Office plant monitor

[tomtastic]

@NeverDie The person behind 'Chirp' actually left a comment in your last link (zerocharactersleft). He posts an interesting link back to his own studies too : https://wemakethings.net/2012/09/26/capacitance_measurement/

[NeverDie]

@tomtastic said in Office plant monitor:

@NeverDie The person behind 'Chirp' actually left a comment in your last link (zerocharactersleft). He posts an interesting link back to his own studies too : https://wemakethings.net/2012/09/26/capacitance_measurement/

Thanks for the link.

For the best results, running the square wave at 80Mhz or faster seems to be important. That's what vegetronix does. Now, the good news is that the clock on an ESP8266 can supply that frequency.. However, all this analog circuitry is beyond my purview, so I inevitably hit a wall with that. Is that something you (or someone reading this) knows how to do? For instance, I don't know whether the chirp guy's circuit that you linked to works as-is at 80Mhz, or whether it requires modification. If the latter, that's where I get stuck not knowing what to do.

[NeverDie]

@tomtastic

It turns out that the circuit the Chirp guy described in the link that you provided is, in fact, what is built into Chirp: https://wemakethings.net/2013/06/07/chirp-plant-watering-alarm/

None of his calculations make reference to frequency, so maybe (?) you could hook up the circuit to 80Mhz and it would "just work." I suppose the switching speed of those transistors might be a factor. I have no insight into that, but it would probably be easy for someone to test. IIRC, the higher frequency makes a capacitive soil moisture sensor much less influenced by soil characteristics other than moisture, so it's really necessary to have that in order to make a good probe.

[Edit: What you don't want is a soil moisture probe that requires frequent manual re-calibration. Ordinary conductive probes all have that as an inherent problem. Hence the hunt for a worthwhile capacitive soil moisture sensor.] ]

[NeverDie]

Completely unrelated, but I just noticed this:
https://www.aliexpress.com/item/SHT10-SHT11-SHT15-waterproof-sensor-case-temperature-and-humidity-protective-cover-soil-sensor-cover-40mm-15mm/32575966509.html?spm=2114.8153822.cb0001.16.lITM8E&scm=1007.13409.76764.0&pvid=0acc75b7-138d-456f-a5bf-5147c2ea763f&tpp=1
So with that, you could just use a regular humidity sensor inside it to judge soil moisture. Pretty cool, yes? Not sure how big it is, but maybe you could even fit your entire sensor node inside it.

[Nca78]

@NeverDie said in Office plant monitor:

Completely unrelated, but I just noticed this:
https://www.aliexpress.com/item/SHT10-SHT11-SHT15-waterproof-sensor-case-temperature-and-humidity-protective-cover-soil-sensor-cover-40mm-15mm/32575966509.html?spm=2114.8153822.cb0001.16.lITM8E&scm=1007.13409.76764.0&pvid=0acc75b7-138d-456f-a5bf-5147c2ea763f&tpp=1
So with that, you could just use a regular humidity sensor inside it to judge soil moisture. Pretty cool, yes? Not sure how big it is, but maybe you could even fit your entire sensor node inside it.

One of the local shops I buy electronic parts from has those. Unfortunately it's too small to house an entire sensor.

[NeverDie]

This thread also has a lot of good background information and links about capacitive soil moisture sensors: https://lowpowerlab.com/forum/general-topics/using-capsense-to-measure-soil-moisture/

[NeverDie]

It might be that one could more or less whack an 80Mhz frequency oscillation chip into the Chirp circuit: https://www.digikey.com/product-detail/en/linear-technology/LTC6905CS5-80-TRMPBF/LTC6905CS5-80-TRMPBFCT-ND/810907

[scalz]

i agree with @NeverDie ;)
It's better to use high freq for a reliable soil moisture, regarding soils, calibration etc. and some studies argues even more than 200Mhz. but with 80-100 it's nice.
I have one design at this freq, non corrosive design, and not same as chirp though, but can't really help you (mine is not open yet, and busy on others projects).
Regarding the chirp design, I think it may need an opamp for better results regarding the 1M resistor etc, and some more tuning if going high freq.

[simbic]

Trying to get this working but getting alot of errors. New to this so bear with me.

