Water Quality Sensors

Abhiram edited this page Aug 24, 2017 · 3 revisions

Water Quality Sensors


  • List of parts
  • Circuit
  • Power consumption
  • Responses in extreme events
  • Digitial Communication
  • Data Sheets/Commands
  • Board Enclosure
  • Coax Extensions
  • Sensors Enclosure
  • Water Proofing
    • Coax Link
    • SNODE Link
  • Water proofing test
  • Calbration
  • Deployment


Open-storm board supports the following water quality sensors manufactured from atlas scientific

  1. Ph
  2. Conductivity
  3. Dissloved oxygen
  4. Oxidation reduction potential
  5. Temperature

Field Deployments in Ann Arbor, MI

Mallets Creek County Farm Park
mallets cfp

List of Parts

Product Quanity Link Price per Piece Image
MALE DC POWER ADAPTER - 2.1MM PLUG TO SCREW TERMINAL BLOCK 1 https://www.adafruit.com/product/369 $2.00 spinmale
LARGE 6V 3.5W SOLAR PANEL 1 https://www.adafruit.com/product/500 $39.00 solarcharger
304 Stainless Steel Strip 1 https://www.mcmaster.com/#1421t184/=18vuf6f $12.51 solarpanel
Submersible Enclosure with Hinged Cover 1 https://www.mcmaster.com/#7740K121 $91.02 enclosure
SparkFun Sunny Buddy - MPPT Solar Charger 1 https://www.sparkfun.com/products/12885 $24.95 sunnyb
Open-Storm Board 1 Custom Build $100.00
Battery 1 http://www.all-battery.com/AT-1S-li-ion-31059.aspx $58.90 battery
Modem 1 $74.60
Antennae 1 http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=42826#Features $4.13 ante
PCB Jumpers 10 https://www.digikey.com/short/31jjw4 $0.22 pcbjump
2 Position Terminal Block Plug, Female Sockets 0.138" (3.50mm) 180° Free Hanging (In-Line) 10 https://www.digikey.com/product-detail/en/phoenix-contact/1840366/277-2417-ND/349178 $2.47 sc2
5 Position Terminal Block Plug, Female Sockets 0.138" (3.50mm) 180° Free Hanging (In-Line) 10 https://www.digikey.com/product-detail/en/phoenix-contact/1840395/277-5721-ND/349180 $6.47 sc5
Plastic Submersible Cord Grip 1 https://www.mcmaster.com/#7310k11/=190jkzg $2.96 glad
Strut Channel 1 https://www.mcmaster.com/#3310t64/=18w7kui strcha
18-8 Stainless Steel Locknut with External-Tooth Lock Washer https://www.mcmaster.com/#96278a005/=18vup3i $0.06 bolt
Torx Rounded Button Head Screws https://www.mcmaster.com/#90910a716/=18vunp9 $0.33 nut
Super-Corrosion-Resistant 316 Stainless Steel Hex Head Screw https://www.mcmaster.com/#93190a712/=18vuqb8 $0.884 nutq
Super-Corrosion-Resistant 316 Stainless Steel Hex Nut https://www.mcmaster.com/#94804a340/=18vups3 $0.396 scre1
Liquid-Tight Flexible Metal Conduit Adapter 1 https://www.mcmaster.com/#7119k73/=18vvtsx $3.22 seal
Liquid-Tight Flexible Metal Conduit https://www.mcmaster.com/#8068k33/=18eneo3 $4.50 conduit
Coaxial Cord https://www.mcmaster.com/#6641t38/=18d9cvs $24.48 cozx
5 Positions Header Connector 0.100" (2.54mm) Through Hole, Right Angle Gold 5 https://www.digikey.com/product-detail/en/molex-llc/0705530004/WM4903-ND/114963 $1.45 circuitboard
5 Position Rectangular Housing Connector Receptacle Black 0.100" (2.54mm) 5 https://www.digikey.com/product-detail/en/molex-llc/0050579405/WM2903-ND/115035 0.34 board1
Socket Contact Gold 22-24 AWG Crimp 25 https://www.digikey.com/product-detail/en/molex-llc/0016020103/WM2512-ND/115063 0.20 crimp
Thick-Wall Unthreaded PVC Pipe for Water 1 https://www.mcmaster.com/#48855k26/=190l34p 16.75 pvc
Thick-wall PVC pipe fitting for water, bushing reducing adapter, 2 x3/4 NPT 1 https://www.mcmaster.com/#4596k439/=190l3l0 $6.93 pcvbruch
Thick-wall PVC pipe fitting straight adapter, 2 socket-connect female x 2 NPT female 1 https://www.mcmaster.com/#4596k849/=190l42j $11.40 pvcsd
Electrically Isolated EZO Carrier Board 5 https://www.atlas-scientific.com/product_pages/components/single_carrier_iso.html $36.00 isolation_board
Ph Circuit 1 https://www.atlas-scientific.com/product_pages/circuits/ezo_ph.html $38.00 ph
ORP Circuit 1 https://www.atlas-scientific.com/product_pages/circuits/ezo_orp.html $38.00 orp
DO Circuit 1 https://www.atlas-scientific.com/product_pages/circuits/ezo_do.html $44.00 do
Conductivity Circuit 1 https://www.atlas-scientific.com/product_pages/circuits/ezo_ec.html $58.00 ec
Temperature Circuit 1 https://www.atlas-scientific.com/product_pages/circuits/ezo_rtd.html $26.99 temp
ORP Probe 1 https://www.atlas-scientific.com/product_pages/probes/orp_probe.html $108.00 orp_probe
DO Probe 1 https://www.atlas-scientific.com/_images/large_images/probes/ph_box.png $198.00 do_p
EC Probe 1 https://www.atlas-scientific.com/product_pages/probes/ec_k0-1.html $144.00 ecp
Ph Probe 1 https://www.atlas-scientific.com/product_pages/probes/ph_probe.html $72.00 php
Temperature Probe 1 https://www.atlas-scientific.com/product_pages/probes/pt1000.html $36.00 tempp

