First of all, would the ATtiny85 be ok, or are there other 5V AVR's that could work? (Everything will be powered from a USB-cable).
There are dozens of other AVRs that could do the same job. But what the job of the ATtiny? The MOSFET itself can switch 5V without a problem and 2A of current is fine for many MOSFETs. Just make sure the threshold voltage is low enough to be switched by a 5V input.
pylon:
There are dozens of other AVRs that could do the same job. But what the job of the ATtiny? The MOSFET itself can switch 5V without a problem and 2A of current is fine for many MOSFETs. Just make sure the threshold voltage is low enough to be switched by a 5V input.
I didn’t realize the ATtiny could run directly off 5V, so I’ll use that.
It’s to control the MOSFET from COM port on a computer.
I thought MOSFET was a simple "drop-in" replacement for a normal relay (which I don't want to use because of the click).
An SSR is a drop-in replacement for relays in most cases but a MOSFET is more like a standard transistor however not current-driven but voltage-driven. You have to carefully choose the right type and you often need more components to drive it correctly, usually at least a drop-down resistor is needed.
pylon:
you often need more components to drive it correctly, usually at least a drop-down resistor is needed.
A pull up or down resistor is typically needed, but a current limiting resistor is not needed, typically, so more often, less components to drive a MOSFET.
I thought a MOSFET was a SSR, but I guess SSR is a different component?
A DC solid state relay probably has a MOSFET inside. An AC SSR usually has a TRIAC inside.
A solid state relay is optically isolated. There is no electrical connection between the "input" and the "output". The coil and contacts on regular electro-mechanical relays are also electrically-isolated. (Of course, they don't have to be isolated in your final circuit.)
Usually a solid state relay doesn't need any additional components, but there are some that require an external current-limiting resistor for the LED.