Before, we have proposed to make a wireless transmitter. Remains now to detect and demodulate the infrared beam. What role will the receiver. In addition, it will include a small amplifier so that the signals received are used directly by a helmet "Walkman." Note, however, that our association will remain monaural. However, this is embarrassing because the primary purpose of our assembly is to transmit sound from a TV then, at least in France, also fatally monophonic. Now you can listen to television or radio ...
Now you can listen to television or radio without antagonizing anyone, since the transmitter and receiver are linked by a wireless infrared diode.
The key element of our receiver is a photodiode in the infrared. Certainly, at its terminals, the electrical signal from the reception beam will remain extremely low. Therefore, before any attempt to decode, we must greatly amplify the first detection. A first stage amplifier, built around a single transistor, wired as close as possible the detector diode will conduct a voltage amplification and allow subsequent stages of work under impedance "less sensitive".
detector components for
R1 = 47 Kohm (yellow, purple, orange, gold)
R2 = 1.5 Mohm (black, green, green, gold) R3 = 1 Mohm (black, brown, green, gold)
R4 = R6 = 470 Kohm (yellow, purple, yellow, gold)
Kohm R5 = 4.7 (yellow, purple, red, gold) C1 = 22 mF
C2 = C3 = C4 = 3.3 nF
T1 = D1 = 2N 3904
infrared receiver diode
Indeed, the infrared diode, at least in this mode of use, has a very high impedance.
But in electronics, working in high-impedance remains difficult because of the extreme sensitivity of such arrangements external electrical noise. So we will liberate this problem from the first amplification stage. Following the latter, a new series of transistors allow us to obtain a voltage image of the infrared signal, easily exploitable. Our receiver will summarize a low-pass filter realized by using three pairs of capacitors, resistors. It is he who will deliver a voltage according to the average beam intensity while ignoring its AC component.
components demodulator
R1 = 1 Mohm (black, brown, green, gold) R2 = 15 Kohm
(brown, green, orange, gold)
R3 = 10 Kohm (brown, black, orange, gold)
R4 = R10 = R12 = R14 = R15 = 47 Kohm (yellow, purple, orange, gold)
Kohm R5 = 22 (red, red, orange, gold)
R6 = R7 = R8 = R11 = R13 = 2 , 2 Kohm (red, red, red, gold)
R9 = 470 Kohm (yellow, purple, yellow, gold)
C1 = C3 = C5 = C2 = 10 nF
C6 = 22 microfarads C4 = 470 nF
microfarad C5 = 22 = C8 = C7
C9 = 330 pF
T1 = T2 = T3 = 2N 3904
the output of this filter, so we get a voltage corresponding to the image of the musical signal to the input of transmitter. Again, we will amplify the power to enforce the helmet. This amplifier is realized using an integrated circuit type UA 741 associated with two transistors connected in push-pull ". Note that a volume knob will be sandwiched between the filter and the last amplifier. It is also good to choose here a model equipped with a switch. Thus, the power of the receiver be obtained simply by turning the volume knob.
components aplificateur
P1 = 470 Kohm potentiometer with switch R1 = R3 = 47 Kohm (yellow, purple, orange, gold) R12 = R13 =
R14 = 22 ohm (red, red, black , gold)
R4 = R5 = 470 Kohm (yellow, purple, yellow, gold)
R6 = R7 = 470 ohm (yellow, purple, red, gold) R11 = R8
= 2.2 Kohm (red, red, red , gold) R10 = R9
= 220 ohm (red, red, brown, gold)
C1 = C2 = 10 nF C3 = 22 mF
C4 = 330 pF C5 = 47 mF
IC = 741 AU = 2N
Q1 3904
T2 = 2N 3906
The wiring the receiver remains relatively difficult because of the large number of components it contains. However, we have divided it into three different modules: the first floor (comprising the detector diode), the preamplifier / demodulator and, finally, the headphone amplifier.
This simplifies our schemes and the wiring. Moreover, it is easier to fit into a housing only three small plates big.
Anyway, it will always take care to cut all the copper strips of the plate wiring in the integrated circuit and at the locations shown on the diagram. Similarly, it must be observed and pin polarity components.
Regarding the supply of our receiver, will be provided by a single 9 volt battery. The entire assembly may be housed in a small plastic housing. It will however make a hole there so that the receiving diode can largely "see" the beam from the transmitter.
Normally, this setup is capable of providing a link of acceptable quality to a distance of four or five meters. However, too much ambient light where the presence of a fluorescent lamp can significantly limit the scope. As soon as we reached the limits transmitting, it manifests itself as a "breath" more and more important in the helmet. Exactly as in the case of reception on FM radio at the range limit, which is, in fact, perfectly normal, since we use an encoding very similar in principle. Likewise, any disruption of the infrared beam, the presence of objects or a person between the transmitter and receiver causes the interruption of transmission.
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