[TriEmbed] TriEmbed Digest, Vol 31, Issue 5
Chip McClelland
chip at mcclellands.org
Wed Dec 2 10:33:51 CST 2015
Brian, Mkaes perfect sense in steady state but could there be transient
differences between the board's Vcc rail and the internal voltage inside
the Arduino? Is this something I need to worry about?
Chip
On Wednesday, December 2, 2015, <triembed-request at triembed.org> wrote:
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> Today's Topics:
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> 1. Re: TriEmbed Digest, Vol 31, Issue 2 (Brian)
> 2. Re: TriEmbed Digest, Vol 31, Issue 2 (Chip McClelland)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 2 Dec 2015 11:25:11 -0500
> From: Brian <triembed at undecidedgames.net <javascript:;>>
> To: triembed at triembed.org <javascript:;>
> Subject: Re: [TriEmbed] TriEmbed Digest, Vol 31, Issue 2
> Message-ID: <565F1B67.7070401 at undecidedgames.net <javascript:;>>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
> On 12/2/2015 11:01 AM, Chip McClelland via TriEmbed wrote:
> > Brian and Shane,
> >
> > Thank you for your responses. Originally, I rejected the diode solution
> > for two reasons:
> >
> > 1) I thought the Arduino pin would end up connected to the Board's Vcc
> > rail exceeding the 40mA capacity but, as you pointed out, the voltage
> > drop across the diode will prevent this.
> >
>
> If the arduino is powered from that same Vcc rail, the silicon in the
> arduino itself will prevent the pin from being overloaded; internal
> junctions will be reverse-biased whether or not an external diode is
> connected. If that weren't true, the arduino would be somehow powering
> itself! You could then become a very rich man!
>
> -B
>
>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 2 Dec 2015 21:58:07 +0530
> From: Chip McClelland <chip at mcclellands.org <javascript:;>>
> To: Shane Trent <shanedtrent at gmail.com <javascript:;>>
> Cc: "triembed at triembed.org <javascript:;>" <triembed at triembed.org
> <javascript:;>>
> Subject: Re: [TriEmbed] TriEmbed Digest, Vol 31, Issue 2
> Message-ID:
> <
> CABQO2+mvBbYR5AQYMpy2ZqPAwHTHFrNLHftGFALWV4_Fnj-6sA at mail.gmail.com
> <javascript:;>>
> Content-Type: text/plain; charset="utf-8"
>
> Shane,
>
> But then the Arduino pin is driven High can directly connected to Vcc, how
> can I make sure it does not try to power the whole board even if briefly
> due to temporary voltage drops?
>
> Chip
>
> On Wednesday, December 2, 2015, Shane Trent <shanedtrent at gmail.com
> <javascript:;>> wrote:
>
> > Chip,
> >
> > About your point 2).
> >
> > The Bluetooth dongle would not see the diode drop, the dongle will see as
> > close to Vcc as the Arduino I/O pin can drive it. The diode drop only
> shows
> > up in your Vcc when you are powering the board from the FTDI cable
> through
> > the diode. With the Bluetooth dongle connected, it will be like the diode
> > is not there at all, unless something really strange happens.
> >
> > Shane
> >
> > On Wed, Dec 2, 2015 at 11:01 AM, Chip McClelland via TriEmbed <
> > triembed at triembed.org <javascript:;>
> > <javascript:_e(%7B%7D,'cvml','triembed at triembed.org <javascript:;>');>>
> wrote:
> >
> >> Brian and Shane,
> >>
> >> Thank you for your responses. Originally, I rejected the diode solution
> >> for two reasons:
> >>
> >> 1) I thought the Arduino pin would end up connected to the Board's Vcc
> >> rail exceeding the 40mA capacity but, as you pointed out, the voltage
> drop
> >> across the diode will prevent this.
> >>
> >> 2) I worried the voltage drop across the diode would not provide the
> >> Bluetooth dongle the voltage it needed. However, it sounds like I might
> be
> >> able to find one with a small enough drop to fix this.
> >>
> >> I will give this a try and thank you for your advice.
> >>
> >> Chip
> >>
> >> On Wednesday, December 2, 2015, <triembed-request at triembed.org
> <javascript:;>
> >> <javascript:_e(%7B%7D,'cvml','triembed-request at triembed.org
> <javascript:;>');>> wrote:
> >>
> >>> Send TriEmbed mailing list submissions to
> >>> triembed at triembed.org <javascript:;>
> >>>
> >>> To subscribe or unsubscribe via the World Wide Web, visit
> >>>
> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> >>> or, via email, send a message with subject or body 'help' to
> >>> triembed-request at triembed.org <javascript:;>
> >>>
> >>> You can reach the person managing the list at
> >>> triembed-owner at triembed.org <javascript:;>
> >>>
> >>> When replying, please edit your Subject line so it is more specific
> >>> than "Re: Contents of TriEmbed digest..."
