epc120
3. System Concept
Out
am
active light be
Micro
Controller
Bus
➊
Interface
(epc100)
SPI-
Interface
light cone
generated by
LED
the
➊
2-Wire Bus
➊
Bus
Termination
50Ω, 100nF
➊
epc120 with PD and LED
➊
Figure 4: System overview
In a system with several reflective light barrier beams, each individual light barrier contains an emitter and a receiver. They are located at the
same place. As a receiver acts a photodiode and as an emitter a LED. Both can be controlled by only one single epc120. In contrast to the
epc11x-family, which are also light barrier chips, the epc120 can be used in a large distributed system. The devices are synchronized over the
2-wire bus line, organized by one epc100 and a microcontroller.
Figure 4 shows a typical distributed light barrier setup with five elements. Each element consist of an epc120, an emitter (LED), a receiver
(photodiode) and a few other components. Every element is connected to the 2-wire bus1, which is controlled by a microcontroller through an
epc100. Because every epc120 element has a unique address, the microcontroller has individual access to all bus components.
Each of the epc120 elements sends light, typically infrared light, focused towards a reflector or an object. It reflects the light back to the
photodiode. If multiple sensors like this would be operated in close proximity, scattered light from all sensors are probably reflected to the
receivers. This would lead to false triggering. Thus, a sequential operation mode has to be implemented. Basically, a master controller
activates one sensor after the other and reads back the status of each individual light beam.
1
If the LED pulse current is rather high, i.e. 1 A, two separate bus wires for the LED supply current are needed. Please refer to Error:
Reference source not found for detailed information.
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
6
Datasheet epc12x - V2.1
www.espros.ch
EPC [ ESPROS PHOTONICS CORP ]
