epc120

3. System Concept

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

Figure 4: System overview

Micro

Controller

Out

2-Wire Bus

epc120 with PD and LED

Bus

Interface

(epc100)

Bus

Termination

50Ω, 100nF

SPI-

Interface

light cone

generated by the

LED

active light beam

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