Version 30 (modified by Eric Hazen, 9 years ago) (diff)


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

Revised (Flex PCB) Design


  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

Proposed pinout for micro HDMI

Pin HDMI Use DOSI Use Notes
1 Hot Plug Detect/HEAC-
2 Utility/HEAC+
3 TMDS Data2+ Photodiode+ Photodiode Anode
4 TMDS Data2 Photodiode GND Shield for Photodiode signal
5 TMDS Data2- Photodiode- Photodiode Cathode
6 TMDS Data1+ LED Power Power for LEDs
7 TMDS Data1 Shield AGND Shield for LED power
8 TMDS Data1- AGND Ground for LEDs
9 TMDS Data0+ A0 Address 0
10 TMDS Data0 Shield DGND Logic GND
11 TMDS Data0- DGND Logic GND
12 TMDS Clock+ LE Latch enable
13 TMDS Clock Shield DGND Logic GND
14 TMDS Clock- DGND Logic GND
15 CEC A1 Address 1
17 SCL/DDC clock A2 Address 2
18 SDA/DDC data A3 Address 3
19 +5V power VCC Logic power (3.3V-5V)