Production…
Analog Lamb, while interesting, is just (a) too expensive (double the price), (b) unproven, (c) uncertified, and (d) has long lead times. Using proven Espressif certified modules seems the safer way to go.
So, we’ve decided to go with a switch to a standard certified ESP WROVER module, and external 16MB flash memory. The circuit board footprint for this is a little larger than the WROOM-32 module we’ve been using, and requires one more 3.3V->1.8V power conversion, but seems the safest way to go.
Accordingly, I’ve agreed with the China guys to proceed along these lines for the main board:
- Change WROOM-32 to WROVER (on circuit antenna version, similar to WROOM-32).
- We can free IO12 (SD_D2), IO13 (SD_D3), and IO4 (SD_D1), by using just 1-line SDCARD. I don’t really want to use IO12 as that is a bootstrapping pin.
- WROVER PSRAM uses IO16 and IO17, so we can’t use that for modem.
- Move modem to IO4 and IO13.
- Change to 1.8V 16MB flash chip (W25Q128FW?). As SDD_VDIO is not exposed, add a simple regulator 3.3V->1.8V for external flash?
- When burning e-fuses, need to take care with 1.8V/3.3V SDD_SDIO fuse - leave at 1.8V.
- Add capacitors for SD CARD and external Flash, as per Espressif example.
- Increase size of solder pad for big capacitors, and USB connector, to make it stronger.
- For the data lines of circuit traces SDCARD, SPI bus, external flash, take care to keep away from power traces or other sources of interference and keep the traces as short as possible.
The change to WROVER is a PITA at this stage, but that 4MB PSRAM should give us more headroom and the extra bill-of-materials costs is just a couple of US$.
For the modem, we’re double-checking the power (which seems ok, but check to be sure), and changing passive -> active antenna. At the moment, it seems to be just a couple of passive components soldered inline between two easily accessible points. For existing developer modems in the field, we’ll try to make a simple upgrade kit (passive->active) for GPS, and post them out. If you don’t need GPS (such as Roadster users), the modem boards are functionally the same as the production ones.