Sink vs. Source (Was, Re: BS2p-24 I/O pins requirements and 74xx families.)
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Posts: 46,084
This is off-topic...
I originally learned electronics from my father, who taught me current flow
from + to -.
The Navy taught me the more "conventional" way of current flowing from - to
+.
Electron flow vs. Hole flow.
So, when a pin sources or sinks current, which terminology is being used?
Steve
Original Message
From: "Allan Lane" <allan.lane@h...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, July 15, 2003 8:20 PM
Subject: [noparse][[/noparse]basicstamps] Re: BS2p-24 I/O pins requirements and 74xx families.
> I believe the lowest power, yet still TTL family,
> is 74HCT. Some of the HCx family are NOT TTL
> compatible, so be careful.
>
> The BS2 can source or sink 23 mA max per pin,
> with a max for all pins of 50 mA.
> (Which means: 2 pins at 23 mA, or 16 pins
> at 3.125 mA each, etc). Note it
> seems to 'sink' better than it 'sources',
> if that matters to you.
>
> If you need more current, the 74HCT595 is
> a very good SPI to parallel converter, with
> more total power available.
>
> For Fan-Out, you need to find the input
> resistance of the chips you want the BS2
> to drive. For Fan-In, I believe the BS2's
> inputs look like 10 Meg-ohm impedances --
> someone may correct me on that.
>
> The big problem with BS2 is that because
> it can drive so much current, if you tie
> two drivers together and have them drive
> in opposite directions, with no resistance
> between them, it is easy to burn out a pin.
>
> The brute-force solution to this
> problem is to put a 220 ohm
> resistor in series with each pin which might
> be tied to another driver. This will guarantee
> that the current won't exceed 22mA, no matter
> what states are active.
>
> I2C I don't know the answer to that one.
>
> --- In basicstamps@yahoogroups.com, "Alberto Calderara"
> <albertocalderara@t...> wrote:
> > Ciao,
> >
> > I'm sure that the problem has been discussed a lot af times... But
> it's not so friendly to me the matter about I/O pins current
> requirements of the BS2p-24 that I'm trying to put inside my circuit,
> therefore I ask your help, dear friends, before I may cook my
> precious Stamp!
> >
> > First thing: a simple rule for establishing the fan-out (and fan-
> in) of the Stamp's I/O pins?
> >
> > Second: what is the best choice about the logic family to interface
> with the Stamp? 74HC, 74LS or what else?
> >
> > Last: are the two I2C ports of the BS2p-24 (and BS2p-40) limited to
> a certain number of I2C devices connected to the same bus?
> >
> > Thanks in advance,
> >
> > Alberto.
> >
> >
> > [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
I originally learned electronics from my father, who taught me current flow
from + to -.
The Navy taught me the more "conventional" way of current flowing from - to
+.
Electron flow vs. Hole flow.
So, when a pin sources or sinks current, which terminology is being used?
Steve
Original Message
From: "Allan Lane" <allan.lane@h...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, July 15, 2003 8:20 PM
Subject: [noparse][[/noparse]basicstamps] Re: BS2p-24 I/O pins requirements and 74xx families.
> I believe the lowest power, yet still TTL family,
> is 74HCT. Some of the HCx family are NOT TTL
> compatible, so be careful.
>
> The BS2 can source or sink 23 mA max per pin,
> with a max for all pins of 50 mA.
> (Which means: 2 pins at 23 mA, or 16 pins
> at 3.125 mA each, etc). Note it
> seems to 'sink' better than it 'sources',
> if that matters to you.
>
> If you need more current, the 74HCT595 is
> a very good SPI to parallel converter, with
> more total power available.
>
> For Fan-Out, you need to find the input
> resistance of the chips you want the BS2
> to drive. For Fan-In, I believe the BS2's
> inputs look like 10 Meg-ohm impedances --
> someone may correct me on that.
>
> The big problem with BS2 is that because
> it can drive so much current, if you tie
> two drivers together and have them drive
> in opposite directions, with no resistance
> between them, it is easy to burn out a pin.
>
> The brute-force solution to this
> problem is to put a 220 ohm
> resistor in series with each pin which might
> be tied to another driver. This will guarantee
> that the current won't exceed 22mA, no matter
> what states are active.
>
> I2C I don't know the answer to that one.
>
> --- In basicstamps@yahoogroups.com, "Alberto Calderara"
> <albertocalderara@t...> wrote:
> > Ciao,
> >
> > I'm sure that the problem has been discussed a lot af times... But
> it's not so friendly to me the matter about I/O pins current
> requirements of the BS2p-24 that I'm trying to put inside my circuit,
> therefore I ask your help, dear friends, before I may cook my
> precious Stamp!
