We will present an economic system for remotely controlling any device, whether electrical or electronic. Its originality lies in its unusual range: 20 km. It has two channels with coding and digital relay outputs with the possibility of a bistable or monostable. This radio uses two modules Aurel exceptional characteristics: 400 mW transmitter and a receiver particularly sensitive.
Control systems remotely via radio, can be divided into two categories:
those commonly called remote radio controls and those referred.
At the first family, the remote controls, owns the systems consisting of a receiver and a transmitter used to open electric gates, activation of alarm systems, control of the car doors, etc..
The transmitters used in these systems are very small, often in the form of a keychain and a maximum power of 10 mW, which allows a range of between 50 and 100 meters at best.
The use of these devices has become part of our daily lives: we do not even realize more that we use it and we certainly at least one in our pockets now!
Obviously, in order to avoid potential interference, all these systems are encoded.
For this, the radio carrier is modulated by different pulse sequences.
Coding systems most used are based on the use of specific integrated circuits, such as the MC145026 or UM86409, or use of microcontrollers, specially programmed, which can raise billions of combinations that modify the code with a random sequence (rolling code).
A family of remote controls, belong all the devices provided for point to point, able to cover much larger distances than those covered by the remote, the order of several hundred meters to several tens of kilometers.
Obviously, the powers used are much higher (up to 5 to 10 watts) and the use of directional antennas is appropriate if one wants to be in scope.
These devices are used in remote alarms or to activate remote devices (lights, pumps, radio relay, etc.).. We can generalize by saying that such a system will find application wherever it is to enable or disable a device with an electrical control located far away.
The project described in these pages, can achieve this result for a very competitive cost.
Obviously, in this case, the transmitter is not a model "porteclés" and while its dimensions are not very important, it does certainly not be back in the pocket of the jacket!
Towards a long-range radio
Our system operates on UHF (precisely on 433.92 MHz). It consists of a two-channel transmitter with a power of outgoing part is 400 mW and a receiver, also in two channels with relay outputs (dry contacts).
It works at 12 VDC.
The transmitter can be activated manually (via push buttons) or via a voltage.
For outgoing parts, it is possible to select an astable mode (pulse) or bistable (memory).
In the first case, the output relay remains active until the signal generated by the transmitter is present on the receiver input.
In the second case, the relay and remains in this state, even if the transmitter signal is not present on the receiver input. A new signal causes a return to the initial state and so on.
Unlike other systems with identical functions, whether commercial or not, the project proposed in these pages has a reduced cost, which is already not negligible, but can also be easily accomplished by anyone with Employment in high-frequency stages, modules Aurel already settled and guaranteed operation (see Figures 13 and 14).
We paid particular attention to the reception floor.
As is known, in fact, a point to point, the benefits of the system depends not only on the transmitter power, but also the sensitivity and selectivity of the receiver. Of course, the antennas are also an important place in the distance covered.
For this application, we used a new receiver superheterodyne (STD-LC), which provides for a reasonable cost, optimal sensitivity and good selectivity (see Figure 13).
To give precise indications as possible on the scope of this system, we conducted many tests in different locations and with different antennas (see Figure 17).
We realize that the tests are merely suggestive of reach, but yet it is the data that most interests him who shall install a system like this.
During testing, we used three types of antennas:
- Two antennas "socks" flexible (Aurel AG433) - two whip antennas and rigid 1 / 4 wave (Aurel AS433) - two directional antennas 5 elements (Yagi Cushcraft Dual Band).
In the first case, we made links to 800 meters outdoors perfectly clear. By cons, urban (thousands of houses between the TX and RX) we have painfully over 100 meters.
To conduct open field trials, we placed the receiver at a height of 2 meters and then we got away with the transmitter (handheld) ensuring interposing between TX and RX are no significant barriers.
Antennas with AG433 we reached 800 meters.
The same test, performed with the antennas AS433, has a bond of more than 2 km. In the latter case, the two antennas were placed approximately 2 meters in height, with a plan for adequate mass.
However the test that surprised us the most (positively) was that done with the directional antenna.
For this test, we installed the receiving antenna on the roof of a house and we went with the issuer and the second antenna on a hill. The elevation was 1000 meters and the distance of 20 km as the crow flies.
Despite this distance, our radio system has always worked perfectly.
In conclusion, we can say that this system allows for point to point between 100 meters and 20 kilometers, depending on antennas and obstacles between the transmitter and receiver.
