Sanguinololu 1.3a fan

Hi everyone,
I'm trying to connect a fan on the heated bed pins (free for now...)
I changed HEATER_1_PIN and TEMP_1_PIN to -1 and FAN_PIN to 12
Now i can start and stop the fan with the M106 M107 commands
But i'm not able to change the speed with M106 Sx (with x a number between 0 and 255)
With a multimeter i saw that the voltage is 0 (M107) or ~10 V (M106) but it doesn't change using M106 Sx
Thanks for the help!

Is pin 12 a PWM-able pin? I don't think so, but I might be wrong.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

This is the table in the wiki page...i'm not sure but i think yes because it was the pin of the heated bed

The heater drivers on Sanguinololu are PWM, so even when set at the minimum the heater output will output a pulse that alternates between 0 and 12v. You'd need an oscilliscope or a low pass filter to watch the output vary.

But also the fan speed doesn't change