MOSFET/circuit troubleshotting :-\

Absolutely! Without one we can only guess. I'm tempted to infer that maybe the MOSFET needs a driver, such as a 2n7000. But that's simply a shot in the dark based on incomplete data. BTW, I assume the OP has observed proper handling precautions for the MOSFET? There's a lot of static around at this time of year.

I've changed it to a 1uF, since I *think* 100nF is 0.1uF... It doesn't change my problem though - motor only slows down, doesn't stop :(

The S and D of the MOSFET are the wrong way around (according to the annotation).

The wiring around the small cap looks totally wrong !

Yes, 100nF = 0.1uF.

It's probably the MOSFET. When something smokes, it's usually the power component. BTW, before you replace it, you are sure you have enough gate voltage available to turn it on?? Your supply rail voltage is pretty low. What's the threshold voltage of the FET you're using? If not known, what's the type number of the FET you're using and we'll tell you...

No it isn't! In the circumstances, there's far too much capacitance in the output circuit as it is. This will make for sluggishness. I'd suggest simply 100nF (*maximum*) ceramic in this case.

I was referring to the power supply decoupling capacitor on the PIC. It won't hurt to use 1uF there.

I've tried about 4, and they all did the same (one was the bigger 1A version I bought) :(

It was at the time - I don't know how, it was fine earlier... I think I took the cap out and put it back wrong, then next time I took a cable out, I put it back according to where I saw the cap going! That was all fixed before my last few posts though :(

Yep :P

I've not got an anti-static strap or anything, but I regularly touch the radiator as I'm working. The static-sensetive stuff all arrives in bags marked so from Rapid :-)

It's only just over 1V, but the motor is *on*. When the pin goes low, the pin output drops to exactly 0, but the motor only slows - this doesn't make any sense?

Nope. If I connect:

Both S & G are connected to ground, and +ve is connected to D via the motor, the motor runs :-\

You're going to love this...

My MOSFET wasn't the wrong way around - I was reading the diagram wrong (it was drawn from the bottom, not the top), *And* I though source = supply and drain = ground, so it was actually connected correctly. My recent tests have all been flawed!

So, connecting everything back up correctly, with the motor *really* connected to Drain, and Source to ground, guess what happens...

The motor doesn't turn at all....

This makes sense, if the 1.xxV coming from the PIC's high isn't enough to drive the MOSFET.

Why the chip is only outputting 1.xxV, I don't know, but at least I've got somewhere to start looking!

:)

According to the datasheet, a low should be < 0.6V, and a high should be Vdd - 0.7V. Vdd is around 4.5V (I've confirmed this with my meter), but the pin high is around 1.3V (low is 0V). I've tried with another chip, with the same results!

Have you got the source and drain the right way round now? There's no point checking the gate-source voltage until this is sorted out. Source should be connected to ground.

I've got two pins configured as outputs, and when high, one is around

I've just written the same program to a new chip, to get the same results... :(

It's a dud then.

1. Do you have the red probe on the pin and the black probe on ground?
2. Is the pin programmed for active pull-up or open-drain? It needs to be an active pull-up.
3. Was anything else connected to the pin when you measured this?

I believe all my problems come down to the one thing - my pic "high" isn't really high.

I've got two chips, both with the same program burnt (I can post, it it helps).

They sit "high" until an input goes low, then they go low too.

Using my meter, is seems these outputs are:

GP4 0.3V (way below the min the datasheet says!) GP5 0.6V

When I make the input low, they go:

GP4 0V GP5 0V

Both chips do the same, and I can't find anything in the datasheet to suggest even if I had something silly enabled/disabled, this would happen.

Any ideas?