A proximity detector

This device detects the approach and the displacement of persons or things within its range and is particularly appropriate to protect the environment or non-enclosed vehicles, such as a booth, a showcase, convertible vehicles, the boats, etc.. The sensitivity adjustment allows easy adaptation of the benefits of this circuit the precise characteristics of the place to be protected.

If you want to protect your car under a little too ambitious of a street robber, you know you can count on a wide variety of burglar, generally similar with respect to the sensors used to detect hazardous conditions and devices (audio and / or light) to give the alarm if you have a convertible or a 4x4 discovered, you must fold your requirements as most commercial locks are not suitable for this type of situation.
This due to the fact that normally locks the car detect intrusion into the cockpit with a radar ultrasound, which only works properly in a closed volume. If you need to protect a vehicle not enclosed, the only alternative is the motion detector, which unfortunately does not give the alarm when the thief starts the vehicle.

Our achievement
This problem is he without a solution? Of course not!
We designed a special sensor that can detect an intrusion into an open vehicle, connected to a traditional lock, for example instead of a vibration sensor, it can trigger a siren or inhibiting the electronic engine or the electronic controls of the boat, etc.. in short, do everything that a sensor alarm car usually (of course with the aim of deterring a thief from continuing with the risk of being arrested).
But especially on a boat that the proposed device is necessary because the water movements caused by waves trigger false alarms and make motion sensors such as volumetric ineffective, however the RF sensor n 'is not sensitive and does not give the alarm in case of intrusion (or approach a little too "tight") in the cockpit.
Our perimeter sensor type or proximity (or approach) because it detects the approach of people and things within its own range, a field whose expansion is adjustable simply by trimmer to keep under control a small utility vehicle like a dinghy, a small boat, a convertible or a caravan.
But you're probably wondering how a camera as easy to adapt to the environment be protected?
Well, first of all say that to detect the approach of a body in an open forum (outdoors), the only effective solution is practicable to work with radio waves.

wiring diagram

Figure 1: Diagram of the proximity sensor.

The electronic circuit of our camera which Figure 1 shows the wiring diagram is an oscillator-RF (radio frequency) operating around GHz, which radiates around him his own lines of flux. When something organic-based soil or ferromagnetic moves in its scope, that something interferes with the oscillator and alter even if only to a limited extent, the working frequency that causes a small voltage change detected by a floor designed for this task and that triggers a timer whose output controls a transistor and open collector line. This line can be used to activate the inputs to pull-supplied or relays 48 VDC maximum (most relays available operating at 12 V, this limitation is not very damaging!).
Let's take a look at the wiring diagram and start by describing the oscillator: it consists of an NPN transistor for high frequency (RF) in plastic case TO-92, configured as a phase shift oscillator.
Its operation can be summarized: once fed, T1 immediately starts to oscillate, because in the spectrum of electrical noise produced by components and by interference picked up by the PCB, there is certainly the tuning frequency of the dipole antiresonant obtained by the superposition of the runway of the collector of T1 with the power (this is an overlay capability and parasitic inductance and the return phase signal on the basis that the rest of the NPN and the oscillation begins precisely the frequency tuning of Lc / DC. The dipole series composed of C10 and the parasitic inductance (formed by a track circuit properly shaped) rings, which determines an increase in the transistor gain and promotes oscillation, which causes the release into the environment of RF electromagnetic radiation course.
The approach of a body of a certain mass (eg a person or just his arm stretched over a convertible vehicle) interferes with the electromagnetic field, which determines a variation in current consumption by oscillator circuit (with a consequent change in the amplitude of the voltage on the collector of BFR90).
The change also occurs because the approach of a body in some way false operation of the oscillator, since it introduces confounding factors that alter the frequency of oscillation.
When you read with the operational amplifier U2a the RF voltage generated by T1, we can follow the progress of the operation of the oscillator and detecting the approach of a body. In practice U2a works within a circuit which is both an amplifier and a crossover double slope (R / C at 40 dB / decade): the RF voltage is filtered R5/C8 then amplified. C3 is the second filter element and is located in the feedback operational amplifier, thereby reducing the gain in the presence of signal, especially as the frequency of the latter is higher.
The rectified and filtered component is required at the door of U2b, mounted differential amplifier; him unidirectional tension obtained by the detected RF signal is then filtered and R6/C5 R7/C6 (two other cells lowpass) and sent to the non-inverting input. Arrives at the inverting input through a component similar to C4. The pin 7 an output voltage almost continuously compared with the reference 5 V positive U2c comparator: the output of the latter is a high logic level whenever the filtered component exceeds the reference amplitude and is at logic zero in the otherwise. When the oscillator is working in normal conditions, the output of U2c is at logic low level and, if the circuit is disturbed by the approach of a body, blood filtered U2b grows in amplitude and force the comparator to be logic high output state: this determines the charge of the electrolytic C7 through diode D4 and resistor R8, which causes the switching of the other comparator in the circuit: u2d. This is the type of hysteresis and thus its release, taking the high logic level (approximately +12 V) biases the base of T2, light LD1 and raises the level of the potential of the pin 12 (its non-inverting input), compared when switching, so as to stabilize conduction avoiding oscillatory phenomenon. The hysteresis ensures that efforts to provide low logic level output of the comparator, C7 should be discharged and have a voltage level much lower than the one who forced the switch 0 / 12 V to pin 14 of U2: practically it must fall to about 3 V, 2 V as already falling in R10. So when C7, charged by 12 V (approximately) provided by U2c following detection of a body near the sensor, to discharge up to 3 V, the output of u2d starts again at zero, because the 5 V reference biases the pin 13 becomes greater than the voltage applied to pin 12. Of course, C7 can not be discharged until U2c returns to rest, that is to say if the sensor continues to detect the presence of someone in the area.
And here comes in part from the circuit until voluntarily left out: it is a unit whose function is to introduce some delay between detection and the other means used to numb the circuit for about 10 seconds after each detection. Returning to the wiring diagram: Note that when the D5 led u2d compare its output to logic high (ie when the output of the circuit is active), which carries just over 11 V to the inverting input of operational U2a ; connection ensures that, when the sensor triggers the alarm, the input stage, that is to say, the filter / detector U2a or inhibited and can not amplify anything. Indeed, the polarization forced to pin 2 is at logic low output of the amplifier.
Zero out of U2a is also at logic low output U2b (the non-inverting input of the latter is coupled continuously through R6/R7 and receives zero volts, while the feedback has a gain unit), which brought back to zero the output of U2 (comparator) as well. In this phase, D7 is reverse biased and prevents the voltage supplied by the output of u2d be applied to the non-inverting pin which would invalidate the function. Following inhibition of return and the rest of the comparator U2c, the electrolytic C7 can unload and take that determines the potential recovery of OUT, 3 V, which occurs in slightly more second.
If you require a greater period of inhibition (eg to have time to deactivate the alarm upon entering the vehicle), you can play on the capacitor value, increasing it to 22 to 33 uF, not to mention that the delay is equal to about 1.5 second per uF capacitance C7. When the time elapses, the pin 14 of u2d returns to zero volts, T2 is blocked off and the detector LD1 U2a is released.
Before concluding, a few more words on the output: it is an open collector line that consumes power when it is active, the OUT point, normally open, one can connect the inputs of logic devices that s' activate when placed at logic 0, but also buzzer, relay and other charges not consuming more than 300 mA, supplied with voltages between 5 and 48 VDC.
Should we connect the relays, it is necessary to protect the collector junction of T2 with a diode mounted in parallel on the coil (the anode facing the positive supply).
See the three wiring diagrams in Figure 5 for further explanation on the output.
The circuit has been designed for use in a vehicle, it is funded entirely with a voltage of 12 to 15 VDC; supply connects to the points + and - (positive and negative battery) to be forwarded to the LM324 quad operational and controller U1 via D1 (its function is to prevent harm can not arise from the presence of negative voltages on the electric circuit of the car when one uses highly inductive loads such as wipers, ventilation or starter).

