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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.

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.

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

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Model/Specs, DigiKey CA Link	EG915N-EA (original model)	BG95M3 Series	EG915Q-NA Series	EG916Q-GL
$/ct (DigiKey)	~$34.52 CAD	~$50.54 CAD	~$54.23 CAD	~$63.99 CAD
Stock (DigiKey)	~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				Image Added
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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