Soft-touch relay switching

[Drew Hallenbeck]

So I've built a few switching circuits that are available out there. I'm thinking about putting my own layout together. Before I order parts to start breadboarding I have a question.
The ones I've built use a 5V regulator and relays with 5V coils. There are similarly sized relays that have 9V coils. Why not just use the 9V relays and eliminate the regulator?
Most trannies or IC's that might be used in such circuits are rated for well known her 9V.
Why use a regulated 5V supply for these switching circuits?

[EBRAddict]

I've never used one or built one, but aren't most microcontroller-driven? I've seen a few modern microcontrollers that will accept 5.5V as power but none up to 9-10V. Same with the input/output pins.

[zombie_rock123]

(For none microcontroller ones) I have no definite answers as to why but my guess would be size and cost - the 5volt ones may just be slightly cheaper?

That said, I've built this one loads of times:
https://paulinthelab.blogspot.co.uk/2013/04/soft-latch-true-bypass-relay-switch-for.html

With these relays:
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=253&products_id=1912&zenid=s1h2og8p22nulp5aj67k708mj2

As with everything else I've built from Paul In The Lab's site, it's awesome.

[cloudscapes]

You need the regulator anyway for the microcontroller. There are no 9 volt micros.