<html>
<head>
<meta content="text/html; charset=windows-1252"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<div class="moz-cite-prefix"><br>
My recommendation for a step down converter:<br>
The AOZ1280CI is cheap, has a wide voltage input range (3-26V),
and can deliver up to 1.2A at 0.8-23V<br>
Another good thing: it switches at 1.5Mhz, so the inductor can be
kept small. <br>
<br>
-Michael<br>
<br>
<br>
<br>
Op 31-3-2017 om 7:30 schreef Mark Webb-Johnson:<br>
</div>
<blockquote
cite="mid:B25F52D6-EAE5-4C4D-95B2-B480D2E873C2@webb-johnson.net"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
<div class=""><br class="">
</div>
<div class="">It seems that a dual voltage design would not be
ideal.</div>
<div class=""><br class="">
</div>
<div class="">
<ol class="MailOutline">
<li class="">We’d have to go 12V -> 5V, and then 5V ->
3.3V.<br class="">
<br class="">
</li>
<li class="">But then USB 5V is not necessarily 5V, so we
would also have to deal with boosting that if necessary.<br
class="">
<br class="">
</li>
<li class="">We could use a dual-output buck converter 12V
-> 5V and 3.3V. But, then we still have to deal with the
USB issue for true 5V.</li>
</ol>
</div>
<div class=""><br class="">
</div>
<div class="">Reading what all you guys are saying (thanks to all
that gave feedback), it does seem that the concerns are
unwarranted.</div>
<div class=""><br class="">
</div>
<div class="">Perhaps we can build the dev boards just pure 3.3V,
and see how it goes. We’d use a high range buck converter to
bring everything down to 3.3V. If we can find one that would
also work in the USB 5V range, then we could just use that. If
not, we use a cheap and simple 5V->3.3V device. I’ll ask the
China guys what they can recommend based on what they have
available and popular in their market.</div>
<div class=""><br class="">
</div>
<div class="">Regards, Mark.</div>
<br class="">
<div>
<blockquote type="cite" class="">
<div class="">On 30 Mar 2017, at 10:33 PM, Collin Kidder <<a
moz-do-not-send="true" href="mailto:collink@kkmfg.com"
class="">collink@kkmfg.com</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="">I'm unsure of why the 3.3v transceiver would
be a problem. CAN wiring<br class="">
is supposed to be differential and it isn't supposed to
matter if it<br class="">
is 20V and 18V relative to local ground or 4V and 2V.
There is isn't a<br class="">
requirement to keep a shared ground between two CAN
devices so how<br class="">
would a remote node even know what the "voltage" of CAN-L
is? Voltage<br class="">
is only defined between two points so if you don't share a
ground<br class="">
between two nodes then the only voltage the transceiver
knows is CAN-L<br class="">
to CAN-H which will range by the proper amount whether you
use a 5V or<br class="">
3.3V transceiver. I've used the SN65HVD series
transceivers in all<br class="">
sorts of things and never had a single problem. I've also
used the<br class="">
ISO1050 isolated transceiver and also had no problems with
different<br class="">
devices. But, if the 5V transceiver is cheaper and you can
get 5V<br class="">
easily enough then maybe that's still the way to go. I'm
just saying<br class="">
in my experience the concern isn't terribly warranted.
