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Friday, December 13, 2013

Tested New Water Detection Circuit

I worked on the Home Environmental Sensor Array at the Milwaukee Makerspace tonight.

First, I made a bit more progress on the enclosure.  I took some wire connectors off of some junk in the hack rack at the 'space and installed them in the bottom of the enclosure.  They will be used for the water sensor wires.  I'm not sure that this will be the long-term solution but for now, it is a semi-permanent way to connect the wires.

I had to move the power cable to another opening to make room for one of the connectors.

I am thinking that I will add a male 120v power connector to the right side of the enclosure.  I might also add a CAT5 network connection for the network cable.   Finally, it would be a good idea to have a whole strip of in and out connectors for the other sensors.  Tom G., another Maker, was at the 'space tonight working on circuit boards for a sensor board he is making.  He is using RJ11 jacks as inputs for his circuit plugs.  Maybe that would work for me as well.

After getting the HESA setup in the enclosure, I tested the simplified circuit that my nephew, Jason suggested.  It is the same circuit that I started out with in the beginning--the Raspberry pi sends power out one wire and looks for power coming back in a second wire.  The difference now is that I have the Raspberry pi creating a pull-down resistor on the input side.  The pull-down resistor ensures that any ambient current goes to ground and does not trigger a false reading.  In other words, the input current is always 0 volts until the real current comes across it.

I ran several experiments on the new circuit to make sure it works.

Experiment #1: Ran the HESA water detection program without connecting the leads.  It basically
continually sends power out one wire and looks for a signal on the other.  The program ran for about fifteen minutes.  I never got a false reading.  Success!

Experiment #2: I put some water from a bottle of purified water that was "mineral enhanced for taste" in a plastic shot glass.  Then, I fired up the circuit and put the leads in the shot glass.  The HESA program immediately detected the current and shut off the power to my simulated water softener.  Success!

Experiment #3: Got some Lake Michigan water out of the tap in the bathroom sink at the Makerspace.  Put the leads in the shot glass.  The HESA program immediately detected the current and shut off the power to my simulated water softener.  Success!

Experiment #4: Used water from the water cooler at the Milwaukee Makerspace.  It is also Lake Michigan water but it goes through a filter.  Put the leads in the shot glass.  The HESA program immediately detected the current and shut off the power to my simulated water softener.  Success!

I think we are ready for final assembly.