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Topic: soil moisture sensor + TURN OFF 3.3V ?? (Read 1 time) previous topic - next topic

kove3374

Hello everyone,
I want to develop an application with Arduino One in order to soil moisture sensing using Decagon EC-5, which are relativamene at low cost.
what's the problem:
those sensors must be supplied with a voltage from 2.5 to 3.5 V, however, being capacitive sensors, I can not powered  them continuously!
I have to power them for about 10ms (about now I can not remember) and then reading the analog channel.
therefore a kind of excitation delay!
but Could I set OFF pin voltage 3.3V?

Could we TURN OFF 3.3V or 5V pins ?????????
thanks
Alessandro

robtillaart


You can use one of the digital pins to switch on/off 5V for 10 ms. as long as it draws no more than ~20 mA it should be no problem. otherwise you should use a power transistor to switch on/off the power supply for the sensor.

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

kove3374

thank you rob,
yes it's true, but for switch OFF 3.3V ?

robtillaart


with a voltage divider you can make 3.3 volt from any 5 volt digitalPin (including analog pins && dont forget pinmode output)

the standard 3.3 volt output cannot be switched. .

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

Grumpy_Mike

Quote
with a voltage divider you can make 3.3 volt from any 5 volt digitalPin

You can but this device takes 10mA so powering it from a potential divider is not much of an option given there is only 40mA available from a digital pin. As a rule of thumb you need at least ten times the current down a potential divider as you are going to draw out of it.

It would be best to switch the power to this sensor from the 3V3 output through a PNP transistor acting as a top switch.

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