IT8946875A1 - SELF-ADJUSTMENT CIRCUIT OF THE SENSITIVITY THRESHOLD IN THE PRESENCE OF SMALL ENVIRONMENTAL DISTURBANCES VARIABLE OVER TIME, ESPECIALLY FOR ULTRASONIC DEVICES - Google Patents

Description

proportional to the frequency differences due to the Doppler effect due to background disturbances with a reference signal (voltage).

TEXT OF THE DESCRIPTION

One of the unsolved problems in the field of ultrasonic anti-theft devices derives from the fact that in the presence of small disturbances in the environment, not due to intrusion of people, the device is activated by launching a false alarm.

It is known that these devices use the Doppler effect in order to detect the presence of moving bodies in an enclosed environment, such as the passenger compartment of a car, and are based on the fact that a signal emitted into the environment at a certain frequency , normally well above the audible range, it is reflected by immobile objects and received by a suitable transducer without the frequency undergoing variations, while when it is reflected by moving bodies it is received with a modified frequency, greater or less than that emitted at depending on whether objects approach or move away from the signal emitter.

Listening to the signal1 allows you to understand, in principle, if there are moving objects in the environment, and what? simply by comparing the frequency of the received signal with the frequency of the emitted signal.

usually the two signals are processed, and the resulting signal proportional to the difference in frequency? sent to a comparator who, when? the level of said resulting signal exceeds a certain threshold, activates the alarm.

In a more? specific, this patent has as its object the determination and regulation of the sensitivity threshold? of the comparator.

Pi? this threshold? low, and more? ? high? the possibility? that false alarms are triggered due to causes independent of intrusion into the passenger compartment of the vehicle. On the other hand ? obvious that the elevation of the threshold decreases the sensitivity? of the device.

the present patent has the purpose of maintaining the level of the threshold always just above a minimum level relating to background or random perturbations not due to intrusions into the passenger compartment.

It starts from the observation that the cause more? frequent of unwanted disturbances? the presence of convective motions of the air due to the temperature variations which? subject to the passenger compartment, such variations being able to be also very sensitive when? the car? parked in the sun. The elimination of unwanted alarms due to these perturbations could be simply obtained by limiting the sensitivity? of the "Doppler" signal processing circuit at resulting frequency differences greater than at least 5 HZ.

What? doing for? the system becomes unable to detect objects or bodies that move with speed? of the order of about 3 cm / sec, and loses (therefore part of its effectiveness. Since, on the other hand, the perturbations of the environment, background or random, vary very slowly over time, the problem arises of automatically adjusting and periodically the sensitivity threshold of the comparator at the average level of the perturbations, at very short intervals, of the order of seconds.

With us? the loss of sensitivity? of the anti-theft will be? limited to raising the threshold beyond said average level, and practically to values very close to those due to background perturbations.

The purpose of the finding? then to make available a system that automatically modifies the sensitivity? of the anti-theft system to vary the background perturbations present in the passenger compartment, as well as? the means for implementing the system.

This purpose? achieved by the invention thanks to a system of adjustment of the sensitivity threshold? of the comparator that controls the alarm, by raising and lowering the comparison voltage of the latter.

The variations of the comparison voltage are caused, according to the invention, by the insertion / disconnection of resistors placed in parallel in the circuit which conducts the comparison voltage to the comparator, said insertion / disconnection being due to the activation of a series of switches in the state solid controlled periodically by a circuit according to the signals received by a series of comparators, which we will call calibration, in a number equal to the number of solid state switches.

These calibration comparators compare a signal proportional to the average of the values of the frequency variations due to the Doppler effect caused both by disturbing factors and by intrusions in the environment, with a comparison voltage that? different, and increasing for each comparator.

Thus the comparators whose comparison tension? lower than the signal proportional to the average of the signals caused by the background noise, they in turn emit a signal which is periodically selected by a state memory, or Flip-Flop, and which activates the respective solid state switch.

the number of solid state switches that is cyclically closed or opened determines, for each period, the sensitivity threshold? of the comparator which triggers the alarm.

The functional and constructive characteristics of the invention will be better highlighted by the detailed description which follows, which relates to a particular particular embodiment of the invention given by way of non-limiting example.

FIG. L ? the block diagram of the part of the alarm circuit which concerns the invention.

FIG. 2 ? the timing diagram of the control signals of the circuit of FIG. 1.

With (rd)? indicated the signal proportional to the frequency difference due to the Doppler effect after which? been processed downstream of the listening transducer of the alarm device, which appears as a voltage signal with modulated amplitude.

It is sent directly to the alarm comparator (CTI) which, when? the signal exceeds the reference value, triggers the alarm (all).

The reference value reaches the alarm comparator (CTI) through a circuit forming the subject of the invention. This last ? consisting of a section for adjusting the reference signal, consisting of the voltage (Vo) which? connected to the alarm comparator (CTI) by means of a circuit that includes a divider (R1-R0) and a group of resistors !, connected in parallel to (RI), (R2), (R3), (R4) and (R5) which are (connected or disconnected by as many respective solid state switches (si), (S2), (S3) and (S4).

The insertion of each of these resistors raises the reference voltage; sent to the comparator (CTI), and therefore in practice raises the sensitivity threshold? of the system.