> >>>
> >>>
> >>> Today's Topics:
> >>>
> >>> 1. IEEE Internet of Things meeting tonight (Wednesday)
> >>> (Rodney Radford)
> >>> 2. Is there a FET trick for this? (Chip McClelland)
> >>> 3. Laser cutter/engraver (Craig Cook)
> >>> 4. Re: Is there a FET trick for this? (Brian)
> >>> 5. Re: Is there a FET trick for this? (Shane Trent)
> >>>
> >>>
> >>> ----------------------------------------------------------------------
> >>>
> >>> Message: 1
> >>> Date: Wed, 2 Dec 2015 05:42:49 -0500
> >>> From: Rodney Radford <ncgadgetry at gmail.com <javascript:;>>
> >>> To: trianglerobotics <trianglerobotics at yahoogroups.com <javascript:;>>,
> TriEmbed
> >>> Discussion <triembed at triembed.org <javascript:;>>, Triangle
> Linux Users Group
> >>> General Discussion <trilug at trilug.org <javascript:;>>
> >>> Subject: [TriEmbed] IEEE Internet of Things meeting tonight
> >>> (Wednesday)
> >>> Message-ID:
> >>> <
> >>> CA+kfaxFKNQLqdvYnsNqmAvbic0U7FA+yg9ffQkgOtH4ffxy5UQ at mail.gmail.com
> <javascript:;>>
> >>> Content-Type: text/plain; charset="utf-8"
> >>>
> >>> Don't forget tonight to attend tonight's innagural meeting of the new
> >>> IEEE
> >>> Internet of Things IoT group on NCSU Centennial campus.
> >>>
> >>> The meeting begins at 6:30pm with food and drink:
> >>>
> >>> https://meetings.vtools.ieee.org/m/36760
> >>> -------------- next part --------------
> >>> An HTML attachment was scrubbed...
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> >>>
> http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151202/f51de483/attachment-0001.html
> >>> >
> >>>
> >>> ------------------------------
> >>>
> >>> Message: 2
> >>> Date: Wed, 2 Dec 2015 18:31:29 +0530
> >>> From: Chip McClelland <chip at mcclellands.org <javascript:;>>
> >>> To: "triembed at triembed.org <javascript:;>" <triembed at triembed.org
> <javascript:;>>
> >>> Subject: [TriEmbed] Is there a FET trick for this?
> >>> Message-ID:
> >>> <CABQO2+nHLX8x1_q9hQCL73L0bjsBW7jSm=
> >>> cccrrTiZS3HZFSXg at mail.gmail.com <javascript:;>>
> >>> Content-Type: text/plain; charset="utf-8"
> >>>
> >>> All,
> >>> Down to the final stretch on my new board - just need one more piece of
> >>> advice.
> >>>
> >>> I am trying to see if there is a way to accomplish something without
> >>> resorting to a physical jumper. I would like to use the FTDI header on
> my
> >>> new board in two ways with respect to the power pin.
> >>>
> >>> 1) when I connect a FTDI connector, it could power the board. The power
> >>> pin
> >>> is connected directly to the board's power rail. This is how it is
> today.
> >>>
> >>> 2) when I connect the Adafruit UART friend, I can turn it on and off
> >>> using
> >>> one of the Arduino's digital pins. In this scenario, I only want the
> >>> power
> >>> pin connected to the digital pin on the Arduino.
> >>>
> >>> Is there some way to automatically switch between these two modes based
> >>> on
> >>> whether there is power supplied by the FTDI adapter?
> >>>
> >>> Thanks,
> >>>
> >>> Chip
> >>>
> >>>
> >>>
> >>>
> >>> --
> >>> Sent from my iPhone - please excuse the typos
> >>> -------------- next part --------------
> >>> An HTML attachment was scrubbed...
> >>> URL: <
> >>>
> http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151202/eec3b42a/attachment-0001.html
> >>> >
> >>>
> >>> ------------------------------
> >>>
> >>> Message: 3
> >>> Date: Wed, 2 Dec 2015 13:53:15 +0000 (UTC)
> >>> From: Craig Cook <cncook001 at yahoo.com <javascript:;>>
> >>> To: "triembed at triembed.org <javascript:;>" <triembed at triembed.org
> <javascript:;>>
> >>> Subject: [TriEmbed] Laser cutter/engraver
> >>> Message-ID:
> >>> <364134559.2216081.1449064395581.JavaMail.yahoo at mail.yahoo.com
> <javascript:;>>
> >>> Content-Type: text/plain; charset="utf-8"
> >>>
> >>> Just heard about this on the Embedded.fm podcast.