Figure 2: Schematic implementation of the components of the proximity sensor.

Figure 2b-1: Drawing to scale 1, double-sided PCB with plated through holes of the proximity sensor, component side.

Figure 2b-2: Drawing to scale 1, double-sided PCB with plated through holes of the proximity sensor, solder side.


Iist ET959
R1 ...... 10 kW
R2 ...... 4.7 kΩ
R3 ...... 270Ω
R4 ...... 270Ω
R5 ...... 4.7 kΩ
R6 ...... 1 MΩ
R7 ...... 1 MΩ
R8 ...... 1 kΩ
R9 ...... 470 kΩ
R10 ..... 680 kΩ
R11 ..... 3.3 MΩ
R12 ..... 1 kΩ
R13 ..... 680Ω
C1 ...... 10 uF 25 V electrolytic
C2 ...... 47 uF 16 V electrolytic
C3 ...... 4.7 nF ceramic
C4 ...... 100 nF multilayer
C5 ...... 4.7 nF ceramic
...... C6 1 nF ceramic
C7 ...... 1 uF 25 V tantalum
C8 ...... 100 nF multilayer
C9 ...... 4.7 uF 25 V tantalum
C10 ..... 10 pF ceramic
Ca ...... track circuit
Jw ...... track circuit
This ...... track circuit
Lb ...... track circuit
Luke ...... track circuit
The ...... track circuit
VR1 ..... 200 trimmer
VR2 ..... 500 k trimmer
U1 ...... 78L05
U2 ...... LM324
D2 ...... 1N4148
. . .
. . .
. . .
D7 ...... 1N4148
LD1 ..... LED 3 mm red
T1 ...... BFR90A
T2 ...... MPSA42

Miscellaneous:
1 holder of this 2 x 7-pin
A specific plastic case (see photo) Unless otherwise specified, all resistors are 1 / 4 W 5%.


