So take this piece of schematic and replace R44 and R52 with 10k and since you have 5V and you want to go as near as 0V as possible on the gate
you might try R68 2k2 and R61 180ohms or even a bit lower if it still doesn't behave properly.
This will take you 5 minutes so try it and tell me if it than works.
If it does you know the fault is in the output of your microcontroller which can be normal since some outputs can be shortprotected or current limited to 15mA or so.
This doesn't work either. The high output of the I/O pin drops to <2V and at the base of the NPN the voltage is ~500mV.
He's only switching at one hertz so gate capacitance and resistor are a non issue.
He's demonstrated that the mosfet can switch on 5v signaling, just not with the mcu.
Your circuit is essentially what he implemented, if you think the gpio driver as the pnp.
The issue is definitely not the mosfet.
Yes, the current rating of the I/O pin isn't the problem - it discharges the mosfet gate just fine. The I/O pin driven voltage at the mosfet gate is a good square wave with sharp edges so it's nothing to do with that.
What if you remove the 1s switching and just drive the pin low? Does the fet ever turn on? What about if you ground the pin with a jumper while the uC is driving it low, does the fet turn on then? If so what changed? Have you tried scoping the voltage drop across the 470R resistor?
No the mosfet doesn't turn on at all with the i/o pin driven low. If I ground it with a jumper then yes it does turn on, and in fact it remains on until the MCU drives the pin high again. If I ground it quickly and at the right time I can see on the scope that the mosfet remains on for a short while until the MCU turns it off. The voltage drop across the 470R is nothing - the full 5V square wave is hitting the mosfet gate.
I think 1s just might not be long enough to get the gate low enough to conduct through that 10k resistor without a significant voltage drop. You could also try switching to a much larger load resistor. Also, are you watching the voltage with a dmm or scope? The "on time" might be so short with that load resistor and a 1s on/off period that you can't catch it with a dmm.
I have a 10k trimmer for the load and it doesn't turn on at all even at a short.
At least he should measure Vgs in both situations they can and will not bevrhe same.
How exactly - I don't want to hook my scope up to Vgs because I'm powering the circuit from a mains PSU so hooking my scope ground clip to the gate/source will create a ground loop..
Using a DMM doesn't seem to work. Measuring Vgs with the DMM alone registers nothing - just 0V on the DMM. But if I connect the scope again to measure the gate voltage it comes back to life but the gate is now switching between 5V and ~2.5V instead of 5V and 0V. Removing the DMM makes it go back to 5V swing. I've no idea.. maybe it's a crap DMM (it was only cheap).