Extending wiring for grow moisture sensor

I’m using the grow hat in my greenhouse and one moisture sensor will be about 2m from the pi zero. I grabbed some wire (22 AWG solid core from the pimironi shop), snipped a 35cm connector wire in half and extended it using some solder-shrink connectors.
The problem is that when I plug it into the pi, the moisture sensor gets quite hot and the pi does not boot - it’s obviously drawing too much current. I don’t really understand why though and don’t really know how to solve it.
I’ve checked the obvious - the wires are not crossed. I checked the resistance pin to pin and on each wire it is 0.5 ohm. I know the higher resistance will cause more current but I wouldn’t have though 0.5 ohm was too bad. I guess it could be an induction issue - maybe solid core is a bad idea.

Anyone have any ideas?



I’d say you got your wires crossed.
Pin 1 to pin 3, and pin 3 to pin 1 most likely.
Pin 1 is Ground and Pin 3 is 3.3V.

That’s what you would think but I’ve checked them multiple times and also used a multi meter to check connectivity end to end. I’ll ask someone else to recheck today :)

Oh wait I’m an idiot. I’m thinking these are the same but of course it needs to be a mirror image because the cable is turned 180 degrees.

Check the continuity of a cable you haven’t modified.
You may find it goes something like this.
< 1-------1 >
< 2-------2 >
< 3-------3 >
And look at the jacket on the wires, see if one has a dot, or strip as a marker on it.

See my comment above - they are crossed because in the pic the red and white should be on opposite sides. When lining up connectors like that the left and right swap. I just wasn’t thinking straight last night :)
It’s obvious now in the morning. Your comment to check again helped. Thank you.

Thats what I was thinking. ;)
If you cut, then turn one end 180, it ends up like this



There are extender cables for the pumps? Don’t see any for the sensors though, other than a longer version of the stock cables.
3-pin JST-SH cables for Grow moisture sensors (pack of 3) – 1m (pimoroni.com)

Rewired it this evening and it all works now. I just need to run the pumps via a relay with their own psu because the length of tube means they draw more power than the pi can provide.

Next question … somewhat speculative is that I need more than 3 pumps and sensors. Anyone got any suggestions for multiplexing? Im going to have more sensors than gpio pins so need a solution where I can address multiple sensors on a few pins.

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Lengthening the cables won’t increase the current draw / power required. It can reduce the voltage that reaches the pumps due to extra resistance. That short of a run shouldn’t affect things, voltage / current wise?

But, the higher up your plants are from the tank of supply water, the harder it is for the pumps to pump the water up hill. It’s a lot easier to pump the water horizontally than vertically. ;)

Yeah is the tube length. It’s about 6 feet long and has a number of droppers in it so needs quite a bit if pump power. I’m driving it via a relay with its own power source and that works fine.

Also answering my own question I think this will work for a mux SparkFun Analog/Digital MUX Breakout - CD74HC4067

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