In file included from C:\...\Arduino\libraries\Moisture_sensor\Moisture_sensor.ino:55:0:

C:\...\Arduino\libraries\MySensors/MyTransportRFM69.h:31:1: error: expected class-name before '{' token

 { 

 ^

C:\...\Arduino\libraries\MySensors/MyTransportRFM69.h:33:36: error: 'RFM69_FREQUENCY' was not declared in this scope

  MyTransportRFM69(uint8_t freqBand=RFM69_FREQUENCY, uint8_t networkId=RFM69_NETWORKID, uint8_t slaveSelectPin=RF69_SPI_CS, uint8_t interruptPin=RF69_IRQ_PIN, bool isRFM69HW=false, uint8_t interruptNum=RF69_IRQ_NUM);

                                    ^

C:\...\Arduino\libraries\MySensors/MyTransportRFM69.h:33:71: error: 'RFM69_NETWORKID' was not declared in this scope

  MyTransportRFM69(uint8_t freqBand=RFM69_FREQUENCY, uint8_t networkId=RFM69_NETWORKID, uint8_t slaveSelectPin=RF69_SPI_CS, uint8_t interruptPin=RF69_IRQ_PIN, bool isRFM69HW=false, uint8_t interruptNum=RF69_IRQ_NUM);

                                                                       ^

In file included from C:\...\Arduino\libraries\Moisture_sensor\Moisture_sensor.ino:56:0:

C:\...\Arduino\libraries\MySensors/MySigningAtsha204Soft.h:55:1: error: expected class-name before '{' token

 { 

 ^

C:\...\Arduino\libraries\MySensors/MySigningAtsha204Soft.h:62:25: error: 'MY_RANDOMSEED_PIN' was not declared in this scope

   uint8_t randomseedPin=MY_RANDOMSEED_PIN);

                         ^

Moisture_sensor:83: error: call to 'MySigningAtsha204Soft::MySigningAtsha204Soft(bool, uint8_t)' uses the default argument for parameter 2, which is not yet defined

 MySigningAtsha204Soft signer;

                       ^

Moisture_sensor:84: error: 'MyHwATMega328' does not name a type

 MyHwATMega328 hw;

 ^

Moisture_sensor:85: error: call to 'MyTransportRFM69::MyTransportRFM69(uint8_t, uint8_t, uint8_t, uint8_t, bool, uint8_t)' uses the default argument for parameter 1, which is not yet defined

 MyTransportRFM69 transport;

                  ^

Moisture_sensor:85: error: call to 'MyTransportRFM69::MyTransportRFM69(uint8_t, uint8_t, uint8_t, uint8_t, bool, uint8_t)' uses the default argument for parameter 2, which is not yet defined

Moisture_sensor:86: error: 'MySensor' does not name a type

 MySensor node(transport, hw, signer);

 ^

C:\...\Arduino\libraries\Moisture_sensor\Moisture_sensor.ino: In function 'void setup()':

Moisture_sensor:112: error: 'node' was not declared in this scope

   node.begin();

   ^

C:\...\Arduino\libraries\Moisture_sensor\Moisture_sensor.ino: In function 'void loop()':

Moisture_sensor:163: error: 'node' was not declared in this scope

   node.send(msgMoisture.set((moistureLevel + oldMoistureLevel) / 2.0 / 10.23, 1));

   ^

C:\...\Arduino\libraries\Moisture_sensor\Moisture_sensor.ino: In function 'int readMoisture()':

Moisture_sensor:200: error: 'node' was not declared in this scope

   node.sleep(STABILIZATION_TIME);

   ^

exit status 1
call to 'MySigningAtsha204Soft::MySigningAtsha204Soft(bool, uint8_t)' uses the default argument for parameter 2, which is not yet defined

I have looked through the code but can't seem to see what is wrong with it.

Please help :)

[mfalkvidd]

@simbic did you modify the sketch in any way? If so, could you please post it?

My guess would be an incomplete #define or using incompatible versions. Which version of MySensors are you using?

[simbic]

@mfalkvidd

I have assembled a copy of @carlierd 's office plant monitor since it looked kinda neat.
When I first tried to upload @carlierd 's Moisture_sensor.ino it complained that several libraries were missing.
So I started google-fu around to find them.
What was missing was:
MyTransportRFM69.h
MyTransport.h
MySigningAtsha204Soft.h
MySigning.h
MyMessage.h

aswell as drivers, that I placed in folder /utility/
ATSHA204.h
RFM69.h
sha256.h

The code is as follows. I have only pressed include mysensors' library since it complained that it was missing.

