FAN controlled by TIP120 and Arduino.

Hello

I am trying to control a fan with arduino as It is explained in this blog:

[bildr.org]

But I want to make it different,...

I want the fan works by default, just in case the arduino fails, or something happens....

The circuit I am trying is the following, modelled with LTSPICE..

..


I am using a pulsed power source as Arduino´s PWM.

The problem is that pwm power source gives me 270 mA back to Arduino...and Arduino only holds 40mA..

Maybe the voltage pwm is not right simulated.,,I do not know too much about circuit simulation...

Can someone give some advice????

Thank you all.

How about copying a proven design, e.g. [reprap.org] ?

To have it on by default, simply connect the 1M resistor not to GND, but to 5V. Using a TIP120 instead of an IRLB8743 is entirely fine if the load is below a few amps. And ... TIP120's are slow, so no 20 kHz PWM. 50 Hz likely works (FAST_PWM undefined in Teacup firmware).

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Generation 7 Electronics	Teacup Firmware	RepRap DIY