[Ovmsdev] Prototyping expansion board

[Craig Leres]

On 2019-04-17 16:24, Mark Webb-Johnson wrote:
> What is the reason to use newer/better cell modems? I presume you are talking about 4G, but given that 3G is currently well supported, and we have a 115200bps link to the modem, what is the purpose?

My friend with the roadster says he gets really sketchy cell coverage 
where he parks the car at home. The last time we talked about it it 
seemed like it shouldn't be difficult to hand build a couple ovms modem 
boards with a different cell module.

> Our modem board design does follow SIMCOM’s recommendations for layout compatibility, and you may be able to find a 4G SIMCOM module that is a drop-in replacement for the SIM5360 we use. We did make a prototype for the 7xxx series 4G NB iot chips, but that was a different size and the layout was quite different. Perhaps the pure LTE 7100/7500/7600 would work better
>
> The modem board is relatively complex and tightly packed. For example, it requires it’s own power supply circuitry as it doesn’t operate from either 3.3v or 5.0v (I think it uses 3.6v, but can’t remember exactly). We don’t use BGA, but it is surface mount technology. Overall, it is probably easier to just take our schematics and board layouts and make your own.

I think that's beyond what we were looking to get into. But if it's 
possible to buy some bare boards and you can recommend likely parts to 
try (SIM7600E?) I'm willing to give it a go.

> The J1850 may be simpler. You could use one of these new prototyping boards to implement it relatively easily. You could also do it externally off the DA26 port, but the I/O is more flexible in the internal expansion area.

Internal sounds like the way for me to go. Looks like you can expect to 
immediately sell some of these boards once they're available!

 > I personally prefer isolated. Allows for the most flexibility. But I
 > have seen designs with connected rows as well.

I'm the opposite, I like rows. And if I want to do something finer grain 
I cut traces with a scalpel.

Here's my favorite proto board:

 
https://www.mouser.com/datasheet/2/58/BPS-DAT-(POW3U)-Datasheet-932637.pdf

Anyway my J1850 circuit is pretty simple (I have a handful of HIP7010 
and HIP7020 chips, one dip and on sop14) so whatever you come up with 
will be fine.

		Craig