1-Wire Stuff (again, sorry)
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Posts: 46,084
Hi,
I've been looking into this 1-wire stuff, like many I'm interested in
getting the temperature form around the house.
I've found some code that Jon williams wrote (appeared in Nuts N
Volts April 2001?).
The code does a number of things, the most interesting for me is the
actual 'proper' search for devices.... none of that "plug 1 device in
and write down the device serial number".
I also found the "Plus pack app kit" pdf which, I think, was a
forerunner of the April code (now I've just double checked and it
isn't - LOL)...
The thing that stuck me was that in the diagram for connecting 2
DS1822s' in the "plus pack" pdf is that there is only one resistor,
is that correct? or should I be putting on in for each 1822? or is it
because the distance between the 2 1822's is so small only one is
needed?...
many thanks
Andy
I've been looking into this 1-wire stuff, like many I'm interested in
getting the temperature form around the house.
I've found some code that Jon williams wrote (appeared in Nuts N
Volts April 2001?).
The code does a number of things, the most interesting for me is the
actual 'proper' search for devices.... none of that "plug 1 device in
and write down the device serial number".
I also found the "Plus pack app kit" pdf which, I think, was a
forerunner of the April code (now I've just double checked and it
isn't - LOL)...
The thing that stuck me was that in the diagram for connecting 2
DS1822s' in the "plus pack" pdf is that there is only one resistor,
is that correct? or should I be putting on in for each 1822? or is it
because the distance between the 2 1822's is so small only one is
needed?...
many thanks
Andy
Comments
andy@h... writes:
> The thing that stuck me was that in the diagram for connecting 2
> DS1822s' in the "plus pack" pdf is that there is only one resistor,
> is that correct? or should I be putting on in for each 1822? or is it
> because the distance between the 2 1822's is so small only one is
>
One resistor is correct. It is the required pull-up for the 1-Wire bus.
Typically, this resistor will have a value of 4.7k, but some circumstances
will force it to become even "stiffer." I just submitted an article to N&V
about a 1-Wire weather station. Due to the cable and it's length, I had to
change the 1-wire bus pull-up to 1k.
-- Jon Williams
-- Parallax
[noparse][[/noparse]Non-text portions of this message have been removed]
So, the next question is... is there such a thing as a variable
resistor IC? The thought being that it would 'automatically' adjust
itself so that the signal would be ok if I happened to plug in a
longer cable??
Andy
--- In basicstamps@y..., jonwms@a... wrote:
> One resistor is correct. It is the required pull-up for the 1-Wire
bus.
> Typically, this resistor will have a value of 4.7k, but some
circumstances
> will force it to become even "stiffer." I just submitted an
article to N&V
> about a 1-Wire weather station. Due to the cable and it's length,
I had to
> change the 1-wire bus pull-up to 1k.
>
> -- Jon Williams
> -- Parallax
>
andy@h... writes:
> So, the next question is... is there such a thing as a variable
> resistor IC? The thought being that it would 'automatically' adjust
> itself so that the signal would be ok if I happened to plug in a
> longer cable??
>
Dallas Semiconductor makes digital pots, but I wouldn't go through that much
trouble. Select your pull-up resistor for the worst-case scenario.
-- Jon Williams
-- Parallax
[noparse][[/noparse]Non-text portions of this message have been removed]
> > resistor IC? The thought being that it would 'automatically' adjust
> > itself so that the signal would be ok if I happened to plug in a
> > longer cable??
> >
>
>Dallas Semiconductor makes digital pots, but I wouldn't go through that much
>trouble. Select your pull-up resistor for the worst-case scenario.
I agree it would be best to select for worst case, as there is really
no down side to using a 1k pullup instead of 4.7k. So the following
would be silly, but one _could_ do it. Use a normal 4.7k pullup, but
also connect a 1k to another BS2 pin configured as an input. If the
data link fails, then turn that pin into a high output, and try
again.
-- Tracy