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This simple circuit can indicate a misuse or tapping of Telephone line through a loud alarm. The circuit is too simple and can be easily assembled on a common PCB. Line voltage of Telephone lines is around 48 volts DC in the On hook state. When the handset is lifted, this voltage reduces to 12 volt DC. This change in voltage level is used to activate the circuit.When the switch S1 is closed, circuit becomes active and the telephone enters into the armed state. The high volt DC from the telephone line passes through R1 and VR1 and bias T1 into conduction. As a result, the collector of T1 goes to ground potential to inhibit T2 from conduction. Buzzer and LED thus remain off. When the handset is lifted, the DC voltage from the telephone lines drops to 12 volts. This turns off T1 and T2 conducts. Buzzer beeps and LED lights indicating that the telephone is using. Setting Connect the circuit to Telephone lines using a telephone plug. The free socket of the telephone or Caller ID can be used...

When you want to mount components on a PCB or a piece of prototyping board, you not only want to do this quickly, but also tidily. The bending of really tidy wire links with the correct pitch is often a tedious chore. The following is a handy aid for doing this. Using a small piece of 0.1 inch (2.54 mm) prototyping board, you can very easily make a handy bending jig for wire links. With a jigsaw, cut the piece of prototyping board into a staircase shape as shown in the drawing. You can make it as big as you need. Make sure that the horizontal cuts are slightly  towards  the outside with respect to the holes, so that clear indentations remain in the horizontal sections. Bending a wire link is now very easy: choose the desired pitch on the jig (dashed line), take a piece of wire and fold it sharply around the indentations corresponding to the selected  pitch. A neat wire  link  is the result, with exactly the right pitch and ready for soldering tightly into the PCB or prototyping boa...

 These two mounting methods were devised to protect PC boards from vibration when installed in the engine compartment of a car. They could also be used in other applications where vibration is a problem. Method 1 involves rigidly mounting the PC board inside a diecast box and then mounting the box itself to provide vibration isolation. As shown, small grommets are installed in suitably sized holes in the sides of the box. The box is then secured to angle mounting brackets using M4 screws, washers and nylock nuts. Method 2 involves mounting the diecast case onto the chassis of the car and then mounting the PC board as shown, using M3 screws, grommets, hollow spacers and nylock nuts. In this case, the grommets are fitted into suitably sized holes in the PC board itself. Once the nuts are tightened, the PC board should be able to move slightly, relative to the box. If there is not enough space on the board to fit the grommets, then Method 1 is the way to do it. Author: David Boyes - ...

Figure 1 shows a simple ambit for converting an audio arresting (such as one that comes from the apostle terminals of a CD player). The ambit basically consists of a buffer/amplifier date and three clarify circuits: a high-pass filter, a mid-pass filter, and a low-pass filter. The achievement of anniversary clarify ambit drives a light-emitting diode of altered color. Simple Sound-to-Light Converter Schematic Circuit Diagram:   The ascribe arresting is fed to the absorber date through C1. The ethics of RF and RV1 should be called so that the absorber is able to drive the three filters absorbed to its output. The low-frequency, mid-frequency, and high-frequency apparatus of the ascribe arresting are alone accustomed to canyon through the low-pass clarify (bottom filter), the mid-pass clarify (middle filter), and the high-pass clarify (topmost filter), respectively, appropriately amid them from anniversary other. Changes in the achievement of a clarify account its agnate achievement ...

Build a Simple Solar Powered Long Range FM Transmitter Circuit Diagram . This is very stable, harmonic free, long range fm transmitter circuit which can be used for fm frequencies this one is unique in that it runs completely on solar power. No battery is required. As long as the sun is shining on the PV panel, the transmitter will transmit. The transmitter bug is useful as a "remote ear", and can be used for anything from listening birds to surveillance work. The mic preamp and oscillator circuits were borrowed from a common circuit found around the Internet, a regulated solar power supply and an RF amp that extends the range of transmitter and improves frequency stability were added.    Simple Solar Powered Long Range FM Transmitter Circuit Diagram Theory The solar power supply consists of a small 18V PV panel which charges a 1000uF electrolytic capacitor. The capacitor keeps the circuit running during brief interruptions of light, such as a bird flying over the PV panel. T...

