I'ld like to play with an SD card and a 16F886 or'690 or so.
Where can I get an SD card reader to, say, SPI?

On Dec 29, 4:24 pm, sdeyo...@hotmail.com wrote:
> I'ld like to play with an SD card and a 16F886 or'690 or so.
> Where can I get an SD card reader to, say, SPI?

Most SD cards can be accessed slowly in SPI mode with no adapter
needed, something they inherited from the older MMC cards.  This spec
is published.  To get the details for implementing the full 4-bit
protocol of SD you have to pay money.   But if you are bridging to spi
anyway, why bother?

Of potential greater software concern is parsing a file system
especially on a system with limited ram.  Nobody says you have to use
a traditional one - you can just treat it as a buffer of bytes.  But
if you do that and want to also access it from a PC, you will need a
setup for raw access to the device - easy under linux, a bit harder
under windows but still possible.

Usual places like digikey have the card slots.  Or you can salvage one
out of a cheap reader.  Or you can solder wires directly to a cheap
card.  Last time I mentioned that, someone said he buys micro-SD cards
and solders wires to the adapter.

<c...@hotmail.com> schreef in berichtnieuws
8...@e24g2000vbe.googlegroups.com...

> On Dec 29, 4:24 pm, sdeyo...@hotmail.com wrote:
> > I'ld like to play with an SD card and a 16F886 or'690 or so.
> > Where can I get an SD card reader to, say, SPI?

> Last time I mentioned that, someone said he buys micro-SD
> cards and solders wires to the adapter.

:-D  Which is exactly what I've done and would have suggested would I not
have read your reply.  Actually, I used a pin-stripe so I could plug the
adapter into a breadboard (to be able to easily experiment with it)

Take care though, as MicroSD cards run on voltages near 3v, and will be
fried if-and-when you connect them to 5v systems.

Allso, do *not* use a simple diode to step-down the voltage if you are
working with a 5v system (something I've seen in several schematics found on
the Web).  The current the different MicroSD cards use varies wildly, and
the varying voltage-drop by the diode could mean you can send some commands
but that the actual reading or writing of the memory fails (due to the
larget power consumption).

Regards,
  Rudy Wieser

"R.Wieser" <a...@not.available> wrote in message 
news:4959ed05$0$5129$e...@dreader23.news.xs4all.nl...
>
> <c...@hotmail.com> schreef in berichtnieuws
> 8...@e24g2000vbe.googlegroups.com...
>
>> On Dec 29, 4:24 pm, sdeyo...@hotmail.com wrote:
>> > I'ld like to play with an SD card and a 16F886 or'690 or so.
>> > Where can I get an SD card reader to, say, SPI?
>
>> Last time I mentioned that, someone said he buys micro-SD
>> cards and solders wires to the adapter.
>
> :-D  Which is exactly what I've done and would have suggested would I not
> have read your reply.  Actually, I used a pin-stripe so I could plug the
> adapter into a breadboard (to be able to easily experiment with it)
>
> Take care though, as MicroSD cards run on voltages near 3v, and will be
> fried if-and-when you connect them to 5v systems.
>
> Allso, do *not* use a simple diode to step-down the voltage if you are
> working with a 5v system (something I've seen in several schematics found 
> on
> the Web).  The current the different MicroSD cards use varies wildly, and
> the varying voltage-drop by the diode could mean you can send some 
> commands
> but that the actual reading or writing of the memory fails (due to the
> larget power consumption).

You have to explain this comment to me.  The voltage drop on a diode once 
you forward bias it should be pretty constant.  In a worst case a diode or 
two plus a load resistor to ensure that minor current at least always flows 
should be OK.  For example, at 3V, it seems like at 10K resistor in parallel 
with the card should do it.

Give me more info.  I don't understand how what you say is possible. 

Hello Jujitsu,

> You have to explain this comment to me.  The voltage drop on a diode
> once you forward bias it should be pretty constant.

Most of the schematics did put the diodes (two of them) directly at VCC of
the card.  This means that the bias current flowing is equal to the current
thru the card.  And that is *way* to low.

Even with a LED & resistor as a dummy-load over the card (taking/wasting
about 15 ma) the voltage varied to much to be of use.    I've even tried to
enlarge the bias-current to way above that and use three diodes instead of
two to account for the lesser voltage-drop per diode.   It just would not
work.

