Am 01.11.2016 um 16:10 schrieb Markus Gaugusch:
>
> 1.) Which value should the pull-up resistor have? I found a posting from
> Jan that 4k7 is wrong, although this value can be found everywhere.
>
The slave chips can sink 4mA. This means at 3.3V, the pullup can go down
as low as 825Ω without damaging the chips. I recommend using 1.5kΩ.
A smaller pullup means working against the capacity of long cables to
achieve a fast raise time. Second, any pullup delivering more than a
continous 1mA allows you to forget about the "strong pullup" needed
otherwise for the DS1820 and other power-hungry chips.
The 4.7kΩ pullup replicated again and again without thinking gives you
700µA at 3.3V only, which leads to slower raise-times and will not
suffice powering a DS1820 during temperature conversion.
> Which pull-up should I use? And do I need pullup=1 for the w1 dtoverlay?
>
You don't need the active pullup when you use the 1.5kΩ pullup.
>
> 2.) The pull up resistor is connected to 3V3, correct?
>
Sure. You have a 3.3V GPIO output, so you have to pullup to 3.3V. If you
pullup to 5V, you fry the GPIO.
> 3.) Regarding owfs I found the last posting from Jan from 2016-10-29 which
> should get me up and running quickly :)
>
Remember you need owfs-3.1p1 for using --w1 on linux-3.16rc1 or later.
Kind regards
Jan
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