arifjt's Blog

Sitting peacefully under a tree at the bottom of your garden, or stretched out beside your swimming pool, you may feel like listening to your favourite music from your hifi. Rather than turning the volume up beyond reasonable limits and risking upsetting all your neighbours or attracting the wrong audience, we suggest building this little wireless audio transmitter/ receiver combination. Using the UHF ISM (industrial, scientific, medical) band and quality FM (frequency modulation), it won’t impair the sound quality and will let you listen nice and discreetly. The transmitter uses a well-known module manufactured for some years now by Aurel as their ‘FM audio transmitter’. It works in the licence-free 433.92 MHz band and so allows our project to operate completely legally as the transmitter is type-approved to quite strict technical specifications. Note however the frequency you’re using is not exclusive as it is shared by many other wireless devices such as headphones and key fobs for garage doors and so on. The equipment is low-power however and should

have a short range. The Aurel module is a complete FM audio transmitter designed for powering from12 V. The only external components required, R5, R6, and C5, form the preemphasis (high-boost) network specifi c to frequency modulation. Used alone, this module offers a typical audio input sensitivity of 100 mV rms. So we are driving it from an opamp with gain adjustable between 0.5 and 5, extending the voltage range from 50 to 500 mV, to make it compatible with any audio device line output. Note in passing that, if you reduce resistor R1 to 2.2 kΩ, you can increase the sensitivity to 2.5 mV so that the transmitter could then be used as a UHF radio mic for use in shows and events, for example. The power supply can be obtained from a 12 V battery or a ‘plug-top’ power supply; diode D1 protects the circuit from reversed polarity by. The receiver is just as simple, since it uses the complementary module to the previous one, again from Aurel, and naturally called their ‘FM audio receiver’. This receiver has a squelch (FM noise silencing) adjustment, set by the voltage applied to pin 15.

Potentiometer P1 connected to this makes it possible to adjust the squelch threshold so as to have a receiver that won’t output noise in the absence of a signal, using the information provided on pin 18. This is High when a signal is present and Low when absent. Here it drives an 8-into-1 CMOS analogue multiplexer, of which only input 8 is used. This solution employs a very cheap, good-quality analogue switch that is easy to use. Its output passing via the volume control P2 and is applied to the well-known small integrated power amplifier LM386. The transmitter’s RF output power of a few hundred milli watts is more than adequate for such an application, and its quality likewise, especially if you combine it witha loudspeaker worthy of the name, with a pair of headphones as the next bestalternative. The Aurel receiver module and CMOS multiplexer both require a 5 V supply; this is stabilized by a standard 3-terminal regulator. The circuit as a whole is powered from 9 V, and is also protected against possible reverse polarity by diode D1. Given the relatively high current consumption of the amplifi er, especially if you use it for longer periods, rechargeable NiMH batteries will obviously be preferable to primary cells, which wouldn’t last very long and will turn out rather expensive in the long term, as well as bad for the environment. As far as the antennas are concerned, for both transmission and reception, simple quarter-wave whips ensure a range of a hundred metres or so – even more if line-of-sight. You can of course buy such antennas ready-made, but a simple piece of stiff wire around 17 cm long (i.e. a quarter wavelength at 433.92 MHz) will do the job just as well, and cost a lot less. Equipped with these two modules you can make the most of your music wherever you like. Don’t forget, though, that outdoors, the best music of all is that of birds, that is, the feathered variety. 

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 flies and other flying insects) are supposedly attracted by the colour 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 fly away from the frequencies emitted by the males when they are on heat. This is where opinions now diverge. 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 effective 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 benefit 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.

High optimized electrolyzed can achieved by using DC pulsed or PWM (pulse width modulation). The voltage and frequency can be adjust for optimized Hydrogen produce. The simple circuit can assembled like this:

By www.elechobby.co.cc

This circuit is very simple less than 12 component, to build DC to AC converter. The principle of this circuit is generating 50/60Hz frequency  by IC CD 4074 and the output complement  pin 10 and 11 of  IC CD4047 to drive MOSFET IRFZ 44 so induction primary transformer is work and get high voltage at out secondary transformer about 220V AC. The output converter wave is still square wave and more close to sine wave with filter C3 220nF.

For more high current output (wattage) use high current battery and the MOSFER must be parallel. For example to get 240W output the battery used is 20A. Or if you use 24V CT transformer you just only use battery 24V/10A. In practice report the commonly is use 9V CT transformer will step up to high voltage output, if using 12V CT transformer were dissatisfied because transformer losses.