Consider adding TS4231 and IR photodiode to device

[jonnew]

Steam VR base stations combined with a TS4231/photodiode allow extremely precise multi-animal tracking. We use them on tethered headstages: https://open-ephys.github.io/bonsai-onix1-docs/articles/tutorials/calibrate-ts4231.html.

However, a wireless device is where this would truly shine since there is zero cost except small power consumption due to transduction and transmission. A single set of base stations and calibration parameters would support N animals.

[danielfrankch]

This is a great idea! Incorporating 3D position tracking is indeed a very useful feature.

The TS4231 itself has a very small packaging.

However, the recommended photodiode BPW34S has a relatively large footprint of 5.4 x 4.3 x 3.2mm and is though-hole packaging. To put it into perspective, the bigger chip on the left (IIM-42352, TDK InvenSense) on my current battery PCB (see image below) is only 3 x 2.5 x 0.91mm. So incorporating the BPW34S + TS4231 suite seems doable, but would need the battery PCB to be bigger, for example have an extension in the front (or in the back) to fit this new sensor. I am still looking into if using a smaller photodiode (for example, 0603 packaging) would also work or not, considering its smaller active area would yield much lower signal.

Secondly, I need to check if I can multiplex the existing 2-pin connection down to the BLE board (currently used for I2C bus) for the 2-pin data connection (E and D pin) of TS4231. I also need to check if I can implement the logic to configure and read data from TS4231 using the current BLE chip's GPIO, instead of using the SteamVR Tracking HDK FPGA.