I am planning to build a small device too scare off the deer that keep eating all my flowerbeds.
For background info, I am using
2 PIR motion sensors
a photoresistor to identify night/day
a SD card/reader
LM386 audio amplifier
6V 100ma small solar panel, a diode
7.4V 1000mAh LiPo
I plan on it being about the size of an aluminum can. The program is simple, only if it is at night and motion is detected then a WAV file is triggered to play from the SD card. I would like the volume to be comprable to those little brookestone pop-up speakers http://www.brookstone.com/mobile-mini-speaker
Here's my question. I am unsure about charging a battery that is powering the circuit at the same time. Is it even possible to add any charge to a battery of that size with a panel that small? If it is, I know I need a diode to prevent the panel from sucking current at night but I am also figuring that the voltage from the battery has to be checked periodically and the voltage in from the panel must be stopped once the battery is full in order to prevent damage to the battery. I am also a bit lost on what kind of speaker will give me some good volume and decent fidelity without breaking the bank. I found this ebay one that fits the size requirements but I need hear some second opinions. http://www.ebay.com/itm/Brand-New-2-2-inch-Neodymium-Full-range-Speaker-From-IDN-Panasonic-/221115532729?pt=US_Radio_Comm_Speakers&hash=item337b8345b9
1. To stop from overcharging, would I use a little DC-DC relay to accomplish this or is there a better way? Or is this such a small voltage that none of this is even necessary?
2. Is this a good speaker option? What would be a better one?
I know I haven't thought of something or what I think I know is wrong, so please, steer me in the right direction!