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Cellulo V2 Electronics
The changes in electronics were due mainly to accessibility to new components in the market, outdated components, searching to increase the computational capacities, adding new features, cameras, batteries, etc. The core changes will be described in the following wiki
The change in electronics was driven by the new technologies and parts accessible in the market, as well as to adequate to the new features that wanted to be implemented. However, during the development of the current version, a big shortage of electronic parts reduced the possibilities of development as well as delayed and rerouted the initial design, it is recommended to follow up the thesis of Dr. Ayberk Özgür, which can be seen in his Ph.D. thesis. The core changes are the following:
- Introduction of ESP32 as a communication module and an auxiliary MCU to control peripheries.
- Introduction of modularity in the PCBs, Core PCB with MCUs camera and big components, driver PCB, battery PCB and finally when necessary, the UI electronics.
- Use of Pogo connectors to connect the different modules.
- Changes in components, especially in the battery management module.
- New Led system and design, as well as touch sensors.
- Substitution of old parts that are no longer accessible.
Due to the circumstances of the market, the initial goal of switching the PIC32, for a more advanced MCU, in particular a new version of STM32, wasn't possible. Based on it, the design of the electronics has been mainly focused on introducing modularity and adapting the old electronics to available parts.
The main PCB was designed to allocate the functionalities from the previous version while introducing an ESP32 as a communication and auxiliary module for the control of peripherals. The design of the main PCB was intended to support the connectivity for the previous LEDs and touch sensors, hence, there are redundant connectors. It is recommended that if it were to be developed a new version, a cleaner, simpler, and without redundancy version would be produced. The main PCB allocates a PIC32 in charge of the core computational process, an ESP32 which controls the Bluetooth communication as well as the new LED stripe and the touch sensors. In addition to the core electronics to make the circuit work, the main PCB also allocates the camera.
The camera consists of an image sensor, model MT9V034, this model is out of date, hence it is required to substitute by another model in future versions, the current version includes this model based in excessive stock available in the development process as well as spare stock that was found, however, it is recommended to migrate to the version in the market.
The camera works with 3 LEDs infrared allocated in the base of the robot, which behaves as a flash to allow the robot to "see".
In the current version, it was decided to test the modularity also for the PCBs, allowing the possibility of producing a robot without locomotion. The conclusion of the test was that it is not that useful, and it is encouraging to revert to future versions. The reasons for that are the allocation of vertical space in the robot, the use of flexible connectors, which are prompt of flaws, and extra costs. The current PCB consists of 3 drivers, the same as the previous version, it is possible to migrate to 2 drivers of double H to accommodate for 3 motors, or 1 double driver and one simple driver to reduce the use of space in the PCB.
The new modularity requires the use of a separate PCB that controls the battery charging. The new PCB also allocates buttons to turn on and off, as well as LEDs for indicating the charging process, battery, and state. In the initial prototype, the voltage converters for adapting the voltage of the battery to the MCU and motors were distributed between the battery PCB and the main PCB, which afterward was switched to both in the main module.
The electronics are the weakest point of the current design, and they acted as a bottleneck. There is a multitude of opportunities to improve. The suggestion is to start by prototyping with a new version of the camera and an STM32, or, ESP32, either stand-alone if the computation is sufficient or dual. Additionally, it is suggested to outsource the creation of the PCB, since it is the step that is more prompt to errors, and as it was in the current version the biggest bottleneck.
Once the new camera has been selected and tested, it is encouraged the redesign the architecture, putting special emphasis on simplicity, reducing the parts, and allocation of power sources and voltage converters. In particular, is encouraged to reduce from Main PCB and driver PCB to one stand-alone PCB. Simplifying the current version by cutting off unnecessary legacy connectors gives room to allocate everything in one PCB.
One weak point of the design, which difficulties the mounting process is the infrared LEDs and how to mount them in the robot. It is encouraged to find a solution to avoid those, or, make a design that allows the LEDs to be allocated somehow in the main PCB, reducing loose wires and extra mounting steps.
Cellulo V1