That flexibility, with the possibility, choosing the proper antenna to meet the most diverse requirements.
After this long, but informative introduction, let us now the circuit of the transmitter.
The transmitter
Figure 1 : Schematic diagram of the transmitter radio.
Figure 2 : Electrical diagram of the transmitter radio.As shown in the block diagram of Figure 1, the radio signal generated by the hybrid module Aurel TX433-BOOST is modulated pulse trains with 12-bit, corresponding to 4,096 combinations (using an encoder type UM86409 ).
The first 11-bit level is imposed by the position of many micro-switches. That the 12th bit, depends on the activation button by which it is selected.
This allows to get 2 channels, which correspond to two different sequences.
If we go to the wiring diagram in Figure 2, we can note that in addition to two buttons, we also find two entries on optocouplers that allow the activation of both channels, using DC voltages.
The values of R10 and R11 are changed according to the voltage available for control. The values shown in the list of components (1 ohm) are suitable for activation voltages between 5 and 24 volts.
If the voltage would be higher, it will increase proportionately the value of these two resistors.
The transmitter operates with a voltage of 12 volts which is sent to the transmitter module U3, where close contacts of relay RL1.
Note that, as a result, the radio module is supplied only during transmission of a command, unlike the rest of the circuit is always turned on.
Additional floors are supplied with a voltage of 5 volts supplied by the integrated circuit U1, a case in 7805 to220, which converts the 12 volt input to a voltage of 5 volts.
The integrated circuit U2 coding, always active, constantly generates a pulse train (present on pin 17) which is applied to the modulation input (pin 2) of the module U3.
As the transmitter module is not powered, this modulation is without effect.
The generated sequence, depends on the dip-switches DS1 and DS2, but also supported the push, P1 or P2.
Recall that the control lines A1 to A12 normally exhibit a high level because they have pull-up resistors built into U2.
At rest, therefore, the line A12 has a high logic level.
By pressing the pusher P1 (FC1 or activating the IN1, which is the same), the transistor T2 becomes conductive and activates the relay, thus feeding the transmitter module.
The radio carrier is generated by a modulated pulse sequence, the last bit has a logic high level.
If we rely on P2 (or by activating FC2 IN2), we get the same effect through the transition in conduction of T1 and T2.
However, in this case, the last bit of the sequence has a logical low because the line A12 is grounded by D2/P2.
The transmitter remains in issue until the button is pressed or until the optocoupler is conductive.
In principle, it only takes two seconds to make sure that the receiver well recognized code.
Even in the function astable, the relay receiver output remains closed during the time of activation of the pushbutton or optocoupler.
At rest, assembly consumes only a few milliamps. By cons, during transmission, the total reached about 100 milliamps.
To increase the RF power, it is possible to increase blood supply to 15/18 volts.
In this case, it is not advisable to keep the show circuit for more than 5 to 10 seconds.
Now for the analysis of the receiver.
Figure 3 : Installation diagram of components of the radio transmitter.
Figure 4 : Photo of the prototype radio transmitter.
Figure 5 : Design of printed circuit scale of a radio transmitter.Component List TX
R1 = 220 kΩ
R2 = 47 kilohm
R3 = 22 kW
R4 = 4.7 kΩ
R5 = 1 kΩ
R6 = 2.2 kΩ
R7 = 2.2 kΩ
R8 = 2.2 kΩ
R9 = 4.7 kΩ
R10 = 1 kΩ
R11 = 1 kΩ
C1 = 470 uF 25 V electrolytic
C2 = 470 uF 16 V electrolytic
C3 = 100 nF multilayer
C4 = 10 uF 16 V electrolytic
C5 = 100 pF ceramic
D1 = 1N4007 diode
D2 = 1N4148 diode
D3 = 1N4007 Diode
D4 = 1N4148 diode
D5 = 1N4007 Diode
D6 = 1N4007 Diode
T1 = BC557 PNP Transistor
T2 = BC547 NPN Transistor
LD1 = 5 mm red LED
L1 = VTK200
U1 = 7805
U2 = Integrated UM86409
U3 = Aurel TX433 Boost Module
DS1 = Dip switch 10 inters
DS2 = Dip switches 1 Inter
FC1 = 4N25 Optocoupler
FC2 = 4N25 Optocoupler
Relay RL1 = 12 V 1 RT to this
NO = P1 Pusher
NO = P2 Pusher
Others:
2 supports 2 x 3-pin
1 support 2 x 9-pin
5 Terminal 2 poles
1 PCB ref. S310
The receiver
Figure 6 : Block diagram of radio receiver.
