Abstract: A photosensitive device with a photodiode and an amplifier is disclosed. The diode is in series with a feedback transistor which forces the voltage derived from the photocurrent to be a logarithmic function of the light intensity. A current mirror is provided which controls the bias current to the amplifier to be proportional to the photocurrent. This arrangement ensures that the amplifier, just as the voltage derived from the photocurrent, becomes faster with increasing light intensity and therefore prevents an unnecessarily high power consumption at low light intensities.

Abstract: A device for controlling a physical system, such as a flow of pedestrians, in an extended area is suggested. In comprises a plurality of identical cell units with preferably hexagonal shape. The cell units are assembled in tile-like manner to form a floor. Each cell unit is equipped with a weight sensor, lamps of different colors, and optical communication ports as well as power connectors for connecting it to its neighboring cells. The cell units can be programmed to generate signals that control the physical system, such as signs understood by the pedestrians. Due to its modularity and simple design, the device is easy to install and maintain.