Mains Pulser Circuit Diagram

The pulser is intended to switch the mains voltage on and off at intervals between just under a second and up to 10 minutes. This is useful, for instance, when a mains-operated equipment is to be tested for long periods, or for periodic switching of machinery. Transformer Tr1, the bridge rectifier , and regulator IC1 provide a stable 12V supply rail for IC2 and the relay. The timer is arranged so that the period-determining capacitor can be charged and discharged independently. Four time ranges can be selected by selecting capacitors with the aid of jumpers. Short-circuiting positions 1 and 2 gives the longest time, and short-circuiting none the shortest.

Mains Pulser Circuit Diagram

In the latter case, the 10µF capacitor at pins 2 and 6 of the timer IC determines the time with the relevant resistors. The value of this capacitor may be chosen slightly lower. The two preset potentiometers enable the on and off periods to be set. The 1k resistor in series with one of the presets determines the minimum discharge time. The timer IC switches a relay whose double-pole contacts switch the mains voltage. The LEDs indicate whether the mains voltage is switched through (red) or not (green). The 100mA slow fuse protects the mains transformer and low-voltage circuit. The 4 A medium slow fuse protects the relay against overload.

Source by : Streampowers

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Mains Voltage Monitor

Many electronics hobbyists will have experienced the following: you try to finish a project late at night, and the mains supply fails. Whether that is caused by the electricity board or your carelessness isn’t really important. In any case, at such times you may find yourself without a torch or with flat batteries. There is no need to panic, as this circuit provides an emergency light. When the mains fails, the mains voltage monitor turns on five super bright LEDs, which are fed from a 9 V battery (NiCd or NiMH) or 7 AA cells. A buzzer has also been included, which should wake you from your sleep when the mains fails.

You obviously wouldn’t want to oversleep because your clock radio had reset, would you? When the mains voltage is present, the battery is charged via relay Re1, diode D8 and resistor R10. D8 prevents the battery voltage from powering the relay, and makes sure that the relay switches off when the mains voltage disappears. R10 is chosen such that the charging current of the battery is only a few milliamps. This current is small enough to prevent over-charging the battery. D6 acts as a mains indicator. When the relay turns off, IC1 receives power from the battery. The JK flip-flops are set via R12 and C4.

Circuit diagram:

Mains Voltage Monitor Circuit Diagram

This causes T1 and T2 to conduct, which turns on D1-D5 and the buzzer. When the push button is pressed, a clock pulse appears on the CLK input of flip-flop IC1b. The output then toggles and the LEDs turn off. At the same time IC1a is reset, which silences the buzzer. If you press the button again, the LEDs will turn on since IC1b receives another clock pulse. The buzzer remains off because IC1a stays in its reset state. R11, R3 and C3 help to debounce the push button signal. In this way the circuit can also be used as a torch, especially if a separate mains adapter is used as the power supply.

As soon as the mains voltage is restored, the relay turns on, the LEDs turn off and the battery starts charging. The function of R13 is to discharge C4, preparing the circuit for the next mishap. If mains failures are a regular occurrence, we recommend that you connect pairs of LEDs in series. The series resistors should then have a value of 100 ?. This reduces the current consumption and therefore extends the battery life. This proves very useful when the battery hasn’t recharged fully after the last time. In any case, you should buy the brightest LEDs you can get hold of. If the LEDs you use have a maximum current of 20 mA, you should double the value of the series resistors! You could also consider using white LEDs.

Source by : Streampowers

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Mains Slave Switcher II Circuit Diagram

As a guide, a one-inch reed switch with 40 turns reliably switched on with the current flowing through a 150-watt lamp (approx. 625 mA) but larger reeds may require more turns. If the master appliance draws less current (which is unlikely with power tools) more turns will be required. The reed switch is used to switch on transistor T1 which in turn switches the relay RE1 and powers the slave appliance. Since reed switches have a low mechanical inertia, they have little difficulty in following the fluctuations of the magnetic field due to the alternating current in the coil and this means that they will switch on and off at 100 Hz.

Circuit diagram:

Mains Slave Switcher II Circuit Diagram

C3 is therefore fitted to slow down the transistor response and keep the relay energised during the mains zero crossings when the current drawn by the appliance falls to zero and the reed switch opens. C1 drops the mains voltage to about 15 V (determined by zener diode D1) and this is rectified and smoothed by D2 and C2 to provide a d.c. supply for the circuit. The relay contacts should be rated to switch the intended appliance (vacuum cleaner) and the coil should have a minimum coil resistance of 400 R as the simple d.c. supply can only provide a limited current. C1 drops virtually the full mains voltage and should therefore be a n X2-class component with a voltage rating of at least 250V a.c.

Warning:

The circuit is by its nature connected directly to the mains supply. Great care should therefore be taken in its construction and the circuit should be enclosed in a plastic or earthed metal box with mains sockets fitted for the master and slave appliances.

