Friday, December 27, 2013

Single Supply fault Monitor Circuit Diagram

This Single Supply fault Monitor Circuit Diagram shows a typical over/under-voltage fault monitor for a single supply. The upper trip points, controlling OUT 1, are centered on 5.5 V with 100 mY of hysteresis Wu = 5.55 V, `L = 5.45 V); and the lower trip points, controlling OUT 2, are centered on 4.5 V, also with 100 mV of hysteresis. OUT 1 and OUT 2 are connected together in a wired OR configuration to generate a power OK signal.


Single Supply fault Monitor Circuit Diagram

Single Supply fault Monitor Circuit Diagram

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Wednesday, December 25, 2013

Environmentally Friendly Mosquito Repeller

With the return of the fine weather, you’ll doubtless be enjoying lazing around of an evening on your patio or in your garden, but even if you’re not surrounded by marshes or other shallow water it’s very likely some intruding mosquitoes will come along to spoil this idyllic scene. Although indoors it’s easy to get rid of them these days, indeed even to prevent them coming into the house, the same can’t be said for the great outdoors.

We might mention the well-known Chinese coils – the only thing Chinese about them is undoubtedly their name – which very often drive people away as much as mosquitoes, if not more! Moreover they are nasty things to handle. There are also UV (ultra-violet) ‘electrocutors’ consisting of a blue lamp surrounded by two closely-spaced grilles between which a high voltage is applied. The mosquitoes (and fies and other flying insects) are supposedly attracted by the color of the lamp and as they approach, get electrocuted in contact with the two grilles.

The only thing you have to do is pull out the drawer from time to time and get rid of the mass of dead insects. Even though the effectiveness of these first two products remains questionable, it is less so than the one we’re nonetheless going to describe here. We’re talking about an ultrasonic mosquito repellent.

The principle, as described by its numerous promoters, is as follows. Only the female mosquitoes bite (that at least is an undisputed scientific fact) and they bite when they need to feed, and above all, to feed their eggs. In this situation, they seek to avoid the males whose ‘job’ has already been done, and so they fy away from the frequencies emitted by the males when they are on heat. This is where opinions now diverge.

Environmentally-Friendly Mosquito Repeller

According to certain publications, the frequency emitted by the male mosquitoes is said to be around 20–25 kHz, and so within the realm of ultrasound. But according to others, it is in the region of 5–7 kHz instead; frequencies that a human ear, even an elderly one, can still hear very well. Rather than spending lots of money (of the order of tens of pounds) buying such a device, which moreover generally have a fixed frequency, we’re suggesting building one yourself so that you can carry out your own research this summer, especially since the circuit proposed is very simple and cheap to build.

As the figure shows, it uses just a single IC, a CMOS type 4047. This very multi-purpose IC can be wired in very many operating modes, including that of the multivibrator or astable used here. The operating frequency is set by the external components C1, R1, and P1; the latter makes it possible to slightly adjust the frequency, given the uncertainty that exists over the most efective value…To best reproduce the high frequencies produced by the generator, the output transducer used is a simple tweeter, but it must be a piezo one.

Such a tweeter behaves in fact much like a capacitor, and so doesn’t overload the CMOS IC outputs that are incapable of supplying a substantial current, as everyone knows who’s ever worked with 400 series CMOS logic. To obtain an output signal of sufficient amplitude while being powered from a single 9 V battery, this tweeter is connected between the 4047’s Q and Q outputs, making it possible to apply complementary (antiphase) signals to the tweeter so it ‘sees’ an alternating voltage of double the supply voltage.

In purely theoretical terms, this quadruples the output power available. In practice, it’s better to regard it as tripling it, but the beneft achieved by doing it this way is nonetheless very real. All that remains is for you to place the project in the middle of the patio table or beside your lounger in order to get a taste of the calm of a summer’s evening without mosquitoes bothering you acoustically or worse, biting. At any rate, that’s what we wish for you…

B. Broussas
Elektor Electronics 2008
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Tuesday, December 24, 2013

Simple Voltage Multiplier Circuit Diagram

This is a Simple Voltage Multiplier Circuit Diagram. This Simple Voltage Multiplier Circuit Diagram we build to day. how to build lets start. Figure 99-l(a)`s circuit exhibits a high-output impedance as a result of the small effective capacitance of the series-connected capacitors, and it exhibits considerable voltage loss due to all of the diode drops. Further, this circuit requires 2 diodes and 2 capacitors to produce a dc output voltage approximately times the rail voltage. Figure 99-1 (b)`s circuit multiplies more effectively using fewer diodes and capacitors. 

