Hello seeed studio forum,
I am sure this is listed somewhere but a search for this info
has been conducted for about an hour now with no luck.
An XIAO SAMD21 microcontroller is being used to send
a signal to a MOSFET transistor and turn on twelve volt
LEDs in a closet.
The green LED on the XIAO comes on when it gets 5 volts
and the indicator LED, D1 on the schematic, operates as expected
but the load LEDs, D2 - D5 are not coming on.
The input and out put from the PIR test normal and the input
to XIAO pin3 tests normal, 3.1 volts.
The nest step is to test the out put from the XIAO to the MOSFET
at pin 4.
What should the expected output voltage from pin 4 of the XIAO be?
I am guessing 2 or 3 volts but would like to know what is expected.
Thanks.
Allen Pitts
Dallas TX
it all depends… i am assuming you are driving the pin digital high in the code… it should be 3v3… but the device may not be able to sink enough current to provide the forward voltage to diode or mosfet…
Hi allenpits,
I believe the output voltage of pin 4 of XIAO will be 3.3V.
There is no resistor to limit the current of LED D2-D3, is it built into the LED?
Q2 STD12NF06 Vgs(th)=3V. it may not be able to turn on completely with 3.3V output of XIAO port. Perhaps a FET with lower Vgs(th) should be selected.
Hello @cgwaltney and @msfujino and the seeed forum,
LEDs D2 - D5 are twelve volt LED automobile back up lights
that have circuitry built in so that providing the lamps w 12 volts
will operate the lamps. No current resistance is needed.
Will test the MOSFET to see if I can get the XIAO to turn it
on.
The strange thing is this circuit was built and installed under
a cabinet in my kitchen and it has worked es expected
for several days.
So a second PCB was loaded and, when the second circuit
would not work, the first circuit was deinstalled and taken
back to the bench to if I had, for instance, installed the
transistor backward or made some construction mistake
but I can’t find it.
If the first circuit XIAO operates the MOSFET why does
the second circuit XIAO not operate the MOSFET?
Thanks.
Allen
1 Like
According to the STD12NF06 datasheet, Vgs(th) ranges from 2 to 4V. I think it will turn on if lucky, and not if unlucky.
This FET is suitable for driving the gate with 5V.
maybe try a logic level shifter to convert 3v3 to higher level or a 5V device like arduino Uno
