manufactured by NEC. The plumb line that is not isolated to the body of the thermistor is arranged. Why is it when you use the wire must be insulated to withstand the high temperatures such as fiberglass insulation against pipe.

Circuit Diagram:

Thermostat by using LM319

What is the size of the thermistor is the disk diameter 7 mm and a thickness of 2 mm. The end temperature control is a standard isolated potentiometer with a knob and / or good Protection against electric shock. Harter can be adjusted with this controller Auto-On and Off, “which automatically adjusts the room temperature. The power control for the triac should be a 2 watt potentiometer with a knob isolated and / or Tree for protection against electric shock.

It can also be set up a 2-watt resistor on the circuit, an appropriate level of heat.“In general, full on,” how would the “Normal” setting when you use the contacts.On the chart, show me a 10 Meg resistance hysteresis. This may be of Lower Austria or higherdepending on how many degrees of difference between you and off cycles.Values between 100 K-ohms and 22 ohms, Meg are acceptable.
Read More »

Photo Sensor Control Relay

Category: ,
A photo or slightly activated relay normally open relay in the closed circuit / contact with the light. In this circuit, a photodiode is used to sense light. The photodiode has a high resistance in the absence of light strikes. The photodiode is connected to the reverse biased state. The only current flowing through it will be due to minority carriers.

Circuit Diagram:

Photo Sensor Control Relay

When light falls on it, the minority current carriers in the wake of increasing the diode provides a low resistance. Because the voltage across the diode will not be sufficient to bias transistor Q1 and will be reset. Where there is darkness, the resistance increases photodiode and the voltage across it will be enough to move forward bias the transistor Q1 of the relay ON. The diode D2 is used as a diode to protect transistor switching transients produced relay. In this way, the load on the relay contacts can be switched on and off using light strikes the photodiode.
Read More »

Easy LED Photo Sensor Circuit With LM1458

Category: ,
Using a common benefit of photovoltaics LED, the circuit can recognize a different output darkness and light.
This circuit is used J-FET for recieve signal to buffer from LED ,About Output voltage,We used IC 1458 or LM1458 , while in the dark is about 7 volts and the drop about 2 volts in full sun. The LED voltage buffered by a junction FET transistor and then applied to the input of an operational inverting amplifier with a gain of about 20 minutes. This is a variation of about 5 volts of darkness and light. You can adjust the 100K potentiometer to set the range of output voltage.

Circuit Diagram.

Easy LED Photo Sensor Circuit With LM1458

Read More »

Light Sensor Alarm Circuit with NE555

Category: , ,
Reagarding this circuit sent out an alarm when its LDR sensor is exposed to light by sun or lamp.A 555 astable multivibrator was used here which sent signal a tone of about 1kHz upon detecting light.The sensor when exposed by light completes the circuit and makes the 555 oscillate at about 1kHz with transistor to drive current.The sensor is also shown in the circuit diagram. It has to placed making an angle of about 30 – 45 degrees to the ground.

Circuit Diagram

Light Sensor Alarm circuit with NE555

Sensitivity can be adjust with P1.
This makes the sun light to flow through it to the ground and prevents the alarm from going on due to the stored light on the sensor.
Read More »

Fluid Level Sensor

Category:
For all electrically conductive Fluid or liquid level measurement, this single-chip circuit is very compact and simple. This circuit is a voltage level sensor encouraged the AC bias supply for the sensor to prevent the electrolysis of the probes used.

This AC excitation, the sensor has a longer life. This circuit is useful for a wide range of water or liquid level measurement and control, heat registers, vending machines, washing machines, water softener, irrigation, reservoir, tank, aquarium or  pumps.The following figure shows the schematic of the circuit.

Fluid Level Sensor

Many types of liquids are electrically conductive and can track by using this level sensor: City / groundwater, seawater, Chopper solution, weak acid, weak base, household ammonia, water and glycol mixture, wet soil, coffee and juices.

Remember that most of the fuel is not electrically conductive, so that this circuit can be used as a fuel level sensor assembly / detector. Some other non-conductive liquid are: pure water, gasoline, oil, brake fluid, alcohol, ethylene glycol, paraffin, dry soil, and whiskey.
Read More »

Dew-Point Sensor

Category:
Dew-point sensors are widely used in sensitive electronic equipment like cameras and copiers etc, to protect them from moisture failure by fast detection of dew. You can easily build one yourself using the readily-available dew sensor element as described here. Alternatively, you can use the tiny dew sensor element of your old VCR or video camera, this simple but highly responsive circuit to protect equipment from dew (condensed moisture) can also be used to prevent condensation on surfaces like cold water pipes and windows.

