Project duration: ~4 months
Projectvorm: Fixed price & production
Period: 2017-2018
Activities: Proof of concept, design electronics and firmware, prototyping, production, support & warranty
Technologies: STM32 Cortex M4, Ethernet, RS485, power-LED, DipTrace, EmBits, LwIP, Telnet, FTP, FreeRTOS, TCP/IP, USB HID, USB MTP
Parts: SFH4715AS, STM32F407, TPS92512HV, LM5069, MAX15062, LAN8720, MIC2128, EMC1001, APDS9301


Automatic number plate recognition (ANPR) systems require flash lighting to function properly during low-light and night situations. Typically, this is done with infrared to eliminate driver distraction, and sometimes to aid in a concealed installations.

Existing solutions were too costly and difficult to get or too bulky for the intended system. Therefore, we were asked to design a replacement flash module, starting with some reverse-engineering and a feasibility study to guesstimate project cost and production cost.

We came to a competitive proposition that gave improved optical performance as well as smaller footprint and various functional improvements such as an auxiliary 12V power supply, fan controller, ethernet connectivity and more I/O capabilities.

Infrared flash unit


LED Module:

  • 15 Infrared Osram 'OSLON®' power LEDs
  • 25° beam lenses *
  • Peak wavelength 850nm
  • Radiant flux 30W, radiant intensity 135W/sr
  • Ambient and infrared light intensity sensor via I2C
  • Temperature monitoring
  • Dimensions 75x112mm


  • Five 2.5A current source outputs with analog and PWM control
  • 7 Isolated inputs for flash trigger, strobe sync amongst others
  • Ethernet configuration & firmware update interface
  • Micro-USB supports firmware update and MTP file access
  • Auxiliary RS485 to camera and/or pan&tilt unit
  • 4 Aux 12V/1A push-pull outputs
  • LED current & voltage monitoring
  • Operating voltage 16-35VDC, survival to 60VDC
  • Inrush current limiter reduces spikes from flash discharge to 2.5A
  • Dual fan controller (12V) with RPM monitor
  • Quiescent current < 1W
  • 12V/5A regulator for cameras and other hardware
  • Dimensions 70x130mm


Since the ANPR camera system is connected by ethernet anyway, we have chosen for an ethernet connection on this device as well. This allows for easy access using Telnet and FTP for configuration and firmware updates. Future firmware could even provide remote control of a pan & tilt unit using Pelco-D protocol over ethernet.

ARM Cortex M3

'OSLON' is a registered trademark of OSRAM Opto Semiconductors