/**
 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 *
 * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
 * Copyright (C) 2013-2015 Sensnology AB
 * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
 *
 * Documentation: http://www.mysensors.org
 * Support Forum: http://forum.mysensors.org
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 * Code and idea from mfalkvidd (http://forum.mysensors.org/user/mfalkvidd).
 *
 */

/**************************************************************************************/
/* Moisture sensor.                                                                   */
/*                                                                                    */
/* Version     : 1.2.5                                                                */
/* Date        : 11/04/2016                                                           */
/* Modified by : David Carlier                                                        */
/**************************************************************************************/
/*                                ---------------                                     */
/*                            RST |             |  A5                                 */
/*                            RX  |             |  A4                                 */
/*                            TX  |   ARDUINO   |  A3                                 */
/*     RFM69 (DIO0) --------- D2  |     UNO     |  A2                                 */
/*                            D3  |             |  A1 --------- Moisture probe        */
/*            Power --------- D4  | ATMEGA 328p |  A0 --------- Moisture probe        */
/*              +3v --------- VCC |             | GND --------- GND                   */
/*              GND --------- GND |  8MHz int.  | REF                                 */
/*                            OSC |             | VCC --------- +3v                   */
/*                            OSC |             | D13 --------- RFM69 (SCK)           */
/*                            D5  |             | D12 --------- RFM69 (MISO)          */
/*                            D6  |             | D11 --------- RFM69 (MOSI)          */
/*                            D7  |             | D10 --------- RFM69 (NSS)           */
/*              LED --------- D8  |             |  D9                                 */
/*                                ---------------                                     */
/*                                                                                    */
/* +3v = 2*AA                                                                         */
/*                                                                                    */
/**************************************************************************************/


#include <SPI.h>
#include <MySensors.h>
#include <MyTransportRFM69.h>
#include <MySigningAtsha204Soft.h>


//Define functions
#define round(x) ((x)>=0?(long)((x)+0.5):(long)((x)-0.5))
#define N_ELEMENTS(array) (sizeof(array)/sizeof((array)[0]))

//Constants for MySensors
#define SKETCH_NAME           "Moisture Sensor"
#define SKETCH_VERSION        "1.2.6"
#define CHILD_ID_MOISTURE     0
#define CHILD_ID_VOLTAGE      1
#define LED_PIN               8
#define THRESHOLD             1.1     // Only make a new reading with reverse polarity if the change is larger than 10%
#define STABILIZATION_TIME    1000    // Let the sensor stabilize before reading
//#define BATTERY_FULL          3143    // 2xAA usually gives 3.143V when full
#define BATTERY_FULL          3100    // CR2032 usually gives 3.1V when full
#define BATTERY_ZERO          2340    // 2.34V limit for 328p at 8MHz
#define SLEEP_TIME            7200000 // Sleep time between reads (in milliseconds) (close to 2 hours)
const int SENSOR_ANALOG_PINS[] = {A0, A1};


//Variables
byte direction = 0;
int oldMoistureLevel = -1;

//Construct MySensors library
MySigningAtsha204Soft signer;
MyHwATMega328 hw;
MyTransportRFM69 transport;
MySensor node(transport, hw, signer);
MyMessage msgMoisture(CHILD_ID_MOISTURE, V_HUM);
MyMessage msgVolt(CHILD_ID_VOLTAGE, V_VOLTAGE);

/**************************************************************************************/
/* Initialization                                                                     */
/**************************************************************************************/
void setup()  
  {
  //Get time (for setup duration)
  #ifdef DEBUG
    unsigned long startTime = millis();
  #endif

  //Setup LED pin
  pinMode(LED_PIN, OUTPUT);
  blinkLedFastly(3);

  //Set moisutre sensor pins
  for (int i = 0; i < N_ELEMENTS(SENSOR_ANALOG_PINS); i++)
    {
    pinMode(SENSOR_ANALOG_PINS[i], OUTPUT);
    digitalWrite(SENSOR_ANALOG_PINS[i], LOW);
    }

