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All Possible Configurations:
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Digital IC Selection
EG915NEAAC-N05-SNNSA
Supports NA
Supports max mavlink datarate
no external camera features keeps cost down
~$30 bucks
Optional GPs port that is uses. Will use a u.fl connector and an onboard antenna we can choose between.
STM32F415RGT6
has USB FS support and a ton of UARTs
$18 is a lot but it’s the cheapest we gonna get
somewhat discussed in LTE Breakout
STM32 pinout given in Discord conversations
First Buck Stage Component Searching
Super glad there’s a lot of options in this voltage range, seems to be getting better with time as automotive bus voltages are rising.
Best from MPS
I kinda wanted to use MPS here, but doesnt seem like any of their stuff solves
Searching Digikey
I like these microchip and Vishay options, the analog devices ones are hella overpriced (as usual).
Microchip options are slightly cheaper and support higher input voltage so will let one of these ride.
Plenty in stock, super cheap, https://www.digikey.ca/en/products/detail/microchip-technology/MIC28516T-E-PHA/13175035 seems like the way to go here! Size doesn't really matter that much for me. Way smaller then having external FETs so I’ll take it.
MIC28516T-E/PHA
Datasheet Rev D: https://ww1.microchip.com/downloads/aemDocuments/documents/APID/ProductDocuments/DataSheets/MIC28516-Data-Sheet-DS20006315.pdf
Setting output voltage to 5.05V target, calculating using https://github.com/UWARG/hardware/tree/master/Scripts .
Layout
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Collection of hardware design guideline excerpts from various component datasheets.
Quectel_EG915N_Series_Hardware_Design_V1.2.pdf
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Modem Re-Selection
We initially selected the EG915N-EA, which only includes bands optimized for usage in Europe and Asia.
This model has band 7 but is missing 12, 13, and/or 71 (as per discussion from Nathan in #rpi-interface-rev-c). Band 7 is (1) limited to certain networks and (2) is 2600MHz, which is fast, but limits ranged performance. 12, 13, and 71 are lower frequency channels and will provide more channels to switch into, as well as better range.
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To watch for when selecting a new modem: We want a pin compatible model with the EG915N, as we have already done extensive layout considerations around this footprint, and we want to maintain the 2 supported SIMs. We want bands 7, 12, 13, and 71.
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Model/Specs | EG915N-EA (original model) | BG95M3 Series | EG915Q-NA Series |
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LTE Bands | LTE-FDD: 1 / 3 / 7 / 8 / 20 / 28 | Cat M1: 1 / 2 / 3 / 4 / 5 / 8 / 12 / 13 / 18 / 19 / 20 / 25 / 26 / 27 / 28 / 66 / 85 Cat NB2: The above and 71 | LTE-FDD: 2 / 4 / 5 / 12 / 13 / 66 / 71(?) |
# of SIM Interfaces | 2 | 1 | 2 |
Screenshot |  |  |  |
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