PWM fan speed control with a 12F683

[mister_e]

Why turn all these off: FCMEN_OFF, IESO_OFF, WDT_OFF ?

Since you're using the internal OSC... there's no need to use the internal/external switchover feature, same goes for FailSafe clock.... check out the datasheet for the whole set of crispy and ... obscure... details

WDT_OFF? It's really up to you to decide, I tend to left it to ON... but, it's always case by case... still the datasheet will provide you some detail about the benefits of WDT to ON.

Are these two statements redundant:
OSCCON = %01110001 ' Internal 8MHz osc.
DEFINE OSC 8

No they're not, the OSCCON line specify the OSC speed to the PIC, while the DEFINE OSC specify the OSC Speed to the compiler.

[AvionicsMaster1]

Got the program and got the circuit set up. It seems to work well with LEDs but feeding the output to a FET, at least the FET I'm using, won't trigger the FET.

I looked at it with a scope and I'm getting barely over a 2V Peak signal. I assumed I'd get 5V square wave pulses spaced to get the right voltage from the PWM module. Did I do something wrong or do I need to find another FET?

I do appreciate the help and your patience.

[sayzer]

What FET?
MosFet?

Need to see the circuit anyway.

[AvionicsMaster1]

Ok forget about the FET and talk to me about the PWM signal. Should it be 5V pulses or 2.2V pulses? If 5V, what do I need to set to make it be that level?

[AvionicsMaster1]

Using Sayzer's code, attached, I've been able to control an LED as desired.

Coupling that to a larger current drawing device is a problem. Of the schematic page provided, the top drawing has pulses at GP2 to the MOSFET of about 2.3 volts and won't power on the fan. I thought once I figured out how to get the pulses up to around 5 volts the FET would turn on and I'd be golden.

The lower schematic adds R1 and R2 so I get around 4.8 volt peaks with varying RMS values but even with the larger pulse size it still won't turn on the fan. I felt really stupid after I figured that one out.

I can connect the gate to +5V and it will turn the FET on and drive the fan. Although I don't think it's bringing the fan up to full speed.

So what in hell am I missing? Why won't the chip drive the FET to turn on the fan?

[amgen]

Check PWM freq,

If too high, the inductance of the motor affects operation, add diode across motor pointing up, returns energy to motor when MOS FET switches off. Hardware PWM freq only goes so low. May need INT to PWM or do it in basic.
The ckt shows P-channel MOS but your N-channel setup is ok.

Don

[AvionicsMaster1]

I didn't have a coil so I tried the cap across the motor and voila!

Thanks.

I still can't get the fan to do three speed steps it's either on or off. Any ideas?