Author Topic: First time with mosfets, am I doing it right? (wireless irrigation system)  (Read 207 times)

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Offline namero999

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  • Country: de
Hello all (and sorry, english is not my native language).

I'm working on a personal project, an automatic watering system. It has the following features:
- esp8266
- analog and i2c ports for sensors (such as temp and soil moisture)
- port for water pump (250mA @ 5V)

In front of the whole thing, I'm putting a soft latching on/off switch, as described in this eev video



I attach the schematic, where I divided the circuit in logical components (the relevant one being Power and Pump, where the 2 mosfets are circled in red).



My questions are:
- is it correct to have a mosfet piloting the main power and one piloting only the pump?
- how can I calculate the current draw of the soft latching on/off circuit? I'm afraid I can't see how much current will pass through it when the pump (or pumps!) will be on, therefore I'm not sure what components I should choose to implement it.

Thanks, generally speaking if you have any feedback on the schematic I'll appreciate it, I'm a beginner on these topics.

Best regards.
 

Offline Arjunan M R

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Which MOSFET are you using for Q4?
 

Offline namero999

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I still have to decide but I think this is my candidate https://www.mouser.de/datasheet/2/308/NTR1P02T1-D-100317.pdf
 

Offline Arjunan M R

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Also, how much current will the pump draw? The maximum continuous drain current of Q1 is 750mA.
 

Offline namero999

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The pump draws 250mA @ 5V and the reason why I chose the 750mA is because I might opt to have multiple pumps (2 or 3) attached to it.
 

Offline Arjunan M R

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If you are going to control 3 pumps using the MOSFET,  you might go with another one. You are probably going to heat up the MOSFET if you draw its max current. I recommend only using a max of 2.
 

Offline namero999

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  • Posts: 4
  • Country: de
Thanks, indeed I am way more inclined towards having max 2 pumps (maybe in a second revision of the project).

When it comes to Q4 instead (so, the "main" mosfets), generally speaking, is that a design that makes sense? One "power" block with the soft latching on/off scheme, and then the rest with a second mosfet for the pump(s)?
 

Offline NivagSwerdna

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Looks good to me.  You could use NDS332P for Q4 if you haven't picked a candidate yet.  Have fun  :)
 
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