wiki:RoblyerCWProbe

Version 10 (modified by Eric Hazen, 8 years ago) (diff)

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CW DOSI Probe for Cancer Monitoring

The proposed probe contains six pairs of LEDs, one photo-detector assembly and drive electronics. Each of the 12 LEDs may be selected individually, with external drive current controlling the output intensity.

The LED pairs are arranged in a circle with a 25.4mm radius, with the photodiode assembly in the center.

A single flexible, multi-conductor cable provides power and control. The HDMI cable seems like a reasonable off-the-shelf solution (with mini-HDMI type C connector on the probe)

Initial (Rigid PCB) Design

Notes:

  1. The 74HCT154 is attractive because of the very small package, but has active-low logic outputs. This requires a small change in the schematic. The control interface should be unchanged. Alternatively, the 4514 decoder is available in a TSSOP24 package which is about 7mm x 8mm

Interface Cable

1 PD_C Photodiode cathode connection
2 PD_A Photodiode anode connection
3 GND-S Ground shield for Photodiode signal
4 GND-S Ground shield for photodiode signal
5 A0 LED address bit 0
6 A1 LED address bit 1
7 A2 LED address bit 2
8 A3 LED address bit 3
9 EN LED enable - active low
10 DGND Logic GND
11 VCC Logic power (3.3V-5V)
12 DGND Logic GND
13 AGND LED GND (power return)
14 AVCC LED power