Have you ever wanted to run a TV, stereo or other appliance while on the road or camping? Well, this inverter should solve that problem. It takes 12 VDC and steps it up to 120 VAC. The wattage depends on which tansistors you use for Q1 and Q2, as well as how "big" a transformer you use for T1. The inverter can be constructed to supply anywhere from 1 to 1000 (1 KW) watts. Simple Inverter Circuit Diagram Parts: C1, C2 68 uf, 25 V Tantalum Capacitor R1, R2 10 Ohm, 5 Watt Resistor R3, R4 180 Ohm, 1 Watt Resistor D1, D2 HEP 154 Silicon Diode Q1, Q2 2N3055 NPN Transistor (see "Notes") T1 24V, Center Tapped Transformer (see "Notes") MISC Wire, Case, Receptical (For Output) Notes: 1. Q1 and Q2, as well as T1, determine how much wattage the inverter can supply. With Q1,Q2=2N3055 and T1= 15 A, the inverter can supply about 300 watts. Larger transformers and more powerful transistors can be substituted for T1, Q1 and Q2 for more power. 2. The easiest and least expen...

One of the common  rounds in the  quizzes is the buzzer round. We are describing here a simple electronic circuit that can be used in any test or quiz competition. In this circuit, only four persons can participate,  and  every  participant is assigned a certain number. Whenever a switch is pressed, the circuit locks the remaining three entries. At the same time, an alarm sounds and the designated switch number is displayed on the seven segment LED display.When a player presses his switch, the corresponding output of IC1 goes high. Let us suppose, when switch S1 is pressed, D1 input of IC1 goes low and its corresponding output Q1 goes high. As a result, current passes through D5 to piezo buzzer PZ1, which creates a beep. At the same time, current also passes through diodes D6-D7 to show the number on the LED display. Simple Electronic Quiz Switch Circuit diagram: Simple Electronic Quiz Switch Circuit Diagram Similarly, when any other switch (S2-S4) is pressed, ...

This is a Simple Single Supply Voltage Regulator Circuit Diagram. The circuit uses a CA3140 BiMOS op amp capable of supplying a regulated output that can be adjusted from essentially 0 to 24 volts. The circuit is fully regulated. Simple Single Supply Voltage Regulator Circuit Diagram

     This is the Simple Fluorescent Lamp Inverter Circuit Diagram. This inverter is very easy to construct, reliable, and even powerful enough to light up a 15W florescent tube (if you cool your transistor well). The only hard-to-find piece of this baby is the so-called yellow inverter transformer. It's a miniature high frequency transformer that has a 25mm x 20mm x 5mm ferrite core, 30 turns of primary, 15 turns of feedback, and 250 turns of secondary all concentric, wound on plastic frame than wrapped with a 'yellow' adhesive tape. If you can't find it in your local electronic shops then search for old portable rechargeble florescent lanterns since they have at least one yellow inverter. Of course you can wind a handmade transformer which would do the same but it is a very difficult task when you don't have an original to inspire and it will still need an appropriate ferrite core. Simple Fluorescent Lamp Inverter Circuit Diagram       This ...

This Simple Voltage to Frequency Converter Circuits Diagram has a 1 Hz-to-30 MHz output, 150-dB dynamic range, for a 0 to 5 V input. It maintains 0.08% linearity over its entire 71/3 decade range with a full-scale drift of about 20 ppm/°C. To get the additional bandwidth, the fast )FET buffer drives the Schottky TTL Schmitt trigger.  Simple Voltage to Frequency Converter Circuits Diagram The Schottky diode prevents the Schmitt trigger from ever seeing negative voltage at its input. The Schmitt`s input voltage hysteresis provides the limits which the oscillator runs between. The 30-MHz, full-scale output is much faster than the LTC1043 can accept, so the digital divider stages are used to reduce the feedback frequency signal by a factor of 20. The remaining Schmitt sections furnish complementary outputs.

Here are a simple circuit of battery charger with extends lead-acid battery life. The circuit provides a first charging voltage of 2.5 V per cell at 25°C to rapidly charge a battery. The charging current decreases as the battery charges, and when the current drops to 180 mA, the charging circuit reduces the output voltage to 2.35 V per cell, floating the battery in a fully charged state.   Charger Extends Lead-Acid Battery Life Circuit Diagram: This lower voltage prevents the battery from overcharging, which would shorten its life. The LM301A compares the voltage drop across R1 with an 18-mV reference set by R2. The comparator`s output controls the voltage regulator, forcing it to produce the lower float voltage when the battery-chaiging current passing through R1 drops below 180 mA. the 150-mV difference between the charge and float voltages is set by the ratio of R3 to R4. The LEDs show the state of the circuit.

This circuit usually used for amplifier that do not require additional device in one box amplifiers. Enhancements such as Equalizer , Tone Control , Mixer , etc.  Only by requiring a potentiometer mono or stereo if stereo power amplifier , and few  cables you can make this circuit easily. See picture below :    First connect the cable from the power amplifier input to pin2 potentio , and connect ground to pin 1 , then connect the output of tuner or other media player to pin 3. Try turning to the right then the sound will be high , and if played left back then the sound will below.

