Top Circuits Page 10

Tones (from the DTMF) on the telephone line are detected by Ul. When a valid tone is received, pin 14 (D..

This circuit switches a tape recorder via PL2. When on-hook, D5 conducts, turns on Ql, and cuts off Q..

This circuit flashes an LED to indicate that your phone rang during your absence. A differential amplifier with hyste..

If you are busy and cannot answer or do not wish to answer your phone, this circuit will give a busy signal without you ..

The circuit requires neither a battery nor an ac supply to make it work. Set the recorder to the record position and ..

This accessory connects to phone and will activate an attention-getting 120-V bell whenever a ringing voltage appears on the ph..

The circuit receives its power from a 15-V wall adapter (not shown). The circuit takes advantage of the fact that th..

The fax mate separates the fax machine from the phorie line, rings the fax machine on command, connects equipment to incoming lines, and senses the end of the message. When a touch tone pound signal (#) is detected, it actuates a ring greater and driver for....

The dc voltage present on a telephone line is usually around 45 to 50 V on-hook and 6 V off-hook. This circuit uses This drop in voltage to activate a relay. The relay controls a cassette tapeTecorder...

When an asterisk * is pressed on the touch-tone phone, TCI a DTMF decoder, controls on-hold logic. Audio from the FM receiver IC4 is.placed on the telephone line when a hold condition is present. RY2 is a DPDT 12-V relay. To place a caller on hold,..

This system will alert you or anyone chosen by automatically dialing a programmed phone number. This is accomplished by monitoring an open- loop or closed-loop sensor switch located in the protected area. Mien the sensor detects a problem (such as a....

Using a Motorola MC34118 speakerphone IC, this adapter can be used with a regular telephone to provide speaker capability. This device is powered from the phone line, but it can be powered via an external power supply if the line loop current is marginally....

The cireiilt is built around a couple of low-cost ICs: an H11C4 optoisolator/coupler with an SCR output (Ul) and an LM3909 LED flasher (U2). It is connected to the phone line in the same manner as any extension phone. A ring signal on the telephone....

Two hybrids (Tl and T2) are used to allow direct connection to a telephone line. This circuit uses the common speech-inversion algorithm where the frequency of an audio signal is inverted about a center frequency. ..

This circuit dials a stored DTMF tone sequence from EPROM when a control line is taken to 0 V. ICl is a Schmitt trigger oscillator, running at around 2 Hz. It clocks a 4024 binary counter. The counter`s outputs connect to the address leads of the EPROM. A....

Section Ul-a is configured as a high-gain inverting voltage amplifier that is inductively coupled to the phone line via LI. Inductor LI is a homemade unit that consists of 250 turns of fine, enamel-coated wire that is wound on an iron core. The op amp....

The LED indicates the status of a remote telephone. The light is off if the phone is hung up. It shines steadily if the phone is off hook, and it flashes on and off while phone rings and for 5 seconds after ringing stops. The flashing oscillator operates....

This system uses a transmitter at around 100 kHz (see Fig. 86-3(a)) to control a remote rece..

The MC34012 tone-ringer chip derives its power by rectifying the ac ringing signal. That signal is normally at 20 Hz and measures between 70 and 130 volts rms. It uses that power for the tone generator and to drive the piezoelectric transducer. The sound....

The circuit can operate lamps and buzzers from the 120 V, 60 Hz power line while maintaining positive isolation betweenthe telephone line and the power line..

The electronic bell needs no power supply. Most of the resistors are not critical, although C2, R2, and R3 work best at the values given. Leaving out Rl will make the unit ring louder. The piezo buzzer may vary from store to store. If it has two leads,....

The speaker emits a distinctive warble tone when ring pulses are applied to the phone line. Use this circuit as a remote bell or disconnect the phone"s ringer for direct use. Rl adjusts the duration of the output; R2 and R3 control the tone"s duty cycle and....

When the telephone rings. or when the handset is lifted, ~the night light is turned on and remains on while the conversation takes place. When the handset is replaced in the cradle, the light remains on for about 11 s. During standby conditions, the -28 V....

When the phone rings, the ring signal from the telephone company lights a neon lamp within a CLM3120 optocoupler. That causes a drop in the resistance of the CdS cell output of the device, turning on transistor Ql. ..

The two neon bulbs will light when more than 100 V is across the ringing circuit. The bulbs provide line isolation between the unit and the telephone line. Finally, they act as a voltage divider for the bridge rectifier made up of D 1 through D4. That....