Source by : Streampowers

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Simple Power-Saving Relay Driver Circuit Diagram

In many circuits, the switching action is performed by a relay, which in turn activates an external load. The power consumed by the relay may be unsuitable for battery-powered applications. Here is a simple solution using some inexpensive components to considerably save power.

Circuit and working

Fig. 1 shows circuit diagram of the power-saving relay driver where resistor R1 and transistor T1 form a standard relay driver circuit.

Power-Saving Relay Driver Circuit Diagram

Once the relay is energised, its pole is pulled in to make contact with the N/O side, and it holds in that position with typically 75 per cent of its nominal-rated voltage. Power consumed by a relay coil during this holding time equals V²/R, where R is resistance of the relay coil and V is the voltage. Here resistors R2 and R3, transistor T2 and capacitor C1 lower the power consumption after actuation by applying less than the normal operating power.

Initially, when power is applied, capacitor C1 momentarily shorts resistor R2 and allows full voltage across the relay to pull the pole contact, and then slowly the current through the capacitor drops.

In the meantime, resistor R2 takes care of the current, ensuring it is just sufficient to hold the relay. The constant current mechanism formed by transistor T2 and resistors R2 and R3 effectively drives the relay at very less power.

Following calculations will help us understand how additional circuitry around relay driver transistor T1 saves power. Relay used here is a 12V, 400-ohm sugar-cube type. You can calculate the power saved as shown below:

Nominal current required for the relay (I)= 12V/400 ohm = 30mA
Power consumed by the relay=I2R=0.03A×0.03A×400 ohm =360mW

After introduction of the circuit:

The current through the coil (I) =VBE/R2=0.6V/47 ohm=12mA
Power consumed by the overall circuit = V×I = 12×0.012=144mW
Power saved=360mW-144mW=216mW

So, we conclude that considerable power can be saved using the additional circuitry.

This makes it fairly simple for anyone to re-design a relay driver to reduce its power consumption without the use of any expensive components.

Construction and testing

An actual-size, single-side PCB for the power-saving relay driver is shown in Fig. 2 and its component layout in Fig. 3.

Switch S1 is used to test the relay driver circuit. You can connect the output of a control circuit, such as a micro controller, to CON2 for controlling the relay circuit.
CON3 helps in connecting to the electrical load. You can connect the load between N/O and pole contacts or N/C and pole contacts.

Fig. 2: An actual-size, single-side PCB for the power-saving relay driver

 

 Fig. 3: Component layout for the PCB

Before connecting the load to CON3, verify the test point voltages given in the table. You
may reduce the value of R1 as per your requirement.

                                                         Sourced By: EFY Author:  T.A. Babu

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Simple Mini High-Voltage Generator Circuit Diagram

Here’s a project that could be useful this summer on the beach, to stop anyone touching your things left on your beach towel while you’ve gone swimming; you might equally well use it at the office or workshop when you go back to work. In a very small space, and powered by simple primary cells or rechargeable batteries, the proposed circuit generates a low-energy, high voltage of the order of around 200 to 400 V, harmless to humans, of course, but still able to give a quite nasty ‘poke’ to anyone who touches it.  Quite apart from this practical aspect, this project will also prove instructional for younger hobbyists, enabling them to discover a circuit that all the ‘oldies’ who’ve worked in radio, and having enjoyed valve technology in particular, are bound to be familiar with. As the circuit diagram shows, the project is extremely simple, as it contains only a single active element, and then it’s only a fairly ordinary transistor. As shown here, it operates as a low-frequency oscillator, making it possible to convert the battery’s DC voltage into an AC voltage that can be stepped up via the transformer.  

Using a centre-tapped transformer as here makes it possible to build a ‘Hartley’ oscillator around transistor T1, which as we have indicated above was used a great deal in radio in that distant era when valves reigned supreme and these was no sign of silicon taking over and turning most electronics into ‘solid state’. The ‘Hartley’ is one of a number of L-C oscillator designs that made it to eternal fame and was named after its invertor, Ralph V.L Hartley (1888-1970). For such an oscillator to work and produce a proper sinewave output, the position of the intermediate tap on the winding used had to be carefully chosen to ensure the proper step-down (voltage reduction) ratio.  Here the step-down is obtained inductively. Here, optimum inductive tapping is not possible since we are using a standard, off-the-shelf transformer. However we’re in luck — as its position in the centre of the winding creates too much feedback, it ensures that the oscillator will always start reliably. 

However, the excess feedback means that it doesn’t generate sinewaves; indeed, far from it. But that’s not important for this sort of application, and the transformer copes very well with it.  The output voltage may be used directly, via the two current-limiting resistors R2 an R3, which must not under any circum-stances be omitted or modified, as they are what make the circuit safe. You will then get around 200 V peak-to-peak, which is already quite unpleasant to touch. But you can also use a voltage doubler, shown at the bottom right of the figure, which will then produce around 300 V, even more unpleasant to touch. Here too of course, the resistors, now know as R4 and R5, must always be present. The circuit only consumes around a few tens of mA, regardless of whether it is ‘warding off’ someone or not! If you have to use it for long periods, we would however recommend powering it from AAA size Ni-MH batteries in groups of ten in a suitable holder, in order not to ruin you buying dry batteries.

