The circuit shown is a simple current limiter ... Using an IRFZ44N, I made a simple LED driver and used an Arduino Uno directly. Remember the Arduino pins go up to 5V and I used the fade example ...

Instead of the relative horror of driving 40 LEDs with a single Arduino, [Martyn] bit the bullet and got a Maxim 7221 LED driver ... and control the entire circuit, [Martyn] used an Arduino ...