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Revision to Connecting and configuring fans


We recommend no more than 1.5A continuous current draw from each fan output, although 3 to 4A for a few seconds while the fan starts up will not harm them.
For details of the configuration options available for various firmware versions see the [[Gcode#Section_M106_Fan_On|M106 gcode section]]
=== Cautions when connecting brushed DC motors e.g. air pumps ===
For more examples see the [[ConfiguringRepRapFirmwareCartesianPrinter#Section_Tool_definition_section|tool definition section]] of the config.g file.
== 4 wire fans and inverting the PWM signal ==
The I parameter on M106 causes the fan output signal to be inverted if its value is greater than zero.
[code]M106 P1 I1 ; invert PWM of fan 1[/code]
This makes the cooling fan output suitable for feeding the PWM input of a 4-wire fan via a diode. If the parameter is present and zero, the output is not inverted. If the I parameter is negative then in RRF 1.16 and later the fan is disabled, which frees up the pin for use as a general purpose I/O pin that can be controlled using M42.

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