Circuit diagram:

Mini High-Voltage Generator Circuit Diagram

Warning!

If you build the version without the voltage doubler and measure the output voltage with your multimeter, you’ll see a lower value than stated. This is due to the fact that the waveform is a long way from being a sinewave, and multimeters have trouble interpreting its RMS (root-mean-square) value. However, if you have access to an oscilloscope capable of handling a few hundred volts on its input, you’ll be able to see the true values as stated. If you’re still not convinced, all you need do is touch the output terminals... 

To use this project to protect the handle of your beach bag or your attachecase, for example, all you need do is fix to this two small metallic areas, quite close together, each connected to one output terminal of the circuit. Arrange them in such a way that unwanted hands are bound to touch both of them together; the result is guaranteed! Just take care to avoid getting caught in your own trap when you take your bag to turn the circuit off!

..::: Do not built this circuit if your not an EXPERT :::..

Streampowers

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Electrification Unit Circuit Diagram

The circuit is intended for carrying out harmless experiments with high-voltage pulses and functions in a similar way as an electrified fence generator. The p.r.f. (pulse repetition frequency) is determined by the time constant of network R1-C3 in the feedback loop of op amp IC1a: with values as specified, it is about 0.5 Hz. The stage following the op amp, IC1b, converts the rectangular signal into narrow pulses. Differentiating network R2-C4, in conjunction with the switching threshold of the Schmitt trigger inputs of IC1b, determines the pulse period, which here is about 1.5 ms. The output of IC1b is linked directly to the gate of thyristor THR1, so that this device is triggered by the pulses.

The requisite high voltage is generated with the aid of a small mains transformer, whose secondary winding is here used as the primary. This winding, in conjunction with C2, forms a resonant circuit. Capacitor C3 is charged to the supply voltage (12 V) via R3.When a pulse output by IC1b triggers the thyristor, the capacitor is discharged via the secondary winding. The energy stored in the capacitor is, however, not lost, but is stored in the magnetic field produced by the transformer when current flows through it. When the capacitor is discharged, the current ceases, whereupon the magnetic field collapses. This induces a counter e.m.f. in the transformer winding which opposes the voltage earlier applied to the transformer.

Circuit diagram:

Simple Electrification Unit Circuit Diagram

This means that the direction of the current remains the same. However, capacitor C2 is now charged in the opposite sense, so that the potential across it is negative. When the magnetic field of the transformer has returned the stored energy to the capacitor, the direction of the current reverses, and the negatively charged capacitor is discharged via D1 and the secondary winding of the transformer. As soon as the capacitor begins to be discharged, there is no current through the thyristor, which therefore switches off. When C2 is discharged further, diode D1 is reverse-biased, so that the current loop to the transformer is broken, whereupon the capacitor is charged to 12 V again via R3. At the next pulse from IC1b, this process repeats itself.

Since the transformer after each discharge of the capacitor at its primary induces not only a primary, but also a secondary voltage, each triggering of the thyristor causes two closely spaced voltage pulses of opposite polarity. These induced voltages at the secondary, that is, the 230 V, winding, of the transformer are, owing to the higher turns ratio, much higher than those at the primary side and may reach several hundred volts. However, since the energy stored in capacitor C2 is relatively small (the current drain is only about 2 mA), the output voltage cannot harm man or animal. It is sufficient, however, to cause a clearly discernible muscle convulsion.

Source by : streampowers

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Simple Stethoscope Circuit Diagram

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 does not occur in acoustic stethoscopes.

Still there are a large number of companies offering electronic stethoscopes that rely on conversion of acoustic sound waves into electrical signals that can be amplified and processed making a faithful sound system, almost equal to the acoustic. Electronic stethoscopes sold commercially using various systems, the most common is a piezoelectric crystal placed in behind a foam rubber membrane as a pickup.

Simple Stethoscope Circuit Diagram

The evolution of electronic stethoscopes also made possible the emergence of new tests as the phonocardiogram and telemedicine which allowed remote diagnostics.

The circuit simpler and less effective sound detection is achieved by a set of a microphone, an amplifier and a speaker or earphone. This method suffers interference from environmental noise but can be used as a simple electronic stethoscope. Precisely, the simplest is that we show here in this article.

Above the electronic stethoscope circuit, its operation is as follows, one capsule, electret microphone is used as sound pickup, the U1A integrated circuit which is a TL072 has the low noise pre-amplifier function. Your gain is less than 3.9, which is due to the high output impedance of the electret microphone.