> >>> https://glowforge.com/
> >>> Looks like a great christmas present ;)
> >>> Craig
> >>> -------------- next part --------------
> >>> An HTML attachment was scrubbed...
> >>> URL: <
> >>>
> http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151202/4c68059c/attachment-0001.html
> >>> >
> >>>
> >>> ------------------------------
> >>>
> >>> Message: 4
> >>> Date: Wed, 2 Dec 2015 10:15:53 -0500
> >>> From: Brian <triembed at undecidedgames.net <javascript:;>>
> >>> To: triembed at triembed.org <javascript:;>
> >>> Subject: Re: [TriEmbed] Is there a FET trick for this?
> >>> Message-ID: <565F0B29.7020501 at undecidedgames.net <javascript:;>>
> >>> Content-Type: text/plain; charset=windows-1252; format=flowed
> >>>
> >>> Let me see if I understand correctly:
> >>>
> >>> When the FTDI is connected, you want power to flow FROM the FTDI
> adapter
> >>> TO your board.
> >>>
> >>> When the Adafruit doohickey is connected, you want power to flow FROM
> >>> your board TO the adapter (the opposite direction) by the same pin.
> >>>
> >>> If that's it, a simple diode between the pin and your board's power
> rail
> >>> is all you need. Oriented to allow current to flow from the connector
> >>> to the power rail and not the other way. Connect both the connector
> pin
> >>> and the Arduino pin to the anode of the diode, and connect the power
> >>> rail to the diode's cathode. If the connected board is supplying
> power,
> >>> the diode will be forward-biased and will conduct. If the board is
> >>> receiving power, the diode will be reverse-biased and will not conduct.
> >>>
> >>> Make sure the diode is rated for the amount of current that will flow
> in
> >>> from the FTDI adapter.
> >>>
> >>> Crude attempt at ascii art:
> >>>
> >>> [FTDI?] ----+---[>|---- +V rail
> >>> |
> >>> -
> >>> ^ [optional]
> >>> |
> >>> arduino pin
> >>>
> >>> [FTDI?] represents the connector pin.
> >>>
> >>> The optional diode is if you want to prevent current flowing into the
> >>> arduino pin from the FTDI adapter, but is unnecessary unless the FTDI
> >>> adapter supply voltage is too high for the pin.
> >>>
> >>> Ordinary diodes do impose a nominally 0.7V voltage drop when in
> >>> conduction, but you can shop for a Schottky diode with a lower voltage
> >>> drop if that will be a problem.
> >>>
> >>> Hope this helps!
> >>> -B
> >>>
> >>>
> >>>
> >>> On 12/2/2015 8:01 AM, Chip McClelland via TriEmbed wrote:
> >>> > All,
> >>> > Down to the final stretch on my new board - just need one more piece
> of
> >>> > advice.
> >>> >
> >>> > I am trying to see if there is a way to accomplish something without
> >>> > resorting to a physical jumper. I would like to use the FTDI header
> on
> >>> > my new board in two ways with respect to the power pin.
> >>> >
> >>> > 1) when I connect a FTDI connector, it could power the board. The
> power
> >>> > pin is connected directly to the board's power rail. This is how it
> is
> >>> > today.
> >>> >
> >>> > 2) when I connect the Adafruit UART friend, I can turn it on and off
> >>> > using one of the Arduino's digital pins. In this scenario, I only
> want
> >>> > the power pin connected to the digital pin on the Arduino.
> >>> >
> >>> > Is there some way to automatically switch between these two modes
> based
> >>> > on whether there is power supplied by the FTDI adapter?
> >>> >
> >>> > Thanks,
> >>> >
> >>> > Chip
> >>> >
> >>> >
> >>> >
> >>> >
> >>> > --
> >>> > Sent from my iPhone - please excuse the typos
> >>> >
> >>> >
> >>> > _______________________________________________
> >>> > Triangle, NC Embedded Computing mailing list
> >>> > TriEmbed at triembed.org <javascript:;>
> >>> > http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> >>> > TriEmbed web site: http://TriEmbed.org
> >>> >
> >>>
> >>>
> >>>
> >>>
> >>> ------------------------------
> >>>
> >>> Message: 5
> >>> Date: Wed, 2 Dec 2015 10:29:44 -0500
> >>> From: Shane Trent <shanedtrent at gmail.com <javascript:;>>
> >>> To: Chip McClelland <chip at mcclellands.org <javascript:;>>
> >>> Cc: "triembed at triembed.org <javascript:;>" <triembed at triembed.org
> <javascript:;>>
> >>> Subject: Re: [TriEmbed] Is there a FET trick for this?
