[Ovmsdev] OVMS CAN-USB Call for Assistance

Mark Webb-Johnson mark at webb-johnson.net
Sat Sep 7 20:43:32 HKT 2013

I'll try . It'll depend on space in the housing. I've got a few I've been playing with.

I like the ones that direct solder:

But the plug-in ones may be better suited as they can be entirely optional:

Regards, Mark.

On 6 Sep, 2013, at 3:52 PM, Mastro Gippo <gipmad at gmail.com> wrote:

> Just a quick request: there should be enough space on the pcb to add a
> bluetooth module. Please add at least the footprint for
> [http://www.ebay.it/sch/i.html?_odkw=hc-05&_sop=15&_osacat=0&_from=R40&LH_PrefLoc=2&_trksid=p2045573.m570.l1313&_nkw=hc-05+-74hc05&_sacat=0]
> This would add the need for an independent power supply, but as I
> recall you were already planning to place the footprints on the pcb.
> I found myself in need for a wireless connection a lot of times,
> usually to get a quick log with my phone. For example, this weekend
> I'm doing a few tests with a tesla model s and I'd love a more stealth
> method to get the data.
> About being stealth, I found myself using ELM327 adapters to get CAN
> data more than a few times, but I have to include a lot of filtering
> due to the slowness of the adapter. That said, the STN1170 is an
> "elm327 on steroids", and may have enough horsepower to log unfiltered
> can data, while being a very good diagnostic tool to interface with
> Torque. http://batman.homelinux.com/blog/stn1170-bluetooth-obdii-adapter/
> I still have not tested it, but maybe will soon. Single chips are
> available for 10$ in single quantities.
> Regards
> MG
> 2013/9/5 HONDA S-2000 <s2000 at sounds.wa.com>:
>> I like the MCP2551, but I don't think it's guaranteed to work without a 5V
>> boost regulator. The USB specifications are clear that the 4.5V minimum
>> needed is not always guaranteed to be present.
>> As for the crystal, it's all about the accuracy of the internal oscillator.
>> USB calls out a precision in the specification, and as long as you meet that
>> you're fine. Older chips had an internal oscillator that was not precise
>> enough. This newer PIC32MX796 has a 0.9% oscillator, meaning that it's
>> plenty accurate enough for USB. I trust Microchip, in that they don't claim
>> their internal oscillator will work for chips that can't do it, but this one
>> can.
>> That said, there's nothing wrong with putting the traces on the board (other
>> than the space they take up). I'm partial to smaller SMD parts like the ECS
>> ECS-120-20-30B-DU, but those are more expensive than the large canned
>> crystals.
>> Does the CAN spec (ISO-11898) say what the required precision is for the
>> clock?
>> The SN65HVD235 has a bus listen-only feature that seems like a really safe
>> option for a project like this. I imagine that the device will mostly be
>> listening to CAN messages and not attempting to inject potentially dangerous
>> messages into an unknown vehicle. Supposedly, the listen feature also helps
>> with autobaud.
>> Brian
>> On Sep 4, 2013, at 19:22, Mark Webb-Johnson wrote:
>>> Looking at the wholesale pricing, and given that we have 5V already and
>>> lots of experience with MCP2551, I think I'll stick with that for the
>>> initial design and then see what the factory says.
>>> At the moment, I'm trying to make a rough design using
>>> PIC32MX795F512H+MCP2551 - DB9 at one end, USB at the other. No final
>>> decision on microcontroller yet, but I just want to get something to the
>>> factory to firm up estimates on what this is going to cost. I'll tell the
>>> factory that the SN65HVD233 is an option for them, if it is easier/cheaper.
>>> The PIC32 is completely overkill for this, and will most likely be 50% of
>>> the BOM cost. But, I really want lots of RAM on this thing. If we drop RAM
>>> requirement to 64KB, we can save a few bucks, but it really doesn't seem
>>> worthwhile.
>>> Regarding the oscillator, every design I've ever done uses an external
>>> oscillator. I know the PICs (and others now) have internal FSCs, but am
>>> concerned about timing accuracies for CAN and USB. The data sheet says the
>>> internal FSC can be used for USB (and incidentally is always used for 48MHz
>>> USB when in suspend mode). Anyone have any experience with this? My gut
>>> feeling is to wire the board for an 8MHz external crystal (and two caps),
>>> and then see if we can get it working reliably with that disabled. If we end
>>> up not needing it, we can leave it unpopulated at manufacture time (saving a
>>> buck).
>>> Regards, Mark.
>>> On 5 Sep, 2013, at 4:01 AM, HONDA S-2000 <s2000 at sounds.wa.com> wrote:
>>>> The MCP2551 requires a minimum Vdd of 4.5V to ensure ISO-11898
>>>> specifications, but USB Vbus is only guaranteed to be 4.01V under certain
>>>> conditions like at the end of a bus-powered hub.
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