The capacitor C2 has a relatively large capacitance, as it filters, leaving only pass the low frequency (20-30 Hz) that are the sounds of a beating heart. The U1B mounted on a Sallen-Key filter low noise with a cutoff frequency of about 103 Hz. R7 and R8 set the gain level of the order of 1.6. The integrated circuit U5 which is a LM386 audio amplifier with an output of 0.25 watts. Part of the U4 integrated circuit can be optional, it is an operational amplifier 741 that controls the two-color LED.

Electronic Stethoscope components list

R1 - 10k ¼ W resistor
R2 - 2.2 ohm ¼ W resistor
R3, R9 - Not used
R4 ¼ W 47 Ohm resistor
R5, R6, R7 - 33K resistor ¼ W
R8 - 56 Ohm resistor ¼ W
R10 - 4k7 ¼ W resistor
R11 - variable resistor of 2.2 logarithmic
R12 - resistor 330 Ohm ¼ W
R13, R15, R16 1K resistor ¼ W
R14 - resistor 3.9 ohm resistor ¼ W
C1, C8 - electrolytic capacitors 470 uF / 16 V
C2 - electrolytic capacitor 4.7 uF / 16 V
C3, C4 - Polyester Capacitors 0.047 uF / 50 V
C5 - ceramic disc capacitor 0.1 uF / 50 V
C6, C7 - electrolytic capacitors 1000 uF / 16 V
U1 TL072
U2, U3 Not used
U4 - 741
U5 - LM386
MIC - electric microphone three terminals

The circuit is very simple and can be mounted on breadboard, on the microphone connection with the circuit should be used shielded cable to prevent noise pickup. You must mount the pickup so that the microphone is placed at a distance from the skin surface but one that is close to the body to protect the microphone from external noise.

Keep the microphone away from the headphones to avoid feedback. Unfortunately, the device offers a very limited application, use it only as a learning circuit, test or demonstration. Link

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Ac line Voltage Announcer Circuit Diagram

Ac line Voltage Announcer Circuit Diagram. The range of this simple ac-voltage monitor is 100 to 140 Vac, with a resolution of 1 V. The speech processor interprets an 8-bit binary input code from an analog-to-digital converter. The processor`s pulse-code-mod ulated output then passes through a filter and an amplifier before driving tbe circuit`s speaker to vocalize the corresponding number. Each time switch S1 is _pressed, the speech-processor program enun ciates tbe monitored voltage readings from 100 to 140 V, depending on the code at the input of a 27C64 EPROM.

 Simple Ac line Voltage Announcer Circuit Diagram

 

 

The voltage-monitoring circuit consists of a bridge rectifier, filter capacitors, and a 10-Kilload resis tor. A divider, RA and RB, limits the input voltage to a maximum 2.55 V. The aid converter, IC4, then sends the voltage reading to tbe 27C64 EPROM, ICS. Pressing Sl sends a negative transient pulse to the write, WR, input of the aid converter, IC4, which initiates a 100-ttS conversion process. [Link]

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Fuse Saver Circuit Diagram

This circuit will be particularly useful to those hobbyists who use a ‘breadboard’ to try out ideas and who also use a simple ‘home-made’ DC power supply consisting of a transformer, rectifier, smoothing capacitor and protective fuse, that is, one without over current protection! In this circuit, the detecting element is resistor R6. Under normal conditions, its voltage drop is not high enough to switch on transistor T1. The value of R6 can be altered to give a different cut-off current, as determined by Ohm’s Law, if required. When a short circuit occurs in the load, the voltage rises rapidly and T1 starts to conduct. 

This draws in the relay, switching its contacts, which cuts off power to the external circuit, and instead powers the relay coil directly, latching it in this second state. The circuit remains in this state until the primary power supply is switched off. Capacitors C1 and C2 hold enough charge (via D3, D4 and D6, which prevent the charge from being lost to the rest of the circuit, whichever state it is in) to keep T1 switched on and power the relay while it switches over, and R2 and R4 provide slow discharge paths. LEDs D1 (red) and D5 (green) indicate what state the circuit is in. Inductor L1 slows the inrush of current when the circuit is switched on, which would otherwise cut off the circuit immediately.

Fuse Saver Circuit Diagram

D2 and D7 provide the usual back-emf protection across the coils. In use, the input of the circuit is connected to the main transformer-rectifier-capacitor-fuse power supply via K1, and the output is connected to the (experimental) load via K2. Note that the input voltage must be a floating supply if Vout– is grounded via the load, as Vin– and Vout– must not be connected together. Some consideration needs to be given to a number of components. First, the choice of relay Re1. For the prototype, this was obtained from Maplin, part number YX97F. This is has a coil resistance of 320 ?, which with R1 forms the collector load for T1. 