Figure 7 : Wiring diagram of radio receiver.The block diagram of Figure 6 allows to clarify the operation.
The radio signal is received and demodulated by a hybrid module Aurel STD-LC.
At the end of, or we find the pulse train, the same one that was generated by the transmitter.
This signal is sent to two decoders integrated circuits, which control lines are common until the 11th between them.
Only changes the level of the 12th bit, which in this case a high level and the other low.
It is obvious that the outputs of both decoders will be activated in the presence of the sequence of bits generated by the transmitter based support on P1 or P2 (or conduction of FC1 and FC2).
Each output can directly drive a relay (momentary operation), but the possibility to obtain a bistable (memory) was also provided through the use of a flip-flop.
In this mode, pressing and releasing one of two buttons activates the corresponding relay, which remains in that position until such action is renewed. But let us look more closely at the wiring diagram of the receiver shown in figure 7.
The receiver is powered with a voltage of 12 volts, which in reality is only applied for the output stage, which are used in both relays.
All other stages operate with a voltage of 5 volts supplied by the controller U1, a 7805 case in TO220.
With 5 volts stabilized, we feed the two decoders integrated circuits (U3 and U4), the dual flipflop 4013 (U2) and the receiver module (U5).
This module Aurel STD-LC, a receiver simply changing the frequency of a low price, barely higher than superregeneration receptors.
Compared to these, the receiver STD-LC, has better sensitivity (-100 dBm), but the bandwidth is much narrower (500 kHz at -3 dB).
This makes the receiver less sensitive to possible disruptions and allows obtaining higher overall benefits to receivers superregeneration.
It all adds up (with equal power emitted by the transmitter) by the possibility of a truly superior range.
As we have seen, the LC-STD module requires a supply voltage of 5 volts. But what is interesting is that it consumes just 3.5 milliamps. The supply voltage is applied to pins 1 and 15 (positive) and 2-7-11 (negative).
The antenna input is on pin 3 and the signal decoded and formatted is available on pin 14.
The train of pulses available at the output of this module is applied to the inputs of two integrated circuits decoders UM86409 (U3 and U4), precisely to pin 16 of each.
In this case, two integrated circuits as decoders UM86409 work together because their pin 15 (mode) is connected to ground.
If we return to the diagram of the transmitter (Figure 2), where the same integrated circuit is used, we see that the pin 15 is connected to positive supply and the integrated circuit functioning as an encoder.
The pins of both integrated circuits corresponding to lines A1 to A11, are put in parallel and are controlled by micro-switches DS1 and DS2.
Obviously, these micro-switches are positioned in exactly the same way as the transmitter.
In case of error, no hope to see the system work! Try opening your door to your apartment with car key ... to see!
The line A12 U3 is permanently connected to the positive and the same line U4 is connected to ground.
In this way, the decoder U3 is activated when it reaches the pulse train generated by the pressure of the pusher P1 (or conduction FC1) and U4 is activated whenever P2 is pressed (or FC2 is conduction ).
When arrive to the proper sequence of bits, the decoder pin 17 goes low.
In the case of a pressing P1 transmitter (or conduction FC1) is the pin 17 of U3, which changes state from a high level (+5 volts) to a low level (0 volts).
This determines the shift in conduction of T3 and T4 (assuming DS4 / 1 closed) and thus activating the relay output corresponding to the first channel.
Similarly, if the P2 button is pressed (or if FC2 is conducted), the pin 17 of U4 goes low, causing the conduction of T4 and T1 (assuming DS3 / 1 closed) and therefore activation of the second relay.
In both cases, besides the activation of relays, LEDs are connected in parallel with the latter, lit.
The outputs remain active during the time that the pressure on P1 or P2 of the transmitter is maintained (or during the entire time FC1 or FC2 is conducted).
In this connection, we recall that both pushbuttons P1 and P2 can not be supported simultaneously.
Similarly, FC1 and FC2 can be conductive simultaneously.
For a bistable output (or even one), it is necessary to open the inverters DS3 / 1 and DS4 / 1 and close DS3 / DS4 and 2 / 2.
By doing this, you connect in series to the output lines, the two flip-flops present within U2, a CMOS integrated circuit type 4013.
In the case of the first channel, recognition of the pulse train causes the transition from the low state to high state logic level present at pin 3 (CK) of the first flip-flop in this U2.
