FIM Setup Construction

The FIM setup can be used to measure the contact surface of insects like Drosophila larvae. It utilizes Frustrated Total Internal Reflection (FTIR) to illuminate the scene.

Overview

In the FIM setup, the LEDs are inserted into the tracking stage and the camera is mounted underneath. To control the illumination, all LEDs are coupled into a custom circuit which is again connected to a micro controller (MC). Both, the camera and the micro controller are connected to a computer. To utilize total internal reflection, our tracking stage is an acrylic glass plate. Furthermore we use infrared LEDs so that the animals do not perceive the illumination. Thus the sensor of the camera should be able to measure IR light. An additional IR-filter shall be used to enhance the overall image quality.

Parts List

  • Infrared light-emmitting diodes (LEDS; e.g. 5 mm HP HDSL-4230 (HP))
  • Acrylic glass surface (approx. size: 320mm x 320mm x 10mm)
  • Sevaral resistors (39Ω or 68Ω, 1kΩ, 560Ω)
  • Transistors (e.g. BC 637 NPN)
  • TTL hex buffers with open-collector ouputs (SN 7407 N)
  • 5V Voltage Regulator (7805)
  • 100nF ceramic capacitors (C320C104K1)
  • Power supply connector (e.g. NEB 21 R)
  • 18 Watt power adaptor (e.g. HNP18-090-C)
  • Matrix board
  • Micro controller (e.g. Arduino Mega 2560)
  • Infrared filter (e.g. pass filter IF 093 Schneider Kreuznach)
  • Camera (e.g. Basler acA2040-25gm)
  • Lens (e.g. KOWA LM16HC)
  • Sufficient computer
  • Additional parts to build a tracking table

Construction

The main idea is to plug the LEDs into the acrylic glass. All light sources are connected to a custom circuit which is connected to a micro controller (MC). The camera is beneath the tracking surface.

The Table

We have constructed several different tracking tables. One table has a custom metal frame and is portable. Another table is inserted into a common worktop. The second table offers more space for larvae preparation and additional hardware.

Mount The LEDs

As you can see in the image, we drilled holes into the acrylic glass to mount the LEDs. This is not necessary to induce total internal reflection. We suggest a distance of 3cm between the actual tracking area and the LEDs to have optimal FTIR results. A heating-up was only measured close to the LEDs. Our tracking area kept the same temperature even after extensive use.

To easily wire the LEDs, we recommend to use another matrix board: plug the LEDs through the board and glue a grid behind the board to wire all light sources in a row. We also add friction tape to isolate the pins of the LEDs.

Custom Circuit

  We use a custom circuit to supply the LEDs with power. Therefore four LEDs are connected in series and two of this series are connected in parallel, resulting in 8 LEDs per sub-circuit. Since we are using 9V voltage, ether a 39Ω or a 68Ω resistor is used for four LEDs. All light sources are connected to a transistor (BC637), which is controlled by an SN7407 open-collector. Since one open-collector chip can control 6 sub-circuits, 48 LEDs can be controlled in total. Assuming a table using 96 LEDs, two open-collectors are sufficient. If more diodes are necessary, more open-collectors can be used to integrate more sub-circuits.

We use 100nf ceramic capacitors and a 7805 voltage regulator to supply the MC and the IC with 5V.

Instead of dimming the light sources using a potentiometer, we utilize a micro controller (MC) to activate/inactivate or dim the LEDs. Thus the open collectors of the custom circuit are connected to an Arduino Mega 2560 micro controller (or any other MC with sufficient PWM connections). In this way both, the diodes and the camera can be connected to the same computer for image acquisition and brightness adjustments.