Its allowed pull-in voltage range is nominally 9 V to 19 V, which limits the input power supply voltage to between around 10 V to 30 V (DC only). R1 could be replaced by a wire link for operation at input voltages below 10 V, or increased in value, as determined by either the application of Ohm’s Law once more or trial and error, for an input voltage above 30 V. Coil L1 was obtained from Farnell, part number 581-240. Finally, the protective fuse for the input power supply should be a ‘slow-blow’ type; ‘fast’ fuses will rupture before the relay has time to switch. Also note that this device is meant to save fuses, not replace them. A mains transformer must always be fused if it is not designed to run safely, i.e., without presenting a fire hazard, even if its output has a continuous short-circuit fault.

Streampowers

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Mains Manager Circuit Diagram

Very often we forget to switch off the peripherals like monitor, scanner, and printer while switching off our PC. The problem is that there are separate power switches to turn the peripherals off. Normally, the peripherals are connected to a single of those four-way trailing sockets that are plugged into a single wall socket. If that socket is accessible, all the devices could be switched off from there and none of the equipment used will require any modification. 

Here is a mains manager circuit that allows you to turn all the equipment on or off by just operating the switch on any one of the devices; for example, when you switch off your PC, the monitor as well as other equipment will get powered down automatically. You may choose the main equipment to control other gadgets. 

The main equipment is to be directly plugged into the master socket, while all other equipment are to be connected via the slave socket. The mains supply from the wall socket is to be connected to the input of the mains manager circuit. The unit operates by sensing the current drawn by the control equipment/load from the master socket. On sensing that the control equipment is on, it powers up the other (slave) sockets.

The load on the master socket can be anywhere between 20 VA and 500 VA, while the load on the slave sockets can be 60 VA to 1200 VA. During the positive half cycle of the mains AC supply, diodes D4, D5, and D6 have a voltage drop of about 1.8 volts when current is drawn from the master socket. Diode D7 carries the current during negative half cycles. Capacitor C3, in series with diode D3, is connected across the diode combination of D4 through D6, in addition to diode D7 as well as resistor R10. Thus current pulses during positive half-cycles, charge up the capacitor to 1.8 volts via diode D3. 

This voltage is sufficient to hold transistor T2 in forward biased condition for about 200 ms even after the controlling load on the master socket is switched off. When transistor T2 is ‘on’, transistor T1 gets forward biased and is switched on. This, in turn, triggers Triac 1, which then powers the slave loads. Capacitor C4 and resistor R9 form a snubber network to ensure that the triac turns off cleanly with an inductive load.

Circuit diagram:

Mains Manager Circuit Diagram

LED1 indicates that the unit is operating. Capacitor C1 and zener ZD1 are effectively in series across the mains. The resulting 15V pulses across ZD1 are rectified by diode D2 and smoothened by capacitor C2 to provide the necessary DC supply for the circuit around transistors T1 and T2. Resistor R3 is used to limit the switching-on surge current, while resistor R1 serves as a bleeder for rapidly discharging capacitor C1 when the unit is unplugged. LED1 glows whenever the unit is plugged into the mains. Diode D1, in anti-parallel to LED1, carries the current during the opposite half cycles. Don’t plug anything into the master or slave sockets without testing the unit.

If possible, plug the unit into the mains via an earth leakage circuit breaker. The mains LED1 should glow and the slave LED2 should remain off. Now connect a table lamp to the master socket and switch it ‘on’. The lamp should operate as usual. The slave LED should turn ‘on’ whenever the lamp plugged into slave socket is switched on. Both lamps should be at full brightness without any flicker. If so, the unit is working correctly and can be put into use.

Note:

1. The device connected to the master socket must have its power switch on the primary side of the internal transformer. Some electronic equipment have the power switch on the secondary side and hence these devices continue to draw a small current from the mains even when switched off. Thus such devices, if connected as the master, will not control the slave units correctly. 
2. Though this unit removes the power from the equipment being controlled, it doesn’t provide isolation from the mains. So, before working inside any equipment connected to this unit, it must be unplugged from the socket.

Source by : Streampowers

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Power Flip-Flop Using A Triac Circuit Diagram

Modern electronics is indispensable for every large model railroad system, and it provides a solution to almost every problem. Although ready-made products are exorbitantly expensive, clever electronics hobbyists try to use a minimum number of components to achieve optimum results together with low costs. This approach can be demonstrated using the rather unusual semiconductor power flip-flop described here. A flip-flop is a toggling circuit with two stable switching states (bistable multivibrator). It maintains its output state even in the absence of an input pulse.

Flip-flops can easily be implemented using triacs if no DC voltage is available. Triacs are also so inexpensive that they are often used by model railway builders as semiconductor power switches. The decisive advantage of triacs is that they are bi-directional, which means they can be triggered during both the positive and the negative half-cycle by applying an AC voltage to the gate electrode (G). The polarity of the trigger voltage is thus irrelevant. Triggering with a DC current is also possible. Figure 1 shows the circuit diagram of such a power flop-flop. A permanent magnet is fitted to the model train, and when it travels from left to right, the magnet switches the flip-flop on and off via reed switches S1 and S2.