YMMV.<br class="">
<br class="">
On Wed, Mar 29, 2017 at 9:07 PM, Mark Webb-Johnson<br
class="">
<<a moz-do-not-send="true"
href="mailto:mark@webb-johnson.net" class="">mark@webb-johnson.net</a>>
wrote:<br class="">
<blockquote type="cite" class=""><br class="">
I’m trying to finalise the OVMS v3 final board layout,
with the factory in<br class="">
China. We have some questions and seek your opinions:<br
class="">
<br class="">
CAN transceivers / power<br class="">
<br class="">
Overall, the OVMS v3 system runs at 3.3V. We have two
power supply sources:<br class="">
USB (where we use a 5V -> 3.3V regulator), and +12V
vehicle power (where we<br class="">
use a +12V -> 3.3V switching power supply, to be as
energy efficient as<br class="">
possible). Diodes are used for reverse-polarity
protection as well as coping<br class="">
with the situation where both usb and vehicle power is
applied<br class="">
simultaneously.<br class="">
<br class="">
Our problem is with the CAN transceivers. I’m used to
the MCP2551 (been<br class="">
using it for a decade or more), but that is 5V so
greatly complicates the<br class="">
power supply arrangements at the +12V side. We can
switch to something like<br class="">
the SN65HVD233 transceiver that works at 3.3V.<br
class="">
<br class="">
But, I am concerned about comments I am reading about
3.3V CAN transceivers<br class="">
and their inability to meet the ISO11898 dominant
condition requirement of<br class="">
3.5V. From my understanding, these 3.3V CAN transceivers
get around this by<br class="">
driving CAN-L to 1V, to still get the differential of
about 2V (recessive<br class="">
condition?). My concern is compatibility.<br class="">
<br class="">
What do people think about this? Any recommendations?<br
class="">
<br class="">
External Connectors<br class="">
<br class="">
The idea is to retain the existing DB9 connector, with
the same basic pin<br class="">
arrangement:<br class="">
<br class="">
DB9-M Signal<br class="">
3 Chassis/Power GND<br class="">
2 CAN-L (primary)<br class="">
7 CAN-H (primary)<br class="">
4 CAN-L (alternate CAN)<br class="">
5 CAN-H (alternate CAN)<br class="">
9 +12V Vehicle Power<br class="">
<br class="">
That leaves pins #1, #6, and #8 free for expansion uses.
It gives us<br class="">
compatibility with existing OVMS cables.<br class="">
<br class="">
We would then add a second connector. The suggestions
here are DB15 normal<br class="">
density, DB25 normal density, or DA-26 high density. My
preference is the<br class="">
DA-26 (as DB25 is the old parallel printer style
connector and very bulky).<br class="">
As well as power lines, expansion cards could wire to
this connector to<br class="">
expose external inputs/outputs.<br class="">
<br class="">
What do people think about the DA-26 connector? I’m
suggesting a female<br class="">
version (as power is carried there, and I don’t want the
pins to get pushed<br class="">
together for a short).<br class="">
<br class="">
Note that we’ve also got a micro-usb socket, as well as
space for GPS and<br class="">
GSM/GNS antennas.<br class="">
<br class="">
<br class="">
Other than that, we are good to go. Things have
stabilised now with<br class="">
Espressif, so we can proceed with building developer
boards.<br class="">
<br class="">
Regards, Mark.<br class="">
<br class="">
<br class="">
_______________________________________________<br
class="">
OvmsDev mailing list<br class="">
<a moz-do-not-send="true"
href="mailto:OvmsDev@lists.teslaclub.hk" class="">OvmsDev@lists.teslaclub.hk</a><br
class="">
<a class="moz-txt-link-freetext" href="http://lists.teslaclub.hk/mailman/listinfo/ovmsdev">http://lists.teslaclub.hk/mailman/listinfo/ovmsdev</a><br
class="">
<br class="">
</blockquote>
_______________________________________________<br
class="">
OvmsDev mailing list<br class="">
<a moz-do-not-send="true"
href="mailto:OvmsDev@lists.teslaclub.hk" class="">OvmsDev@lists.teslaclub.hk</a><br
class="">
<a class="moz-txt-link-freetext" href="http://lists.teslaclub.hk/mailman/listinfo/ovmsdev">http://lists.teslaclub.hk/mailman/listinfo/ovmsdev</a><br
class="">
</div>
</div>
</blockquote>
</div>
<br class="">
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
OvmsDev mailing list
<a class="moz-txt-link-abbreviated" href="mailto:OvmsDev@lists.teslaclub.hk">OvmsDev@lists.teslaclub.hk</a>
<a class="moz-txt-link-freetext" href="http://lists.teslaclub.hk/mailman/listinfo/ovmsdev">http://lists.teslaclub.hk/mailman/listinfo/ovmsdev</a>
</pre>
</blockquote>
<br>
<br>
</body>
</html>