LED Ringlight

The Project:

LED Ringlight

A simple LED Ringlight for illuminating objects  for a camera system mounted on an articulated robot. The light had pairs of LED’s that were individually controlled via PWM. It also had a serial USB interface to a computer for level adjustment.

Design Constraints

  • Size – The board had to be mounted on a small articulated robot. It also had to fit around the camera lens.
  • Illumination – If the LED’s didn’t light up the object enough there would be no point in having it.
  • Timeline – This was just a bump in the road for my thesis, it had to be done quickly
  • Flexibility – Initially this board may have been used to adjust light levels for object segmentation, in the end this feature was not used, but each pair of LED’s were individually adjustable based on an output PWM signal from the Controller. USB connectivity was also added to the device with microchips CDC library.

My Role

  • Circuit design – Specify parts and develop the circuit.
  • Board design – Creating the shape of the board and the layout of components.
  • Coder – Write the software for the Microcontroller and the PC.

Lessons Learned

  • Microchips USB Firmware – Microchips CDC library was used as a base for this project. Because of this every event occurring on the chip had to be event driven. Timers were used for updating PWM Levels etc…
  • LED Forward Voltage – The typical forward voltage was used for the design allowing two LED’s per channel to run in series, this in practice did not work and board modifications to have the LED’s run in parallel were made.
  • Previous Designs must be checked – The system as well as being controlled by a USB port was activated via a parallel interface implemented by another designer, the old design used 5 LED round segments. The new design required too much power for this existing layout and had to be changed.
  • Camera Shutter Speeds VS PWM – While testing the different PWM levels of the Ringlight it was found that some levels caused varying levels of brightness to appear in the camera image. The camera shutter speed was fast enough so that the PWM periods were not properly blended. The overall PWM period was reduced and the problem disappeared.

Pictures

Comments are closed.