AN07 – epc600
Handbook Time-of-flight range finder chip
General Description
The epc600 chip is a general purpose, monolithic, fully integrated
photoelectric CMOS device for optical distance measurement and
object detection. Its working principle is based on the three-dimen-
sional (3D) time-of-flight (TOF) measurement.
The system-on-chip (SOC) contains:
■ A full data acquisition path with the driver for the LED, the photo-
receiver, the signal conditioning, the A/D converter and the signal
processing.
■ An on-chip controller managing the data acquisition and the data
communication.
■ A 2-wire interface for the command and data communication.
■ A supply-voltage power management unit.
This document is a supporting document to facilitate development
work with the epc600 TOF Range Finder. It contains product- and
application related information which may arise while working with
the epc600 and complements the epc600 TOF Range Finder
datasheet.
epc600 - Features
■ Complete data acquisition system for distance measurement or
object detection on chip. Allows for minimum part count designs.
■ On-chip high power LED driver.
■ Easy to use operation in combination with a tiny microprocessor.
■ Absolute distance measurement with digital data output.
■ Integrated signal-processing.
■ High sensitivity and resolution for measured distances up to 15m
at 10MHz LED modulation frequency.
■ Response time of less than 1ms possible.
■ Digital data output with 12 bit distance data.
■ Excellent ambient-light suppression up to >100kLux.
■ Integrated ambient-light meter (“Luxmeter”)
e.g. for brightness control
■ Voltage supply with low power consumption.
■ Easy to use 2-wire interface with simple command set.
■ Fully SMD-compatible flip-chip CSP24 package with very small
footprint.
epc600 - Applications
■ Light barrier with powerful ambient-light suppression
■ People and object counting sensor
■ Door opening and safety sensor
■ Limit and proximity switch
■ Machine control and safety sensor
■ Water tap and toilet flushing sensor
■ Single spot parking sensor
■ Distance measurement gauge
Product example
Figure 1: Distance Sensor based on the epc600 TOF Range Finder
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Table of Contents
General Description............................................................................................................................................................................................1
epc600 - Features..............................................................................................................................................................................................1
epc600 - Applications.........................................................................................................................................................................................1
Product example................................................................................................................................................................................................1
Introduction.........................................................................................................................................................................................................3
1. epc600 system integration........................................................................................................................................................................3
1.1. Hardware design tips and tricks............................................................................................................................................................3
1.1.1. I/O levels.............................................................................................................................................................................................3
1.1.2. -5V charge pump ...............................................................................................................................................................................3
1.2. Microcontroller firmware architecture example......................................................................................................................................3
2. Optical system..........................................................................................................................................................................................5
2.1. Transmitter: LED and TX lens system ..................................................................................................................................................5
2.1.1. Illumination distribution of IR LEDs.....................................................................................................................................................5
2.1.2. Illumination distortion through lens system........................................................................................................................................5
2.2. Receiver: epc600 and RX lens system .................................................................................................................................................6
2.3. Optical bandpass filter ..........................................................................................................................................................................6
2.4. Noise, stray light....................................................................................................................................................................................6
2.5. Optical decoupling of emitter and receiver............................................................................................................................................7
2.6. External LED driver................................................................................................................................................................................7
3. Measurement principles of the epc600 ....................................................................................................................................................8
3.1. Distance calculation: Principle...............................................................................................................................................................8
4. Operating the epc600...............................................................................................................................................................................9
4.1. Operation strategies and use cases for the epc600..............................................................................................................................9
4.2. Integration time and signal quality.......................................................................................................................................................11
4.3. Integration time search algorithms......................................................................................................................................................12
4.3.1. Example: Automated parking gate...................................................................................................................................................12
4.4. Operating range as a function of integration time...............................................................................................................................13
4.5. Multiple objects in the field of view......................................................................................................................................................14
5. Compensation, Correction, Calibration...................................................................................................................................................17
5.1. Distance Error......................................................................................................................................................................................17
5.1.1. Effects due to the application conditions..........................................................................................................................................17
5.1.2. Effects due to the measurement system..........................................................................................................................................18
5.2. Algorithm..............................................................................................................................................................................................19
5.2.1. Temperature Compensation.............................................................................................................................................................19
5.2.2. Reflectivity Compensation................................................................................................................................................................20
5.3. Calibration............................................................................................................................................................................................20
5.3.1. Temperature Calibration...................................................................................................................................................................20
5.4. Before – after example with epc600 TOF Range Finder.....................................................................................................................21
5.5. Use cases............................................................................................................................................................................................21
5.5.1. Threshold detection..........................................................................................................................................................................21
5.5.2. Measuring a distance........................................................................................................................................................................22
6. Troubleshooting......................................................................................................................................................................................23
6.1. FAQ......................................................................................................................................................................................................23
6.1.1. epc600 chip level..............................................................................................................................................................................23
6.1.2. epc600 system level.........................................................................................................................................................................23
6.1.3. epc600 Camera TOF and Eval-kit....................................................................................................................................................24
Addendum........................................................................................................................................................................................................25
C Source Code..........................................................................................................................................................................................25
2Wire Module Master.................................................................................................................................................................................25
IMPORTANT NOTICE.....................................................................................................................................................................................28
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Introduction
The epc600 TOF Range finder is a highly complex system-on-chip (SOC) device. It is not just a TOF imager but much more a complete
sensor core that allows the design of minimal part count sensor systems. This complexity, combined with the relatively new TOF technolo-
gy, may rise questions when designing a sensor product based on this chip. Such questions can relate to the actual operation of the chip,
system design aspects and to the actual application with an industrial sensor product.