The working of the dew sensor element (DS1) is based on the change in resistance of a conductive polymer in a thin film on a small ceramic substrate. When the sensing polymer becomes wet, its resistance increases drastically because the polymer expands to increase the distance between the conductive particles,in the circuit, the dew sensor element (DS1) is connected to inverting input pin 2 of op-amp UA741 (IC1). Resistors R2 and R3 and VR1 preset provide the reference voltage at the non-inverting input pin 3 of the opamp. When a high humidity is detected, the output of IC1 changes state to switch on galvanic-isolator IC 4N35 (IC2) through optocoupler driver transistor BC337 (T1).

Adjust preset VR1 such that IC2 is disabled when the sensor (DS1) detects low humidity and enabled when humidity is high,The circuit operates off 12V DC, which may be provided by a separate mains adaptor. It can operate off lower voltages as well, provided you select the right components,aluminium cabinet. Mount the dew sensor element on the front panel of the cabinet using a double-sided bonding tape. For maximum bond strength, the metallic surface of the cabinet on which DS1 has to be mounted should be thoroughly cleaned and dried. You can use isopropyl alcohol as the cleaning solvent.

Use a long wire to connect sensor DS1 so that it can be extended to desired distance. Using a shielded cable for the purpose would eliminate transient problems,This dew-point sensor can precisely sense the dew-point and activate any externally connected relay or similar controller to sound an alarm. A small amount of hysteresis added to the comparator helps it to avoid oscillations of the information.

Dew-Point Sensor

As shown in the circuit, safe and secure galvanic isolation is provided at the output of IC1 using optocoupler 4N35 (IC2). Both the terminals of the internal phototransistor of IC2 are hanging, so you can interface this circuit to any analogue/digital gadget after suitable modification at its trigger input. Further, for simple purposes, you can replace optocoupler IC2 with an electromagnetic relay. For this, just remove resistor R6, capacitor C2 and IC2 and connect the electromagnetic relay between the emitter of transistor T1 and ground. Don’t forget to add a free-wheeling diode in anti-parallel with the relay coil.
Read More »

Color Sensor

Category: ,
Colour sensor is an interesting project for hobbyists. The circuit can sense eight colours, i.e. blue, green and red (primary colours); magenta, yellow and cyan (secondary colours); and black and white. The circuit is based on the fundamentals of optics and digital electronics. The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered. The circuit makes use of only ‘AND’ gates and ‘NOT’ gates.

Circuit Diagram

Color Sensor

When a primary coloured light ray falls on the system, the glass plate corresponding to that primary colour will allow that specific light to pass through. But the other two glass plates will not allow any light to pass through. Thus only one LDR will get triggered and the gate output corresponding to that LDR will become logic 1 to indicate which colour it is. Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corres- ponding to the mixed colour will allow that light to pass through while the remaining one will not allow any light ray to pass through it. As a result two of the LDRs get triggered and the gate output corresponding to these will become logic 1 and indicate which colour it is.

When all the LDRs get triggered or remain untriggered, you will observe white and black light indications respectively. Following points may be carefully noted :
1. Potmeters VR1, VR2 and VR3 may be used to adjust the sensitivity of the LDRs.
2. Common ends of the LDRs should be connected to positive supply.
3. Use good quality light filters.

The LDR is mounded in a tube, behind a lens, and aimed at the object. The coloured glass filter should be fixed in front of the LDR as shown in the figure. Make three of that kind and fix them in a suitable case. Adjustments are critical and the gadget performance would depend upon its proper fabrication and use of correct filters as well as light conditions.
Read More »

Infrared Beam Barrier and Proximity Sensor

Category: ,
This circuit can be used as an Infrared beam barrier as well as a proximity detector.the circuit uses the very popular Sharp IR module (Vishay module can also be used). The pin nos. shown in the circuit are for the Sharp & VIshay modules. For other modules please refer to their respective datasheets.

The receiver consists of a 555 timer IC working as an oscillator at about 38Khz (also works from 36kHz to 40kHz) which has to be adjusted using the 10K preset. The duty cycle of the IR beam is about 10%. This allows us to pass more current through the LEDS thus achieving a longer range.

Infrared beam barrier and proximity sensor

The receiver uses a sharp IR module. When the IR beam from the transmitter falls on the IR module, the output is activated which activates the relay and de-activated when the beam is obstructed. The relay contacts can be used to turn ON/OFF alarms, lights etc. The 10K preset should be adjusted until the receiver detects the IR beam.

The circuit can also be used as a proximity sensor, i.e to detect objects in front of the device without obstructing a IR beam. For this the LEDs should be pointed in the same direction as the IR module and at the same level. The suggested arrangement is shown in the circuit diagram. The LEDs should be properly covered with a reflective material like glass or aluminum foils on the sides to avoid the spreading of the IR  beam and to get a sharp focus of the beam.

When there is nothing in front of them, the IR beam is not reflected onto the module and hence the circuit is not activated. When an object comes near the device, the IR light from the LEDs is reflected by the object onto the module and hence the circuit gets activated.
Read More »

Temperature Sensor with Digital Output

Category: ,
This is a very simple to implement Temperature Sensor. It uses LM35DT as a semiconductor temperature sensor which operates with a +5 volt DC.

It produces an analog output voltage, proportional to the change in surrounding temperature in Celsius scale (2mv/C). The analog output of the sensor is then passed to the ADC0804 IC which produces an 8-bit binary output (digital output) correspoding to the analog input voltage. The digital output from ADC is then used to glow the LED which indicates the high/low logic (LED ON: Logic 0, LED OFF: Logic 1).

The output of the ADC can be interfaced to a 7-segment diaply using a 7-segment driver or the digital output can be interfaced to a PC / microcontroller. The bottom portion of the schematic shows a fixed and a variable power supply which inputs 220 volts AC from the wall outlet in your house, the transformer then steps-down it to 18 volts AC (9-0-9 centre-tapped), which is then converted to DC using bridge rectifier.

Temperature Sensor with Digital Output

The fixed regulator IC (7805) produces a +5 volts regulated output which is used to operate the Sensor and the ADC0804 IC. It also outputs a variable voltage controlled by a 5K variable resistor which is used to adjust the scaling of the ADC0804 (normally for full scale, it is set to 2.5 volts).

Further modification may include an automatic control circuitry interfaced to the ADC which automatically ON/Off the

device whose temperature is to be control/monitor. The automatic control can be achieved by OP-AMP based comparators or using

Read More »

Vibration Sensor Detector

Category: ,
With the help of a simple ceramic piezo-electric detector it is possible to assemble an interesting and useful Impact sensor unit,which can be used to detect impact and vibration on doors, showcases, windows etc. The shock sensor (Ceramic piezo-electric detector) uses a “unimorph” diaphram, which consists of a piezo-electric ceramic disk laminated to a metal disk. The sensor supplies a voltage proportional to the acceleration of the impact or vibration, for example 40mV/G ie output is near 2V for 60G impact.

Here a low voltage, low current Impact sensor unit is realised using a standard ceramic piezo-electric detector which drives a monostable multivibrator (IC1) circuit to activate a npn silicon transistor (T1). Open collector output of this transistor switch can be interfaced to an external alarm/switch circuit for further processing. Since current consumption of the circuit is very low (from 5 to 6 mA only) any common 3V button cell can be used to power the sensor unit.When an impact is sensed, the monostable drives the transistor switch to ON , for a finite duration determined by the incircuit values of RC timing components R3 and C2.

Vibration/Impact Sensor Circuit Schematic

Vibration SensorDetector circuit


The M74HC123 (IC1) is an high speed DUAL retriggerable CMOS MONOSTABLE MULTIVIBRATOR (MMV) fabricated with silicon gate C2MOS technology, with all inputs protected against static discharge and transient excess voltage. There are two trigger inputs, negative edge and positive edge. Here, only one monostable part with positive edge triggering (pin 2) is used. After triggering, the output maintains the monostable state for the time period determined by the external resistor R3 and capacitor C2.

Read More »

Security Light & Switch with PIR Sensor

Category: , ,
Moderately priced Passive Infrared (PIR) Sensor modules are now widely available. By using these ready made and pre-configured PIR sensors, even an average electronics hobbyist can construct his/her own Motion Sensor Unit. The one evening project presented here is based on a common and very popular PIR module SB0061.

SB0061 is a pyroelectric sensor module,developed for human body detection. A PIR detector combined with a fresnel lens are mounted on a compact size PCB together with an analog IC (SB0061) and limited components to form the module. High level output (3.3V) of pre-settable variable width (5Secs -18 Minutes) is provided.

