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i just plugged a CPU fan to the tinkerKit connector output ~5 directly.  Can I control this with analogWrite(pin5,255); for max speed correct and analogWrite(pin5,0) for no speed?

Is there any internal resistance for any pin or screw terminal on the arduino motor shield?

How can I control which Channel to use, A or B? smiley-sad-blue
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> i just plugged a CPU fan to the tinkerKit connector output ~5 directly.  
> Can I control this with analogWrite(pin5,255); for max speed correct
> and analogWrite(pin5,0) for no speed?

That only works for loads that draw less than 40 mA at 5V.  Won't work directly for a 12V fan.  You need a transistor to switch currents higher than 40 mA.

> Is there any internal resistance for any pin or screw terminal on the arduino motor shield?

What do you mean by "internal resistance"?
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resistance behind any pin.  Such that pin 13 has 220 ohm resistance.  Right?  No resistor required on pin 13 for an led
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resistance behind any pin.  Such that pin 13 has 220 ohm resistance.  Right?  No resistor required on pin 13 for an led

Pin 13 connection does not have a series resistor between the shield pin and the AVR pin. The on board resistor wires from the AVR pin to the resistor to the on-board led. The shield pin 13 is wired directly to the AVR pin so that you must still use an external series resistor with an external led even if wired to pin 13. You should make sure you understand that and if needed study the arduino schematic drawing of your board if you do not.

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resistance behind any pin.  Such that pin 13 has 220 ohm resistance.  Right?  No resistor required on pin 13 for an led

Only some of the early models had a resistor between the ATmega and Pin 13.  And only on Pin 13.

Newer models, like the UNO, don't have a resistor between the ATmega and Pin 13.  They also have a buffer between Pin 13 and the on-board LED to keep the LED from loading down Pin 13 when it's used as an input.
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