larryd:
Drive the relay with a transistor.
.
Thanks! I didn't know you could get relays this small, Definitely a much more feasible option now.
MorganS:
Find a relay with 3 output terminals: NC, COM and NO.COM is the common pin between the other two. One wire goes to that.
NC stands for "normally closed". That is, when the relay is off, this contact is "closed" which connects it to COM. Your other wire goes to that. Now the current will flow when the relay is NOT energised.
Is there something else that could do this? Not the biggest fan of electro-mechanical components and surely there is something that can do this when a transistor does the opposite?
kenwood120s:
So just to clarify:
- If the Arduino is active, it will read an existing PWM signal and some other signals, and construct a new PWM which goes to the fan
- If the Arduino is inactive, the existing PWM will go direct to the fan, and the other signals are ignored
Is that correct?
Correct! Sorry my explanation wasn't so great, Little bit scatter brain at the moment.