This determines the output switching on (Q, pin 1) which changes state from 0-1 or 1-0.
When sending the pulse train is interrupted by stopping the pressure on the button of the transmitter, the level present at pin 3 of U2 returns to logic low level, but this has no effect on the output of flip-flop.
In other words, the new state is maintained even when the transmission is complete.
To change the status of the output level, it is necessary to again press the button of the respective channel transmitter (or pass the optocoupler conduction concerned).
This determines a new edge on the clock pin of flip-flop and consequently the switching device.
The outputs of the bistable present in U2 are connected via DS3 / 2 and DS4 / 2 to transistors T1 and T2 that drive the relays.
In other words, the output stage is identical to the previous case.
To avoid getting shorted outputs of flip-flop, do not simultaneously close the switches 1 and 2 DS3 or DS4.
If the bistable operation mode does not interest you, you can simply not install the integrated circuit U2 (but why not?).
Some other components complete the circuit: the diode mounted in parallel on the relay coils to eliminate the overvoltages caused by inductive components, clock networks of both decoders (R14/C11 and R15/C12) chosen to obtain a operating frequency of 1 kHz, the system reset (reset) flip-flop (C3/R10) and some filter capacitors scattered along the supply line to eliminate the phenomena of motor-boating and more generally to make the power supply clean.
The diode D3 prevents the receiver can be damaged by a possible reversal of polarity of power.
With our prototype, we used miniature relays with contacts capable of switching a maximum current of 1 ampere.
Where this value is insufficient for some applications, it is possible to activate a relay with superior characteristics using the relay contacts origins.
After analysis of the two wiring diagrams, it only remains to deal with practical aspects of this project.
Figure 8 : Installation diagram of components of the receiver transmitter.
Figure 9 : Photo of the prototype receiver transmitter.
Figure 10 : Design of printed circuit across a radio receiver.Iist RX
R1 = 1 kΩ
R2 = 100 kΩ
R3 = 4.7 kΩ
R4 = 4.7 kΩ
R5 = 47 kilohm
R6 = 15 kΩ
R7 = 1 kΩ
R8 = 100 kΩ
R9 = 4.7 kΩ
R10 = 100 kΩ
R11 = 4.7 kΩ
R12 = 47 kilohm
R13 = 15 kΩ
R14 = 220 kΩ
R15 = 220 kΩ
C1 = 10 nF 250 V polyester
C2 = 10 nF 250 V polyester
C3 = 2.2 uF 25 V electrolytic
C4 = 100 uF 25 V electrolytic
C5 = 100 nF multilayer
C6 = 470 uF 25 V electrolytic
C7 = 100 nF multilayer
C8 = 470 uF 25 V electrolytic
C9 = 100 nF multilayer
C10 = 220 uF 16 V electrolytic
C11 = 100 pF ceramic
C12 = 100 pF ceramic
C13 = 220 uF 16 V electrolytic
D1 = 1N4007 diode
D2 = 1N4007 diode
D3 = 1N4007 Diode
T1 = BC547 NPN Transistor
T2 = BC547 NPN Transistor
T3 = BC557 PNP Transistor
Q4 = BC557 PNP Transistor
LD1 = 5 mm red LED
LD2 = 5 mm red LED
U1 = 7805
U2 = Built 4013
U3 = Integrated UM86409
U4 = Integrated UM86409
U5 = Module Aurel STD LC
DS1 = Dip switch 10 inters
DS2 = Dip switches 1 Inter
DS3 = Dip switch 2 inters
DS4 = Dip switch 2 inters
Relay RL1 = 12 V 1 RT to this
Relay RL2 = 12 V 1 RT to this
Others:
2 Brackets 2 x 9-pin
1 Support 2 x 7-pin
1 Terminal 2 poles
2 3-pole
1 PCB ref. S311
Using a system of transmitting and receiving antennas equipped with rigid 1 / 4 wave type AS433, mounted on a metal ground plane adapted, we get the best results by keeping a speedy implementation, simple and all mobile maintaining a total cost of achieving very interesting. In our tests, we obtained a range greater than two kilometers in the absence of obstacles.
Figure 11 : The radio transmitter with an antenna AS433.
Figure 12 : The radio receiver equipped with the same antenna.
Figure 13a : As a transmitter, we opted for a hybrid module CMS TX433-BOOST society Aurel.This module operates on 433.92 MHz (with a SAW resonator). It is able to provide the RF antenna power of 400 milliwatts at 12 VDC.
