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Topic: External Power Supply on RF 315/433 MHz Transmitter-receiver Module (Read 5744 times) previous topic - next topic

OldSteve

If you keep the sensor powered all the time, it will be destroyed in under a month.
I learned that from experience.  :smiley-confuse:
If you keep the sensor powered all the time, it will be destroyed in under a month.
I learned that from experience.  :smiley-confuse:
That quickly!
A good argument, then, for only powering it when needed. When Alex first mentioned damage if the unit was left powered, I was thinking in terms of the circuitry, hence my comments. Completely overlooked electrolysis. :(
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Whandall

I saved the destroyed headers, but I could not find them right now to show you the remains.

After less than a month only the pcb remained, the copper including plating was gone.
Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of. (D.Adams)

OldSteve

I saved the destroyed headers, but I could not find them right now to show you the remains.

After less than a month only the pcb remained, the copper including plating was gone.
Ah right, I hadn't realised the probes were just normal copper-clad PCB. (I just had a close look at the pic that Alex posted, and his is the same.) Knowing that, I can see how the life would be short. I've seen electrolysis used for etching PCBs, too, and it's fairly fast. I forget exactly what voltage was used, but I have the circuit here somewhere in my magazine collection.

I guess that something more substantial would be better for the probes, then, especially if it was to be continually powered. Short lengths of copper rod, maybe, like the rod that's driven into the ground for an electrical earth rod.
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Whandall

Platinum, gold, nickel or stainless steel would be much better than tin plated copper, or a copper wire.

The dissolved copper could probably even damage the plant you are monitoring.

My bonsai survived one dissolved sensor as yet.  ;)
Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of. (D.Adams)

OldSteve

The dissolved copper could probably even damage the plant you are monitoring.
Possibly, if enough sensors were dissolved into the soil, but I think that many plants are reasonably tolerant to copper, since it's sold as a fungicide for use on plants:-
Quote
ACTIVE CONSTITUENT: 93g/L COPPER (Cu) present as Copper Ammonium Complex
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DrAzzy

Platinum, gold, nickel or stainless steel would be much better than tin plated copper, or a copper wire.
Sad that all they'd need to do is spring for ENIG and the sensors would stop destroying themselves...
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OldSteve

Sad that all they'd need to do is spring for ENIG and the sensors would stop destroying themselves...
I thought about that, but wouldn't such a thin layer scratch easily when pushed into and removed from the soil a few times, especially if there were sharp, hard pebbles, then begin to corrode from the scratches?
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aarg

I think you can do moisture sensing by measuring capacitance. Then you don't have to expose metals to the soil.
  ... with a transistor and a large sum of money to spend ...
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OldSteve

I think you can do moisture sensing by measuring capacitance. Then you don't have to expose metals to the soil.
But doesn't something metallic still have to be in contact with the soil to measure capacitance?
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