Moisture sensor corrosion

Hi,

I've bought a moisture-sensor from ebay (china) and after a few weeks of use the sensor is corroded.

Does anybody know a sensor that doesn't corrode ? What are your experiences ?

Thanks ! Maik

Corrosion can be caused by putting DC across the sensor. Is that what you did?

There is no sensor that doesn't corrode.

If you're careful in how you drive them, the cheap ones can last months. Expensive professional ones will last years.

Also consider that this corrosion is leaching meal ions into your soil.

Grumpy_Mike: Corrosion can be caused by putting DC across the sensor. Is that what you did?

I've read out the analog-Pin every 10 seconds... Maybe I should only read it once or twice per hour ?

Does the arduino only put current across the sensor when I call

sensor = analogRead(8);

or is there always current(and corrosion) on the sensor even if I don't read the value ? And can somebody tell me what the component that is put between the arduino and the sensor does ?

Thanks :)

If you want to reduce corrosion but still use DC, don't connect the sensor (presumably via a resistor ) directly to the +5 rail, but to an arduino output pin , and only tum it on when you wish to take a reading.

Allan

Does the arduino only put current across the sensor when I call

sensor = analogRead( 8 );

No it is there all the time. You will have a pull up resistor from the analog input to 5V. Connect that to an output pin and send it high just before the operation and set it to an input just after. That will minimise the corrosion but reversing the polarity is even better. So the ground of the sensor is connected to an output pin as well as the resistor to 5V. Then at the end of one reading reverse the high and low pins and take another dummy reading. You discard this, then set both output pins to be inputs.

There are a couple of capacitive soil moisture sensors you could try. They do not involve metal-to-soil contacts so corrosion is reduced (it is always a problem for electronics in a damp environment).

https://www.dfrobot.com/wiki/index.php/Capacitive_Soil_Moisture_Sensor_SKU:SEN0193

https://www.tindie.com/products/miceuz/i2c-soil-moisture-sensor/