> >>> Message-ID:
> >>> <
> >>> CAAFjd3rLUnu7yEoCyOjVsbejMFUmAucAfH0FkNZuTwGCHXOoLQ at mail.gmail.com
> <javascript:;>>
> >>> Content-Type: text/plain; charset="utf-8"
> >>>
> >>> Chip,
> >>>
> >>> If I follow, I believe you can achieve your goal by connecting the
> power
> >>> terminal on your incoming FTDI connector directly to your Digital I/O
> pin
> >>> and then connect this node to your PCB Vcc via a diode (or a Schottky
> >>> diode
> >>> for a slightly lower voltage drop).
> >>>
> >>> This would power your board from the FTDI through the diode when
> >>> connected,
> >>> so your board is operating at one diode drop below the FTDI's Vcc. But
> >>> the
> >>> UART Friend would only see power when you drive the FTDI pin's Vcc pin
> >>> high
> >>> via the digital I/O pin. When powered via the I/O pin the extra diode
> >>> will
> >>> do nothing since the chip is powered from VCC, the I/O pin will be
> >>> incapable of rising a diode drop above Vcc so the diode will never be
> >>> forward biased. You would want to ensure you never try to drive the I/O
> >>> pin
> >>> low when FTDI cable is connected.
> >>>
> >>> Shane
> >>>
> >>> On Wed, Dec 2, 2015 at 8:01 AM, Chip McClelland via TriEmbed <
> >>> triembed at triembed.org <javascript:;>> wrote:
> >>>
> >>> > All,
> >>> > Down to the final stretch on my new board - just need one more piece
> of
> >>> > advice.
> >>> >
> >>> > I am trying to see if there is a way to accomplish something without
> >>> > resorting to a physical jumper. I would like to use the FTDI header
> on
> >>> my
> >>> > new board in two ways with respect to the power pin.
> >>> >
> >>> > 1) when I connect a FTDI connector, it could power the board. The
> power
> >>> > pin is connected directly to the board's power rail. This is how it
> is
> >>> > today.
> >>> >
> >>> > 2) when I connect the Adafruit UART friend, I can turn it on and off
> >>> using
> >>> > one of the Arduino's digital pins. In this scenario, I only want the
> >>> power
> >>> > pin connected to the digital pin on the Arduino.
> >>> >
> >>> > Is there some way to automatically switch between these two modes
> >>> based on
> >>> > whether there is power supplied by the FTDI adapter?
> >>> >
> >>> > Thanks,
> >>> >
> >>> > Chip
> >>> >
> >>> >
> >>> >
> >>> >
> >>> > --
> >>> > Sent from my iPhone - please excuse the typos
> >>> >
> >>> > _______________________________________________
> >>> > Triangle, NC Embedded Computing mailing list
> >>> > TriEmbed at triembed.org <javascript:;>
> >>> > http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> >>> > TriEmbed web site: http://TriEmbed.org
> >>> >
> >>> >
> >>>
> >>>
> >>> --
> >>>
> >>> A blog about some of my projects. http://fettricks.blogspot.com/
> >>> -------------- next part --------------
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> >>> >
> >>>
> >>> ------------------------------
> >>>
> >>> Subject: Digest Footer
> >>>
> >>> _______________________________________________
> >>> TriEmbed mailing list
> >>> TriEmbed at triembed.org <javascript:;>
> >>> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> >>>
> >>>
> >>> ------------------------------
> >>>
> >>> End of TriEmbed Digest, Vol 31, Issue 2
> >>> ***************************************
> >>>
> >>
> >>
> >> --
> >> Sent from my iPhone - please excuse the typos
> >>
> >> _______________________________________________
> >> Triangle, NC Embedded Computing mailing list
> >> TriEmbed at triembed.org <javascript:;>
> >> <javascript:_e(%7B%7D,'cvml','TriEmbed at triembed.org <javascript:;>');>
> >> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> >> TriEmbed web site: http://TriEmbed.org
> >>
> >>
> >
> >
> > --
> >
> > A blog about some of my projects. http://fettricks.blogspot.com/
> >
>
>
> --
> Sent from my iPhone - please excuse the typos
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>
> End of TriEmbed Digest, Vol 31, Issue 5
> ***************************************
>
--
Sent from my iPhone - please excuse the typos
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