Argon 3.7V Battery Power vs. USB

I have a project to help me detect water in the basement. I have both an Argon & Proton. Both are wired the same to D0 and a ground (a wire on each). When you put the 2 wires in water, they are supposed to send an alarm notification.

I recently added an Argon for the capability of using a 3.7V Lithium Ion battery backup if power goes off. I had the code running on a Proton with the USB. When I installed the code on the Argon and use USB, all works fine (although more sporadic than Proton). However, when I run the Argon on battery only (3.7V LI), it doesn’t work. You can touch the 2 wires together on battery power only and it sends the alarm. Stick the 2 wires in water on battery power, they don’t send the alarm.

I suspect it has something to do with the amount (extra) power output by the USB but I’m lost as to how I can fix this. I’m looking for some advice on how to make this work on battery power.

Thanks in advance for your ideas!

We can’t see your code, so I’d have to ask: Are you using pinMode(D0, INPUT_PULLUP)?
If you do, the conductivity of the water may be too little to trigger the input.
What happens when you put the wires into a glass of water and gradually add salt?
Clean water isn’t really that good of a conductor. You may need a stronger pull-up (lower resistance) to drive a higher current to actually produce a detectable voltage drop.

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As an alternate approach - this product provides more sensitivity and will work down at 3V3

or a bit more pricey but has a buzzer and additional IO

however you will need to use this (or similar) level translator as it is a 5V only device

@ScruffR, You are absolutely spot on with the conductivity. I had just come to the same line of thinking this morning, so I added a bit of salt to the water in the cup, then tried it. It now consistently reads the presence of water. This is supposed to work in a sump pump so I may have to consider @shanevanj’s suggestions (can’t add salt to the sump pump pit).:wink:

@ScruffR, I’m not an electrical engineer, so would you add a resistor between the wire from the D0 and the water and if so, what size or how do I determine a good size?

Thank you both!

A pull-up resistor would look like this


For the Argon Vcc should come off the 3v3 pin to prevent damaging the input pin when no current flows. 4k7 would be a good value, but you could go down to 1k.
In your case the switch would be the presence/absence of water.

@ScruffR, Your diagram seems very clear but I admit, I’m not an engineer with the hardware. But, let me see if I understand correctly.

I’ve run a wire from the 3V3 pin on the Argon (with the 4.7K resistor) to a blank pin on the breadboard (to get some place to work with connecting wires). I jump wired the D0 pin to a blank pin to the right of the 3V3 wire on the breadboard. I hooked a wire next to the D0 wire and this runs to the switch. When I complete the circuit in the water, it doesn’t work. If I remove the 3V3 wire, it works. I even switched the 3V3 and D0 wires places and still doesn’t work. What am I messing up?

And, I used the sump pump water, so I’m getting a better conductivity as well, so it does work without the 3V3 now. I tried distilled water and it doesn’t work.

Thanks for your help!