Infrared Backlight (A3046)

Contents

We begin by transferring some of the design on the (A2045 Proximity Mask Head) to a larger backlight with 25 LEDs. The A2045 board was used for preliminary CPM1 experiments.

Figure 1: Circuit schematic for the A204601A Backlight.

This board has the same LWDAQ interface as A2045 but has more LEDs and is easily mountable. We include M3 holes on the corners of the backlight and design a diffuser holder that places the diffuser exactly 50mm from the backlight.

Figure 2: Finished backlight mounted on an optical breadboard.

We then design a new board that will have its connectors on the bottom and flex connectors on every edge. This allows us to connect multiple backlights together and expand the area covered by diffuse IR light until we run out of available current. We also load a barrel jack connector onto the backlight so that we can give it auxillary power.

Figure 3: Two infrared backlights side by side with their connectors mounted.

Description

[05-AUG-22] The Infrared Backlight (A3046) provides a flash of diffuse, infrared light distributed over a panel that acts as the background for silhouette images. The Infrared Backlight is one component of our Contactless Position Measurement System (CPMS). Development of the CPMS is funded by the United States Department of Energy (DoE) under Grant 13557088.

Versions

Design

Development

[05-AUG-22] Create manual page.

[11-NOV-23] We attempt to adjust the brightness in an attempt to reduce the necessary exposure time required to achieve enough contrast between the silhouette and the backlight. We begin by adjusting the resistance of R5 and R6. We notice that too much voltage is dropped across the power supply resistors and transistors. To circumvent this we swap out Q4-Q7 with the ZXTN2031F NPN transistor which can handle more current than the UN2215. We then replace R1, R4, R12, and R13 with three 47 ohm resistors in the 2010 packages. This not only ensures that the backlight can handle increased power consumption but it also reduces the resistance on the power supply by almost 80 percent. As a result, much more current can flow through each chain of LEDs (roughly 4.75 times more). The infra-red LEDs can easily handle this amount of current, but the visible indicator LEDs on the back of the PCB would either burn out or be too bright to look at depending on which visible LED we choose. We avoid this by soldering a 51 ohm resistor in parallel with the visible LED only.