This circuit detects the 20 Hz, "" 86-V rms ring signal on telephone lines and initiates action in an electrically isolated circuit. Typical applications would include automatic answering equipment, and interconnect/ interface and key systems. The circuits....

The ac ringing voltage (typically 40 to 90 V at 26 Hz) is rectified by U1, the tone-ringer IC, and is used to drive ..

In this circuit, the ringing voltage on a telephone line causes NE-1 to break over, triggering SCR1, which ..

This circuit detects the 20-Hz approximately 86-Vrms ring signal on telephone lines and initiates action in an electri..

The circuit is based on the TCM1506 ring detector/driver integrated circuit. It is a monolithic IC specifically designed to replace-the telephone`s mechanical bell. The chip is powered and activated by the telephone-line ring, which can vary from 40 to 150....

This circuit is intended for use in a small private telephone installation. The ringing tone sequence is 400 ms on, 200 ms off, 400 ms on, 2 ms off. In the accompanying diagram, N1 and N2 form an oscillator that operates at a frequency of 5 Hz, which gives....

In this page we will show how you can simply construct such a meter, which is good to have one, to show not only the existence of radioactive materials but also the dangers arising from them. The Geiger–Müller counter can be compared to a photometer. The....

A single 6.75 V mercury battery powers the counter, which features a 1 mA count-rate meter as well as an aural output. A regulated 900 V supply provides stable operation of the counter tube. A multivibrator, built around a differential power amplifier IC2,....

The circuit can be tuned to respond to signals between 50 MHz and 500 GHz. The economy model is shown in Fig. 1, and the deluxe model is shown in Fig. 2.The first op amp in each circuit functions as a current-to-voltage converter. In the economy model IClb....

A commercial diode is the detector in this highly accurate radiation monitor. The lowdrift FET-input op amp amplifies detector current to a usable level, and the chopper-stabilized amplifier then provides additional gain while minimizing any error caused by....

A sensitive radiation monitor may be simply constructed with a large-area photodiode and a quad operational amplifier. Replacing the glass window of the diode with Mylar foil will shield it from light and infrared energy, enabling it to respond to such....

The Geiger tube needs a high voltage supply which consists of Ql and its associated components. The transformer is connected in reverse; the secondary is connected as a Hartley oscillator, and Rl provides base bias. Dl, D2, C4, and C5 comprise a voltage....

A simple inventer and NAND gate can be connected to yield a highly compact and reliable digital frequency detector. This circuit can detect frequencies up to 3 MHz with 50% duty cycles. When a frequency, j,, appears at the input, points A and B detect a....

The high-speed peak detector uses a highly accurate, fast s/h amplifier controlled by a highspeed comparator. The s/h amplifier holds the peak voltage, until the comparator switches the amp to its sample mode, to capture a new, higher voltage level. The....

This rf probe is coupled with a fiber-optiCJ:able to the test equipment. It utilizes inexpensive components to improve probe performance at UHF frequencies. The receiving antenna in this probe feeds an envelope-detector diode. After amplification by the....

Transistor Q1-configured as a source-follower buffer stage, offering a bit under unity voltage gaingives tbe unit a high-impedance input of about 1 MO shunted by about 10 pF, which keeps only minimal loading on tbe equipment being tested. C1 serves as....

This logic probe has four channels and uses two IF quad comparators to drive four bicolor LEDs. SI and SIB program the co..

A simple detector of radar signals uses the junctions of the input transistors of an LM1458 op amp as RF detectors. The lead..

The circuit, built around a single integrated circuit (Ul, an MC3403P quad op amp), three transistors (Q1-Q3), and a few support components,.receives its input from the antenna (ANT1). The signal is fed through a high-pass filter, formed by CI, C2, and Rl,....

The circuit is built around a 4049 hex inverter (Ul), a pair of 555 osciliator/timers (U2 arid U3), two transistors, a Geiger-Muller tube, and a few additional support components. The first 555 (U2) is configured for astable operation. The output of U2 (a....

Ql is a pnp power transistor used in conjunction with a ferrite transformer to form a blocking-type oscillator. This oscillator is a fixed- frequency type, and the feedback to sustain oscillations is from capacitor CI. Because of the turns ratio of Tl, the....

Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....

The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....

The metal detectors can be classified according to their principle of operation in those three categories: BFO, TR/IB and PI. Each of these methods has advantages as well as disadvantages. The ideal metal detector (do not look for it because it does not....