While LCR meters are readily available at reasonable cost, they do not measure the Q of an inductor. This circuit enables you to measure the Q of inductors with the aid of an RF signal generator. A capacitor is connected in parallel with the inductor to form a tuned circuit. By varying the frequency, you can measure the resonance frequency of the tuned circuit and its -3dB bandwidth. The Q is then the resonance frequency divided by the -3dB bandwidth. Transistor Q1 is an emitter follower acting as input buffer to drive RF transformer T1. The secondary winding of T1 then drives the parallel tuned circuit formed by the inductor under test (Lx), T1’s secondary and tuning capacitor VC. The tuned circuit so formed is buffered by JFET Q2 and transistor Q3 which form a cascode stage with about 3dB of gain. The JFET provides a high impedance so that the loading of the tuned circuit is minimal (note: an MPF102 can be substituted if you cannot obtain a 2N5485). The RF output from Q2's collec...

Most small internal-combustion engines commonly used in the model-building world use glow plugs for starting. Unfortunately, glow plugs have an operating voltage of 1.5 V, while fuel pumps, starter motors, chargers and the like generally run on 12 V. This means that a separate battery is always needed to power the glow plug. The standard solution is to use an additional 2-V lead storage battery, with a power diode in series to reduce the voltage by approximately 0.5 V. However, this has the annoying consequence that more than 30 percent of the energy is dissipated in the diode. Naturally, this is far from being efficient. 12-V Glow Plug Converter Circuit Diagram: The converter presented here allows glow plugs to be powered from the 12-V storage battery that is usually used for fuelling, charging, starting and so on. A car battery can also be used as a power source. Furthermore, this circuit is con-siderably more efficient than the approach of using a 2-V battery with a series power dio...

This circuit is ideal to control the cooling fan of heat generated electronic gadgets like power amplifiers. The circuit switches on a fan if it senses a temperature above the set level. The fan automatically turns off when the temperature returns to normal. The circuit uses an NTC (Negative Temperature Coefficient) Thermister to sense heat. NTC Thermister reduces its resistance when the temperature in its vicinity increases.IC1 is used as a voltage comparator with two potential dividers in its inputs. Resistor R1 and VR1 forms one potential divider connected to the non inverting input of IC1 and another potential divider comprising R2 and the 4.7K Thermister supplying a variable voltage to the inverting input of IC1. VR1 is adjusted so as to give slightly lesser voltage at the non inverting input than the inverting input at room temperature. DC Fan Controller Circuit Diagram In this state, output of IC1 will be low and the Fan remains off. When the temperature near the Thermister incr...

This is the Simple Two 555 Timers Bell Circuit Diagram. This simple scheme uses two Bell 555 timer. The frequency controlled capacitors, which should be preserved are almost identical in value with each other to achieve the best results. Fine tuning is done with the R1 and R2. The decay time is controlled by R3. Simple Two 555 Timers Bell Circuit Diagram Sourced By: Streampowers

The stethoscope is a medical or veterinary use tool, in which the professional can hear the heartbeat, breath or other bodily sound of his patient. We can say that the operation of the stethoscope is simple, the recorded sound is amplified and taken directly to the ear by a pipe. The stethoscope is also called phonendoscope, it has two different pickups sound the bell and diaphragm. The traditional stethoscope is an acoustic equipment, and its pickup of sounds, are specific, the bell and one of the pickups that come in contact with the body, and its function is to capture bass. Have the diaphragm is used to capture the treble, all for a physical process, without the use of electronic circuits. The Electronic Stethoscope An electronic stethoscope or estetofone , has the ability to overcome low levels of noise, electronically amplifying body sounds. But this electronic system turns out to be limited the microphone audio frequency responses (pickup) and speaker, something that doe...

This is a Simple Signal Injector Circuit Diagram. The unit provides a square-wave output that is rich in harmonic content. The circuit`s output frequency can be varied from 50 Hz to 15 kHz. The heart of the circuit is a 555 a stable connected in its equal mark/space mode. The frequency is controlled by potentiometer R2 and capacitor Cl. Resistor R3 controls the output level with the output ac-coupled through C3. Simple Signal Injector Circuit Diagram

This circuit was taken from a dancing flower. A motor at the bottom of the flower had a shaft up the stem and when the microphone detected music, the bent shaft created the flower wiggle and move. The circuit can reply to a whistle, music or noise. Simple Dancing Flower Circuit Diagram

This is a Simple G - Purpose Preamplifier Circuit Diagram. This amplifier is useful for audio and video applications. Gain is set by Rf and the voltage gain of this amplifier is approximately 1 + i//560, where R/vs, in ohms. Bandwidth depends on gain selected, but typically it is several MHz. R/= 5.1 KOhmhm, which produces a gain of 10 (20 dB) voltage. Simple G - Purpose Preamplifier Circuit Diagram