Conex Club Magazine - no.4 - 2005

Conex Club Magazine - no.4 - 2005 - Inflatable barrier

Reading time: 3 minute

The main topics presented

1. Inflation barrier

For perimeter protection, and especially for outdoor use, infrared barriers are the most suitable. Mounted correctly, IR barriers offer a high degree of security with low costs.

This infrared barrier system, transmitter and receiver, signals the passage of a person, a vehicle, an animal or any other object and interrupts the barrier.

It can also be used to control an entrance (door or gate) or to any system that can be controlled by this assembly. The minimum safe operating distance is around 4m.

The infrared mini-transmitter is equipped with two infrared (IR) LEDs, and the receiver with a phototransistor (IR). The receiver is equipped with an electronic buzzer which acoustically signals the interruption of the infrared barrier.

The receiver can be completed with a relay interface that triggers an installation to open a gate or other optical, acoustic, etc. alarm.

2. Detector for 220Vac / 50hz electrical paths embedded in the wall

What could be more unpleasant, that when you have to rebuild a power supply route, you have to use a chisel and a hammer and move pieces of the wall.

Only the idea of ​​resorting to such a procedure forces you to research modern solutions based on electronic detectors that are not primarily destructive.

The detector presented allows the detection of the path of an electrical circuit through plaster, with a high accuracy - less than 2cm, the suggestive display of the position being made on a bar-graph type display, with LEDs.

The assembly is based on integrated circuits TLC271 (LinCMOS programmable low-power operational amplifier) ​​and AN6884 (5-Dot LED Driver Circuit).

3. UHF Tx and Rx with voice command activation

By using a voice-controlled circuit (VOX), the standby current of the transmitter is reduced to a value of max. 2mA, which ensures a period of extended autonomy.

The high frequency Aurel type floor, TX-FM Audio, ensures the broadcast on a range located in the range 50… 300m, depending on the environmental conditions.

The VOX floor ensures the optimization of battery consumption. Thus, the transmission mode is active only during the voice signal. It is assumed that, within one day, the total duration of voice messages is one hour and an alkaline battery with the capacity of 600mAh.

If the voice command circuit is used, autonomy is ensured for a period of approx. 10 days. In its absence, the period of autonomy is reduced to only two days.

4. LM1875 - 20W audio amplifier with low distortion

The LM1875 integrated circuit produced by National Semiconductor is part of the category of high-performance audio circuits, with low signal distortion, THD, up to 0.01%.

Response speed (dynamics) is high, typical value 8V / us. The limit values ​​are: supply voltage 60V, maximum input signal from -Vdc to + Vdc, the maximum junction temperature being 150C. The load limit current is max. 4A.

It offers various protections in DC and short circuit to the ground. Range of supply voltages: 16… 60V; typical recommended value for the indicated power, 25V. It can be supplied from a single or double voltage source.

Physical presentation: TO220 capsule. For cooling, an aluminum radiator with radiator-ambient thermal resistance is recommended (see the table of radiators presented in Conex Club no. 12/2004) less than 2.2 W / C.

5. VT_ series photoresistors

Conex Electronic offers a new range of high quality photoresistors, produced by PerkinElmer.

Introduces himself photoresistor models, from the VT2_, VT8_ and VT9_ series. The first series is presented in a capsule with a glass lens, the other two being made of plastic.

It must be remembered that the electrical resistance of a photoresistor is inversely proportional to the intensity of the incident light (its own resistance decreases if the photoresistor is illuminated).

Photoresistors are characterized by an electrical resistance to light, RL and darkness (minimum), RD (eg range 6… 18 KOhm at exposure to light of different intensity and minimum 100 KOhm at dark).

The dissipated power is small and results, depending on the voltage at the terminals of the photoresistor, a current that can cross it in the order of units or tens of mA.

6. Twilight automatic supplied directly to the 220Vac / 50Hz mains

The presented assembly offers the function of switching a power relay when the ambient light of the day (from a building hall, office, industrial hall, etc.) falls below a predetermined intensity.

It is practically designed to control the opening of electric lighting of incandescent bulbs (indoor or outdoor) at dusk and respectively, turning off the lighting at the beginning of the day, in the morning.

The light transducer is a photoresistor, mounted on the side of a resistive bridge, role of comparing predetermined thresholds (imposed and measured). The actual comparison function is performed with an operational amplifier in comparator configuration.

Description of the wiring diagram

The light transducer used is, like most twilight automata, a photoresistor (resistor that changes its own resistance depending on the light intensity - recommended VT83N1).

The basis of the assembly is an operational amplifier (LM308), in positive voltage voltage comparator configuration, which ensures the maintenance of the current state, thus eliminating the annoying "clamping" of the relay around the switching threshold!


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