Electromagnetic Radiation

Electromagnetic Radiation is energy in the form of a wave of oscillating electric and magnetic fields, the wave travels through a vacuum at a velocity of 2.998 x 10^8 meters per second (186,284 miles per second). The Wavelength of an electromagnetic wave determines its properties , x-rays , infrared , microwaves , radio waves and light are electromagnetic radiation. 

                                                             WAVELENGTH

Electromagnetic Spectrum

nm = nanometer  ( 1 nm = 0.000000001 meter)

u    = micrometer ( 1 u    = 0.000001 meter)

mm= millimeter    ( 1 mm= 0.001 meter)

m   = meter          ( 1 m   = 39.37 inches)

km = kilometer     ( 1 km = 1000 meters)

Receiver for Fiber-Optic IR Extender

There are various types of remote-control extenders. Many of them use an electrical or electromagnetic link to carry the signal from one room to the next. Here we use a fibre-optic cable. The advantage of this is that the thin fibre-optic cable is easier to hide than a 75-Q coaxial cable, for example. An optical link also does not generate any additional radiation or broadcast interference signals to the surroundings. We use Toslink modules for connecting the receiver to the transmitter. This is not the cheapest solution, but it does keep everything compact. You can use a few metres of inexpensive plastic fibreoptic cable, instead of standard optical cable for interconnecting digital audio equipment. The circuit has been tested using ten metres of inexpensive plastic fibre-optic cable between the receiver and the transmitter (which is described elsewhere in this issue).

The circuit is simplicity itself. A standard IR receiver/demodulator (IC1, an SFH506) directly drives the Toslink transmitter IC2. We have used the RC5 frequency of 36 kHz, but other standards and frequencies could also be used. Both ICs are well decoupled, in order to keep the interference to the receiver as low as possible. Since the Toslink transmitter draws a fairly large current (around 20 mA), a small mains adapter should be used as the power source. There is a small printed circuit board layout for this circuit, which includes a standard 5-V supply with reverse polarity protection (D2). LED Dl is the power-on indicator. The supply voltage may lie between 9 and 30 V. In the absence of an IR signal, the output of IC1 is always High, and the LED in IC2 is always on. This makes it easy for the transmitter unit to detect whether the receiver unit is switched on. The PCB shown here is unfortunately not available readymade through the Publishers' Readers Services.

source : https://archive.org/details/ElektorCircuitCollections20002014/page/n13/mode/2up?view=theater

Transmitter for Fibre-Optic IR Extender

This circuit restores the original modulation of the signal received from the remote-control unit, which was demodulated by the receiver unit at the other end of the extender (see 'Receiver for fibre-optic IR extender').

If no signal is received, the Toslink transmitter in the receiver is active, so a High level is present at the output of the Toslink receiver in this circuit. Buffer IC2a then indicates via LED Dl that the receiver unit is active. The received data are re-modulated using counter IC3, which is a 74HCT4040 since the Toslink module has a TTL output. In the idle state, IC3 is held continuously reset by IC1. The oscillator built around IC2c runs free. When the output of the Toslink receiver goes Low, the counter is allowed to count and a carrier frequency is generated. This frequency is determined by the oscillator frequency and the selected division factor. Here, as with the receiver, we assume the use of RC5 coding, so a combination has been chosen that yields exactly 36 kHz. The oscillator frequency is divided by 2 9 on pin 12 of the counter, and 18.432 MHz 2 9 = 36 kHz. The circuit board layout has a double row of contacts to allow various division factors to be selected, in order to make the circuit universal. You can thus select a suitable combination for other standards, possibly along with using a different crystal frequency. The selected output is connected to four inverters wired in parallel, which together deliver the drive current for the IR LEDs D3 and D4 (around 50 mA). A signal from the counter is also indicate that data are being transmitted, via LED D2. This has essentially the opposite function of LED Dl, which goes out when D2 is blinking. In the oscillator, capacitor C3 is used instead of the usual resistor to compensate for the delay in IC2c. As a rule, this capacitor is needed above 6 MHz. It should have the same value as C load of the crystal, or in other words 0.5C1 (where CI = C2). At lower frequencies, a lkQ to 2kQ2 resistor can be used in place of C3.

A yellow LED is used for the power-on indicator D5. The current through this LED is somewhat higher than that of the other LEDs. If you use a red high-efficiency LED instead, R5 can be increased to around 3kQ3.

The circuit draws approximately 41 mA in the idle state when the receiver is on. If the receiver is switched off, the transmitter emits light continuously, and the current consumption rises to around 67 mA.

The PCB shown here is unfortunately not available readymade through the Publishers' Readers Services.

source : https://archive.org/details/ElektorCircuitCollections20002014/page/n1/mode/2up?view=theater

Electronic Stethoscope

In order to listen to your heartbeat you would normally use a listening tube or stethoscope. This circuit uses a piezo sounder from a musical greetings card or melody generator, as a microphone. This transducer has an output signal in the order of 100 mV and its low frequency response is governed by the input impedance of the amplifier. For this reason we have chosen to use an emitter follower transistor amplifier. This has a high input impedance and ensures that the transducer will have a very low frequency response. At the output you just need to connect a set of low impedance headphones to be able to listen to your heartbeat.

Replacing the emitter follower with a Darlington transistor configuration will further increase the input impedance of the amplifier.

source : https://archive.org/details/ElektorCircuitCollections20002014/page/n3/mode/2up?view=theater

DIY Front Panel Foils

It is fairly easy to produce professionally looking, permanent front panel foils ('decals') for use on electronic equipment if you have a PC available along with an inkjet printer ( or similar). Plus, of course, matt transparent sheet of the self-adhesive type as used, for instance, to protect book covers. This type of foil may be found in stationery shops or even the odd building market. One foil brand the author has used successfully goes by the name of Foglia Transparent. The production sequence is basically as follows:

1. The decal is designed at true size (1:1 or 100%) with a graphics program or a word processor, and then printed in black and white on a sheet of white paper (do not use the colour ink cartridge). Allow the ink to dry. Cut the foil as required, then pull the adhesive sheet from the paper carrier sheet. Keep the carrier paper handy, it will be used in the next phase.

2. Once the ink has dried, the transparent foil is placed on top of the decal. The foil is lightly pressed and then slowly pulled off the paper again (see photograph). Because the adhesive absorbs the ink to a certain extent, the mirror image of the decal artwork is transferred to the adhesive side of the foil.

3. For further processing, first secure the foil on the carrier paper again. Next, cut the decal to the exact size as required by the equipment front panel. Finally, pull off the carrier sheet again and apply the transparent foil on to the metal or plastic surface.

source : https://archive.org/details/ElektorCircuitCollections20002014/page/n13/mode/2up?view=theater