 Simple Voltage Multiplier Circuit Diagram

Simple Voltage Multiplier Circuit Diagram


The parallel arrangement of the capacitors lets you use smaller capacitors than those required in Fig. 99-1(a). Alternatively, when using the same capacitor values of Fig. 99-1 (a), the output impedance will be lower. Whereas the clock source directly drives only one of the two strings of capacitors in Fig. 99-1(a), Fig. 99-l(b)`s clock drives both strings with opposite phases. 

This drive scheme doubles the voltage per stage of two diodes. A final diode is necessary to pick off the dc output voltage because both strings of capacitors now carry the - p ac input-voltage waveform. The ICL7667 dual-FET driver accepts a TTL drive swing and provides a low-impedance push-pull drive to the diode string. This low impedance is particularly helpful when using a long string to raise output voltage to more than 100 V, starting from a low rail voltage.  
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Saturday, December 21, 2013

Simple LED Torch

A common problem with small torches is the short life-span both of the batteries and the bulb. The average incandescent torch, for instance, consumes around 2 Watts. The LED Torch in Fig. 1 consumes just 24 mW, giving it more than 80 times longer service from 4 AA alkaline batteries (that is, up to one months continuous service). Although the torchs light output is modest, it is nonetheless quite sufficient to illuminate a pathway for walking.

Circuit Diagram :

Simple torch-Circuit Diagram

Fig. 1 : Simple LED Torch Circuit Diagram


The LED Torch is based on a 7555 timer running in astable mode (do not use an ordinary 555). A white LED (Maplin order code NR73) produces 400 mcd light output, which, when focussed, can illuminate objects at 30 metres. Try Conrad Electronic for what appears to be a stronger white LED (order code 15 37 45-11). A convex lens with short focal length is placed in front of the LED to focus the beam. If banding occurs at the beams perimeter, use another very short focal length lens directly in front of the LED to smooth the beam.

If a different supply voltage is preferred, the value of resistor R3 is modified as follows:

9V - 470 Ohm
12V - 560 Ohm

See my "Wind-up Torch" feature article in the October 2000 edition of Everyday Practical Electronics for a completely battery-free go-everywhere torch.

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Thursday, December 19, 2013

Simple But best Regulator Circuit Diagram

This is the Simple But best Regulator Circuit Diagram.The best characteristic of this regulator is that the output voltage can be adjusted down to 0 V. The regulation is provided by an integrated regulator Type LM317. As is normal in supplies that can be adjusted to 0 V, this IC is used in conjunction with a zener diode. This diode provides a reference voltage that is equal, but of opposite sign, to the reference voltage (U,) of the regulator, as shown in Fig. 74-1 (a). 

Potential divider R1/R2 enables the output voltage to be adjusted. In this circuit, the negative reference voltage is derived in a different manner: from the regulator with the aid of an op amp (Fig. 74-1 (b)). The op amp is connected as a differential amplifier that measures the voltage across Rl and inverts this voltage to Ur. An additional advantage of this method is that at low-output voltages, a change in the reference voltage has less effect on the output voltage than the circuit in Fig. 74-1 (a). The prototype, constructed as shown in Fig. 74-1 (c), gave very satisfactory results. 

 Regulator Circuit Diagram

Simple But best Regulator Circuit Diagram


The op amp need not meet any special requirements: a 741 works fine, although an LF356 gives a slightly better performance. The negative supply for the op amp can be obtained with the aid of a center-tapped mains transformer.
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Tuesday, December 17, 2013

Watch Dog For Telephones

Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap/misuse indications. Quite often they do not offer guaranteed protection against unauthorized operation. A very simple and unique circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described here.

This little circuit keeps continuous watch over the telephone lines and sounds an alarm in case of any misuse. In addition it transmits a loud tone through the telephone lines to prevent further misuse. When switch S1 is turned on, the normal (on-hook) telephone line voltage at the output of bridge-rectifier diodes D1 to D4 is approximately 48 volts, which being well above the break-down voltage of zener diode D5, the diode conducts.


As a result transistor T2 gets forward biased. This effectively grounds the base of transistor T1 which is thus cut off and the remaining circuit does not get any power supply. In this state, only a small (negligible) current is taken by the circuit, which will not affect the telephone line condition. However, when handset of any telephone connected to the telephone lines is lifted (off-hook), line voltage suddenly drops to about 10 volts.

As a result, transistor T2 is switched off and transistor T1 gets forward biased via resistor R1. Now, the astable multivibrator built around timer IC1 starts oscillating and the speaker starts sounding. Output of the astable multivibrator is also connected to the base of transistor T1 through capacitor C5. As a result, only a loud (and irritating) tone is heard in the ear-piece of the unauthorized telephone instrument.

This circuit can be constructed on a veroboard using easily available low-cost components and it can be connected to any telephone line without the fear of malfunctioning. No extra power supply is required as it draws power from the telephone line for operation.

Note:
  • Please disconnect the gadget when you are yourself using the telephone as it cannot distinguish between authorized and unauthorized operation.
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