In the end I just took a simple one transistor, zenerdiode and resistor
solution, which works fine up until this moment.

Hope that clarifies it

Regards,
  Rudy Wieser


-- Origional message
Jujitsu Lizard <j...@gmail.com> schreef in berichtnieuws
i...@giganews.com...
> "R.Wieser" <a...@not.available> wrote in message
> news:4959ed05$0$5129$e...@dreader23.news.xs4all.nl...
> >
> > <c...@hotmail.com> schreef in berichtnieuws
> > 8...@e24g2000vbe.googlegroups.com...
> >
> >> On Dec 29, 4:24 pm, sdeyo...@hotmail.com wrote:
> >> > I'ld like to play with an SD card and a 16F886 or'690 or so.
> >> > Where can I get an SD card reader to, say, SPI?
> >
> >> Last time I mentioned that, someone said he buys micro-SD
> >> cards and solders wires to the adapter.
> >
> > :-D  Which is exactly what I've done and would have suggested would I
not
> > have read your reply.  Actually, I used a pin-stripe so I could plug the
> > adapter into a breadboard (to be able to easily experiment with it)
> >
> > Take care though, as MicroSD cards run on voltages near 3v, and will be
> > fried if-and-when you connect them to 5v systems.
> >
> > Allso, do *not* use a simple diode to step-down the voltage if you are
> > working with a 5v system (something I've seen in several schematics
found
> > on
> > the Web).  The current the different MicroSD cards use varies wildly,
and
> > the varying voltage-drop by the diode could mean you can send some
> > commands
> > but that the actual reading or writing of the memory fails (due to the
> > larget power consumption).
>
> You have to explain this comment to me.  The voltage drop on a diode once
> you forward bias it should be pretty constant.  In a worst case a diode or
> two plus a load resistor to ensure that minor current at least always
flows
> should be OK.  For example, at 3V, it seems like at 10K resistor in
parallel
> with the card should do it.
>
> Give me more info.  I don't understand how what you say is possible.

On Jan 1, 6:28=A0am, "R.Wieser" <addr...@not.available> wrote:
> Hello Jujitsu,
>
> > You have to explain this comment to me. =A0The voltage drop on a diode
> > once you forward bias it should be pretty constant.
>
> Most of the schematics did put the diodes (two of them) directly at VCC o=
f
> the card. =A0This means that the bias current flowing is equal to the cur=
rent
> thru the card. =A0And that is *way* to low.
>
> Even with a LED & resistor as a dummy-load over the card (taking/wasting
> about 15 ma) the voltage varied to much to be of use. =A0 =A0I've even tr=
ied to
> enlarge the bias-current to way above that and use three diodes instead o=
f
> two to account for the lesser voltage-drop per diode. =A0 It just would n=
ot
> work.
>
> In the end I just took a simple one transistor, zenerdiode and resistor
> solution, which works fine up until this moment.
>
> Hope that clarifies it

No, in fact something is very wrong.  When you say that you enlarged
the bias crrent and added another diode "to account for the lesser
voltage drop per diode", that is a bit like a friend who would say "I
cut this board off three times and it's *still* too short!"

Do I misunderstand what you are saying?  The voltage drop across a
diode shouldn't vary a lot (depending on the definition of "a lot") if
you double the current.  So if your design uses 10 mA and you add a
resistor to draw 10 mA of current, you should see a fairly stable
voltage as the design current changes between 0 and 10 mA.  If you
have a much wider range of current you need to add a small regulator.
A zener diode can be used instead of a regulator.  It makes the
circuit draw a constant current that must be more than the max of the
design without the zener.  Are you familiar with zener regulator
circuits?

Rick

Hello rickman,

> No, in fact something is very wrong.  When you say that you
> enlarged the bias crrent and added another diode "to account
> for the lesser voltage drop per diode", that is a bit like a friend
> who would say "I cut this board off three times and it's *still*
> too short!"

Hmm ... I can only tell you what I observed.  When using a larger current
the voltage over the diodes dropped.  Same as with the parallel
stabilisation I also tried.

