Powering a portable Capacitive Soil Moisture Sensor

Hi guys,

I'm turning to you guys for some advice. I am fairly new with the IoT but my latest project I have used an Arduino Uno to read from a capacitive soil moisture sensor. It worked fine, however, it had to be plugged into my USB and my laptop had to be running for it to work and log the data.

I have bought an ESP8266 wifi board to try and solve this problem by connecting to wifi and transmitting the data over wifi, but the new board (ESP8266 ) only has a 3.3v output and the capacitive soil moisture sensor seems to not give accurate readings on those voltages.

I've used the old Arduino Uno to power a breadboard and when I connect this power up to the sensor to use as a power source it works and gives accurate readings. But the idea is to go as compact as possible and wireless so that I can end up with a small portable unit that is fully battery operated and that uploads the data through wifi.

I am considering to power the sensor with a battery but not sure how to achieve this? Should I start with a 9v battery and convert it to 5v? I've found some forums that suggest things like IC7805 series voltage regulator? Is this the best option or is there a better way? Will it overheat? I assume a relay switch would also be a good idea then I can do the readings when needed like in intervals instead of continuous monitoring.

It's feeling like there must be an easier way to power up this sensor? As I said I am fairly new with this so any advice would be appreciated.

The main components I've used:

Capacitive soil moisture sensor v1.2: https://www.amazon.co.uk/gp/product/B07V2BBVQR/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1

WiFi Internet ESP8266 Development board: https://www.amazon.co.uk/gp/product/B06W9HLD4X/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1

Arduino Uno rev3: Arduino Uno Rev3 | Arduino Official Store

Thank you so much and looking forward to your ideas and advice.
Jason Lodder

Your sensor needs 3.3-5v. It has an onboard voltage regulator therefore as long as you supply 3.3-5V the results should be the same. Is it possible you are supplying less than 3v? You did not mention what you’re using to power the ESP8266. A separate power supply (not one from the ESP8266) should help you get consistent readings. Relay switches are not efficient for battery powered devices... think transistor or MOS. If you have a power problem as this skinny’s, you should monitor this using a meter or Oscope to see if there are load drops while the module is transmitting that causes fluctuations. First diagnose then find a solution. Stop guessing.