Sump Pump Watchdog hack


The sump pump is a device that works hard to keep your home dry but is prone to failure, and if you have any valuables in your basement or crawlspace, even a light flood can cause a lot of damage and potential health problems (mold!). It tends to fail in a big storm when it gets really busy pumping water away from around your home (worse if you lose power too). Heard a few horror stories and not having some kind of backup or monitoring it is the perfect recipe for a disaster waiting to happen.

My trusty SonarMote is of course an independent sensor which alerts me when the water reaches an unsafe level in the sump well. It’s mounted on the bottom of the sump well lid and it measures the distance to the water surface. My gateway app graphs that level and also provides a means to alert me via SMS or email.

This year the pump’s mechanical float decided to get stuck again and then fail, so I had to either buy a whole new pump, or find an alternative to the float part. Turns out there’s a device called The Basement Watchdog. It’s very simple in its operation – has its own float, which triggers a circuit that activates a 120v outlet for a fixed amount of time, cheap and perfect.

As soon as I installed this, I noticed my SonarMote measurement graph was messed up. That’s because the device would tend to empty out the well very sporadically and for a short delay, and the level would only vary by very little, not very visually helpful.I wondered how hard can it be to hack the Watchdog to make it stay on for longer and pump more water. Unsurprisingly the circuit is based on the TI ne555 timer chip which after a little investigation is obviously running in monostable configuration. Here’s a nice video walkthrough that explains this mode in more detail if you’re not familiar with the 555 timer. In a nutshell there is a trigger (the float) which activates the 555 timer output to go HIGH (activates relay and turns pump ON) for a fixed amount of time (configured by a resistor and capacitor RC discharge circuit), after which it goes LOW (and switches off the pump).In my Watchdog, the timer is determined by a 100K resistor and 47uF capacitor. The 555 monostable timer formula is Tw=1.1*R*C which results in a ~5 second activation of the pump, which is way too low and explains the unappealing graphs I’ve been getting:

To change this output time there are 2 options – desolder the resistor and solder a larger value (a bit messy and risking to damage the circuit), or solder a parallel capacitor to the existing one. I chose to solder another capacitor since capacitors in parallel combine their capacitance and required no desoldering. So adding 2 wires to the existing cap and using another cap at the other end makes it easy to change the cap overall value or even use a variable capacitor. If you wanted to change the resistor instead, you could add a potentiometer and case-mount to to allow changing the timing any time later, but I thought that’s overkill, I just needed a bit longer delay. So here’s the 220uF capacitor I added and taped to the relay to prevent any movement/shorts:

Simple enough, the result was an increase to ~30 seconds which empties out the well almost completely and yields nice graphs again, I don’t anticipate having to ever touch this again:

This is the graph for one day, from empty to trigger point:

This is also helpful to see weather patterns, here’s a dry period followed by a few days of heavy rain:


New products!

I am quite happy to announce a few new products (or new revisions), some of which people have been asking for a long time, now finally available at the shop!
First there is the IOShield which is now available as an assembled PCB with optional “24VAC input package” which allows you to place it in places where you have 24VAC input, like I did in the wireless sprinkler controller project.

Then there is a small BellMote run with OSHPark purple PCBs. Completely automate your doorbell with this kit which allows you to detect, trigger, and disable your doorbell, all wirelessly via Moteino gateway.

Next up is the SonarMote which finally has a new revision (R2) which addresses some bugs, has a simpler BOM and is even lower power – just 10uA average when the Moteino is properly slept – sample sketches here. A wide range of applications are possible, from parking sensor, inventory control, sump pump monitor, and others.

Finally we have the MiniBoost which is a small SIP form boost regulator that yields 5V from an input voltage of 2-4V. Up to about 1A is possible from a charged LiPo battery (4V) and will easily carry a moderate load like a RaspberryPi. It uses the same boost regulator as the MightyBoost but the SIP size makes it very versatile for breadboard projects. It’s perfect for projects where you have a main working voltage of 3.3V but you have some sensor that needs a hefty 5V source. Comes with onboard green power LED. It has is the same pinout and size as the legendary 7805 regulators:

It takes a long time to go through prototype stages and then manufacture electronics of high quality, all as a small operation like I have. I hope to get more time to put more documentation and assembly instructions together for these kits and boards. Some of them have already been introduced as prototypes and have a fair amount of information available. There are also other things I’d like to blog about, just not enough time, stay tuned for more!

SonarMote kits available

I have a limited offering of SonarMote kits. These are great for sump pump monitoring or parking aid (have a long car and a short garage?). Lots of people asked me to put these up, now the’re finally there. See the SonarMote page for more details/code and other project ideas, I will continue to add documentation there. The 1/16″ lasercut acrylic case plans and sample sketches are posted here. They work with 3.7v LiPo batteries which will recharge via the USB connector and they are also programmable via USB serial (FTDI onboard the PCB). They require a Moteino (no radio for projects like parking air or visual/audio feedback distance trackers, or with radio for things like the sump pump). It plugs right into the Gateway Framework and will start monitoring and logging distance as soon as you turn it on:


I love my standalone parking aid sensor based on SonarMote, it will light up the RGB LED green – yellow – then blink red faster and faster as you approach a set limit. When battery is low it blinks blue (every couple months or so on a small LiPo, recharge it via USB). Here are some action photos, also shown with an optional OLED display which plugs right into the SonarMote.

Unfortunately I cannot include LiPo batteries at this time because of the over complicated logistics and restrictions of shipping batteries. Most places online probably are breaking the rules when they ship you more than 2 batteries of certain capacities (by air) … but let them do it, sorry about that.

Sump pump fails: SonarMote intercepts!

Yesterday the first significant storm of the season moved in the area and it rained heavily into the evening hours. Nice for the grass, I just fertilized it the other day. But bad for sump pumps which work really hard to keep the water out of the house, they usually fail during a big storm. I came back home very late and was very tired, went straight to bed so I didn’t notice anything. This morning when I checked the Moteino Gateway interface (coming soon!), I was alerted that the sump pump SonarMote was reading an unusually low value. The SonarMote sensor that sends the readings was still operational since the data was still coming. So could the sump pump have failed? Here’s the graph that recorded the increasing frequency of the pump operation until the failure ocurred (lower value means water is closer to the sensor and hence fuller well tank):

So I head down to the basement to check and sure enough, the sump well was full of water and the sump pump did not work. So I remove the pump to inspect it and as I was getting ready to head to Home Depot before the new pumps are all gone, I fiddle with it and it turns out the plunger was stuck in a low position so it was not actuating the pump. I could get it mobile again and it seems that fixed it, but it might fail again if there’s debris/sand inside the plunger cylinder, so I will keep an eye on this. Anyway after putting it back in the well here’s the pattern picked up by the SonarMote. Very frequent starts as the stagnant water in the perimeter drains into the sump well and the pump works hard to get the water out as it refills the tank:

Without being aware what’s going on, eventually the water would have overflown into the basement. Sure glad I have that sensor to alert me in time.