> Do I misunderstand what you are saying?  The voltage drop
> across a diode shouldn't vary a lot (depending on the definition
> of "a lot") if you double the current.  So if your design uses 10
> mA and you add a resistor to draw 10 mA of current, you should
> see a fairly stable voltage as the design current changes between
> 0 and 10 mA.

On a system which defines its supply-voltage in tenths of a volt (the
MicroSD card) a drop of 0.05 volts is a lot, and 0.1 volts a full step on
its scale.

The voltage-change I observed was in that order.  Enough to make the card
switch itself off.

Allso, the card itself draws less than a single mA when the memory is not
accessed, but can draw upto 50 mA when doing so (probably write-mode, the
data-sheets do not specify)

> Are you familiar with zener regulator circuits?

I think so.

Regards,
  Rudy Wieser

P.s.
Looking tru my stored info regarding the specifics to the current-draw I
noticed your name on a post from back in 25-11-2006 (3.3v <> 5v interfacing
@ 15Mhz) :-)

-- Origional message

rickman <g...@gmail.com> schreef in berichtnieuws
7...@b1g2000yqg.googlegroups.com...

No, in fact something is very wrong.  When you say that you enlarged
the bias crrent and added another diode "to account for the lesser
voltage drop per diode", that is a bit like a friend who would say "I
cut this board off three times and it's *still* too short!"

Do I misunderstand what you are saying?  The voltage drop across a
diode shouldn't vary a lot (depending on the definition of "a lot") if
you double the current.  So if your design uses 10 mA and you add a
resistor to draw 10 mA of current, you should see a fairly stable
voltage as the design current changes between 0 and 10 mA.  If you
have a much wider range of current you need to add a small regulator.
A zener diode can be used instead of a regulator.  It makes the
circuit draw a constant current that must be more than the max of the
design without the zener.  Are you familiar with zener regulator
circuits?

Rick

On Jan 1, 5:09=A0pm, "R.Wieser" <addr...@not.available> wrote:
> Hello rickman,
>
> > No, in fact something is very wrong. =A0When you say that you
> > enlarged the bias crrent and added another diode "to account
> > for the lesser voltage drop per diode", that is a bit like a friend
> > who would say "I cut this board off three times and it's *still*
> > too short!"
>
> Hmm ... I can only tell you what I observed. =A0When using a larger curre=
nt
> the voltage over the diodes dropped. =A0Same as with the parallel
> stabilisation I also tried.

When you say larger current, was this the current through the diodes
or in parallel with the diodes?  If it was through the diodes, maybe
you are using a tunnel diode with negative resistance...


> On a system which defines its supply-voltage in tenths of a volt (the
> MicroSD card) a drop of 0.05 volts is a lot, and 0.1 volts a full step on
> its scale.

What is "a lot" depends on the spec.  What is the voltage tolerance
stated in the spec?  If you are talking about a 3.3 volt supply, they
are typically 5% and sometimes 10%.  That would be 0.15 volts + or -.
Anything within this range is completely acceptable.


> The voltage-change I observed was in that order. =A0Enough to make the ca=
rd
> switch itself off.

Exactly what voltage did you measure?  Even if you are outside of the
spec'd voltage range, devices like this seldom cut off right at the
stated limit.

I am not recommending diodes to drop the supply voltage for a logic
device, but they should work in many applications.  However, there is
nothing wrong with using a simple three terminal regulator.  They are
cheap, small and simple.

One place where a diode is perfect for power supply voltage adjustment
is when using a CMOS switch as a voltage shifter.  The supply voltage
on the switch chip needs to be above 3.3 volts and 5 volts is a bit
too much.  4.3 volts is about perfect to allow the switch to pass 3.3
volt signals while limiting the output from rising much above 3.3
volts.  However, the chips I use have the diode on the inside.


> Allso, the card itself draws less than a single mA when the memory is not
> accessed, but can draw upto 50 mA when doing so (probably write-mode, the
> data-sheets do not specify)
>
> > Are you familiar with zener regulator circuits?
>
> I think so.

Oh, I read back and see a zener is what you used.

> P.s.
> Looking tru my stored info regarding the specifics to the current-draw I
> noticed your name on a post from back in 25-11-2006 (3.3v <> 5v interfaci=
ng
> @ 15Mhz) :-)

Yes, is that post relevant?