PIR Motion Sensor Circuit Schematic

Security Light & Switch with PIR Sensor

Circuit diagram of the PIR Motion Sensor Light and Switch based on SB0061 shown here can be used for security or corridor lighting in power saving mode. The 12V DC supply required for the whole circuit can be fed from any standard 12V ac mains adaptor/battery.

Working of the circuit is simple and straight forward. When any movement is detected within near 5-6 metres, around 3.3 Volt is appeared at the base of Transistor T1 and it conducts to fire the next relay driver transistor T2. As a result, the 12V DPDT relay is energized to power the White LED through current limiting resistor R3. Spare relay contacts can be used as a switch to control any suitable external load. The white LED and the relay remains ON for a duration based on the mono time setting in SB0061, ie from 5 Secs to 18 Minutes.

Read More »

Digital Weight Scale Circuit with IC ADD3701

Category: ,
Welcome back to diyelectronicsprojects.com, we are present circuit for digital weight circuit .This uses a potentiometer as the weight sensing with seven segment LED element.

An moving object on the scale of the potentiometer wiper, an amount proportional to the weight.Conversion led the wiper voltage of digital information, decode and display interfaces to the numerlc.

Digital weight scale circuit with IC ADD3701



Read More »

Parking Sensor

Category:
Description.

This simple circuit can be used as an aid for sensing the distance between the rear bumper of the car and any obstacle behind the car. The distance can be understood from the combination of the LEDs (D5 to D7) glowing. At 25cm D7 will glow, at 20 cm D7&D6 will glow and at 5cm D7, D6 and D5 will glow. When the obstacle is beyond 25 cm none of the above LEDs will glow.

Circuit diagram with Parts list.

Parking sensor circuit

Two ICs are used in the circuit. The IC1 (NE555) is wired as an astable multivibrator for driving the IR Diode D1 to emit IR pulses. The operating frequency of the transmitter is set to be 120Hz.The IR pulses transmitted by D1 will be reflected by the obstacle and received by the D2 (IR photo diode).The received signal will be amplified by IC2a.The peak of the amplified signal will be detected by the diode D4 and capacitor C4.R5 and R6 compensates the forward voltage drop of D4.The output voltage of the peak detector will be proportional to the distance between car’s bumper and obstacle.

Parking sensor circuit
The output of peak detector is given to the inputs of the other three comparators IC2b,IC2c and IC2d inside the IC2(LM324).The comparators switch the status LEDs according to the input voltage their inverting inputs and reference voltages at their non inverting inputs. Resistances R7 to R10 are used to set the reference voltages for the comparators.

Notes.
  • Assemble the circuit on a good quality PCB or common board.
  • The D1 & D2 must be mounted close (~2cm) to each other, looking in same direction.
  • The D1 can be a general purpose IR LED.
  • The D2 can be general purpose IR photo diode with sun filter.
  • The transmitter as well as receiver can be powered from the car battery.
  • For proper working of the circuit, some trial and error is needed with the position of D1 and D2 on the dash board.
  • All capacitors must be rated 25V.
  • The ICs must be mounted on holders.

Read More »

Heartbeat Sensor (Tranduscer)

Category:
To build a heart-beat transducer not as difficult as imagined. Circuit below shows a simple heart-beat transducer.This circuit made from an infrared phototransistor and infrared LED.This transducer works with the principle of light reflection,in this case the light is infrared.The skin is used as a reflective surface for infrared light. The density of blood in the skin will affect on the IR reflectivity.

Heartbeat Sensor (Tranduscer)

The pumping action of heart causes the blood density rises and falls. So that we can calculate the heart rate based on the rise and fall of intensity of infrared that reflected by skin.


Read More »

One Direction Motion Sensor

Category:
This is a one direction motion sensor circuit. This motion sensor circuit is used to detects an object passing in one direction, ignoring an object that going to opposite way. This circuit uses two sensors to identify the movement only  in one direction. The basic principle of this circuit is simple, where one sensor is used to generate a short pulse, and the other sensor is used to block of turn of the gate. The phototransitors give high output on their collectors when there is an object blocking the light.  By a 0.4uF differentiator capacitor, the interruption of light at Q2 sensor will produce short pulse at point C. But this short pulse will only appear at the output if  a high signal appears at A.

One Direction Motion Sensor

This condition will be satisfied if the light to  Q1 is blocked by the object when the object is passing through Q2, means that the direction should be from Q1 to Q2.
Read More »

Transmitter Detector for FM Bug Surveillance

Category: ,
The circuit was constructed using a few components that is powered by a 9 V battery for sensing the presence of bugs transmitting within the frequency modulation range.

