Hi, after a year I went back to the effort of making new Meshtastic Hardware.
Since last post I was proposing a NVDC capable Power supply design was not receiving any feedback, the idea was dropped. Now with a practical plan to make a better integrated RAK4631 based board:
The design is specifically targeted at JLCPCB’s 4 layer capabilities and LCSC’s component stock. Any one interested in testing these board could contact me. The design files will be available after testing and necessary correction is done.
The topology area of a 2.9’’ e-paper is very close to two 18650 battery cells combined, so two cells connected in parallel as the system power could be seated underneath the display.
And planning to use a bipolar cylinder 1m antenna (pointing downward) and a GPS chip antenna upward (like a light cyber). The device diameter will likely fit the GPS antenna and the circumference of HF Antenna. A camera stand thread will be like to be the hard point for mounting solution, if feasible. (Fusion 360 designs after board smoke test)
The screen resolution is 296*128, two informative Meshtastic UI can be displayed in parallel and the conversation(3rd) can be used as it is, i really don’t want to use cell phone in any part of sensitive communications.
There’s no obvious advantages if new design or market demand once could drive a batch production. Currently have no RF testing equipment on hand so I could only blind choose a module with smallest profile and avoid any RF issues.
Better BLE/Baseband solution would be nrf52833 based SiP modules especially from ublox(512K/128K). This module is in mass production EOF will be long enough for some years. Before anyone who’s will to port a nrf52833 arduino firmware, RAK module will likely remain an elegant choice.
Hi einzeln00,
check out our “1W Custom PCB” discord channel, we are also working on hardware, but with the esp32 platform. Our group effort is hosted at github: GitHub - PlumRugOfDoom/project-hydra-meshtastic-pcb
Maybe you can steal some ideads from our project (PAM2312, CJ2301 fet, …), we had a somewhat lengthy discussion on where to get parts since there is a global component shortage. We ended up with parts that were easily available at LCSC, since this also means that you can order an assembled PCB from JLCPCBs assembly service.
I really like your PCB layout, but remember to add keepout zones underneath the power inductors. No GND plane, pcb tracks and vias allowed
I had a glance on your schematics, and is that a JBT level translation on board? Interesting. I am not really experienced in how to keep BOM cost down since my job was to meet “demanding customers”’ technical spec sheets… Each year FEs from TI or Analog come quarterly and we just adopt new components to meet the status quo of building costs
I have downloaded the components’ datasheet you recommended. I will give it a try in some later new designs. And updated my Layout to add two keep out zone underneath the power inductors.
I will look into your Kicad source file later.
I am not interested in ESP’s product since early days so many dongles and mutations everywhere, blindly pick just one of them lead me some frustrating experience in just blinking an LED in Arduino…
Hi einzeln00,
the two BJT transistors are used to do a so called “auto-reset” via the DTR and RTS uart control signals. Think of it as “reset” and then “go into programming mode” for the esp32. Regarding the choice of parts, it’s more about ease of accessibility and not cost down. Having the perk of business relations with a large semiconductor manufacturer is really useful especially during a shortage but I don’t think that the meshtastic project will receive such kinds of perks any time soon.
The keepout zones are required since some if not all power inductors have a conductive casing, and you may run the risk of shorting something out if you route tracks and copper planes underneath. You rely on just a few µm of soldermask as insulator. Have look at for example this inductor: https://datasheet.lcsc.com/lcsc/2109162030_PANASONIC-ETQP3M1R5KVP_C542312.pdf page 11 in the datasheet.
And regarding the ESP32 platform, sure, it can be very frustrating to set up by hand. Take a look at platformio with atom or vscode. You will be up and running in no time since everything is automated.
Going with the NRF platform is great for low power and always on bluetooth (=> mobile device), but the esp32 platform is currently somewhat more mature and you have the wifi and webui capability.
The board design had some reversed polarities and P/N mosfet confusion in the design, luckily there’s no need to remake PCB to correct them, just by soldering with correct orientation could be OK. But one thing I missed is GND to the switch. Now all click switches need a wire to make them work.
According to RAK Arduino BSP files (variant.h resides in your Local Data folder), I have tested IO pins and they worked, and the Adafruit LED pin Also works. Now we can blink the LED2 (which is the default Adafruit Feather Express LED).
I am now pulling my hair to get the EPD work, Arduino pin toggle doesn’t work with SPI port, I don’t know if this is default behavior that you can not override an dedicated SPI pin (CS and CLK both tested with toggle function but not detecting any voltage). I will try to mount I2C MEMS sensor to try get it work first maybe.
Thank you for time read this, and thank you in advance if you have any idea about SPI debugging on Arduino BSP.
After some rudimentary tests the first impression is the RAK4631 expansion board is wonky. This may due to hand soldered socket connection is not ideal, however what really this board bothers me and lead to the decision of abandon this design, is the IO mapping. The idea of RAK’s WISBLOCK is about expansion, but arduino BSL and to be compatible with multiple MCU platform is flawed in it’s core. Threre’s no way to verify your design if you are expanding a new sensor board, or verify their official expansion board, when you hooking up something and doesn’t work.
After all these I decided to make a nrf52840 board from scratch, and inherent all the design ideas where all these efforts has been invested.
This 4-layer design has integrated an TI’s BQ52895M buck/boost USB charging IC, to mange Lithium battery fast charging at 3A/12V if you have a proper USB charger (yes, they can run at this capacity), or wiring out an OTG cable with 4-14V voltage. All I/V are automatically monitored by IC’s hardware logic, and I2C controlled by new firmware which will be developed once hardware is done.
Battery and GPS sockets are JST SH 1.0 type, recommended for Mateck M8Q-5883 which has a i2c compass.
Lora radio is e22 1W 900M module. SWT connector is 1.27mm pin.
Board will run Adafruit Feather Express nrf52840 BSP, and two leds are copied from it, should work as expected for uploading indication and blink test.
While this board design is sent to fab, 3D printed case will be designed.
but I don’t think that the meshtastic project will receive such kinds of perks any time soon.
