SUMP PUMP -now! A flooded crawl space

IoT Sump Pump in my Nuts & Volts Magazine. A flooded crawl space after 2 1/2" of rain in one day. I get the message!
All I have to do is turn on the modified-for-the-pump yard-light switch. And turn it off when the pump runs dry, that is until more water collects. Sounds like a job for a COMPUTER !!

CAUTION be careful as there is 120vAC - that can hurt/kill you!!

PROCEED at your own risk- (I tripped a circuit breaker already!)

Okay - I have a spare ProStart board ; they are now on sale for a mere $10. Get two float switches -- oh did I mention I saved about $20-25 by not buying a pump with an included switch!!? yeauuh...

Three or four connections is all it should take for the ucontroller to be usable. The relay driver is the source of some issues - needs more milliamps than the outputs can deliver. $o now I buy an 'opto-i$olated relay board'. (this is used to turn on the 120vAC to the outlet for the pump) [^1] (I did save some $20 dollars, didn't I?!) Some 3/4" PVC to mount the float switches on - a low/off limit and a high/on limit - it wasn't a self-priming pump.

float switches

Wire is needed to connect it all, BTW telephone house wire/or/ethernet wire is a good source of solid core wire if you solder, I do. (but only for your signals - not the 120vAC - use appropriately sized wire) A two gang electrical box to house the relay and ucontroller pretty well rounds out the parts needed.

Now the hard part and lessons learned!.

  1. A digital low doesn't make a good'low/ground' reference for a digital input.
  2. Many ucontroller inputs on modern devices will float - due to being 'tri-stated'.
  3. Switches need asoftware debounce time to settle on a signal level - hey! at 48Mhz how long does it take to read an input??
  4. Unfiltered wall-warts (AC/DC adapters) are current sensitive in regards to their output voltage.

Previous lesson learned[^1A]


  1. The 3.3v operating voltages (and even 1.8v now) are now more threshold level sensitive. Had to use the GND signal of the ProStart to feed one side of my float-switches. One input kept switching hi/lo/hi/lo!!
  2. Even the GND didn't keep one float-switch input from hi/lo/hi/lo-ing. So - on the bottom of the board I soldered two 30+Kohm resistors to +3.3v. With 1) and 2) I now had good solid signals --

pullups added

  1. but 3 needed addressing. [^2] Still some ambiguity in my program.
    WAIT(300) to the rescue. Thank you ARMbasic. Didn't have to do the 'old way' FOR/NEXT increment counter routine.
  2. Then there is the wall-wart issue. 6vdc @ 300ma wall-wart couldn't handle the relay turning on at a mere 75ma!! A surge was probably happening. I had to build a 5v regulator for the relay board and also used it for the ProStart - it does have a 3.3v regulator on it to handle its own power needs with a little to spare.

5v regulator

I used a 50 ohm load across the wall-wart to drop the voltage down to about 7.4vdc. (open/no load state was 11.5vdc !!) That was too much - the relay would not stay ON; so I changed it to 75 ohm. (I used 3 ceramic 150 ohm resistors in parallel, but cut one out of the circuit.)

Its been fun(!?) putting on boots, crawling under the house and adjusting the pole to make sure the pump starts/stops correctly! BUT I don't have to turn the modified-for-the-pump yard-light switch on and off ANYMORE.



[^1] A friend reminded me that relays are rated for a 'resistive' load and an 'AC' load. My relays are only 10amps resistive - the pump is an AC/inductive load and will have current surges that can 'fry/weld' the contacts.

So in my final design I used the relay board to turn on an industrial relay for protection. This bigger relay has a 120vac coil but the current is very minimal. {I know - a relay to turn on a relay}

[^1A] My 812/HVAC project (on the Coridium forum) didn't work because the motor on/off cycles fed back into my relay circuitry-causing reboots and hangs. That was/is the reason for the 'opto-isolated' relay board.

[^2] Switches and relay contacts typically take 10-20 millisecs. to settle into their final state - during which time the signal oscillates.

[^3] A better solution is to acquire a USB/5v wall wart and use it - 500ma -plenty of power and a regulated output. Mine still 'droops' the output voltage a little!!

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