  //Start MySensors and send the sketch version information to the gateway
  node.begin();
  node.sendSketchInfo(SKETCH_NAME, SKETCH_VERSION);

  //Register all sensors
  node.present(CHILD_ID_MOISTURE, S_HUM);
  node.present(CHILD_ID_VOLTAGE, S_MULTIMETER);

  //Setup done !
  blinkLedFastly(3);

  //Print setup debug
  #ifdef DEBUG
    int duration = millis() - startTime;
    Serial.print("[Setup duration: "); Serial.print(duration, DEC); Serial.println(" ms]");
  #endif
  }

/**************************************************************************************/
/* Main loop                                                                          */
/**************************************************************************************/
void loop()
  {
  //Get time (for a complete loop)
  #ifdef DEBUG
    unsigned long startTime = millis();
  #endif

  //Get moisture level
  int moistureLevel = readMoisture();

  //Send rolling average of 2 samples to get rid of the "ripple" produced by different resistance in the internal pull-up resistors
  //See http://forum.mysensors.org/topic/2147/office-plant-monitoring/55 for more information
  //Check if it was first reading, save current value as old
  if (oldMoistureLevel == -1)
    { 
    oldMoistureLevel = moistureLevel;
    }

  //Verify if current measurement is not too far from the previous one
  if (moistureLevel > (oldMoistureLevel * THRESHOLD) || moistureLevel < (oldMoistureLevel / THRESHOLD))
    {
    //The change was large, so it was probably not caused by the difference in internal pull-ups.
    //Measure again, this time with reversed polarity.
    moistureLevel = readMoisture();
    }

  //Store current moisture level
  oldMoistureLevel = moistureLevel;

  //Report data to the gateway
  long voltage = getVoltage();
  node.send(msgMoisture.set((moistureLevel + oldMoistureLevel) / 2.0 / 10.23, 1));
  node.send(msgVolt.set(voltage / 1000.0, 2));
  int batteryPcnt = round((voltage - BATTERY_ZERO) * 100.0 / (BATTERY_FULL - BATTERY_ZERO));
  if (batteryPcnt > 100) {batteryPcnt = 100;}
  node.sendBatteryLevel(batteryPcnt);

  //Print debug
  #ifdef DEBUG
    Serial.print((moistureLevel + oldMoistureLevel) / 2.0 / 10.23);
    Serial.print("%");
    Serial.print("   ");
    Serial.print(voltage / 1000.0);
    Serial.print("v");
    Serial.print("   ");
    Serial.print(batteryPcnt);
    Serial.print("%");
    int duration = millis() - startTime;
    Serial.print("   ");
    Serial.print("["); Serial.print(duration, DEC); Serial.println(" ms]");
    Serial.flush();
  #endif

  //Sleep until next measurement
  blinkLedFastly(1);
  node.sleep(SLEEP_TIME);
  }

/**************************************************************************************/
/* Allows to get moisture.                                                            */
/**************************************************************************************/
int readMoisture()
  {
  //Power on the sensor and read once to let the ADC capacitor start charging
  pinMode(SENSOR_ANALOG_PINS[direction], INPUT_PULLUP);
  analogRead(SENSOR_ANALOG_PINS[direction]);
  
  //Stabilize and read the value
  node.sleep(STABILIZATION_TIME);
  int moistureLevel = (1023 - analogRead(SENSOR_ANALOG_PINS[direction]));

  //Turn off the sensor to conserve battery and minimize corrosion
  pinMode(SENSOR_ANALOG_PINS[direction], OUTPUT);
  digitalWrite(SENSOR_ANALOG_PINS[direction], LOW);

  //Make direction alternate between 0 and 1 to reverse polarity which reduces corrosion
  direction = (direction + 1) % 2;
  return moistureLevel;
  }

/**************************************************************************************/
/* Allows to fastly blink the LED.                                                    */
/**************************************************************************************/
void blinkLedFastly(byte loop)
  {
  byte delayOn = 150;
  byte delayOff = 150;
  for (int i = 0; i < loop; i++)
    {
    blinkLed(LED_PIN, delayOn);
    delay(delayOff);
    }
  }

/**************************************************************************************/
/* Allows to blink a LED.                                                             */
/**************************************************************************************/
void blinkLed(byte pinToBlink, int delayInMs)
  {
  digitalWrite(pinToBlink,HIGH);
  delay(delayInMs);
  digitalWrite(pinToBlink,LOW);
  }

