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Topic: Mosfet gate voltage (Read 1 time) previous topic - next topic

TeslaIaint

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Those voltage readings are good. So if we use a 220-ohm resistor between the MCU and MOSFET gate, and just drive the pin with digitalWrite() rather than PWM, when the pin is driven high, what are the voltages on either side of the 220-ohm resistor?


You want me to take the motor out of the circuit or leave it in?

Jack Christensen


You want me to take the motor out of the circuit or leave it in?


Leave it in please
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

TeslaIaint

I measure anywhere from 1.2V to 4.96V on both sides of the resistor. It jumps all around. I'm going to try to wire up a TIP 120 and see how the motor responds to that.

Jack Christensen

Yet when driving a pure resistive load, the voltage looked steady, correct? Does the motor spin at a constant speed or does it act as though it's getting variable voltage?
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

TeslaIaint


Yet when driving a pure resistive load, the voltage looked steady, correct? Does the motor spin at a constant speed or does it act as though it's getting variable voltage?


Yes, when driving the pure resistive load, the voltage was steady. Sometimes the motor spins at a constant speed and sometimes it acts as though it's getting a variable voltage.

I'm really starting to believe it's a breadboard issue. I wired up the TIP 120, and it worked fine. I switched back to the mosfet, and it worked as advertised, and I even measured the right voltages in the right places.

A little later I will solder this circuit onto a perfboard and test it. I'll let you know what happens.

Thanks for all your help!

Jack Christensen

Interesting ... agree it seems to be pointing to breadboard or wiring or something similar.

How many miles on that breadboard? I'm pretty surprised that I don't have more breadboard issues than I do, they're really quite rare, but most of mine are relatively new.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

majenko


Interesting ... agree it seems to be pointing to breadboard or wiring or something similar.

How many miles on that breadboard? I'm pretty surprised that I don't have more breadboard issues than I do, they're really quite rare, but most of mine are relatively new.

Mine are all ropey as hell and half the tracks don't grip any more - those that aren't melted from overheating components ;)

TeslaIaint

Haha I've used this breadboard quite a bit, and there are even some spots where the plastic is a bit melted. I think it's time to retire it.

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