Hello,
I've got ledstrips around 0.5m each for every stairstep. I want to make them able to fade in and out for each apart. Each strip need around 200-250mA.
I tried to use the 2n7000, but i can't let the led totally fade out. All I can manage to do with these is to get the from fully on to a little less fully on. 
Now my question is, how could I chose which transistor I need.
13 steps?
Use AOI514 to sink current from each strip.
CrossRoads:
Use AOI514 to sink current from each strip.
Great component though it is, isn't a FET with 17-46A current capability a little overkill for switching 250mA?
However, 2n7000 is really on the edge, if not over, its max current. Maybe they have become damaged and won't switch fully off?
Can you post a schematic. We should check if the transistors are being correctly used.
Paul
No, that's the maximum beyond which it would be damaged. The gate threshold voltage is 0.8~3V, so 5V should switch it on ok. Your problem is switching them off.
Now, where is that schematic? Just show one transistor and strip.
PaulRB:
Now, where is that schematic? Just show one transistor and strip.
You are switching the high side with an N channel fet. Switch the low side.
No, that's a photograph. Suggest you google the word "schematic".
That's not a schematic either, but at least we can tell what's connected to what now.
That looks correct to me. What is that resistor: red-red-brown or red-red-purple? Red-red-purple would be too high.
Try taking the wire from the pwm pin and connecting it direct to 5V and then to ground. What happens?