• Heat issues

    nagup • 05/16/2023 at 19:58 • 0 comments

    The major parts have arrived and been tested. Found that the wireless charging module and coil get really hot (starts to soften the 3D-printed wall plate). 

    Now I need to think of a clean way to manage this heat but I can't put a heatsink on the coil because the motor shaft needs to go through it (a potential solution is to get some round aluminium blanks with holes in the middle and have thermal pads in between). The controller board can just have a heatsink installed on it and hopefully, convection can keep them both cool enough.

    The coil or PCB is whining sometimes at the start and end of charging (when the tablet is removed from the coil) but I dont think it will be that audible when it's all closed off and in the wall. The good news is that the tablet is able to charge while being 8 mm away from the coil, I did wonder if the distance was causing the coil to heat up but I used a thermocouple probe on the coil when it's directly under the tablet and it still heats up so that rules the distance idea out, I may try out running the charger at 5/9v which reduces the wattage of the charger and so should reduce heat but I still want to be sure the module won't destroy itself at 12V.

  • Strengthening design and other improvements

    nagup • 05/14/2023 at 21:19 • 0 comments

    In the first design, I was going to use an SG90 servo which has a 21-tooth spline shaft, but I needed to extend its length, I got a quote to SLA print this tiny part (to replicate the splines correctly) and each 10mm extension was £6, way too much. So I went for a geared micro motor and will attach an encoder on the back to control the shaft position, I need it to rotate 90 degrees and back reliably. Another part of this locking system is to have a home position switch, I need to figure out how and where I can implement this. 

    The locking horn is a standard servo horn with a grub screw to interface with the motor's D shaft. It is also made of metal, which is good because I am trying to design this project as robust as possible as it will be used almost daily.

    New on this design is the rear enclosure which will house the electronics and some thought about how to release the tablet in case the device does not unlock or is completely dead. I managed to implement 2 ways to release the tablet which I will demonstrate in eventually, I plan to design a circuit board with the following features:

    - H bridge (DC motor needs to go CW/CCW)

    - ESP32 module (brains)

    - LED driver (Brightness control for the LED strip)

    - MOSFET/SSR to switch the Qi wireless charger on and off (HomeAssistant will tell each charger when to turn on because the HA app exposes the battery level in HA and I can create an automation to start charging once the battery hits 20% and off at 80%, these levels are the best for lipo batteries to be kept at)

    - Maybe other features as well to make use of the ESP32, perhaps a temperature sensor because the tablet will be mounted at light switch level and will give a better reading of the actual temperature in the room.

    Some things to be tested/ investigated:

    - How does the wireless charger being on, affect the ESP32's wifi connection as it will be directly behind it

    - Does the LED strip get too hot at full brightness, it is a COB strip and its high density of LEDs may cause an issue of overheating, leading to premature failure of the strip

    - Strength of the magnets and supporting frame to reliably hold the tablet in place but also keep it square and not visibly tilted, while unlocked

    - Effectiveness of the locking mechanism and the possibility to manually remove the tablet and then the whole unit in case of complete failure.

    Parts are on the way, and I need to print the parts out, for now, PLA will do but not sure how PLA changes with time, if it becomes brittle etc now that it's exposed to the humid air, I think at the last stage I would print it in PETG.