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How long can a jst3aa wire be


#1

Hello,
I am using the fez panda 1, fez component shield and seeedstudio moisture sensor. Because the seeedstudio mositure sensor has a wired grove connection Iextended the wire and connected it to the fez component shield. How long could the wire be.
Thank You,


#2

It can be infinetely long. But the real question is how long can it be before the results returned by the sensor are no longer accurate.

If you think about what you’re doing, you’re adding capacitance and resistance to the circuit. You’ll see a voltage drop because of the resistance change - although how much you would have to test. Then you can do some maths to compensate if needed.

How long do you NEED to extend it? Why don’t you propose it, or better still, do an experiment. Measure the value from the sensor on its standard wire in a known situation, then check again with your extended wire.


#3

Thank You,


#4

FWIW Brett - nice answer.

Regarding the last part, as I am also a HW n00b, there may be a reluctance to try things for fear of breaking things. Your answer explained what would happen, rather than just saying give it a try and find out.

Because FEZ makes it easy for software guys to play around with hardware, there’s quite a few posters without an electronics background. I know it’s not always easy for HW l33t guys to answer simple questions, but the way it’s done is very helpful (speaking for myself).

I appreciate this forum, not just for GHI’s amazing support, but all the helpful people on here.


#5

After my initial post I was thinking about this specific sensor as well, and wondered what your intended use for this would be. When I thought about it, there’s a chance this is one of two things - a plant sensor that says to water it, or a rain sensor that says if the lawn is too wet, don’t turn the sprinkler on. In those scenarios, I would expect you’re going to set some arbitrary value as your threshold (with potentially a fuzz-factor, I don’t know how repeatable readings are?), so adding a hunk of extra wire is probably not going to significantly change the returned value, and given there’s not really a definite line that says it’s too wet or dry (well I expect that’s the case) you may just need to drop your set-point to adjust. Should be relatively simple.


#6

I am just using it for a plant sensor.
@ mhectorgato thats 100% true.