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I was going to do my first project of temperature monitor , so I was making list what would I need , I discovered that temperature sensor to raspberry pi jumper cables are small in length, my raspberry box is lying near TV under table which is not ideal place for tempearature sensor to be placed. enter image description here is it possible to have longer wire connecting on GPIO of raspberry pi ?

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  • Please edit your question and include which temp sensor you are using? Which protocol it uses to communicate, and what you mean by short and long? – Steve Robillard Aug 22 '16 at 11:51
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The simple answer is it won't hurt to try anything. Signal loss is a product of resistance, and all conductors have some inherent resistance, which decreases with the wire thickness (gauge) and increases with its length. So if the wire is too long or otherwise includes too much resistance to work, it simply won't work, and no harm done.

Anecdotally, I'll say than several segments of commonplace 22 or 24 gauge copper strand jumper connected together for several feet work fine. However, you can easily calculate the voltage drop using Ohm's law if you know the current load and approximate size of the wire you're using. If you are not sure, assume 24 gauge since it won't be smaller than that. From the picture I would guess those wires are stranded copper with the ends tinned, although aluminum is sometimes used too.

Anyway, this online voltage drop calculator, which includes a chart of resistances for wires of different types so you can do the math yourself if you want, claims that at the load stipulated on the Adafruit product page (2.5 mA), at 3.3V 5 feet of 24 gauge copper strand will drop the voltage by 0.03%, i.e., not enough to be relevant.

In fact, judging by that, presuming the idealized context such calculations tend to presume, you would need close to a thousand feet of such wire before the voltage at that load would drop enough (say 5%) to become most likely infeasible. Although since the device will work with 3, with a drop to 3.1V on the way out, the drop to 2.9 on the way back would still be feasible on the pi if it is consistent since I believe that still counts as above the "high" threshold for signals.

In real life I have no idea how reliable that estimate is, but presuming you mean you just want to insert a few feet of wire, it should be fine. You can use heavier gauge speaker wire to connect actual jumpers, since it is easier to find in rolls and offers less resistance. This is probably better than connecting more multiple segments as each connection could introduce an unpredictable amount of resistance.

why jumper wire are small length?

Convention, convenience, and efficiency would be the obvious answer. How long should they be? If I sell you a $5 device with 10' of lead on it, a significant portion of the cost will be that wire and 99% of users are just going to chop it and save (or throw away!) the extra wire. You need enough to keep it simple to use and that's it. 9" is plenty; if you want more you can attach more.

Obviously just don't keep wrecking the ends and cutting the wire down until you have none left, although even if you do likely you can open this up and solder some to whatever's inside easily enough. If you solder the wires together (note you may not need to, although stripping and twisting thin wire may break if you do it repeatedly -- a caveat about soldering is it will tend to melt the plastic unless you can cleverly sink the heat before it gets there), desoldering braid and a magnifying glass will help get it apart.

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