Hi,
I am using 4 AAA batteries (6V), to power up a setup, which includes 2 geared motors (they operate at 6v and 500mA at max load.), Arduino mini micro controller, 8 LED, 6 LDR. Will I have any problem with this??
Absolute maximum operating voltage for the ATmega328P is 6.0V per the datasheet. Four fresh alkaline cells will put out a little more than that. I'd be willing to bet an adult beverage that it'd be OK, but at the same time I probably wouldn't do it, as I do try to live within the datasheet specs.
I would probably use 7805 for the arduino, what about the rest? Is it advisable to use a single 6v supply to all these components? Or should I use 2 separate power supplies?
You could put a series diode between the battery positive and the arduino Voltage input. That would knock the voltage down .4-.6 volts and keep you within AVR chip specifications. The cathode end of the diode would wire to the arduino.
Lefty
Diode seems to be a good idea..
thank you.. 
FelixFelicis:
I would probably use 7805 for the arduino, what about the rest? Is it advisable to use a single 6v supply to all these components? Or should I use 2 separate power supplies?
A 7805 requires higher then 6vdc to meet it's minimum drop out voltage spec for the regulator chip. You would have to use a low drop out regulator, or as I already stated just use a series diode like a 1N4001.
Lefty
kk..I will use a diode.
Is it advisable to use a single 6v supply to all these components? Or should I use 2 separate power supplies?
FelixFelicis:
kk..I will use a diode.Is it advisable to use a single 6v supply to all these components? Or should I use 2 separate power supplies?
Well I would try it with just one. If you have problems due to electrical motor noise you can either add some filtering capacitors or go with two 6volt battery packs. Sometime you just have to try stuff to see how it's going to work out rather then make all the perfect decisions from the start. 
Lefty
Or just power the arduino from the 3rd battery instead of the 4th.
While you will start with a 6v supply the voltage will soon drop at which point you will have problems. I thing you would do much better with a 9V supply and one or more voltage regulators ( the system used on the UNO) for example.
Mark
PS - There is a section of the form devoted to power and power supplies.
M
holmes4:
While you will start with a 6v supply the voltage will soon drop at which point you will have problems. I thing you would do much better with a 9V supply and one or more voltage regulators ( the system used on the UNO) for example.
If by "9V supply" you mean a standard 9V battery; that won't not have enough charge capacity to run two motors and eight LEDs for long, especially with the extra power losses from voltage regulators. Instead I suggest using six AAA batteries (with appropriate voltage regulators). There are battery holders readily avaiable for this configuration.
Why are you all so insistent on wasting all the battery capacity as heat in the regulator?
4AAs will do fine. Will have 3-4 hour so of life driving the motors.
Get 2 sets of rechargable NiMH batteries & have some fun.
To kind of reiterate what others have said,
-
7805 has a dropout voltage of about 2V, so with a series diode, 1N400x, you'll need
a battery voltage = 8V MINIMUM. -
It's generally not the best idea to try and run the motors and controller off the
same battery, although I do it all the time. I use 6 NiMH rechargeable cells [7.2V],
plus an LDO v.reg [LM2940], plus schottky series diode, so the v.reg will operate on
about 6V input. -
Better to use AA cells than AAA cells for motor driving, as you can get 2500 mAhr
NiMH cells, which will last quite a long time.
Thanks for all your suggestions...
My project is compact. So I cannot afford to have 7805, until its vital. I dont care about how fast they drain. Diode seems to be a good option.
AAA batteries dont occupy much space. I prefer AAA than AA.
But, I am still thinking about 6v LiPo batteries!! Any suggestions?
LiPo with switching regulator.
Hmm.. thats nice, but I have 2 geared motors the max current at full load is 500mA for each one. and apart from this I have other loads! is this still advisable?
Didn't realize that was 500mA each.
Need to search a little more for a higher current model then.
Kk...
Is it better to use these Lipo batteries or 4 AAA batteries in series is better??