Go easy on me this is my first tute:P
Disclaimer: i take no responsibility for any issues you may encounter using this product.
there prob wont be any but just covering my ass:P
Step 1: Components and pcb
Capacitor (ceramic preferable) = 10nf
Electrolytic capacitor 220uf = 16v
IC socket (8pin)
DPDT relay (MUST BE DECENT QUALITY)=12V
N-channel MOSFET(varies according to job)
Resistor = 33k
Resistor = 10k
Resistor = 100k
Resistor = 1k
Resistor = 51R
Potentiometer (PCB mount) = 1M
PCB of course or breadboard if you wish to test first
be aware if you wish to have the output hooked up to a motor you may need different fets to the one listed and also may need another diode to protect it, DC computer fans dont have current spike problems. feel free to ask me any questions and ill do my best to answer them for you.
Its up to you of which method you pick to get your circuit, i have used a photoexposure process and a veroboard, both work ok, the veroboard was more compact but it was messy and dirty.