Additionally water quality sensors would need the calibration liquids from atlas scientific.


Water quality sensor has three components

  1. Probe (water quality sensor)
  2. EZO Isolation board
  3. Circuit board

Probe (i.e sensor) in immersed in water, where it measures a particular attribute. This reading is reported from the probe as voltage (a analog reading) . This analog reading is converted into a digital reading by the circuit board. Circuit board would differ for each probe. If coax cable (which transmits the analog reading from the probe to the board) is not properly connected, the readings reported might be significantly skewed. It is advised to use a isolation board. Isolation

5 water quality sensors are connected in parallel to the board, even though they are powered using 3 different pins on the board.

  • SDA, SCL, GND are connected in a single circuit
  • 5v-power is powred using 3 pins. Each pin on the board is restricted on the amount power that they can draw from the board.

Following Wiring convention is followed though out the sensor

  • SDA - Geen
  • SCL - White
  • Power - Red
  • Ground - Black

Detailed wiring instructions are linked here.(Link the wire pdf) Untitled Diagram.jpg

Preparing the parallel circuit

Snip the wire ends Soder the lead Crimp the wire end
![IMG_3375.JPG](/:storage/56o4r7lii7bep14i.JPG =600x700) ![IMG_1187.JPG](/:storage/h0y6ehaulmyam7vi.JPG =600x700) ![IMG_9412.JPG](/:storage/4gzvcvia80jjdcxr.JPG =500x700)

Make sure the flap is raised, this flap acts as a lock that holds the crimped wire in the pin.

Crimped wire into the 5pin holder 5pin female holder fixed to circuit board They are locked in place
IMG_8050.JPG IMG_2649.JPG IMG_4427.JPG

Finished Circuit


Power Consumption

Sensors when connected to the open-storm board consume a average of 330 mA for ~7-10 sec. These measurements vary based on firmware used.

