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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

    • https://www.monolithicpower.com/en/mp4575.html

    • https://www.digikey.ca/en/products/filter/voltage-regulators-dc-dc-switching-regulators/739?s=N4IgTCBcDaILIAUAsBWA7CkBdAvkA

    • I kinda wanted to use MPS here, but doesnt seem like any of their stuff solves

  • Searching Digikey

    • https://www.digikey.ca/en/products/filter/pmic/voltage-regulators-dc-dc-switching-regulators/739?s=N4IgjCBcoBwOxVAYygMwIYBsDOBTANCAPZQDaIAzAJwBsNArCALqEAOALlCAMrsBOASwB2AcxABfQmABMVRCBSQMOAsTIhZFONIAsIQtp06IhGDRjSazNp0g9%2BwsZJD04FeYuV5CJSOTAADAE0cCYaOtT0VoS6NGAU7jE6NFRUYdKuNDrS%2Bhr0MNRyMfS02bmWFAFUMOVwxoG1MGBmjTD06fA0WrmVlnA1hCk0srmhFBG5MNkwRSBUOnD51iAcXLyCohJSVTXQCmhY3mp%2BlNIUcQgsK7b2G05S1XJ7noeqvuQBzM4AtDnPUPwAK5vdSMJg-J7IAF8YE%2BdQQcHOKx7AQAEy430CORsXFy7AAnqxcFxUdgUOJxEA

    • 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 A: https://ww1.microchip.com/downloads/en/DeviceDoc/MIC28516-70V-8A-Hyper-Speed-Control-Synchronous-DC-DC-Buck-Regulator-with-External-Soft-Start-DS20006315A.pdf

      • 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

1 2

Model/Specs, DigiKey CA Link	EG915N-EA (original model)	BG95M3 Series	EG915Q-NA Series	EG916Q-GL Series
$/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: 1 B1 / 3 / 7 / 8 / 20 / 28 Spec Sheet	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 Spec Sheet	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. Spec Sheet	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 Spec Sheet
# of SIM Interfaces	2	1	2	2
Specs Screenshot
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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