epc110

Figure 4: Principle of controlled light barrier application using a micro-controller

The photo diode current is compared to two threshold levels. The result OUTH from the higher comparison level may be used to detect the

light reserve.

Evaluation of a single light pulse

The photodiode is operated against ground and is reverse biased at a constant voltage of 1.2V. The input impedance of pin PD is kept low

(<1 kOhm @ 100kHz) in order to minimize the influence of the parasitic capacitance of the photodiode. To ensure proper operation under high

ambient-light conditions, the photo diode DC current can be up to 2 mA.

The resulting current from the light pulses are converted to a voltage, filtered, amplified and compared to two different threshold levels. The

lower threshold SENSN (input related 60nA typical) is used for the detection of the signal, the higher threshold SENSH (input related to

96nA typical) is used to provide an output when a certain signal reserve is achieved.

To detect the received light pulse properly, the given threshold must be at least five times higher than the rms value of the noise floor

generated by the circuitry without AC light stimulation.

The comparator results are digitally filtered and output at pin OUT and OUTH.

The parameter TPER defines the scan period in the standalone light barrier application but has also an impact to the settling time of the

receiver in the controlled mode application. It this case it has to be set corresponding to the scan period. Refer to the description of the TPER

command.

For each single light pulse, received and detected by the photodiode, the threshold levels for output OUTN and for output OUTH can be set by

programming (parameter SENSN resp. SENSH). They are processed according to the following principle to propagate the output signals

Signal output OUTN

Light reserve OUTH

I

PD

Threshold levels:

OUTN

INT

Light pulse detection

Light reserve detection

I

PD

OUTH

INT

t

t

t

t

t

t

Figure 5: Pulse evaluation

© 2011 ESPROS Photonics Corporation

Characteristics subject to change without notice

7

Datasheet epc110 - V2.1

www.espros.ch

AN epc100 light curtain Transmitter

LST

VDD33

VDD

epc100

GND

OUTH

PD

OUTN

EN

LED

GND

VDD

µC

VDD

OUT

GND

IN1

IN2

EN

R

Stab

R

LED

OUT

11.02.2011

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