This handbook provides information on such aspects. It is a complementary document to the epc600 data sheet and shall support the de-
veloper during the specification and design process of a sensor system based on the epc600 TOF Range Finder.
1. epc600 system integration
The following section describes some general hardware requirements that should be observed during the development. There is a propos-
al for a modular structure a software, which can be used as a base for the implementation. Some optical design aspects are also illustrat -
ed.
1.1. Hardware design tips and tricks
1.1.1. I/O levels
The epc600 has a 5V interface. This means that it is not compatible with 3.3V TTL compliant I/Os. It is recommended to use a CMOS 5V
interface.
SDATA is a bi-directional signal with a open drain driver on the epc600 side. On the processor side, an open drain driver needs to be set
up.
SCLK is a unidirectional signal which has to be driven by the microprocessor.
1.1.2. -5V charge pump
The epc600 requires a dual-voltage supply of +8.5V and -5V.
While the +8.5V supply can be regulated down from higher voltage levels in a straight forward way, the -5V generation requires other ap-
proaches. Figure 2 shows such a proven solution, based on a LTC1983-5 regulated charge-pump inverter.
VIN
1
VOUT
2
C+
3
C-
4
GND
5
SHDN
6
IC1
LTC1983-5
-5V
10uF
C3
10uF
C1
C2
1uF/50V
10k
R2
GNDGND
R1
470R
GND
D1
BZX84-C5V6
8V5
Figure 2: -5V charge pump
1.2. Microcontroller firmware architecture example
The epc600 requires a small microcontroller for operation. The microcontroller triggers the measurement and receives the measurement
data at the end of one completed measurement cycle.
On a higher layer level, compensation and correction algorithms may be implemented. Such corrections are not required in every case, as
the chip already delivers high levels of accuracy. However, for applications that require a certain measurement performance, software
compensation and correction will facilitate the job. Such corrections may for example account for temperature based drift effects or they
may relate to ambient light and target reflectivity.
Typically, a sensor system may also require some sort of calibration. This calibration compensates variances and tolerances of parts and
components that apply to all parts of the sensor system and not only to the sensing element.
Figure 3 shows an example how such a software can be structured. A basic source code example of the 2wire_master module is listed in
the addendum.
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Figure 3: Typical firmware
■ main_thread: Main program that initializes the firmware internal structures, the hardware peripheral modules (ie: I/O interface, RS232,
USB...) and maintains the scheduler coordinating functionality between these different structures. All of the requests are centralized here
and are executed as soon as possible.
■ communication: Treats all requests coming from the application master or coming from the main thread to the Master.
■ epc600_module: This module contains the “epc600” algorithm (including functionality such as integration time adjustment according to
the data coming from the epc600).
■ 2wire_master: This module is the translation layer between the firmware and the epc600.
■ epc600_comp: (optional): This part implements the correction needed for the application needs.
■ epc600_table: (optional): This module contains information such as calibration data (which may be chip specific).
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epc600_module
epc600_comp
epc600_tables
2wire_master
main_thread
communication
ec600 chip
Application Master
Two-wire
protocol
dedicated
protocol
epc600 Firmware Architecture Example
2. Optical system
The optical system connects the the sensor to the outer world. It maps the scene to be observed to the epc600 TOF Range Finder. A good
optical system is crucial and the design should be left to the specialist. The epc application note AN02 helps as a starting point for such a
lens design, both for the RX and TX part.
The following sections highlight some important points to consider and may help to avoid pitfalls.
2.1. Transmitter: LED and TX lens system
LED emitter systems are never perfect. This non-ideal behavior needs to be accounted for when designing the emitter lens system. The
following paragraphs illustrate such non-ideal behavior.
Figure 4 illustrates the system setup of the epc600/610 Evaluation Kit. This setup was used to generate the subsequent examples.
Distance Camera/object [m]
5 cm
2 lluminations
LED's
Camera
Board
epc600
Figure 4: Characteristic of the emitter spot.
2.1.1. Illumination distribution of IR LEDs
Test setup epc600 camera board with SFH4059 LEDs without any additional TX lens system.
DC current supply of the LEDs on the board: 70 mA DC.
SONY Handycam DCR-PC4E (S/N 4816), Operational mode: Super nightshot, PC readout.
White paper target with 5cm grid.
Target located at 1 meter.
Expected results A rough verification of the radiant intensity distribution of the LEDs as specified on the LED datasheet.
Figure 5: Radiant intensity distribution of standard IR LEDs (SFH4059)
Results The radial intensity distribution as specified on the LED data sheet is qualitatively confirmed in these shots. How-
ever, there are some light non-linearities in the intensity (Figure 5)
2.1.2. Illumination distortion through lens system
Test setup epc600 camera board with dual SFH4059 LEDs with and without additional TX lens system.
DC current supply of the LEDs on the board: 70 mA DC .
SONY Handycam DCR-PC4E (S/N 4816), Operational mode: Super nightshot, PC readout.
White paper target with 2.5cm grid and 5cm grid of points.
Target located at 1 meter for the setup without optics.
Target located at 6 meter for the setup with optics.
Expected results Without optics: A rough verification of the radiant intensity as specified on the datasheet.
With optics: A perfect square surface with uniform illumination.
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LED1 LED 2