SoilWatch 10 monitored by XBee 3; sleep mode

[mattsj]

Hello, I am planning to monitor a SoilWatch 10 (3 Volt version) using an XBee 3 (Zigbee), both powered by battery.

Can you see any reason why this would not work?

I may have to use a switch mode regulator to provide steady voltage to XBee (and from XBee to SoilWatch 10), e.g. from 4-6V down to 3.3V?

Once I get it working, I will refine it to use a sleep mode in the XBee, to save battery.  e.g. take a soil moisture reading every 6 hours. (I want the battery to last several weeks, e.g. using four 2000mAh AA cells).  Will the SoilWatch 10 draw 24 milliAmps all the time if I do not switch it off between my 6-hourly samples? 

If I do switch the SoilWatch 10 off and on, e.g. using a transistor, how long should I wait after turning it on, before taking a reading from the SoilWatch 10?

[pinolec]

Hi,

I have no experience with Xbee or Zigbee at all. So I cant help you on that.

The SoilWatch 10 will continuously consume around 14mA (since rev 2). 
The startup time of the sensor is less than 100ms. So 100ms wait is enough.

As long as you keep the power down during the sleep below 100uA and limit the on time to minimum then it should last around 1 year.
here you can calculate how long the battery will last: https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-battery-life

Kind regards,
Piotr

[mattsj]

thanks Piotr
Where does the 100uA constraint come from, in your comment "keep the power down during the sleep below 100uA"

[pinolec]

With 100uA you can run 2000mAh battery for just over 2 years. But you don't want to run just in sleep mode so this will leave some energy for other tasks.
Run the numbers through the calculator at digikey.com and see how long will your device last.

I just found better calculator: https://www.geekstips.com/battery-life-calculator-sleep-mode/

Regards,
Piotr