Circuit diagram:

In order for this to work in both directions of travel, another pair of reed switches (S3 and S4) is connected in parallel with S1 and S2. Briefly closing S1 or S3 triggers the triac. The RC network C1/R2, which acts as a phase shifter, maintains the trigger current. The current through R2, C1 and the gate electrode (G) reaches its maximum value when the voltage across the load passes through zero. This causes the triac to be triggered anew for each half-cycle, even though no pulse is present at the gate. It remains triggered until S2 or S4 is closed, which causes it to return to the blocking state.The load can be incandescent lamps in the station area (platform lighting) or a solenoid-operated device, such as a crossing gate. The LED connected across the output (with a rectifier diode) indicates the state of the flip-flop. 

The circuit shown here is designed for use in a model railway system, but there is no reason why it could not be used for other applications. The reed switches can also be replaced by normal pushbutton switches. For the commonly used TIC206D triac, which has a maximum current rating of 4 A, no heat sink is necessary in this application unless a load current exceeding 1 A must be supplied continuously or for an extended period of time. If the switch-on or switch-off pulse proves to be inadequate, the value of electrolytic capacitor C1 must be increased slightly.

Source by : http://streampowers.blogspot.com/2012/06/power-flip-flop-using-triac.html

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Supply Voltage Monitor Circuit Diagram

A circuit for monitoring supply voltages of ±5 V and ±12 V is readily constructed as shown in the diagram. It is appreciably simpler than the usual monitors that use comparators, and AND gates. The circuit is not intended to indicate the level of the inputs. In normal operation, transistors T1 and T3 must be seen as current sources. The drop across resistors R1 and R2 is 6.3 V (12 –5 –0.7). This means that the current is 6.3mA and this flows through diode D1 when all four voltages are present. However, if for instance, the –5 V line fails, transistor T3 remains on but the base-emitter junction of T2 is no longer biased, so that this transistor is cut off. When this happens, there is no current through D which then goes out.

Streampowers

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Non-Contact Power Monitor circuit Diagram

Here is a simple non-contact AC power monitor for home appliances and laboratory equipment that should remain continuously switched-on. A fuse failure or power breakdown in the equipment going unnoticed may cause irreparable loss. The monitor sounds an alarm on detecting power failure to the equipment. The circuit is built around CMOS IC CD4011 utilising only a few components. NAND gates N1 and N2 of the IC are wired as an oscillator that drives a piezobuzzer directly. Resistors R2 and R3 and capacitor C2 are the oscillator components. The amplifier comprising transistors T1 and T2 disables the oscillator when mains power is available. In the standby mode, the base of T1 picks up 50Hz mains hum during the positive half cycles of AC and T1 conducts.

Circuit diagram:

   

Non-Contact Power Monitor circuit diagram

  

This provides base current to T2 and it also conducts, pulling the collector to ground potential. As the collectors of T1 and T2 are connected to pin 2 of NAND gate N1 of the oscillator, the oscillator gets disabled when the transistors conduct. Capacitor C1 prevents rise of the collector voltage of T2 again during the negative half cycles. When the power fails, the electrical field around the equipment’s wiring ceases and T1 and T2 turn off. Capacitor C1 starts charging via R1 and preset VR and when it gets sufficiently charged, the oscillator is enabled and the piezobuzzer produces a shrill tone. Resistor R1 protects T2 from short circuit if VR is adjusted to zero resistance.

The circuit can be easily assembled on a perforated/breadboard. Use a small plastic case to enclose the circuit and a telescopic antenna as aerial. A 9V battery can be used to power the circuit. Since the circuit draws only a few microamperes current in the standby mode, the battery will last several months. After assembling the circuit, take the aerial near the mains cable and adjust VR until the alarm stops to indicate the standby mode. The circuit can be placed on the equipment to be monitored close to the mains cable.

 Source by : Streampowers

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Tri-Waveform Generator Circuit Diagram

The Tri-Waveform Generator can be used for a number of different uses. The one that I use it for is a signal generator to test circuits. The frequency range is 20 to 20khz. and can be adjusted by R1. The duty cycle or the time that the waveform is high and the time that the waveform is low can be adjusted by R4. The purpose of R2 and R3 are to clean up any distortion on the sine wave output. To do this you must hook up the sine wave output to and oscilloscope and adjust R2 & R3 to make the sine wave as accurate as possible.

Source by : Streampowers

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Audio Controlled Mains Switch Circuit Diagram

It is often useful for audio or video equipment to be switched off automatically after there has been no input signal for a while. The function of the on-off switch in such equipment is then taken over by switch S2 in the accompanying diagram. It remains, however, possible to  switch off manually by means of Si. Automatic  switch-off occurs after there has been no input  signal for about 2 minutes: this delay makes it possible for a new record or cassette to be placed in the  relevant machine.

