Virtual net in a real environment


Acad. Ms. Arq. Silvia Lenyra Meirelles Campos Titotto

Department of Design and Architecture, Faculty of Architecture and Town Planning,

University of São Paulo



Acad. Eng. Felipe Estrella Barros

Department of Energy and Automation, Polytechnic School,

University of São Paulo



Profa. Dra. Clice de Toledo Sanjar Mazzilli

Department of Design and Architecture, Faculty of Architecture and Town Planning,

University of São Paulo







This project consists on an installation of several common laser beans (models of

laser beans that are normally used on presentations), mirrors and a light sensor (LDR - Light Diode Resistor).

The laser beans are positioned with their aims focused on the mirrors. Through the

reflection of the mirrors, it is possible to create virtual obstacles. If a person or an

object crosses the laser, the light sensor notices the interruption and will trigger an

alarm. A source power will be developed in order to replace the laser beans'

batteries and the alarm circuit. The alarm circuit will be also designed for this work.


Working Principle

The conception of this project is directed to the study of the environment response due to a human action. Based on that subject, an environment was prepared with several visible rays of laser. If one of theses rays is interrupt (eg. someone crosses it), an alarm will be triggered. Therefore, the space of the environment is sensible to the presence of people.

It can be also quite interesting to try to dodge the rays, as if it was a virtual barrier or labyrinth existing in a real space.


Technical Issues


Power Source

The reason to develop the power source is to replace the laser beans batteries - which don’t have autonomy greater than a couple hours - and also to feed the trigger circuit (see circuit diagram on figure 1).

The AC input chosen was 220 V, because it is the voltage provided in Europe.

There are two different outputs. One output is stabilized, with DC 5 V and 5 W maximum power. It has the purpose to feed the laser beans. The 7805 voltage regulator is the one that best suits to the lasers connections, because it’s voltage output is 5 VDC, while the beans need 4.5 V. The difference of the voltage will be solved through the insertion of a resistor in series with each bean.

The other output will be used on the alarm circuit. It is not stabilized and has 12 VDC voltage with 40 W maximum power output.


Figure 1 – Stabilized 5 V power source


Laser Beans

This experiment will have 4 laser beans, fed by the 5 V power source. Each laser bean works with a 4.5 V  voltage and 20 mA current. Therefore, using the Ohm’s law, follows:




The resistor R calculated in (1) will be set in series with each laser bean, as represented on figure 2.


Figure 2 – Connection of the beans to the Power Source


Alarm Circuit

The alarm circuit consists on a LDR sensor (Light Diode Resistor) that operates as a trigger of the BC327 transistor. If the ray of laser stops falling upon the LDR (eg. a person or an object has crossed the laser ray), it will make the transistor enter on its conducting procedure. If the transistor starts conducting, it will energize the relay. The relay has an electric seal that keeps it energized even if the transistor stops conducting. The siren is connected through the relay to the 12V power source, therefore, if the relay is activated, the alarm is triggered.


The only way to reset the alarm is to push the pushbutton break.

The alarm circuit’s sensibility is adjusted by the potenciometer.

The circuit diagram is shown on figure 3.


Figure 3 – Alarm circuit diagram


Mirrors and support

The project will have 13 mirrors, with dimensions of 50x50 mm and transparency equal or greater than 70%. They will be attached on 55x55x20 mm cubical pieces of wood.

A hole of 6mm2 will transpose the lateral of the wood, in parallel with its surface. Through this hole, it will be stick a piece of cable, very hard and with thickness of 6 mm2. Glue can be used in order to fixate the wire inside the hole.

The support can also be made of wood. A rectangular base of heavy wood (about 5 kilos) should be enough. A vertical wood stick made of brown stick can be settled trough a hole on the base.

The mirrors will be placed on the vertical stick through 6 mm2 horizontal perpendicular holes, which will receive the wire from de mirrors.

The mirrors adjusts will be made by deforming and twisting their wire. The laser beans and the LDR sensor can also be attached through this 6 mm2 wire to the bases.

Another possibility to fixate the lasers and the mirrors is to attach the devices on common professional microphones stabling systems (see figure 6 ).


Room environment

It is imperative to prepare the room for almost complete darkness, otherwise the lasers won’t be seen. To provide a carrier in the air that helps to make the rays of laser more visible, a glycerin smoke machine can be used.


The Results

This installation was simulated in a CAD system, and some angles of it were rendered in order to demonstrate the environment. On figure 4, there is an isometric view of the installation, made on a square space.


Figure 4 – Isometric view of the installation


Figure 5 shows the top and side views of the installation.


Figure 5 – Top view (on the left); side view (on the right)


The mirrors and lasers were sketched with an attaching system based on microphone stabling devices.


Figure 6 – Four mirrors set on a wood base (on the left); Four laser beans and a mirrors set on a wood base (on the right)