The practical realization
As it is a unit working on the borders of the UHF and microwave, it is essential to follow a few good rules to ensure smooth operation.
First, the printed circuit board: it is a double sided with plated holes 2b-2b-1 and 2 give the drawings to scale 1: 1. If you make it yourself, carefully follow the pattern of tracks (especially the face welds) because of the oscillating circuit chokes are designed and even building "pests" are taken into account to swing it.
Indeed, at frequencies around 800 to 1000 MHz, a track well-calculated and well done can be a self and a reconciliation of two tracks can also be a capacitor (few pF no more).
The required accuracy requires reliance on the good photogravure from photocopies or scanned images as found on the journal's website. Caution, do match the two sides with some positioning holes.
You can also get the PCB double sided plated through holes made from any one of our advertisers.
Anyway, when you have before you mount all components (all side "components"), as shown in Figures 2a and 3a and the list of components: most are through but some (although not CMS) are welded to the tracks and pads of the face "components".
Mount bracket first integrated circuit and check out these welds first, then mount resistors (R2 and R4 except standing), diodes, capacitors small, the bulk electrolyte (coated), the LED, the two transistors, the regulator and two trimmers.
Attention to the polarity of tantalum capacitors and electrolytic that of diodes, LEDs, transistors, regulators and the integrated circuit (for the latter, repèredétrompeur U to the controller).
Double check your solder (or short-circuit between tracks or pads or cold solder joints) and well all polarities again. And at least twice.
You can now install the plate in the specific box (see Figure 4), insert the chip into its holder (in a good way).
Once you have set the stage and you put the lid, the LED flush it (especially if you have set the length of the legs).
Both son power red / black from the vehicle battery by entering the small lateral recess visible on the photograph, the wire open collector output from OUT devices (control panel, buzzer, relay, etc.). exits there as well.

Figure 3: Photograph of a prototype of the proximity sensor, component side, where all components are mounted with some without CMS, are welded to the surface.

Figure 3b: Photograph of a prototype of the proximity sensor, solder side, where any component does is mounted (the trails around the welds of the three legs of the transistor act as inductors and capacitors).

Figure 4: Installation in the plastic housing of the specific proximity.

Figure 5: The sensor has an open collector output which consumes power when it is activated, the OUT point normally open, you can connect the inputs of logic devices (Figure A) that are activated when they are set to logical zero, as well as buzzers, relays and other charges not exceeding 300 mA, supplied with voltages between 5 and 48 VDC. Should we connect the relays (diagram B), it is necessary to protect the collector junction of T2 with a diode in parallel with the winding (with the anode facing the positive supply). The sensor is designed to be coupled to the control panels of various types, equipped with normally open and inputs that are activated when they are placed at logic zero (ground): it is enough to unite the masses of the circuits have the common reference (Figure C). The use in vehicles is not the only possibility: for example, at an exhibition of precious objects, the device can give an alarm when someone "lets her hand" a little too near protected objects, arranged on a stand or in a display case not closed.



volumetric sensors Unlike ordinary cars, the system proposed here is a proximity based on the principle of interference body moving with the electromagnetic field radiated RF product and in the immediate environment. This feature makes it effective even if the car door is left open because it does not affect the internal volume but on the actual presence of a mass moving in a perimeter established at the time of adjustment.
That's why we recommend you use the same device to protect convertibles, spiders and other convertibles or small boats.
The presence of glass, fabric, plastic parts or wood (excluding all metals, does not affect the operation of this device, because radio waves pass through easily these materials; repeat, this is not the case metal, him, adopt the RF waves capturing flux lines of magnetic and electromagnetic fields.
In a car, the device is installed between the front seats or behind, so it is at the center of the cockpit. Adjusted for maximum sensitivity, the sensor can trigger the alarm even if someone presses his face against the glass of a window to see what's inside! In a convertible it fires only if someone holds out his arms inside, but remains indifferent to the hand from side to walking on the sidewalk without looking or look in the cockpit. You must install it to believe it

Figure 6: Open ... the sensor.

settings
In this circuit two adjustment trimmers have been provided: VR1 adjusts the intensity of the field emitted by the oscillator and determines the boot; VR2 adjusts the sensitivity. To set the device you use the LED, which is in series with the base of T2 reflects the events of the output; feed circuit (test with power of 12 to 14 VDC 200 mA) and turn first axis VR2 fully clockwise to adjust the sensitivity maximum.
If the LED lights because of your presence is that the oscillator works, otherwise, the cursor slowly turn trimmer in one way or another, until the LED light. If this is difficult to obtain, change the value of C10, choosing values between 1 and 47 pF: it is indeed possible that the oscillator has trouble booting.
The small box is easy to hide in the vehicle, as shown in Figure 6. Avoid placing it on the ground because it would be too close to the sheet metal floor. Remaining in a boat dock, remember to protect the casing against the weather (you can coat it with clear silicone sealant, a thin layer is sufficient) Apart from the protection of vehicles (including boats), you can use the sensor a stand or in a display case not closed to protect against pickpocketing valuables that you want to expose.
You can also control access to potentially dangerous places (high voltage, chemicals, etc..): In these cases you can pair it with a buzzer (there are producing very loud sounds). More generally, the device can be used whenever you want to control access to undesirable or dangerous to people (and why not animals?) In a given environment of open type or outdoors.