Products > SoilWatch 10

sleep mode for soil watch 10

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pinolec:
In this application, it shouldn't be a lot of difference between BJT and MOSFET. The NPN will be good as well.

Regards

jeanpaullm:
Hi , I was wondering if the circuit that was posted above worked with 3.3V circuits

pinolec:
It will work as long as you choose the transistor which works at 3.3V
Look for logic level MOSFETS with VGS threshold lower than 2V or best if the RDs(on) is specified for voltage 3.3V or lower.
I think I have mentioned somewhere on the forum example transistors which will work.

regards,
Piotr

javierb:
Hi, what is the difference between connect the sensor thought transistor or direct to a digital pin and manage it with pinmode, digitalWrite and delay?

pinolec:
This is a good question.
In general, microcontrollers are not designed to deliver currents in the range of 20mA efficiently. Some microcontrollers are specified for less current. But even if the microcontroller can deliver 20mA, usually will suffer a voltage drop. In other words at 20mA there will be some voltage drop. Please see the voltage drop for 3V and 5V supply (from ATmega328P datasheet).
 


The voltage drop at worst 4.4V is still within the range of supply voltage of SoilWatch 10 sensor.

 

Now the voltage drop is below the specified voltage for SoilWatch 10. This will simply not work as expected.

This is the main reason we should use a transistor. With transistor, there will much less voltage drop.

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