I've had a search of the forum and just wind up confused. I am very new to this but really enjoying it; I am making a device to lure rare birds in to nest in a specific area we protect. This means playing a recording of their songs a couple of times a day for a few hours over a week or two.
I have an Arduino Uno, and a Adafruit music maker shield, plus two speakers and a RTC unit.
To power this, I wondered if I could use a 12V leisure battery - something like this - so it will run for several days, but even after reading through other posts on the forum I'm confused about what I need.
Do I need a DC-DC step down buck charger or not?
Can I just plug it straight into the Arduino?
Should I use a car-cigarette lighter socket - usb plug thingy?
Thank you for your help!
You can plug 12V into the Vin on the Uno. The voltage is than dropped to 5V by the onboard 5V regulator. The problem with that approach is that the 5V regulator is rated for about 1 Watt of dissipation. To keep the dissipation under 1W no more than about 145mA can be drawn from the regulator. The Uno, itself, draws about 50mA, leaving less than 100mA for the rest of the circuitry connected to the regulator. Drawing close to 100mA from the 5V regulator will make it get pretty warm and it will shut down if ti gets too hot. If you use a step down regulator to drop the voltage from 12V to 5V and connect that 5V to the 5V of the Uno, you bypass the 5V regulator and the full current from the step down is available to the circuitry connected to the 5V line.
Thank you - that's a good explanation. So we should use an actual stepdown board rather than just plugging in a car-socket USB power plug?
So we should use an actual stepdown board
Yes, 7-9V for the RAW input (barrel jack) or 5V for Vcc (which is also the 5V output of the Arduino).
Here is a good selection of high quality modules.
jremington:
Yes, 7-9V for the RAW input (barrel jack)
But that is just as bad (almost) as plugging 12 V into it.
Not a serious suggestion,
No, 7-9V in the RAW jack is fine, and MUCH better than "plugging 12 V into it", which often does not work at all.
So we should use an actual stepdown board rather than just plugging in a car-socket USB power plug?
The car socket USB power plug drops the 12V to 5V and bypasses the on board regulator so it is virtually the same as a step down converter and is a good option, as well.