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v0.4 Scratchpad

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cayden edited this page Aug 18, 2022 · 24 revisions

Internal document for planning the next iteration of the glasses and PCB for version 0.4

v0.3 bugs

  • connect 3.3VA to 3.3V
  • change TP4056 to correct package, or replace it
  • work with mechanical for better mounting holes
  • fix silk screen so all is printed

Audio Input

We need >= 4 microphones for the next iteration.

One option is to use the built in I2S interface on the ESP32 and use all I2S microphones. Note that we can't do 4 PDM mics as PDM only works on one I2S channel.

Another option is to add an external I2S IC, such as:

IMU

We want IMU for head position, movement, activity tracking, posture, etc.

6-DoF sensor: LSM6DSL 3DOF Sensor: LIS2DH12TR

Battery management

We need a more efficent power solution that works from ~4.2V down to ~2.7V to use the full range of our LiPoly batteries. We also need a discharge and charging solution that balances the batteries for safety and longevity. We also want a coloumb counter so we can always know the current charge state of the device.

  • 1-2 cells battery fuel gauge in series: bq28z610 8K stk on LCSC A$6.95/ea

HMI (audio, visual)

v0.3 has no user-input/computer-output modalities. We need to be able to give live information to the user. We want a display and speaker to do so. We will be adding a speaker to this design. Due to resource constraints, we can't yet add a display, but we can add RGB LED indicators to the inside of the glasses from (such that only the user can see them).

Speakers
Finding small speakers is not easy.  Common cheap ones seem to be 15mm x 11mm for rectangular ones, and 13mm round seems common, but I have seen down to 10mm round all on AliExpress
Smallest on Mouser:  https://au.mouser.com/c/electromechanical/audio-devices/speakers-transducers/?length=12%20mm&mounting%20style=Board%20Mount&product=Speakers&shape=Rectangle~~Rectangular&termination%20style=SMD%2FSMT&rp=electromechanical%2Faudio-devices%2Fspeakers-transducers%7C~Shape
12mm x 6mm x 2mm
10mm on Digikey:  https://www.digikey.com.au/en/products/detail/cui-devices/CDM-10008/2791823

Environmental sensing (maybe)

We are considering adding environmental sensors, like UV sensors, to the v0.4 board to help users sense exposure to various environmental conditions:

UV Light sensors research:

  • SI1145-M01-GMR - XON A$11.33 Sunlight/UV approx. IC - Ordered AE: 2021-10-14
  • VEML6075 - UV Light sensor - 0 stock Mouser/XON/LCSC
  • LTR390 - UV Light sensor 0 stock Mouser/XON/LCSC
  • UVIS25 - STM UVA/UVB sensor. 0 stock, Mouser/XON/LCSC - Ordered board via AE: 2021-10-14

Proximity sensor

We wish to put the device in low power mode when it's not being worn. To do so, we need a proximity sensor (or related) to tell when the glasses are off the user's head.

  • this ambient light sensor claims to detect down to 20mm (says nm, so presume its a typo) C492375 LTR-553ALS-01 SMD Ambient Light and Distance Sensors i2C ROHS

Questions to answer

  • do we need RTC?
  • do we need on-board storage?
  • do we need environmental sensing?
  • do we need proximity sensing/sleep mode YET?
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