Exteme events

While these sensors are out in the feild, there could be instaces when the sensors report skewd values. The following readings are what you can expect when such events happen.

Response of the circuit when the coax cables are not connected
Ph 0.00
ORP 1020.00
DO 61.94
Conductivity 0.0
Temperature -1023.000
Response of the circuit when shorted
Ph 7.003
ORP 0.1, -0.1
DO 0.06
Conductivity Really high value
Temperature -1023.000
Response when water interfears with the circuit

In water sensor is short

Ph 2.63 Keeps decreasing
ORP Rapid rise
DO Rusults seem consitant
Conductivity keeps rising
Temperature -1023
Response in when not submerged

These repsonse tend to vary drastically. But once DO sensors are calibrated, they tend to show a value of ~8 when the sensor is dry


Digital Communication

$$I^2C$$ protocol to communicate with the sensors. Detailed implementation can be found in perfect cell/atlas_wq_sensors.c.

These sensors by default are in UART mode, they can be converted to $$I^2C$$ though i2c,

command. For more details refer data sheet.

Data Sheets

Futher information about the operation and capabilities/limitations of the sensors can be found in the data sheets (linked below)

Node Enclosure

Open-storm board is encolsed in a water proof encolosure to protect the electronics from elements (rain, snow ...)


Coax Extensions

Depending on the feild conditions, distance between the sensors and node is adjusted. Currently 25ft and 10 ft coax extesnions were used. To build a differnt node, only the coax and conduit lenghts in the above order have to be altered.

Water Proofing the coax link

Coax link (coax extension + wq sensors) needs to water proofed. Any water in the link skews the reading.

Two layers of water seal is used to prevent the water from damaging the coax connection.

  1. Self Adhesive Tape IMG_0532.JPG

On top of the self adhesive tape multiple layers(3 layers) of the liquid tape is added to reinforce the seal.

  1. Liquid Tape IMG_0536.JPG

Water proofing the conduit

Coax extenders are enclosed in a flexible conduit to avoid any external damage.


Sensors enclosure

To protect the sensors from the gravel and other things in the stream they are stored in a pvc tube. This thick walled pvc tube has holes in the bottom, where sensors are held in place by rubber stopper. These holes allow the water to enter into the enclosure. IMG_5453.JPG

Enclosure of the coax cables is conneted to the sensors enclosure using a thereaded connector.


Seal the coax extender link

  1. Water Sealing Putty
  2. Liquid Tape Layer

Water sealing putty is appied to seal the pcv link and allowed to set. A layer of liquid tape is added on top this for prevent any seepage. Care must be taken near the coax ends.

Water Proofing Test

Once the both the coax and pvc links are sealed, their integrity is tested by taking a reading when the coax links are dry and then the entire node is immeresed in water and readings are checked periodically. If the readings are consistent, sensors are ready to be deployed.

  1. Coax Seal Testing Image uploaded from iOS.jpg


Sensors need to calibrated before they can be deployed in the feild. Each one of the sensors have a unique method. Refer to calbration section in the data sheets.

Once these sensors are tested and calibrated they are placed in the enclosure. IMG_2390.JPG


Deployment procedure might depend on the feild conditions. But in general they involve a pole mounted node and the wq sensors deployed such that they are immeresed in water for major part of the storm. But if they are placed to close to the bed, they might incur damage though contact from mud.

Image uploaded from iOS (1).jpg

General Issues experienced

  1. Protocol lock reset from UART to $$I^2C$$ This issue has been addressed in the firmware update from atlas.
  2. Coax seal integrety In the event water enters the coax connection. Sensor measurement are skewd, link have to be dried and redeployed.
  3. Conductivity sensor check Conductivity sensor is just measuring the current in the water. A quick test to test its integrity would be to check for a short on the sensor end (copper colored part) and coax cable
  4. Sear force seems to damage ph and conductivity sensor. This issue is yet to be addressed.
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