An amplifier for Arduino
For my project, the Arduino output is not enough so digging on the net and asking to a friend some help, I managed to build an amplifier to feed my 3 computer fans.
This circuit can be used as an amplifier to switch on and off a DC motor and to regulate its spinning speed with a PWM source generator. In my case the PWM generator would be the PIN 9, 10 and 11 from the Arduino board.
Given that the adapter that I will use to drive my 3 computers fan has a voltage of 12V and an intensity of 1,5A, a common npn transistor would not do the job and burn quite fast. From the datasheet, you can see that the BDX53, the transistor that I chose is used to drive small drills, for example, so perhaps it would be quite good for the completion of my project. The diode, put in parallel, is used to control and limit the extra tensions that can be generated by the adapter that would damage the transistor. A good one to use is the 1N4007. The regulation of the spinning speed of the motor is set by the frequency and duration of the on and off status of the PWM, but you don’t have to worry about, as the calculation would be made by the Arduino board. You should only write analogWrite on the code, together with the output pin chosen and an integer between 0 and 255 (e.g. “analogWrite(9, 255)” would set up the maximum output. I hav found out that PWM frequency of on and off status vary beetwen 20.000 and 30.000 Hz, so that the board does not produce any sound that can be heard by the human hear.
Below you will find a scheme to explain how PWM works. The faster the frequency between the on and off status is, the higher is the faked analog voltage output. The slower it is, the lower the voltage.
Below an image on how to connect the BDX53F to the circuit:
And here is how it looks completely built for all the three PWM channels of Arduino:
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