This circuit is a metal detector capable of detecting large metallic objects. at a depth of 2m to 3m. It depends on the size of the object, and often on the type of soil. Construction is very easy to implement even for a beginner. The necessary components....

This circuit really is the simplest inducer balancing metal detector (IB, Inductlon Balance) that can be built. The LB metal detection method has a satisfactory depth of penetration and good distinction between iron-based and noble metallic objects. Several....

The search coil, CI and C2 form a tuned circuit for the oscillator which is tuned near the center of the broadcast band. Tune a portable radio to a station near the middle of the band, then tune C2 until a squeal is heard as the two signals mix to produce a....

Using an oscillator running at 455 kHz, the metal-detector circuit produces an indication on the meter Ml. When the oscillat..

The metal locator uses a one-transistor oscillator and an AM radio to detect metal. Transistor Ql is a pnp transistor that is connected to an oscillator. Resistor Rl provides the correct base bias and capacitors C3 and 04 and the search coil determine the....

Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....

A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....

The main (and only) job of this circuit is to activate a buzzer or a relay, each time the level of humidity takes a specific value. Main stage is a memory based on a flip-flop consisting of gates and IC1a IC1 b. The output of this step activates an....

The operation of the circuit is based on the difference in the primary impedance of a transformer when its secondary is loaded and when it is open-circuit. The impedance of the primary of Tl and resistor Rl are in series with the load. The triac's....

To calibrate the gauge, connect the battery and press the probes gently into a pot containing a plant that is just on the verge of needing water (stick it in so that only an inch of the probe is left visible at the top). Turn the potentiometer until the "OK"....

This circuit combines two LTC1043s with a based humidity transducer in a simple charge-pump based circuit. The sensor specified has a nominal 400 pF capacitance at RH = 76%, with a slope of 1.7 pF/% RH. The average voltage across this device must be zero.....

The sensor circuit is adaptable to different liquids and sensors. The constant-current source drives current through the sensing probe and a fixed resistor..

Use this circuit to keep the fluid level of a liquid between two fixed points. Two modes, for filling or emptying are possible by simple reversing the contact connections of Kl. The loads can be either electric motors or solenoid operated valves, operating....

The circuit draws so little current that the shelf-line of the battery is the limiting factor. The only current drawn is the leakage of the transistor. The circuit is shown in the form of a water level alarm but by using different forms of probe can act as a....

The alarm is built around two audio oscillators, each using two NAND gates. The detection oscillator is gated on by a pair of remote probes. One of the probes is connected to the battery supply, the other to the input of one of the gates. When water flows....

The circuit uses four NAND gates of a 4011 package. In each oscillator, while one gate is configured as a straightforward inverter, the other has one input that can act as a control input. Oscillator action is inhibited if this input is held low. The first....

The unit consists of a sensor, timer, and electric water pump. The sensor is embedded in the soil, and when dry, the electronics operate the water pump for a preset time. The circuit is composed of a level sensitive Schmitt trigger, variable time monostable,....

With SI open the circuit functions as a doorbell. With SI closed, rain falling on the sensor will turn on Ql, triggering Q2 and the thyristor and activating the bell, R4 provides the holding for the thyristor while Dl prevents any damage to the thyristor....

This circuit is designed to detect the presence or absence of aqueous fluids. An ac signal generated on-chip is passed through two probes within the fluid. A detector determines the presence of the fluid by using the probes in a voltage divider circuit and....

When the water level is low, the probe is out of the water and SCRl is triggered on. It conducts and imposes a heavy load on transformer Tl"s secondary winding. That load is reflected back into the primary, gating triac TRl on, which energizes the load. If....

Although many circuits use the varying-capacitance method for checking liquid levels, this simple resistive circuit is much easier to construct. Even a tank of a liquid, such as water, has sufficient conductive salts in solution for this method to work.....

This monitor uses a common 7 41 amp configured as a comparator and a low cost nontransistor as an output driver. With no liquid detected, a voltage of about 2. 92 V is present in the op amp"s inverting input at pin 2. The 100-KO resistors establish a....

The sensor is an RC oscillator in which, a water-absorbent plastic film is the insulator in the capacitive element. The capacitance of the film increases with the amount of water it absorbs from the air, and thus reduces the oscillation frequency. A....

A simple bridge rectifier and a 12-V regUlator powers the MOSFET sensing circuit. The unregUlated output of the bridge rectifier operates the drain solenoid via switch S1: The sensor itself is built from two electrodes: one made of copper, -the other....

This circuit will power up a water pump when the water reaches a predetermined level. Then it turns itself off when the..