 

The audio input to the proposed circuit may be  taken from the output of the relevant TV set, amplifier, or whatever. The input earth is held at + 6 V  with respect to the circuit earth by potential divider  Ri-R2-R3-R4. The two 741s function as comparators: the output of ICi goes high when the in- put signal is greater than + 50 mV, whereas the out- put of IC2 goes high when the input signal  becomes more negative than -50 mV. Resistors  R6, R7, and R8 form an OR gate that drives transistor Ti. If the output of either ICi or IC2 is logic  1, Ti conducts.

 

Audio Controlled Mains Switch  Circuit diagram :

 

Audio Controlled Mains Switch Circuit Diagram

The 555  operates as a retrigger able monostable,  whose period is determined by Rio and Ci. The  device is triggered when its pin 2 is earthed by the  closing of S2. Its output, pin 3, then remains high  for 1 to 2 minutes, depending on the leakage cur- rent of the 555. 

The monostable resets itself as soon  as the potential across Ci exceeds a certain value.  As long as there is an input signal to the circuit, Ti conducts and Ci remains uncharged. As soon as  the audio signal ceases, Ti switches off, and Ci  charges until the potential across it is sufficient to  reset the 555. The monostable may also be reset by  closing Si, which connects pin 6 of the 555 to + 12 V.

 

When IC3 is reset, Ci is discharged via its pin 7. Resistor Rrn serves as protection, because without it Ti could short-circuit the supply lines. When the output of IC3 goes high, T2 conducts,  the relay is energized, and the relay contacts switch on the mains voltage as appropriate. To counter the induced potential when the relay contacts close, which could damage T2, diode Di has been connected in parallel with the relay coil.

Source by : Streampowers

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Power Flip-Flop Using A Triac Circuit Diagram

Modern electronics is indispensable for every large model railroad system, and it provides a solution to almost every problem. Although ready-made products are exorbitantly expensive, clever electronics hobbyists try to use a minimum number of components to achieve optimum results together with low costs. This approach can be demonstrated using the rather unusual semiconductor power flip-flop described here. A flip-flop is a toggling circuit with two stable switching states (bistable multivibrator). It maintains its output state even in the absence of an input pulse.

Flip-flops can easily be implemented using triacs if no DC voltage is available. Triacs are also so inexpensive that they are often used by model railway builders as semiconductor power switches. The decisive advantage of triacs is that they are bi-directional, which means they can be triggered during both the positive and the negative half-cycle by applying an AC voltage to the gate electrode (G). The polarity of the trigger voltage is thus irrelevant. Triggering with a DC current is also possible. Figure 1 shows the circuit diagram of such a power flop-flop. A permanent magnet is fitted to the model train, and when it travels from left to right, the magnet switches the flip-flop on and off via reed switches S1 and S2.

Power Flip-Flop Using A Triac  Circuit diagram:

In order for this to work in both directions of travel, another pair of reed switches (S3 and S4) is connected in parallel with S1 and S2. Briefly closing S1 or S3 triggers the triac. The RC network C1/R2, which acts as a phase shifter, maintains the trigger current. The current through R2, C1 and the gate electrode (G) reaches its maximum value when the voltage across the load passes through zero. This causes the triac to be triggered anew for each half-cycle, even though no pulse is present at the gate. It remains triggered until S2 or S4 is closed, which causes it to return to the blocking state.The load can be incandescent lamps in the station area (platform lighting) or a solenoid-operated device, such as a crossing gate. The LED connected across the output (with a rectifier diode) indicates the state of the flip-flop. 

The circuit shown here is designed for use in a model railway system, but there is no reason why it could not be used for other applications. The reed switches can also be replaced by normal pushbutton switches. For the commonly used TIC206D triac, which has a maximum current rating of 4 A, no heat sink is necessary in this application unless a load current exceeding 1 A must be supplied continuously or for an extended period of time. If the switch-on or switch-off pulse proves to be inadequate, the value of electrolytic capacitor C1 must be increased slightly.

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Mini High-Voltage Generator Circuit

Here’s a project that could be useful this summer on the beach, to stop anyone touching your things left on your beach towel while you’ve gone swimming; you might equally well use it at the office or workshop when you go back to work. In a very small space, and powered by simple primary cells or rechargeable batteries, the proposed circuit generates a low-energy, high voltage of the order of around 200 to 400 V, harmless to humans, of course, but still able to give a quite nasty ‘poke’ to anyone who touches it.

Quite apart from this practical aspect, this project will also prove instructional for younger hobbyists, enabling them to discover a circuit that all the ‘oldies’ who’ve worked in radio, and having enjoyed valve technology in particular, are bound to be familiar with. As the circuit diagram shows, the project is extremely simple, as it contains only a single active element, and then it’s only a fairly ordinary transistor. As shown here, it operates as a low-frequency oscillator, making it possible to convert the battery’s DC voltage into an AC voltage that can be stepped up via the transformer.

