Am 30.04.2016 um 10:35 schrieb John Bass:
> OK, just had a read around the good old internet, and found other
> people with the same issue, down to power yet again..
>
> So popped another 1k in parallel thus 500ohms and now it works :-),
> but not reliable :-( getting the odd 85
>
> There is the issue is 500ohms too low for the bus etc...??
>
The limit is in the current the slaves may sink (for communication).
Their output transistors are rated 4mA, and 500 Ohms gives you 7mA,
that's too much for a DS18B20 (and many others).
Go as low as 1k at 3.3V. That gives you enough current to power the
slaves, good rise times, and a safety margin for slave's sinking capability.
Kind regards
Jan
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