Originally, this circuit was used to sense a low-water level in a Christmas tree stand, but the circuit can be use..

Running a bath can end in a minor domestic disaster if you forget to turn off the taps in time. This indicator activ..

At the heart of the Full-Cup Detector is a 555-oscillator/timer configured to produce a 15-Hz click, until ..

If you choose to make your own moisture sensor,; this foil pattern should come in handy. A sensor connected to J1 causes S..

Using a capacitor sensor to detect a water level is a simple method of sensing. This circuit uses C5, which..

An infrared LED and a phototransistor are used for each eye. Half of a 556 timer IC (ICl-a) functions as an as table multivibrator oscillating at a frequency of about 1 kHz. That IC drives transistor Ql which in turn drives the two infrared LED's, LED1 and....

This circuit has stable threshold characteristics from its dependence on the-photo diode current in the Ll4Cl to generate a base emitter voltage drop across the sensitivity setting resistor. The double phase shift network supplying voltage to the ST-4....

An automatic control maintains a lamp at a constant brightness over a wide range of supply voltages. This circuit utilizes the consistency of photodiode response to control the phase angle of power line voltage applied to the lamp and can vary the power....

Monitoring a flame and directly switching a 120-V load is easily accomplished using the Ll4G1 for point sources of light. For light sources which subtend over 10° of arc, the L14C1 should be used and the illumination levels raised by a factor of 5. ..

This self-biasing configuration is useful any time srnall changes in light level must be detected, for example, when monitoring very low flow rates by counting drops of fluid. In this bias method, the photodarlington is de bias stabilized by feedback from....

A school drama needed lamps that automatically turned on and off when spot lights did the same. Lamp switching had to be wireless, durable, dependable, simple and inexpensive. With stage and spot lights off, very little light falls on the CdS photocell, so....

This circuit is designed to detect a low light level at the sensor, amplify the signal, and provide a TTLlevet output. When the optical sensor detects low-levellight, on condition, its output is small and must be amplified. An amp with very low input bias....

This circuit"s frequency of oscillation increases directly with light intensity. The greater the light intensity, the higher the frequency of the oscillator. The 555 timer operates in the astable oscillator mode where frequency and duty cycle are....

If R, the sensor matching resistor, is equal to the "dark" resistance of the cadmium sulfide cell, the amplifier output will range from 0 to "" 2 as the lightlevel ranges from "dark" to "bright." The circuit in Fig. B operates similarly, but use the....

This circuit provides a very low cost method of controlling light levels. Circuit power is obtained from a relatively high source impedance transformer or motor windings, normally used to drive the low-voltage lamps used in these functions. It should be....

A flashing light of high brightness and short duty cycle is often desired to provide maximum visibility and battery life. This necessitates using an output transistor, which can supply the cold filament surge current of the lamp while maintaining a low....

In solar cell array applications and solar instrumentation, it is desirable to monitor the approximate position of the sun to allow efficient automatic alignment. The Ll4Gllens can provide about 15° of accuracy in a simple level sensing circuit, and a....

For a dark photocell, high resistance, the vohage across the diac rises rapidly with the line voltage due to the current through C 1, triggering the diac early in the cycle. ..

The op amp is alternately an inverter or buffer, under control of the switch polarity. As a buffer, the gai..

Using only an 8-pin IC and a few discrete components, you can build the infrared optical interrupter. The NE567..

This circuit modulates the current through a lamp filament. Use a low-voltage lamp with a thin, straight filament. They h..

The circuit"s threshold is set by resistor R2. When the intensity of the light falling on the LDR is lowered, resistance of ..

When the light beam that falls in the CDS photocell is interrupted, transistor (EN3904) conducts thereby triggering SCR1 (CI06) and activating alarm bell. SI resets the SCR. The alarm bell should be a self-interrupting electromechanical type...

The light-sensitive CDS cell R8 configured in a bridge circuit with IC1 as a comparator causes ICl`s output to go high when light strikes the CDS cell R8, triggering SCR1...

The TL081 is used as a comparator in a Wheatstone bridge circuit. When the CDS cell resistance decreases due to exposure to light, the output from IC2 cause the low-frequency oscillator (a) and (b) to generate a 10-Hz square wave, gating the 1000 Hz....

Two op amps used in a bridge circuit configuration detect high and low light levels. Potentiometer R2 sets the dark level and Rl controls the light level. R3 is set so that about lA the supply voltage appears across R4 at the desired light level. ..