Using a centre-tapped transformer as here makes it possible to build a ‘Hartley’ oscillator around transistor T1, which as we have indicated above was used a great deal in radio in that distant era when valves reigned supreme and these was no sign of silicon taking over and turning most electronics into ‘solid state’. The ‘Hartley’ is one of a number of L-C oscillator designs that made it to eternal fame and was named after its invertor, Ralph V.L Hartley (1888-1970). For such an oscillator to work and produce a proper sinewave output, the position of the intermediate tap on the winding used had to be carefully chosen to ensure the proper step-down (voltage reduction) ratio.

Here the step-down is obtained inductively. Here, optimum inductive tapping is not possible since we are using a standard, off-the-shelf transformer. However we’re in luck — as its position in the centre of the winding creates too much feedback, it ensures that the oscillator will always start reliably. However, the excess feedback means that it doesn’t generate sinewaves; indeed, far from it. But that’s not important for this sort of application, and the transformer copes very well with it.

The output voltage may be used directly, via the two current-limiting resistors R2 an R3, which must not under any circum-stances be omitted or modified, as they are what make the circuit safe. You will then get around 200 V peak-to-peak, which is already quite unpleasant to touch. But you can also use a voltage doubler, shown at the bottom right of the figure, which will then produce around 300 V, even more unpleasant to touch. Here too of course, the resistors, now know as R4 and R5, must always be present. The circuit only consumes around a few tens of mA, regardless of whether it is ‘warding off’ someone or not! If you have to use it for long periods, we would however recommend powering it from AAA size Ni-MH batteries in groups of ten in a suitable holder, in order not to ruin you buying dry batteries.

Mini High-Voltage Generator Circuit  diagram:

Warning!
If you build the version without the voltage doubler and measure the output voltage with your multimeter, you’ll see a lower value than stated. This is due to the fact that the waveform is a long way from being a sinewave, and multimeters have trouble interpreting its RMS (root-mean-square) value. However, if you have access to an oscilloscope capable of handling a few hundred volts on its input, you’ll be able to see the true values as stated. If you’re still not convinced, all you need do is touch the output terminals...

To use this project to protect the handle of your beach bag or your attachecase, for example, all you need do is fix to this two small metallic areas, quite close together, each connected to one output terminal of the circuit. Arrange them in such a way that unwanted hands are bound to touch both of them together; the result is guaranteed! Just take care to avoid getting caught in your own trap when you take your bag to turn the circuit off!

Source by : Streampowers

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Mains Frequency Monitor Circuit Diagram

Here is a simple frequency counter designed to monitor the 240VAC mains supply. It as a frequency range of 0-999Hz, so it could also be used with 400Hz equipment. Standard TTL/CMOS logic is employed for the counters and display drivers, while an ELM446 (IC1) generates accurate 1Hz pulses for gating. This device utilizes a 3.579545MHz crystal for its timebase, as commonly found in TV and video circuits and even on old PC motherboards.

Mains Frequency Monitor  Circuit diagram:

Mains Frequency Monitor Circuit Diagram

Source by : Streampowers

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Electrical Isolation For I2C Bus Circuit Diagram

When the SDA (Serial DAta) lines on both the left and right lines are 1, the circuit is quiescent and optoisolators IC1 and IC2 are not actuated. When the SDA line at the left becomes 0, current flows through the LED in IC1 via R2. The SDA line at the right is then pulled low via D2 and IC1. Optoisolator IC2 does not transfer this 0 to the left, because the polarity of the LED in IC2 is the wrong way around for this level. This arrangement prevents the circuit holding itself in the 0 state for ever. As is seen, the circuit is symmetrical. So, when the SDA line at the right is 0, this is transferred to the left. The lower part of the diagram, intended for the SCL (Serial CLock) line, is identical to the upper part.

Electrical Isolation For I2C Bus Circuit diagram :

Electrical Isolation For I2C Bus Circuit Diagram

Resistors R1, R4, R5, and R8, are the usual 3.3 kΩ pull-up resistors that are obligatory in each I2C line. If these resistors are already present elsewhere in the system, they may be omitted here. The current drawn by the circuit is slightly larger than usual since the pull-up resistors are shunted by the LEDs in the optoisolators and their series resistors. Nevertheless, it remains within the norms laid down in the I2C specification.

Source by : streampowers

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Electronic Fuse Employs A Relay Circuit Diagram

The hobby circuit below uses an unusual method to generate about 12,000 volts with about 5uA of current. Two SCRs form two pulse generator circuits. The two SCRs discharge a 0.047uF a 400v capacitor through a xenon lamp trigger coil at 120 times a second.

Electronic Fuse Employs A Relay Circuit Diagram

The high voltage pulses produced at the secondary of the trigger coil are rectified using two 6KV damper diodes. The voltage doubler circuit at the secondary of the trigger coil charges up two high voltage disc capacitors up to about 12KV. Although this circuit can’t produce a lot of current be very careful with it. A 12KV spark can jump about 0.75 of an inch so the electronic circuit needs to be carefully wired with lots of space between components.

Source by : Streampowers

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