Rick

Hello rickman,

>When you say larger current, was this the current through
> the diodes or in parallel with the diodes?  If it was through
> the diodes, maybe you are using a tunnel diode with negative
> resistance...

When using the parallel stabilisation I only measured the voltage over them
(as that is what I was interrested in).  In that case the larger
current-draw (1mA -> 30~50 mA) by the card ment so much voltage-drop over
the resistor (in series with the diode//Card) that nothing was left to work
with.

The diodes I used where all 1N4148.

> Exactly what voltage did you measure?

I'm not quite sure anymore, but the voltage dropped from somewhere around
3.1v to a bit below 2.9v . Thats at least a a 0.2v variation.

> However, there is nothing wrong with using a simple three
> terminal regulator.  They are cheap, small and simple.

*If* you can get them in small ( <10 ) quantities.  I could not, so a basic
one transistor solution was what I had to fall back upon.

> Oh, I read back and see a zener is what you used.

In the course of testing I tried zeners as well as simple diodes.  The final
solution (using a transistor) uses a 3v9 zener.

>> Looking tru my stored info regarding the specifics to the
>> current-draw I noticed your name on a post from back in
>> 25-11-2006 (3.3v <> 5v interfacing @ 15Mhz) :-)
>
> Yes, is that post relevant?

Not for the current discussion, but it did help me to with what to do for
the signals themselves.

Regards,
  Rudy Wieser


-- Origional message
rickman <g...@gmail.com> schreef in berichtnieuws
6...@33g2000yqm.googlegroups.com...
On Jan 1, 5:09 pm, "R.Wieser" <addr...@not.available> wrote:
> Hello rickman,
>
> > No, in fact something is very wrong. When you say that you
> > enlarged the bias crrent and added another diode "to account
> > for the lesser voltage drop per diode", that is a bit like a friend
> > who would say "I cut this board off three times and it's *still*
> > too short!"
>
> Hmm ... I can only tell you what I observed. When using a larger current
> the voltage over the diodes dropped. Same as with the parallel
> stabilisation I also tried.

When you say larger current, was this the current through the diodes
or in parallel with the diodes?  If it was through the diodes, maybe
you are using a tunnel diode with negative resistance...

> On a system which defines its supply-voltage in tenths of a volt (the
> MicroSD card) a drop of 0.05 volts is a lot, and 0.1 volts a full step on
> its scale.

What is "a lot" depends on the spec.  What is the voltage tolerance
stated in the spec?  If you are talking about a 3.3 volt supply, they
are typically 5% and sometimes 10%.  That would be 0.15 volts + or -.
Anything within this range is completely acceptable.

> The voltage-change I observed was in that order. Enough to make the card
> switch itself off.

Exactly what voltage did you measure?  Even if you are outside of the
spec'd voltage range, devices like this seldom cut off right at the
stated limit.

I am not recommending diodes to drop the supply voltage for a logic
device, but they should work in many applications.  However, there is
nothing wrong with using a simple three terminal regulator.  They are
cheap, small and simple.

One place where a diode is perfect for power supply voltage adjustment
is when using a CMOS switch as a voltage shifter.  The supply voltage
on the switch chip needs to be above 3.3 volts and 5 volts is a bit
too much.  4.3 volts is about perfect to allow the switch to pass 3.3
volt signals while limiting the output from rising much above 3.3
volts.  However, the chips I use have the diode on the inside.

> Allso, the card itself draws less than a single mA when the memory is not
> accessed, but can draw upto 50 mA when doing so (probably write-mode, the
> data-sheets do not specify)
>
> > Are you familiar with zener regulator circuits?
>
> I think so.

Oh, I read back and see a zener is what you used.

> P.s.
> Looking tru my stored info regarding the specifics to the current-draw I
> noticed your name on a post from back in 25-11-2006 (3.3v <> 5v
interfacing
> @ 15Mhz) :-)

Yes, is that post relevant?

Rick

Try these 3:

http://www.sparkfun.com/commerce/product_info.php?products_id=7832

http://www.sparkfun.com/commerce/product_info.php?products_id=204

http://www.sparkfun.com/commerce/product_info.php?products_id=8567





<s...@hotmail.com> wrote in message 
news:o...@4ax.com...
> I'ld like to play with an SD card and a 16F886 or'690 or so.
> Where can I get an SD card reader to, say, SPI?