i need your help on this. I have this custom board build with a TMP102 sensor and a mega328, so far i am able to get around 50 hours of operation with a 850 mha lipo battery. i am sleeping the arduino and then i wake it up with the watch dog timer, the average current comsume per hour is 12 to 15 mha. So i think thats good considering is a matrix display.
How ever i would like to have it outside for ever!!!
So since is low power i think i can have it hook to a solar cell outside and when the solar cell is dead(cloudy or raining) i can power ir from my lipo battery.
I have this in hand
and for the solar cell i plan to use
now the issue i have is the circuit to select if i will be powering with battery, use the solar panel as power or use the solar power and charge the battery at same time.
i dont know if the charger can be conected at all times and that will do the switching automatically when the solar power is dead.
if thats not the case i will need to use a voltage comparator to compare lipo againts solar cell and that will trigger to use battery? do you know any good circuits that will do this?
Take a look at the Seeduino Stalker (Seeeduino Stalker v2.3 | Seeed Studio Wiki), there you have almost everything you need on one board, including the battery charger and automatic switching logic, as well as a RTC that is capable of waking up the ATmega at any time, so your sleep states may be more than the 8s the watchdog provides.
if thats not the case i will need to use a voltage comparator to compare lipo againts solar cell and that will trigger to use battery? do you know any good circuits that will do this?
Take a look at the schematics of the Stalker.
thats a good idea but is kind big and 39 bucks
Seeedstudio provides complete Eagle files for the stalker, so you're free to use the parts you do need and omit the stuff you don't (for space). I have no solution for the price but I don't think it's exceptionally expensive. In most cases it's cheaper than doing it yourself, the PCB alone may cost more.
If you are looking for low power consumption, you would be better off using a reflective LCD display instead of an LED display, unless you need to read it in the dark. Otherwise, I think you'll need a large solar panel area.