> >
> > First thing: a simple rule for establishing the fan-out (and fan-
> in) of the Stamp's I/O pins?
> >
> > Second: what is the best choice about the logic family to interface
> with the Stamp? 74HC, 74LS or what else?
> >
> > Last: are the two I2C ports of the BS2p-24 (and BS2p-40) limited to
> a certain number of I2C devices connected to the same bus?
> >
> > Thanks in advance,
> >
> > Alberto.
> >
> >
> > [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
Comments
I think even the Navy went back to 'positive') was
that current flows from the '+' terminal to GND.
Note that the current that flows is 'positive'
current, that is, 'positive' charges flowing
from '+' to '-'. The graphic for a diode have
a little 'arrow', which points in the direction
of 'positive' current flow.
Having said that, a chip 'sinks' current when
it provides a low-resistance path to ITS
ground pin for a positive current, flowing
from a '+' source of voltage. A chip
'sources' current when it provides a
path for positive current from ITS
VCC pin out through one of the chip's pins,
to another device.
And yes, what is 'really' happening is that
negative charges ('electrons') are 'flowing'
(current) in a 'negative' direction
(from '-' voltage to '+' voltage). But since
the outcome is the same, and I find it REALLY
difficult to warp my mind that way, I
usually stick with the positive charges,
positive voltage, positive current convention.
--- In basicstamps@yahoogroups.com, "Steve Ziuchkovski"
<zman97211@y...> wrote:
> This is off-topic...
>
> I originally learned electronics from my father, who taught me
current flow
> from + to -.
>
> The Navy taught me the more "conventional" way of current flowing
from - to
> +.
>
> Electron flow vs. Hole flow.
>
> So, when a pin sources or sinks current, which terminology is being
used?
>
> Steve
>
>
Original Message
> From: "Allan Lane" <allan.lane@h...>
> To: <basicstamps@yahoogroups.com>
> Sent: Tuesday, July 15, 2003 8:20 PM
> Subject: [noparse][[/noparse]basicstamps] Re: BS2p-24 I/O pins requirements and 74xx
families.
>
>
> > I believe the lowest power, yet still TTL family,
> > is 74HCT. Some of the HCx family are NOT TTL
> > compatible, so be careful.
> >
> > The BS2 can source or sink 23 mA max per pin,
> > with a max for all pins of 50 mA.
> > (Which means: 2 pins at 23 mA, or 16 pins
> > at 3.125 mA each, etc). Note it
> > seems to 'sink' better than it 'sources',
> > if that matters to you.
> >
> > If you need more current, the 74HCT595 is
> > a very good SPI to parallel converter, with
> > more total power available.
> >
> > For Fan-Out, you need to find the input
> > resistance of the chips you want the BS2
> > to drive. For Fan-In, I believe the BS2's
> > inputs look like 10 Meg-ohm impedances --
> > someone may correct me on that.
> >
> > The big problem with BS2 is that because
> > it can drive so much current, if you tie
> > two drivers together and have them drive
> > in opposite directions, with no resistance
> > between them, it is easy to burn out a pin.
> >
> > The brute-force solution to this
> > problem is to put a 220 ohm
> > resistor in series with each pin which might
> > be tied to another driver. This will guarantee
> > that the current won't exceed 22mA, no matter
> > what states are active.
> >
> > I2C I don't know the answer to that one.
> >
> > --- In basicstamps@yahoogroups.com, "Alberto Calderara"
> > <albertocalderara@t...> wrote:
> > > Ciao,
> > >
> > > I'm sure that the problem has been discussed a lot af times...
But
> > it's not so friendly to me the matter about I/O pins current
> > requirements of the BS2p-24 that I'm trying to put inside my
circuit,
> > therefore I ask your help, dear friends, before I may cook my
> > precious Stamp!
> > >
> > > First thing: a simple rule for establishing the fan-out (and
fan-
> > in) of the Stamp's I/O pins?
> > >
> > > Second: what is the best choice about the logic family to
interface
> > with the Stamp? 74HC, 74LS or what else?
> > >
> > > Last: are the two I2C ports of the BS2p-24 (and BS2p-40)
limited to
> > a certain number of I2C devices connected to the same bus?
> > >
> > > Thanks in advance,
> > >
> > > Alberto.
> > >
> > >
> > > [noparse][[/noparse]Non-text portions of this message have been removed]
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the
Subject and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
However, the Navy still teaches negative current flow. Every time I see sink
or source I double-guess myself!