  • Frequency Modulation (FM) – transmits its signal or information over a carrier wave by changing its frequency but it can also be taken into account as a special case of phase modulation where the carrier phase modulation is the time integral of the FM modulating signal
  • Transmitter – an electronic device that can produce or amplify a carrier wave signal, modulates it with a significant signal, and radiates the resulting signal from an antenna which are being utilized in television, telecommunications, and radio
  • Radio Frequency (RF) – operates within the range of 3 Hz to 300 GHz
  • Field Effect Transistor (FET) – used for amplifying weak signals by controlling the current and the shape of an electric field where the flow of current or the conductivity of material is only through a single type of semiconductor material

Transmitter Detector for FM Bug Surveillance

Bugs are also known as listening devices, wireless microphones, transmitters and telephone gadgets which are easy to use and very effective. The FM bugs are typically designed to work in the commercial range of 87 MHz to 108 MHz. The bug detectors will pickup almost anything that transmits in this frequency band. In some case, when a bug made of sensitive microphone is broadcasting in close proximity, it may produce a feedback whistle in the detector.

The inductor used in the circuit has a value of 0.389 uH molded as an RF coil. It is tuned for broadband and possesses a quality factor at about 170. The coil picks up the signal and is rectified by the OA91 gold bonded germanium diode. It has low power consumption and very low noise level. The minimal DC voltage will give the deflection on the meter, having 250 uA full scale deflection, while reversing the bias on the FET. For higher sensitivity, the meter to be used should contain a full scale deflection of 50 uA or 100 uA. The FET used in this circuit can be the 2N3819 or MPF102 which offers good performance at mid to high frequencies and a low cost type. It has low noise and leakage, very high system sensitivity, high speed switching capability, wideband high gain at 100 MHz, high low-level signal amplification and high quality of amplification.

The use of the detector is applied in a sweeping motion while being carried around a room, and when a bug is nearby, a feedback whistle will be heard. Even a small battery transmitter can cause deflection the meter from a distance away from it. During the construction of an FM transmitter, this detector will provide a valuable part of the equipment.

Bugs or listening devices can be utilized in several forms of equipments such as phone line bug, credit card UHF bug, pen style UHF bug, long range UHF bug, calculator style UHF bug, phone line FM bug, powerboard bug, wall contact microphone, super directional listening set, inline microphone, digital voice recorder, monocular scope and wrist watch walkie talkie. Bugs can also come in the form of radio transmitters which transmits sounds over the radio frequency; in the form of lasers where it aims a laser that has sine waves on an object and analyzing the returned laser beam; in the form of contact microphones and speakers which both contains a diaphragm to interact with the air, a power source, and 2 coils of fine wire; in the form of hardwired devices like stereo speakers, power lines, wired intercoms, phone lines and LAN cabling; in the form of visible light transmitters which functions by modifying the voltage flowing in a light source; and in the form of infrared transmitters which utilizes infrared lights to transmit sound rather than radio waves.

There are quite a lot of detection tools that detect wiretaps, wireless video transmitters, radio interference, electronic eavesdropping, and bugs. In testing the telephone trunks for wiretaps, a device known as time domain reflector (TDR) is used which acts as radar for wires that gives a waveform display in its scope unit. Another tool for testing telephone taps is telephone sequencer which can separate out all fifty wires in a standard telephone wall connection and it comes in the form of a patch bay. There are detectors known as non-linear junction detectors which consists of a headphone and meter that gives sound and visual feedback in the presence of a semiconductor material. In radio transmission wire tap bugs, the radio spectrum analyzer and field strength meter is used. The field strength meter uses a slope detector by having an audio listening circuit. The radio frequency spectrum analyzer that shows the waveform of the carrier that is tuned on using the built-in scope.
Read More »

Monitoring and Detection of Temperature

Category:
The circuit is designed to produce a temperature monitoring scheme using an operational amplifier and a relay with triggering procedures.

In electronics engineering, operational amplifiers or op-amps was developed to provide a gain block whose performance is totally predictable from unit to unit and perfectly defined by the characteristics of an external feedback network in the design of analog computers. Amplifiers are created to increase the amplitude of a signal, normally a voltage or a current. Basically, an op-amp is a type differential amplifier that has a greater input impedance and minimal output impedance, that is commonly driven by a dual polarity power supply ranging from 5 Volts to 15 Volts.

