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Digital IC Selection
EG915NEAAC-N05-SNNSA
Supports NASupports 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.
Modem Re-Selection
Regional Band Compatibility
We initially selected the EG915N-EA, which only includes bands optimized for usage in Europe and Asia.
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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.
Other models
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https://www.quectel.com/lte-iot-modules/
https://www.quectel.com/download/quectel_eg91xqbg9xeg9x_series_compatible_design_v1-1/
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EG915N-EA
https://www.quectel.com/download/quectel_eg915n_series_hardware_design_v1-2/
Quectel_EG915N_Series_LTE_Standard_Specification_V1.3
BG95M3
https://www.quectel.com/download/quectel_bg95_series_hardware_design_v1-6/
Quectel_BG95_Series_LPWA_Specification_V2.0-4-1.pdf
EG915Q-NA / EG916Q-GL
https://www.quectel.com/download/quectel_eg91xq_series_hardware_design_v1-3/
Quectel_EG915Q_Series_LTE_Standard_Specification_V1.6
Quectel_EG916Q-GL_LTE_Standard_Specification_V1.1
Comparison Table
Model/Specs, DigiKey CA Link | ||||
|---|---|---|---|---|
$/ct (DigiKey CA) | ~$34.52 CAD | ~$50.54 CAD | ~$54.23 CAD | ~$63.99 CAD |
Stock (DigiKey CA) | ~200 | ~1,236 | ~236 | ~37 |
Dimensions | 19.9x23.6, 2.4mm | 19.9x23.6, 2.2mm | 19.9x23.6, 2.4mm | 22.5x26.5, 2.4mm |
Pin-to-pin compatible? | - | Kind of, footprint includes an arc-ed pad | Yes. (need confirmation from more eyes) | Yes (with few changes, listed below). |
LTE Bands | LTE-FDD: B1 / 3 / 7 / 8 / 20 / 28 | Cat M1: B1 / 2 / 3 / 4 / 5 / 8 / 12 / 13 / 18 / 19 / 20 / 25 / 26 / 27 / 28 / 66 / 85 Cat NB2: The above and 71, without 26 and 27 | LTE-FDD: B2 / 4 / 5 / 12 / 13 / 66 *EG915Q-AF model has bands 14 and 71 on top; however, can’t find it on DigiKey. | LTE-FDD: B1 / 2/ 3/ 4/ 5/ 7/ 8/ 12/ 13/ 18/ 19/ 20/ 25/ 26/ 28/ 66 LTE-TDD: B34 / 38/ 39/ 40/ 41 |
# of SIM Interfaces | 2 | 1 | 2 | 2 |
Specs Screenshot |  |  |  |  |
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Notes | Due to this being several mm bigger than the EG915N, the existing placement and routing would have to be heavily adjusted. |
Notable pinout differences between EG915N-EA and EG91xQ series devices:
GNSS debug pins on Q model (109, 110)
AUX_RTS and AUX_CTS removed on Q model (now RESERVED pins)
USIM2 no longer has a DET pin on Q model (no card detect)
Q model uses previously RESERVED pins for CAM SPI functionality (95, 78, 97, 98, 115, 93, 94)
Q model has backup power pins for the GNSS antenna (117, 118, 112)
Pins for SLEEP and WAKEUP have been renamed (among others)
MIC-related pins have been removed (now RESERVED pins: 119, 121, 122, 126, 120)
Final Selection
EG915Q-NA selected. See chat in #rpi-interface-rev-c for more.
Model is available on DigiKey Canada
2 SIM connections, USB 2.0
Has bands 12 and 13, the low frequency bands best for long-range communications
Missing 7 and 71 but these high-speed bands matter less for the purpose of the device
Exact same footprint as EG915N-EA (routing won’t have to be redone)
Layout
Collection of hardware design guideline excerpts from various component datasheets.
Quectel_EG915N_Series_Hardware_Design_V1.2.pdf
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https://www.quectel.com/download/quectel_eg91xq_series_hardware_design_v1-3/
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