I am trying to power an atmega328p, and the esp8266 for one of my projects.
I am trying to drive a relay to switch lights on and off. The problem is that the relay runs on 12v, the atmega runs on 5v and the esp8266 runs on 3.3. I was thinking of using a board mount power supply to use 120v ac, to get 12v for the relay, then use a 7805 regulator to get 5v for the atmega, and finally use a LM3940IT to get 3.3v for the esp8266. I do know that the esp8266 can not be run off of the atmega's 3.3v pin 🙁
What I am wondering is am I totally off on what I am hoping to do. Is there a better way? I have found a couple articles about switch power but, not as much as I would like.
I am also concerned about the amount of amperage needed for everything. I will use a Darlington transistor to drive the relay from the atmega, I am not sure how much power that will consume.
Here is the board PSU
http://www.mouser.com/ProductDetail/RECOM/RAC04-12DC-230/?qs=F5OEftmZcCAbIVZkvUf1yw%3d%3d
I would really appreciate any help.
Thank you very much.
Best Answer
What you're doing is certainly feasible, as long as you're willing to handle the waste power. The one change I'd suggest is replacing the PSU with a RAC04-12SC. You don't need the -12 that your specified PSU provides, and going to a single 12 volt output will giver you 333 mA, which may be enough. Note that, if the PSU is going full out, it will provide 4 watts, and the 7805 will have to dissipate 2.8 watts minus the power in the relay coil. This is certainly possible, but you must use a good heat sink, with proper care for thermal connection.