my favorite xmas presents included the tentacle shield, water quality kit probes and electronics i received from atlas-scientific as well as whitebox labs.

i have used atlas devices for a while and even tried to create my own interface boards like the one shown below

i had numerous production challenges with this original setup but that which bothered me the most was the electrical noise on the sensors due to lack of galvanic isolation. the ph sensor measures electrical currents whereas the ec probe produces electricity. this galvanic dance is shown below. even though the ph sensor is in the fishtank whereas the ec/tds sensor is in the growbed, the noise comes when the water from the growbed touches the fishtank and completes the electric connection during the drain cycle.

so i slowed on this approach for a while. with the coming of the v2 controller it was easy again to use atlas devices since the v2 board has 4 serial ports and 2 i2c ports – but the sensor noise again

then atlas produced the newer i2c devices which i never used until now with the tentacle shield. the tentacle shield is a 4 channel galvanically isolated electronics board for enabling the using of atlas-scientific devices on the arduino boards. using this with the v2 controller was very easy and in a very short while i was getting reliable readings even though i had not calibrated the probes.the whitebox test program all ran without a hitch. all i had to connect was sda, sdl, +5v and gnd to the v2 controller as shown below. sda and sdl are pins D20 and D21 on the v2 controller, then upload the test code to the atmega 2560 using the micro usb ftdi connection on the board

the v2 platform is json based so i wrote a quick tentacle driver for the v2 controller. now if you connect a tentacle shield to a v2 controller the json output will include entries like based on which circuits and probes connected.

{

“nutrientTemp”:16.37,

“ph”:8.40,

“opr”:168.00,

“ec”:444,

“tds”:239.00,

“salinity”:0.21,

“specific_gravity”:1.00,

“dissolved_oxygen”:0.31,

“oxygen_saturation”:3.40,

}

the live json streams can be found here.

now that that output from the tentacle shield was v2 json compliant, it was very easy for me to shoot it through the v2 platform for the following visualization

the live trends can be found here see the live stream (not sure if this url will be indefinite)

the test is still ad hoc so i put the electronics in a mini garden frame to protect them from splashing water drops, put the probes in the closest garden – the office kitchen garden. the sensors are literally next to one another as shown below in the indoor smart garden kits.

and the galvanic noise is gone as shown below:

the code base diff’s can be seen here …. tentacleShieldDiff

this is so much fun already .. i can see how the drain cycle of my growbed adds oxygen to the system or even the effects of feeding and bacterial activity

the only disadvantage of this setup is it takes at least 4 seconds to read all the sensors. the atlas sensors require at least 1 second each before they can stabilize for accurate readings. which is ok .. but the v2 control can support more than 50 sensors. to poll all the supported sensors reliably was taking 6 seconds, now it takes 10 seconds with the full water quality stack. which is ok for this particular application. it is easy to drop of things not being used for optimization.