/**************************************************************************************/
/* Allows to get the real Vcc (return value in mV).                                   */
/* http://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/   */
/**************************************************************************************/
long getVoltage()
  {
  ADMUX = (0<<REFS1) | (1<<REFS0) | (0<<ADLAR) | (1<<MUX3) | (1<<MUX2) | (1<<MUX1) | (0<<MUX0);
  delay(50);  // Let mux settle a little to get a more stable A/D conversion
  //Start a conversion  
  ADCSRA |= _BV( ADSC );
  //Wait for it to complete
  while (bit_is_set(ADCSRA, ADSC));

  //Compute and return the value
  uint8_t low  = ADCL;                  // must read ADCL first - it then locks ADCH
  uint8_t high = ADCH;                  // unlocks both
  long result = (high << 8) | low;
  result = 1125300L / result;           // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
  return result;                        // Vcc in millivolts
  }

I have just installed Arduino IDE, and are using the latest mysensors library 2.1.1.

Another thing it complains about is:

Invalid library found in C:\...\Arduino\libraries\Moisture_sensor: C:\...\Arduino\libraries\Moisture_sensor```

which is wierd since I have just copy+pasted it from here:
https://www.openhardware.io/view/123/Office-plant-monitor

aswell as built the sensor from there.

If you can help, I would be very glad, as I just hoped it would be smooth sailing using mysensors. Build, upload and let it work its magic.

Tack på förhand!
Simon

[mfalkvidd]

@simbic that sketch is made for MySensors 1.x so it won't work with MySensors 2.x.

You either need to convert it (guide: https://forum.mysensors.org/topic/4276/converting-a-sketch-from-1-5-x-to-2-0-x) or use/create one for 2.x, for example https://www.mysensors.org/build/moisture

[NeverDie]

@Nca78

I see now that they have expanded their selection of waterproof sensor shells:

https://www.aliexpress.com/item/2pcs-Waterproof-Temperature-and-humidity-sensor-shell-SHT10-SHT21-SHT15-shT11-sht20-SHT75-sensor-protective-sleeve/32725766858.html?spm=2114.10010108.1000013.6.PVGRb3&traffic_analysisId=recommend_2088_3_81019_new2&scm=1007.13339.81019.0&pvid=b9edd7ff-9069-4c39-be95-b2d3ca8bdf17&tpp=1

https://www.aliexpress.com/item/2pcs-YS1560J-Temperature-and-humidity-sensor-shell-Waterproof-temperature-sensor-protective-cover-SHT10-SHT15-SHT20/32725840346.html?spm=2114.10010108.1000013.25.PVGRb3&traffic_analysisId=recommend_2088_13_81019_new2&scm=1007.13339.81019.0&pvid=b9edd7ff-9069-4c39-be95-b2d3ca8bdf17&tpp=1

https://www.aliexpress.com/item/TM16-115-temperature-and-humidity-sensor-protective-cover-waterproof-SHT10-SHT11-SHT20-SHT21-SHT15-SHT75-sensor/32578099865.html?spm=2114.10010108.1000013.10.gZI6yC&traffic_analysisId=recommend_2088_5_82199_new&scm=1007.13339.82199.0&pvid=3cc09c58-99e7-4a67-834a-3313c87ab573&tpp=1

Perhaps one of those might be big enough? Or, if not, perhaps it could be joined onto a larger waterproof cavity, and just the sensor itself goes into it? Unfortunately for me, the parts appear to be metric. However, maybe a search would yield some kind of metric-to-imperial union, at which point I could then leverage cheap local parts from Home Depot or the like, to fabricate a larger cavity for the rest of a wireless mote.

On the face of it, it seems plausible. It's main virtue is simplicity. Not sure what the failure modes are, or how they might be avoided if there are any. Plainly, you don't want to use components which might rust or otherwise corrode from humidity. Probably my biggest worry would be the possibility of condensate forming on the humidity sensor and skewing results until it evaporated. However, a sensor heater, such as some sensors (e.g. si7021: https://www.aliexpress.com/item/Industrial-High-Precision-Si7021-Humidity-Sensor-with-I2C-Interface-for-Arduino/32524005324.html?spm=a2g0s.13010208.99999999.350.t9NHvJ ) already have, might remedy that if it were to occur.