The adjustment section? controlled by a circuit which essentially realizes the average of the signals (rd) proportional to the frequency differences due to the Doppler effect, comparing them at determined intervals with fixed reference values by means of comparators calibrated at predetermined values, which comparators, in the case in which the average of the signals (rd) exceeds the threshold of one or more? of them, command the closure of one or more? of the above mentioned solid state switches (SI} .... (S4).

A part of the signal (rd) as defined pi? above it is separated into (Al), through the diode (DI) and reaches the switch (S5) whose open or closed position? determined by the command signal (a) whose course? marked in FIG. 2.

This signal? normally high, and the position of the switch (S5)? normally closed.

Signal (a) goes low every few seconds, preferably two seconds, for a few milliseconds, and when does signal (a)? low, the switch (S5)? open.

The switch (S5) connects (DI) with a second separator amplifier (A2), from the direct connection deriving two groundings, in parallel with each other, one of which includes a capacitor (Cl) and the other a switch to the solid state (S6).

The switch (S6)? commanded by a command signal (b) whose trend appears in FIG. 2, and what? the inverse of (a), in the sense that when (a)? high (b)? zero and vice versa.

Downstream of the separator amplifier (A2)? provided a solid state switch (S7) whose position depends on the command signal (c), the course of which? always marked in FIG. 2, and what? identical to signal (b), but shifted towards the origin so as to exactly anticipate the latter without overlapping.

The configuration d? above? such that the maximum charge voltage of the capacitor (Cl) relative to the period, equal to the peak of the separate part of the signal (rd), arrives downstream of the circuit-breaker (S7) for each closing period of (S5).

In fact, during the closing of (S5) and the corresponding opening of (S6) (Cl) is charged.

Just before (S5) opens (S7) closes and (S6) closes immediately after (S5) opens. So, before (S5) closes, with (S7) already? reopened, the charge voltage? di (Cl) is transferred, after being limited by the resistance (R6), to the capacitor (C2). The charge voltage of (C2) therefore varies every two seconds, that is to say at each period in which the signal (a)? high, depending on the variation of the signal (rd) due both to the intrusions of moving bodies and to background disturbances. A part of the charge voltage of (C2), determined by the presence of the resistor (R7) placed in parallel with (C2), constitutes the input data common to the series of calibration comparators (CT?), (CT3), (CT4 ) and (CT5).

The threshold of sensitivity? of said comparators? increasing from (CT5) to (CT2) thanks to the resistors (R12), (Rii), (RIO), (R9) and (R8) which are placed on the connection between the voltage point (Vo), each single comparator (CT2 ) ... (CT5) and grounding.

By way of information, we specify that the reference voltage of the comparator (CT5)? the following

and so? Street.

The signals emitted by the single comparators reach as many status memories or Flip-Flops, (FI). (F4) connected in order to the comparators from (CT2) to (CT5).

State memories (FI) to (F4) are cleared at the time? inserted the alarm device by a signal (e), the trend of which appears in FIG. 2.

The state memories (F1) to (F4) are activated by a signal (d), substantially a voltage pulse which is emitted, as shown in FIG. 2, every fifteen pulses (a), i.e. every 30 seconds or so.

When the state memories from (FI) to (F4) are activated by the signal (d), the signal emitted by the comparators (CT2) to (CT4), is sent to the switches (SI) and (S4) which will be closed or opened by varying the threshold value of the comparator (CTI).

Basically, every 30 seconds, that is to say every time a command pulse (d) is issued, the sensitivity threshold? di (CTI) adjusts to the average of the signals (rd) of the previous thirty seconds.

The characteristics of the components of the circuit illustrated are given below in relation to the example described above.

Claims (4)

CLAIMS 1. Circuit of self-adjustment of the sensitivity threshold? ultrasonic anti-theft devices with Doppler effect, of the type comprising an alarm comparator able to compare a voltage signal in modulated amplitude proportional to the frequency variation due to the Doppler effect due to the background disturbances of the environment under control and to the presence of any moving bodies inside it, with a sample signal, characterized by the fact that the sample signal is sent to the comparator through a voltage divider circuit whose upper branch includes at least two resistors! in parallel, of which at least one is connected and disconnected by a switch which in turn is activated in opening or closing by a voltage signal transmitted cyclically through a status memory, and emitted by a respective calibration comparator which compares the average of the signals proportional to the frequency differences due to the Doppler effect due to background disturbances with a reference signal (voltage). 2. Self-adjusting circuit according to claim 1, characterized in that the signal is proportional to the frequency variation due to the Doppler effect? an amplitude modulated signal, which is amplified and separated, and whose maximum values in periods from 1 to 3 seconds are stored in a first capacitor, the values of a number of periods from 10 to 20 being limited and accumulated in a second capacitor and presented to the at least one calibration comparator. 3. Self-adjusting circuit according to claim 1, characterized in that the reference signals (voltages) reach the at least one calibration comparator through a resistance divider circuit, so as to increase for each calibration comparator. 4. Adjustment circuit according to claim 1, characterized in that the signal emitted by the at least one calibration comparator is sent to a state memory which, when? subject to an external command pulse, it copies it as it is and sends it to the switch relating to the at least one resistor placed in parallel in the circuit through which the reference voltage is sent to the alarm comparator.