Hi, with Arduino I made a project using a finger print sensor that opens the door for me. I have noticed that only when the house light comes and goes quickly does it open the door for me because the momentary power loss causes the relay to close. while he goes away for a few more than a few seconds this does not happen. my question is: can I power the Arduino with 12v and connect a 9v battery so that when the light goes off it is powered by the battery?
if yes, is the battery used when powered by the 12v power supply? or will he use the 9v only when the 12v is missing?
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Schematics and code please, and an understandable description in engineering terms of the issue.
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there is no code to sell. mine is a simple question. i just want to know if connecting two power supplies, one 12v and one 9v, which one is used. the 9v battery should power the Arduino in the event of a power failure.
Okey. Know that "Arduino" doesn't specify anything. There are some 20 different ones.
Regarding 9 volt, don't use the PP3, fire alarm battery. It doesn't provide current, only 9 volt at very low loads..
Regarding 12 volt, be careful using a lead battery. Fully charged it will exceed the maximum allowed Vin for f ex an Arduino UNO. 7.5 to 12.0 volt I think the spec is for an UNO, and some more types.
But yes, having a backup battery connected to Vin at the same time as powering the board via USB is possible. Just one remark: The controller board has almost no capacity to power any other circuitry. Maybe a little LED.
You can use appropriate diodes in each of the + voltage feeds where the anode is connected to the source and the cathodes are connected together then to your power supply. You can reverse this but this will be easier for you to understand. These diodes automatically select the higher voltage source. Be sure all the grounds are connected.
The input voltage range of Vin is about ~6-20V BUT that is what it will survive and operate at without anything else drawing power from the onboard regulator. The voltage above 5V is dissipated as heat by the regulator causing it to get very hot. Watts equals voltage drop across the regulator times current.
If you are serious about this project draw an Annotated schematic, a frizzy picture is just a wiring layout and is useless. Also post links to each of the hardware items that give technical information, market places such as Amazon do not give all of the needed information, just enough to sell it.
There are many CAD programs on line for free, I use KiCad.
I think the OP is asking if he can power the board with a backup 9v battery.
We get that, but his question is largely ambiguous and a schematic would help considerably.
I think that's asking a lot of the average poster. I mean it in the sense of if they knew engineering terms they would've used them.
Don't connect both 9 and 12 volt like that. Use one power source only. Using serial diodes would help.
That is not a schematic. Apart from that problem, it is missing all of the components that connect to it.
I agree about the diodes. Google things like, "battery backup circuit" "backup circuit diodes" etc...
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