Has anyone tried either one of the above or anything similar? For instance, perhaps wrapping a mote in Tyvek and sealing the seam with Dupont housewrap tape would work just as well.

[Nca78]

@NeverDie they are all very small inside (5-6mm) so are only suitable for very thin PCB with SMD version of the sensor, even the breakout of si7021 that you linked is too big.

[NeverDie]

@Nca78
Golly, even an nRF52832 chip all by its lonesome self is bigger than 5-6mm. Those shells must be intended for just the sensor and nothing but the sensor (except maybe connecting wires). That would explain the presence of gland seals on some of them, such as:

https://www.aliexpress.com/item/Temperature-and-humidity-sensor-jacket-shell-protective-cover-waterproof-SHT10-SHT15-SHT20/32785090319.html?spm=2114.10010108.1000014.6.oDKhCV&traffic_analysisId=recommend_3035_null_null_null&scm=1007.13338.80878.000000000000000&pvid=2f02fcf9-5f96-485c-b076-6d892d6d2ae5&tpp=1
or
https://www.aliexpress.com/item/100pcs-lot-Free-shipping-SMD-resettable-fuse-SMD1206P150TF-60-1206-1-5A-1500MA-60V-PPTC/32422603296.html?spm=2114.search0104.3.126.qYG2gx&ws_ab_test=searchweb0_0,searchweb201602_5_10152_10065_10151_10068_10130_10084_10083_10119_10080_10082_10081_10110_10178_10136_10137_10111_10060_10112_5360018_10113_10155_10114_10154_438_10056_10055_10054_10182_10059_100031_10099_10078_10079_10103_10073_10102_10120_10189_10052_10053_10142_10107_10050_10051-10120,searchweb201603_5,ppcSwitch_5&btsid=4b333183-9955-44bb-a985-eb0a3aed0e3f&algo_expid=ad603dac-549a-4315-8ae9-50a2bd436e1b-17&algo_pvid=ad603dac-549a-4315-8ae9-50a2bd436e1b
or
https://www.aliexpress.com/item/50pcs-lot-Free-shipping-SMD-ceramic-gas-discharge-tube-BC401M-1812-400V-2KA-4-5X3-2X2/32428795826.html?spm=2114.search0104.3.119.qYG2gx&ws_ab_test=searchweb0_0,searchweb201602_5_10152_10065_10151_10068_10130_10084_10083_10119_10080_10082_10081_10110_10178_10136_10137_10111_10060_10112_5360018_10113_10155_10114_10154_438_10056_10055_10054_10182_10059_100031_10099_10078_10079_10103_10073_10102_10120_10189_10052_10053_10142_10107_10050_10051-10120,searchweb201603_5,ppcSwitch_5&btsid=4b333183-9955-44bb-a985-eb0a3aed0e3f&algo_expid=ad603dac-549a-4315-8ae9-50a2bd436e1b-16&algo_pvid=ad603dac-549a-4315-8ae9-50a2bd436e1b

[NeverDie]

@Nca78 said in Office plant monitor:

@NeverDie they are all very small inside (5-6mm) so are only suitable for very thin PCB with SMD version of the sensor, even the breakout of si7021 that you linked is too big.

I haven't confirmed it, but FWIW according to: http://www.wxforum.net/index.php?topic=32182.0
"The model shown in this link is too small for I2C boards, but seller has much larger models. L-04 has 12.8mm opening, L-06 has 17 mm and L-10 has 23mm opening."

[NeverDie]

@NeverDie
I've since had some communication with the seller. He said, "We have these dimensions," in reference to the photo below that he had attached:

[NeverDie]

The seller says I can buy 3 of the 1" diameter units at $5/pc.

The communication with the seller is like playing 20 questions, but I only get to ask one question at a time, with typically one day turnaround for an answer. If I ask more than one question per interaction, he doesn't really answer any of them. So, getting truly meaningful answers is a slow process.

[Nca78]

@NeverDie that sounds expensive, and I'm worried that at this size it's going to be difficult to stick in the soil for small plants...

[NeverDie]

@Nca78
Well, for small potted plants, you might have to re-pot the plant. However, the nice benefit that would arise is: no visible sensors, which carries with it very high WAF.