Yes, and I said it shouldn't be there.
Returned value of the A/D depends on two things. input voltage and VCC.
Did you measure VCC of the Attiny when turning the pot.
I've added the cap there because the voltage was a bit noisy without it. Someone has recommended to add a cap in another topic I've found about LM35.
I've measured VCC. The pot doesn't influence it.
When you do, do not connect the LED the way you have shown it.
1) it is the wrong way round
2) there is no current limiting, with such a high powered LED you need a constant current supply to control it not a simple PWM signal.
It is best if you post a photograph of your wiring so we can check the ground arrangement. I would also add better capacitors to that regulator you need to look up the actual data sheet from the manufacturers you are using to find the minimum values.
What is the write way?
C7 should be 10nF to 100nF at most, you're crow-barring the supply everytime Q2 switches on. Perhaps
you meant there to be a decoupling cap to ground for the motor?
R5 should be more like 150 ohms, your powering a motor from that transistor, so the base needs enough current.
Q1 needs a pull-down resistor from gate to source, 10k to 100k will do, value not critical, to keep it from
switching on during reset/power cycling.
Any reason for the large value of R6? 150 ohms is fine, if you are using PWM you likely need a gate driver IC
Should I connect C7 to GND or the way it is now is ok?
R5 - will do it.
Q1 pull-down resistor from G to GND right?
R6 - will do it.
I do agree with Smajdalf.
Vgs and Qg of this fet are both too high for the Attiny.
Make sure you got those protective glasses on when you power up the LED.
I can change it to IRL1404ZPBF.