[Ovmsdev] OVMS v3 First Board Layout

[Mark Webb-Johnson]

Attached is the almost final schematic for OVMS v3. Only one minor typo where the SPI CS line for the MAX7317 should be SP_CS3 (incorrectly marked as SP_CS2 on the attached schematic). Other that that, it seems fine.

Rather than the OVMS v2 fixed fuse, we’ve now got a resettable 0.75A/1.5A fuse on the incoming 12V. We’re trying to use the (recommended here) AOZ1280CI buck converter for both 12V and 5V down to 3.3V. The entire board past that point is 3.3V. We’ve got a BTS452R for switched 12V output, a 128Mbit external flash, CP2102 for USB-async, MAX7317 for I/O expansion, SD card, 3 CAN bus (one on board, two using MCP2515, and all three using SN65HVD233D 3.3V transceivers).

Also attached is the PCB layout overview. Board at the moment is a hair under 10cm x 10cm (larger than OVMS v2) - we’re constrained by all those external connectors and two large internal expansion sockets.

Any comments/suggestions, as always, appreciated. We’re going to PCB fabrication later this week, and with luck I’ll have a couple of boards in my hands late next week (or early the week after). Then I’ll finalise the Quality Control firmware (a firmware option to simply test and exercise all the components on the board). If the boards are ok, we’ll then get the size and layout finalised and produce a small hand-soldered run for developers (late this month).

The side project of looking at 3G/4G modems has also started. This is going to be on one of those optional expansion slots to allow us to use different modems for different functions. I’m used to SIMCOM, but it seems their selection is getting complicated (particularly for 4G). I see the SIM5320A has 3G and GPS, which seems good but is quite dated now.
SIM5320A:Dual-Band UMTS/HSDPA 850/1900MHz, Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz
SIM5320(J)E:Dual-Band UMTS/HSDPA 900/2100MHz, Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz
SIM5320J:Dual-Band UMTS/HSDPA 850(800)/2100MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz
It does have the CMUX, which is very nice (gives us four virtual ports over the single async port, so easier to deal with AT command control).

If anyone has any suggestions for the modem, it would be helpful. Something with GPS would be ideal.

Regards, Mark.


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