Figure 1 : Wiring diagram of the micro-spy.With this micro-spy, you get two advantages: autonomy infinite and perfect camouflaged age of the circuit. It is achievable in two versions, 10 mW for a range of 200 to 300 meters and 400 mW for a range close kilometer!
The wiring diagram
The wiring diagram of our micro-transmitter visible in Figure 1. It is immediately possible to see both versions: the left part is the basic version of 10 mW, the right part of the amplifier is 400 mW.
The power
We have provided a DC 12 V 180 mA able to run both version 10 mW than 400 mW. TF1, a classic transformer 230 V / 50 Hz 2 VA delivering the secondary a 12 V ac will therefore be the case. The voltage rectified by the diode bridge PT1 is applied, both smoothed by the capacitor C1 at 12 volt regulator U1 All L1/C3 form a low pass filter blocking RF leakage that could be self-oscillating controller U1.
The transmitter
The setup proposed here is a micro-transmitter UHF ultra-stable frequency modulation. It offers excellent sound fidelity that allows you to listen to the voice but also all the sounds and noises in the room where it will be.
Its compact dimensions are directly related to employment of the now famous Aurel module TX-FM audio. This hybrid (U2) 16-pin S.I.L. (Single in line), includes a frequency modulator, a SAW oscillator 10 mW into 50 ohms working at 433.75 MHz to meet the CE ETS 300 220, although in our case, it matters little. Our module accepts input (pin 4) a typical signal of 100 mV amplitude. In our application, it is our preamplified microphone with his stage transistor amplifier common emitter that we provide. If we enter a little into detail, the NPN transistor T1 associated with resistors R5, R4 and the resistance against reaction R3, form an amplifier with a gain of about 40. More than enough to guarantee a very high sensitivity electret microphone knowing that provides at its output a few millivolts (ten).
Note that light amplification can maintain a good SNR (signal to noise ratio) and also reduces noise and interference generated by the sector, which in our case, be more present. The microphone volume is supplied with 5.1 volts through the zener DZ1 and resistors R1 and R2. The electrolytic C4 filter any noise from the sector 50 Hz to prevent their ampli ed at the same time as the microphone signal.
Capacitors C5 and C6 are used to transmit the signal by blocking the DC component. C5 transmits the signal to the amplifier formed by Q1 and C6 to the audio input (pin 4) of the hybrid transmitter U2. The choice of capacitor values is not innocent because they also have the role of cutting the 50 Hz In this application, the module U2 is working in the typical configuration with the exception of the filtering that we have not used . Instead of the high-pass filter we find the resistive network (R6/R7), which attenuates the input signal of the FM demodulator. R6 increasing decreases the sensitivity and vice versa.
Version 10 mW
If you want to settle for 10 mW version, simply connect the antenna to the patch marked "10 " in Figure 2. A simple quarter-wave (17 cm) made with a stiff wire will do. It will not mount U3, R8, R9 and C7.
Version 400 mW
400 mW version is neither more nor less than 10 mW version to which was added a power amplifier.
If you look at the diagram visible in Figure 1, will be seen easily. A pin 15 of U2, instead of connecting the antenna, the RF signal is recovered to attack the input of the amplifier U3, the PA433, also manufactured by Aurel. This is a booster working at 433 MHz capable of providing RF power of 400 mW near a load of 50 ohms. The antenna, in this version, will be connected to pin 14 of U3. Of course, we must not forget to mount R8, R9 and C7 and the strap connecting the pin 15 of U2 at pin 2 of U3.
The practical realization
The installation presents no particular difficulty. Simply mount the components in the usual order of lowest to highest. No adjustment is necessary (except, possibly, the microphone sensitivity as we have seen before). Remember, the shield between the transformer and the RF section.
Figure 2 : Schema component layout version 10 and 400 mW.
Figure 3 : Photo of a prototype version of the micro-spy 400 mW.
Figure 4 : Design, scale 1, the printed circuit of the micro-spy sector ÉcouterLire phonétiquement Dictionnaire - Afficher le dictionnaire.Component List
R1 ...... 820 Ω
R2 ...... 4.7 kΩ
R3 ...... 470 kΩ
R4 ...... 4.7 kΩ
R5 ...... 100 Ω
R6 ...... 22 kW
R7 ...... 2.2 kΩ
R8 ...... 100 kΩ
R9 ...... 5.6 kΩ
C1 ...... 470 uF 25V electr.
C2 ...... 1000 uF 16V electr.
C3 ...... 100 nF multilayer
C4 ...... 100 uF 25V electr.
C5 ...... 100 nF ceramic
C6 ...... 100 nF ceramic
C7 ...... 100 nF multilayer
DZ1 ..... 5.1 V 0.5 W zener
T1 ...... BC547B
L1 ...... Choke VK200
U1 ...... Regulator 7812
U2 ...... Aurel module TX-FM AUDIO
U3 ...... PA433 module Aurel
PT1 ..... diode bridge 1A
TF1 ..... transformer. 2 VA 230/12 V
MIC ..... capsule microphone preamp.
Miscellaneous:
1 ....... 2 pole terminal block
1 ....... 17cm antenna (wire enamel. 12/10)
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