Figure 13b : Block diagram and pinout TX433-BOOST.
Figure 14a: Regarding the reception we have used a new superheterodyne receiver, always at Aurel, the STD-LC. This hybrid receptor in CMS provides for a low cost, optimal sensitivity and good selectivity.
Figure 14b : Block diagram and pin STD-LC.The installation of the radio
For both devices, we designed and made a printed circuit specific. These circuit boards can be easily achieved by the usual means (see Figure 5 for receiver and transmitter for Figure 10).
For those who choose the form of the kit, they will find among the components, the two printed circuit boards and drilled with a screen components.
The transmitter to avoid errors on components, it should mount an item at a time, starting with the transmitter.
All components are soldered directly on the PCB, with the exception of the two optocouplers and UM86409 integrated circuit, for which we have provided adequate supports.
Do you help the layout diagram of the components of Figure 3 and the photo in Figure 4.
First insert the lowest components and passive components.
Continue with capacitors, diodes, dip switches and relays.
Remember to place the inductor AF and achieve single strap provided.
Finally, mount the terminal blocks and the hybrid module Aurel TX433-BOOST. It can be implemented only in one direction, so no risk of error.
At this point you can insert the two optocouplers and the integrated circuit decoder in their respective support. The two pushbuttons are connected to their respective terminals, using two short pieces of wire.
Before placing the assembly on, connect an antenna or dummy load at the RF output.
For the antenna, you can use a piece of rigid wire 17 centimeters long. The most important thing is to never leave the module TX433-BOOST without charge.
After connecting the assembly to the power source of 12 volts, check with a voltmeter, you feel it is a voltage of 5 volts on pin 18 of UM86409 (power pin).
Position now eleven bits with the microswitches as you like and try to first press the button P1 and P2.
Check that the LED illuminates and the relay glue.
Using an ammeter, you can also control the current consumption is a few milliamps to stand at about 100 milliamps in emission.
If you have a receiver for radio control 433.92 MHz, with the same type of encoding and with the same clock frequency, you can, after having set its DIP switches in the correct order (same as on the transmitter ), verify that the transmitter generates the RF carrier modulated correctly.
Otherwise, you must first realize the receiver.
As we mentioned earlier, our transmitter can be activated manually using the two push buttons, but also with a DC voltage generated by an automatic control system with remote activation.
Imagine, for example, want to automatically control the opening and closing a valve that feeds a pond.
An automatic control system generates a voltage when the level drops below a certain limit.
This voltage is used to activate the transmitter that sends the control pulse to the receiver, which opens the valve. When the water reaches the maximum level, the voltage is generated, the TX does not transmit and receiver closes the valve.
To verify operation of this section, apply to the input IN1, a DC voltage between 5 and 24 volts and check that the circuit takes office just as in the case of manual activation.
If the input voltage exceeds this limit, increase in proportion to the value of the resistor R11.
Perform the same test, with the input IN2, acting, if necessary, the value of R10.
Let us now the realization of the receiver.
The receiver in this case also, the assembly has no particular difficulties.
All components are placed on a printed circuit compact enough but no more so you do not make the realization difficult.
As for the transmitter, the integrated circuits are mounted on stands.
Thus, in case of malfunction, it is easy to quickly replace an integrated circuit to attempt a diagnosis.
The module Aurel STD-LC can be inserted in only one direction on the plate, avoiding any risk of error.
It is also possible to use the receiver module NB-EC, despite a different pinout can be implemented and used without problem.
The sequence of mounting operations of the receiver is identical to the transmitter. With the layout diagram of Figure 8, check the component values that you mount on the PCB. The photograph of Figure 9 will give you an idea of the deck over.
If in doubt, take a look at the wiring diagram.
Particular attention should be paid to the establishment of polarized components and semiconductors, which must be placed in the right direction. Obviously!
The assembly is completed, before supplying the receiver, give a last look at your achievement to verify that all components have been inserted correctly and that there is no short circuit between two adjacent tracks, which occurred during the welding phase.
Finally, check, using a voltmeter to the output of the controller, you feel it is a voltage of 5 volts.
It only remains now, just check the correct operation of the receiver.