Monitoring and Detection of Temperature

The circuit contains a relay that is triggered by the op-amp (UA741 or UA341) circuit upon reaching the predetermined temperature without the presence of a hysteresis within the circuitry. Hysteresis is the result of a delay in making changes such as reducing or rising power, which can cause the relay to respond quickly after the change. The circuit also employs a NTC thermistor with 47K ohm resistance. The adjustment of the potentiometer balances the circuit and will be altered with a swift variation in temperature then will boost the relay. This will exchange the position of thermistor and potentiometer, thus producing a cold warning.

During the calibration of the device at room temperature, half the supply voltage will enter the op-amp while modifying the potentiometer to permit the function of relay, while the thermistor operates at needed temperature.Placing the device on hot environment, a multimeter can be used to read the thermistor resistance as it decreases. Then set the preset at current temperature to start the trigger on the circuit. The loss of relay power may be a result of temperature drop, producing a relay chatter or bad contact.
Read More »

Induction Receiver

Category:
The induction receiver shown below is very sensitive and can serve a variety of purposes. It is excellent for tracing wiring behind walls, receiving audio from an induction transmitter, hearing lightning and other electric discharges, and monitoring a telephone or other device that produces an audio magnetic field ("telephone pickup coil").

The receiving coil could be a "telephone pickup coil" if available or a suitable coil from some other device. The coil in the prototype was salvaged from a surplus 24 volt relay. Actually, two relays were needed since the first was destroyed in the attempt to remove the surrounding metal so that a single solenoid remained. Epoxy putty was used to secure the thin wires and the whole operation was a bit of a challenge. A reed relay coil will give reduced sensitivity but would be much easier to use.

The experimentally inclined might try increasing the inductance of a reed relay by replacing the reed switch with soft iron.  Avoid shielded inductors or inductors with iron pole pieces designed to concentrate the magnetic field in a small area or confine it completely (as in a relay or transformer) unless you can remove the iron. The resulting coil should be a simple solenoid like wire wrapped around a nail. Don't try to wind your own - it takes too many turns.  Evaluate several coils simply by listening. Coils with too little inductance will sound "tinny" with poor low frequency response and other coils will sound muffled, especially larger iron core coils. This prototype was tested with a large 100 mH air core coil with superb results but the 2 inch diameter was just too big for this application.

The other components are not particularly critical. The 2N4401 can be just about any NPN general purpose small-signal transistor. The TL431 is a shunt voltage regulator but it is being used as an audio amplifier in this circuit. In fact, the whole device is nothing more than a low noise, high gain audio amplifier with a pickup coil connected to the input and other amplifiers will work equally well. the circuit is built into a 8 mm cassette box with the power switch and earphone jack in the back. The circuit board is a piece of pink countertop laminate which looks good against the violet hue of the cassette box. The battery fits nicely into the box and a piece of foam fills in the remaining space. These video cassette boxes make nice project boxes, unlike audio cassette boxes which are too flimsy.

Induction Receiver

When you first turn on the unit you will probably hear a lot of buzzing from the wiring in the room. Rotate the receiver in a horizontal plane to find a "null" where the hum is minimal. If you can get a reasonable null, you should be able to hear distant lightning crackles or other magnetic noises. If you cannot get a null then go outside away from the building. Try holding the coil near electronic devices like your computer monitor, telephone (when in use), cell phone readout, etc.  You can trace power wires behind a wall or ceiling by listening for a sharp increase in hum as the coil passes near the wire. Make sure that current is flowing in the wires to be traced by turning on a lamp or other appliance. (Here is an experiment to try: Build a line voltage lamp flasher that can be connected to the circuit to be traced. The desired wire will now have an on and off buzz - buzz sound that will be easy to distinguish. I wonder if you could even identify a specific breaker or fuse?)

Other wires can be traced if they are carrying alternating current in the audio range or a signal generator can be connected to produce the current. Connect the generator to the wire to be traced and connect the generator's "ground" to the house wiring ground.  Also ground the far end of the wire you are tracing so that current flows in the wire. This ground connection can also just be a temporary wire laying on the floor running from the generator ground to the far end of the wire you wish to trace. for the ambitious: try wrapping one or two turns of wire around the whole house and connect the loop to the output of an audio power amplifier (one channel of a stereo should work). Add a 4 ohm, high wattage resistor in series to protect the amplifier. You should be able to pick up the magnetic field fairly easily anywhere within the loop with the power amplifier supplying just a few watts of power.
Read More »
 
I
DIY Stuff