The science of Sutro: The Smart Water Monitor
The ‘How it Works’ page has about $6 in page-value. This means that the page is responsible for convincing (and converting) our friends to purchase and become part of the Sutro family.
When we audited the page, we realized that the ‘intent’ of WHY people were coming to this page was to understand more about the technology, and we weren’t quite doing that.
We had some marketing fodder, some why it’s important, but the biggest part of marketing is just being practical. Is figuring out the why, and not trying to build up some gimmick on trying to convince people to buy something.
The majority of decisions that people make are emotional not driven by some logical cost benefit analysis (as much as we think we do that).
OK, so I’m going to build this as a draft for the substitute for the Google Doc that I would give to our marketing team.
Here we go!
Tracing the journey of a drop of water in the Sutro
You have a body of water in your backyard, it’s a swimming pool. The premise is simple you purchase the Sutro, drop it in your pool and get readings on your app.
What happens in between?
The Sutro is a complex piece of robotics, just imagine that there are bunch of small little scientists that live and work inside the floating robotic laboratory.
The drop(s) of water are pulled into the floating monitor
A “sample” of water is pulled from about an arm’s length and travels about 7 inches into the flow cell. The flow cell is where all the magic happens.
Once the drop reaches the flow cell, the pump stops pulling the water into the device, and the entire lab process starts.
“The scientists” begin to pump reagent (reactant) into the flow cell. Think of it as food coloring that is pushed into the flow cell, and allows the reactant (or reagent) to react with the water.
This requires a quick aside on the cartridge itself. The Sutro cartridge is 5 reagents inside of syringes, plugged into the microfluidic chip (which is where this flow cell lives, that I mentioned above).
For those of you who own swimming pools and have seen the red dropper to measure pH, we use the same liquid, and actually do the same process.
Small amounts of reagents are then dosed
The 5 reagents (as mentioned above), are the exact same that you would see in a Taylor test kit, a strip test kit, or a LaMotte test kit (we actually use LaMotte reagents).
If you have a swimming pool (or spa), you’ve definitely seen or used one of these before.
The reagents that we use are:
- pH — phenol red (the red color that you’d usually use to measure pH)
- Free chlorine — DPD1A and DPD1B
- Alkalinity — Total alkalinity indicator and super light sulfuric acid reactant
We use about 3uL (microliters) to measure alkalinity and about 8uL of the pH and free chlorine reagents. Just for a matter of reference, a drop of water is about 20–50 uL (depending on surface tension).
Then, an array of colors is measured
The Sutro is a colorimeter, and very similar to how us (humans) would look at color. We take a baseline without color and then once the reagent is pushed into the flow cell, we take a balance of the colors.
We have an RGBW (red, green, blue, white) LED array and a photo sensor array. There is one side that projects the light and the other side that catches the light.
This is actually how many spectrophotometers work.
Flying across, the data gets sent to the hub
Communications in water is tough. WiFi and bluetooth use 2.4 and 5GHz (you’ve probably seen those two bands on your home Xfinity WiFi). The issue is these are smaller wave length, which means that you can actually carry higher bandwidth information. Think about a video call and streaming your next amazing Justin Bieber video.
The Sutro’s data is much smaller (we can actually fit it into a size of a text message), it’s just bytes not kilobits or gigabits. But, we need to make sure that it sustainably gets between the monitor and the hub. So we opted for our own proprietary 900MHz link.
From the hub, up and to the cloud it goes!
All those LED values get projected into a 4x4 array. We have an RGBW LED and an RGBW photo-diode array (which is able to basically see the light). Through millions of data points, tests, and calibrations against our own cartridge, reagents, and light — we’ve been able to build out an algorithm that can output a simple pH, free chlorine, and alkalinity value.
Back down to the Sutro App on Android or iOS
At the end of all of this, we want to give you what you need to do and when you need to do it. The Sutro system allows you to scan in your chemicals that you purchase from Leslies Pool Supply, Home Depot, or your neighborhood pool and spa supply store. If you’d like to see more, John Rigby did this amazing review of the Sutro system you can see it here!
Really cool, huh?
Well, first I now have something to give to the marketing team- so we can increase our page-rank value. Secondly, what we’ve built is a remix of technology that already exists but just made it super small.
Utilizing microfluidics, we’ve been able to take existing reagent chemistry, and bring it down to smaller than the size of a drop of water.
It’s tough business building hardware that works like a laboratory tool, but it’s really rewarding when we’ll better understand water and how to treat it.
Music I was listening to while I wrote this
Wolfgang Haffner — Kind of Tango (2020 — Album)
This is day 17 of my #90DayOfProse challenge