Figure 15: The transmitter modulates the RF signal generated by the module Aurel TX433 BOOST, via an encoder type UM86409. The first 11-bit level is set using 10 micro interrupor dip-switch DS1 and the unique micro-switch DS2. The 12th bit depends on the activation button is selected. This applies to both decks. The dip switch DS3 and DS4, present on the receiver, are used to configure the type of operation of relays, bistable or astable. It is important tokeep in in mind that changing modes of operation ,we must reverse the dip switches dip-switchesinterested and always switch to OFF first . To correctly position the switches of DS3 and DS4, use the function table, considering no other combination is valid.
Figure 16: Our system operates on UHF 433.92 MHz. It consists of a two-channel transmitter, whose output power is 400 mW and a receiver, of course, two channels each controlling a relay also.
Figures 17 : Schematic of minimum and maximum distances covered according to the antennas used.
Figure 18 : The radio transmitter with an antenna "coil".The development
For the development, set the eleven micro-switches that are on DS1 and DS2, in the same order as those of the transmitter and then close DS3 / 1 and DS4 / 1 (ON) to allow pulsed operation.
About these last two dipswitchs, we recall that the two micro-switches DS3 and DS4 are never activated simultaneously.
In other words, we must first position between ON and OFF the micro-switch and active position from OFF to ON the other micro-switch.
During the first test runs, it is sufficient to use as an antenna, a short piece of rigid wire 17 centimeters.
Place a few meters from each other, the transmitter and receiver and try to press one of two buttons on the transmitter.
If everything works properly, the corresponding channel LED should illuminate and the relay is sticking. The outgoing part must remain active during the time that the plunger is pushed.
Perform the same test for the second channel and verify that the LED and relay are activated under the same conditions as above.
If the receiver shows no signs of life, check the positioning of micro-switches, a discrepancy between the position of those of the transmitter and receiver of those is probably the cause of this dysfunction.
Now check the operation of the two flip-flop, opening microswitches DS3 / 1 and DS4 / 1 (OFF) by closing DS3 / DS4 and 2 / 2 (ON).
With micro-switches positioned in this way, by pressing the button transmission, the channel concerned to step up and should remain in this state even when the button is released.
This state is maintained until the relevant button is pressed again.
After checking the functionality of transmitter and receiver, it only remains to perform the range checking using the antenna that best fits your own requirements and above depending on the distance that the system should cover.
Testing scope
We have maintained our own tests earlier this Article. More than a thousand words, Figure 17 will help you in choosing the antenna as a function of distance to cover.
Just remember the three types of antennas we have tested:
- "Boudin" hose (Aurel AG433).
This type of antenna adapts easily to any box, plastic or metal and has a high capacity for flexibility and strength.
The performances were 100 meters in town and 800 meters in open country.
- Rigid Whisk 1 / 4 wave (Aurel AS433).
These antennas exhibit excellent performance when attached to a metal ground plane (see photos).
We covered a distance of 200 meters in the city and 2 km without hindrance.
- Guideline 5 elements (Yagi Cushcraft Dual Band).
The antennas we used for our tests are the 5 items with a gain of 8 dB. They helped make connections 1 km in town and 20 km in the absence of barrier.
Nothing prevents you from trying other antennas, for as they are available to run on 434 MHz. You can also mix, that is to say a whip antenna mounted on the rigid receiver and a Yagi antenna on the transmitter or the reverse. Remember to put the Yagi so upright so that the polarizations are identical.
Only tests based on distance and terrain will determine the type of antenna used by preference.
The results are truly exceptional, considering the simplicity and low cost circuits for transmission and reception.
There are directional antennas with a large number of elements. They may gain up to 20 dB or more. It is therefore evident that the distance of 20 kilometers, although already very interesting, could easily be exceeded.
The transmitter and receiver can be housed inside plastic or metal boxes.
In the latter case, make sure the tracks of the PCB does not touch the metal walls of the enclosure, to prevent short circuits.
Regarding food, we recall that in all cases, consumption does not exceed 100 milliamps.
To power the transmitter and receiver, small blocks are ideal areas, provided they deliver a voltage of 12 volts with a current adequate.
It is also possible to use batteries or rechargeable batteries.
However, we must not forget that if at rest, consumption of the transmitter does not exceed 10 milliamps, it increases to 100 milliamps during the show. Consumption of the receiver is around a maximum of 70 milliamps with all outputs active.
What the law says
In France, the LPD band transmitters are limited to a power of 10 milliwatts BY (radiated power) and must have a fixed antenna can not be dismantled.
The description of this radio is particularly aimed at foreign readers living in a country where legislation is more flexible.
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