Dallas 1 wire support

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john0101
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Dallas 1 wire support

Unread post by john0101 » Wed Sep 25, 2019 10:35 pm

I'm trying to work through the 1 wire DS 1820 temperature sensor example shown on the Wiki
I have set up several of these on Raspberry PI's but the issue of the gpio's on XU4 only generating 1.8v and the need to go with a level shifter has made it more complex

I am not an electronics expert by any means and only a modest logical developer
I have difficulty with the breadboard diagram on the wiki
the area circled and arrowed is what puzzles me (without a formal wiring diagram) as it seems to show the gnd and v terminals of the DS1820 shorting the pins 1 & 2 on the GPIO
Image

on the usual DS1820 there are 3 wires gnd 5v and data
I presume in this diagram the central pin is the data which connects to the v supply via 4.7k resistor (this is as my rasp pi
BUT the other 2 pins appear to connect to both the +
'+' and the gnd eh???
that surely cannot be? Are they shown connecting to both '+' rail and 'gnd' rail because polarity is unimportant ? in other words one goes '+' and the other gnd but not both to both ??
Sorry this is a very newby question but the image is very very ambiguous and I know just enought that '+' and 'gnd' should not be shorted

Can any kind soul help with a simple explanation ?

PS the other diagrams showing a set up for parasitic power , external power and multiple DS1820s in parallel are also very unhelpful as the do not show the gpio connections

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odroid
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Re: Dallas 1 wire support

Unread post by odroid » Thu Sep 26, 2019 9:00 am

I believe 1-wire devices can be powered from the data pin alternatively. The other 2 pins connect to both the GND. So there is nothing wrong in the schematics probably.
And you can use multiple 1-wire devices with a single GPIO.
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john0101
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Re: Dallas 1 wire support

Unread post by john0101 » Fri Sep 27, 2019 5:02 pm

thanks
Ok I can see that if both gnd and+ wires on the 1820 are connected to gnd there is no short - I wasnt aware they could work like that but the diagram IS breadboard image IS ambiguous
I cannot understand the wiring diagrams as I have little on the xu to relate to the labels

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