MOSFET as a Switch

Other Hardware General Electronics
1

I am looking at the "Temperature and humidity sensor - battery powered" project by Nick Gammon.

I would like to build this project using 3.6V LiSocal2 battery and suface mount components.

I have conducted a couple of tests with the MOSFET switching and am not able to get it to work.
I have tried both FDN338P and FDV304P which are P-Channel Digital devices.
In the attached schematic, +VBAT is 3.6V.
The 330R (R7) is driven from the Arduino D7.
D7 is configured as a Output, with default HIGH. "digitalWrite (POWER, LOW); // turn power ON"

I am not a hardware specialist and would appreciate someone with the knowledge to review my design.

FDN338P.png
FDN338P.png824×552 4.55 KB

2

I would say the best approach is to first test your output stage. I suggest you perform these steps:

  1. Disconnect the Arduino.

  2. put some load on the drain, perhaps a 1k to ground

  3. Connect what would have been the Arduino side of R7 to ground, the drain should be at or near +Vbat

  4. Disconnect the Arduino side of R7, the drain should be near zero and the gate should be near +Vbat.

Tell us which steps did not work. If all worked we need to look at the Arduino side. Perhaps the grounds are different?

BTW This is always a good troubleshooting approach....divide and conquer :slight_smile: