[Mezzanine] Sensors board Rev B - call for review

King, Lawrence lking at qti.qualcomm.com
Wed Oct 21 21:05:59 UTC 2015


Hi Grant

Your "stackable" connector rendering shows pins on the top of the board, but to me "stackable" means you should have a female socket on the top of the board so that you can stack another 96Boards mezzanine board above this one. Realistically it is unlikely anyone will be stacking anything above this board because anything stacked on top would block access to almost all of the onboard features. Do the pins interfere with Arduino Boards stacked above?

About the 3.3V/5V selection, I believe a lot of users will prefer jumper pins over soldering,  a switch is also good. If you need to have a wired 'default' I believe the 3.3V is used a lot more often than 5V and is less likely to cause things to blow up if the user didn't check the setting.

Silkscreen for the connectors on the front edge says "I2C" and I2C0", I think it should something like be "I2C-96B" and "I2C-ARD" you also have a vertical I2C which should also be labeled "I2C-ARD".

You have two different types of level shifters TXS and TXB, any reason for this?

Lawrence KingĀ  lking at qti.qualcomm.com 
Engineer, Sr. Staff/Manager
Qualcomm Canada Inc.
(905)482-5403 desk (x25403)
(416)627-7302 cell


-----Original Message-----
From: David Mandala [mailto:david.mandala at linaro.org] 
Sent: Wednesday, October 21, 2015 10:00 AM
To: Grant Likely <grant.likely at linaro.org>; mezzanine at lists.96boards.org
Cc: 96boards-team <96boards-team at linaro.org>; George Grey <george.grey at linaro.org>; Koen Kooi <koen.kooi at linaro.org>; Mark Brown <mark.brown at linaro.org>; King, Lawrence <lking at qti.qualcomm.com>; Gandhi, Ketal <ketalg at qti.qualcomm.com>
Subject: Re: Sensors board Rev B - call for review

Grant,

Comment below:

On 10/21/15 8:30 AM, Grant Likely wrote:
>>  On Tue, Oct 20, 2015 at 9:11 PM, David Mandala <david.mandala at linaro.org> wrote:

[snip]

>>> 3) The board has a solder bridge jumper (QS1) for selecting between 
>>> running the IO at 3.3V and 5V. 5V is the default for compatibility, 
>>> but someone who knows what they are doing can switch the solder 
>>> bridge to run at 3.3V for everything. (Most sensor devices appear to 
>>> be 3.3V these days. The ATMEGA will happily run at either 3.3V or 
>>> 5V)
>>>
>>> Q: Is a solder jumper the best way to select the voltage level? Or 
>>> should I put a physical switch on the board?
>>
>>
>> Personally I'd use a 3 pin jumper, pin 1-2 is 3.3VDC operations, pin 
>> 2-3 5VDC operations.  My second choice would be a switch.  Last 
>> choice would be a solder bridge, you might be surprised how many 
>> people shy away from a soldering iron.
>
> I have a concern here. A solder jumper I'm not too worried about, but 
> I don't like the idea of routing all of the supply current through a 
> shunt. I figured I'm not the first person to deal with this, so I went 
> and took a look at what others have done. This is what I found on the 
> Seeeduino design which can be run at both 3.3V and 5V:
>
> http://www.seeedstudio.com/wiki/images/c/ca/Seeeduino_v4.2_sch.pdf
>
> The 3.3/5V selection switch is merely a signal routed to a couple of 
> mosfets which gate the power. That removes the power supply trace from 
> the jumper or switch entirely. I assume it is done that way to reduce 
> noise on the supply rails. I'm wondering if I should do the same here.

If you have space for the parts, that makes the most sense to me. I too was worried about a small circuit board switch carrying power load, Generally jumpers have bigger chunks of copper bridging the posts, but not shunting the power makes the most sense. That makes the idea of a small circuit board switch much more attractive.

David


>
> g.
>


--
David Mandala <david.mandala at linaro dot org> http://www.linaro.org/ Public Key id: 45B2D952 Murphy TX, 75094 +1.972.891.8436


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