I have been checking the specs and can't find this info so wondering if anyone has any thoughts.
I have some micro solar panels (from an old toy) that can generate 10v and average about 100mA (though obviously this changes based on amount of available light, cloud etc) and ideally I'd like to use these to drive an outdoor sensor for temp, light etc and write it to a memory card.
My question is really around the arduino baseline current draw. I know I can provide 40mA per I/O pin but what is it going to draw doing nothing more than either going round an empty loop() or running the blink test or something?
Is 100mA enough to do this? If not what IS the minimum required (and yes I understand if I want to drive anything plugged into the board I'm going to need MORE than the minimum) - I'd like to work out what I have to play with first before I start planning too far.
ps: yes I'm also aware that at some point the panels will cease to provide enough power for the arduino to run at all (ie at night). I'm fine with this.
I have a 3.3v promini running on 3.7V LiPo set up as remote control, connects to 5V/Vcc pin and does not use onboard regulator. MAX1811 battery charge control chip. RF 434 MHz TX module.
Keypad interrupts it, wakes up to send out keypress, goes back to sleep.
Draws ~9mA in sleep mode, jumps to ~15mA while transmitting.
Power LED, battery charge chip,TX module all contribute to overall current draw.
Suggest using a switching regulator to get the 10V down to 5V, then supply power to the 5V pin directly, vs wasting your small amount of current heating up the 5V regulator.
example Pololu Step-Down Voltage Regulator D24V3AHV
Or maybe get a LiPo battery also and a battery charging chip, charge the LiPo when sunlight available, run off the LiPo battery.
Thanks crossroads - okay so probably not going to have much drama providing that even when it's cloudy (even in a storm and it was bucketing rain today I was getting ~30mA so that should be enough).
Great point around the voltage regulator and going in direct on the 5v pin had totally forgotten you could do that. On something like a Duemilanove or equiv which runs at 5v it reckons min input tolerance is 6v (presumably to deal with any dips in supply?) so should I switch down to 5v or just above that do you reckon? Or I could go get a 3.3v pro mini or similar I guess...
Main reason I ask that is that my solar panels actually supply 5.3v each and I have them in series to deliver 10.6v so potentially I could get 1 panel to drive the arduino and either have more amps to play with or else use it for something else... maybe that pro mini is looking more useful after all?
@ajfisher,
5.3V going in to the 5V line will be okay.
I have run duemilanove off 3 AAs, still going fine down at 4.25. Specs say it should be in tolerance at 16 MHz all the down to ~3.9V.
@Terry,
The charging circuit is just the MAX1811 wired per its data sheet. 5V in from USB or wallwart to charge the LiPo battery, only needs a couple of Rs & Cs to set the control mode.
Panel mount jack 5.5mm/2.1mm for a wallwart plug, or a USB to 5.5/2.1mm plug adapter
Charges to 4.2V at 500mA current setting (altho this schematic might show 4.1V/100mA settings since I didn't have battery info when I first built it).
@zoomkat, where's the challenge of readymade? I did get a 25% off coupon from Harborfreight today, need to order ON April 24 only with it.
Thanks everyone. Agree with crossroads - why go ready made when you can build your own - especially when I have a whole stack of recycled solar panels sitting right in front of me?
So I guess that's a good example of official tolerance and actual based on what you chuck into it. On that basis then I can just go direct from one panel and then do something else with the other which is pretty cool.
