I'm making some sensor nodes out of pro minis connected via nrf24l01+ PA LNA modules
I want to use an N-channel mosfet to cut power to the radio modules prior to the nodes sleeping to eliminate the problems with getting these cheap radio modules to sleep reliably.
I'm struggling to figure out how to choose the right N-channel mosfet for the job and was hoping someone could suggest an appropriate component, or direct me to any kind of tutorial on how to choose the right component?
I'm powering the nodes from 3 x AA batteries, so i'd like to be able to switch the gate with as little as 2V if possible.
Why low-side switching? That breaks continuity of RF ground, note.
The module takes 110mA or so I believe, so any nFET with an on-resistance of 1 ohm or less and suitable
current handling would do.
I'm powering the nodes from 3 x AA batteries, so i'd like to be able to switch the gate with as little as 2V if possible.
Makes no sense at all. The nRF24L01 requires 2.7 to 3.3V supply to work at all(*), and 3 AA batteries give
4.5V.
Any logic-level MOSFET rated at Vgs=4.5V ought to be fine. I'd recommend using a p-MOSFET and
do high-side switching to eliminate any breakage in RF ground (which could lead to various problems).
BJT transistor could also be used for switching this module, 0.11A isn't very high.
(*) unless you level-convert all the logic signals to the nRF's Vcc. The 5V tolerance of the inputs
is conditional upon this supply voltage range, if you read the datasheet for the nRF24L01.
Ok thanks for the heads up with the potential problems with grounding of the radio. I know power draw and associated issues is a real problem with the devices, but was hoping the transistor wouldn't create any significant issues. I'll play around and see what the results are..
IRT using 3xAA batteries.. In my hands, I power both the rf module and 3V pro micro directly with a 3xAA batt pack on vcc with voltage regulator removed and it's super stable until the batteries drain to the point when they only supply around 2.4V and the arduino starts to crap out. So it seems the RF modules can tolerate less than 2.7V. It has to be said I'm using a fairly cheap voltage meter so it could be innacurate.
These units will be remote (100's of km's from me) and I only want to change the batteries once every year if I can help it, so I need the switch to work at the lower voltage range that these batteries will provide as they drain.