Steve
Original Message
From: "Allan Lane" <allan.lane@h...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, July 15, 2003 8:51 PM
Subject: [noparse][[/noparse]basicstamps] Sink vs. Source (Was, Re: BS2p-24 I/O pins
requirements and 74xx families.)
> The convention I use (and almost all documentation,
> I think even the Navy went back to 'positive') was
> that current flows from the '+' terminal to GND.
> Note that the current that flows is 'positive'
> current, that is, 'positive' charges flowing
> from '+' to '-'. The graphic for a diode have
> a little 'arrow', which points in the direction
> of 'positive' current flow.
>
> Having said that, a chip 'sinks' current when
> it provides a low-resistance path to ITS
> ground pin for a positive current, flowing
> from a '+' source of voltage. A chip
> 'sources' current when it provides a
> path for positive current from ITS
> VCC pin out through one of the chip's pins,
> to another device.
>
> And yes, what is 'really' happening is that
> negative charges ('electrons') are 'flowing'
> (current) in a 'negative' direction
> (from '-' voltage to '+' voltage). But since
> the outcome is the same, and I find it REALLY
> difficult to warp my mind that way, I
> usually stick with the positive charges,
> positive voltage, positive current convention.
>
> --- In basicstamps@yahoogroups.com, "Steve Ziuchkovski"
> <zman97211@y...> wrote:
> > This is off-topic...
> >
> > I originally learned electronics from my father, who taught me
> current flow
> > from + to -.
> >
> > The Navy taught me the more "conventional" way of current flowing
> from - to
> > +.
> >
> > Electron flow vs. Hole flow.
> >
> > So, when a pin sources or sinks current, which terminology is being
> used?
> >
> > Steve
> >
> >
Original Message
> > From: "Allan Lane" <allan.lane@h...>
> > To: <basicstamps@yahoogroups.com>
> > Sent: Tuesday, July 15, 2003 8:20 PM
> > Subject: [noparse][[/noparse]basicstamps] Re: BS2p-24 I/O pins requirements and 74xx
> families.
> >
> >
> > > I believe the lowest power, yet still TTL family,
> > > is 74HCT. Some of the HCx family are NOT TTL
> > > compatible, so be careful.
> > >
> > > The BS2 can source or sink 23 mA max per pin,
> > > with a max for all pins of 50 mA.
> > > (Which means: 2 pins at 23 mA, or 16 pins
> > > at 3.125 mA each, etc). Note it
> > > seems to 'sink' better than it 'sources',
> > > if that matters to you.
> > >
> > > If you need more current, the 74HCT595 is
> > > a very good SPI to parallel converter, with
> > > more total power available.
> > >
> > > For Fan-Out, you need to find the input
> > > resistance of the chips you want the BS2
> > > to drive. For Fan-In, I believe the BS2's
> > > inputs look like 10 Meg-ohm impedances --
> > > someone may correct me on that.
> > >
> > > The big problem with BS2 is that because
> > > it can drive so much current, if you tie
> > > two drivers together and have them drive
> > > in opposite directions, with no resistance
> > > between them, it is easy to burn out a pin.
> > >
> > > The brute-force solution to this
> > > problem is to put a 220 ohm
> > > resistor in series with each pin which might
> > > be tied to another driver. This will guarantee
> > > that the current won't exceed 22mA, no matter
> > > what states are active.
> > >
> > > I2C I don't know the answer to that one.
> > >
> > > --- In basicstamps@yahoogroups.com, "Alberto Calderara"
> > > <albertocalderara@t...> wrote:
> > > > Ciao,
> > > >
> > > > I'm sure that the problem has been discussed a lot af times...
> But
> > > it's not so friendly to me the matter about I/O pins current
> > > requirements of the BS2p-24 that I'm trying to put inside my
> circuit,
> > > therefore I ask your help, dear friends, before I may cook my
> > > precious Stamp!
> > > >
> > > > First thing: a simple rule for establishing the fan-out (and
> fan-
> > > in) of the Stamp's I/O pins?
> > > >
> > > > Second: what is the best choice about the logic family to
> interface
> > > with the Stamp? 74HC, 74LS or what else?
> > > >
> > > > Last: are the two I2C ports of the BS2p-24 (and BS2p-40)
> limited to
> > > a certain number of I2C devices connected to the same bus?
> > > >
> > > > Thanks in advance,
> > > >
> > > > Alberto.
> > > >
> > > >
> > > > [noparse][[/noparse]Non-text portions of this message have been removed]
> > >
> > >
> > > To UNSUBSCRIBE, just send mail to:
> > > basicstamps-unsubscribe@yahoogroups.com
> > > from the same email address that you subscribed. Text in the
> Subject and
> > Body of the message will be ignored.
> > >
> > >
> > > Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
> > >
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>