Electronic – arduino – Having difficulties using a darlington (BD681) to drive a 12V fan from an Arduino

arduinodarlingtontransistors

I'm trying to power a 12v fan using a darlington so I can control the speed from an Arduino. When I wire up as below nothing happens, even though I'm sending a PWM signal:

Circuit diagram http://img809.imageshack.us/img809/5261/wireissue.png

Have I wired up the transistor incorrectly?

Transistor: http://www.bitsbox.co.uk/data/transistor/BD681.pdf

Best Answer

The diode in your drawing is backwards.

As such, all the current is flowing through the diode, and you're not getting enough voltage to even turn the fan on.

enter image description here

Related Solutions

Electronic – Arduino controlled PWM PC Fan

One thing to note is that


if (pwmVal != 255) {
    pwmVal += 10;
    ...

is not going to stop at 255, since pwmVal will be 250, then 260, e.t.c. One way to fix this would be write


if(pwmVal < 255)
{
   pwmVal += 10;
}
else
{
   pwmVal = 255;
}

By the way your code is written, if DEBUG is set to 0, nothing will happen (pwmVal will be set to 0). If DEBUG is set to 1, the fan speed will increase at a rate set by "wait" (which isn't defined in this code), until it gets to it's maximum. The value will also be printed to the serial port.

Electronic – arduino – Controlling a 4-wired fan PWM Signal using Arduino allows only two settings

Fans don't use stock pwm frequencies. The PWM control frequency needs to be 25khz. A 16mhz arduino can do this relatively easily through software. Just search "4 wire fan arduino" and there's quite a few posts on it, including sample code to set the prescaler frequency so the output PWM is at 25khz.

Best Answer

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Electronic – arduino – Controlling a 4-wired fan PWM Signal using Arduino allows only two settings

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