I have a 24x15 LED array connected to a Arduino Mini with a radio receiver. I have everything working just fine but since I am not quite proficient in many things electricity, I thought I would ask for some advice from the community.
If I try to power the LEDs and radio receiver from just 4 AA batteries, the receiver doesn't get enough amps (I am assuming) and doesn't work (but the LED array works just fine). This is why I ended up in my current situation. I tried giving the radio receiver only 2 AA batteries but that did not work as well.
What would be the best way to wire this up to use the minimum number of batteries possible?
The radio needs 5V and does not have a regulator on board, so you need to give it a regulated 5V. You may be able to take this from the 5V pin on the Arduino depending on how much current it needs. Otherwise you will need to add a separate 5V regulator for it. Right now it looks like you are using 4AAs directly which could be anywhere from 5-6 volts and it really should be a set 5V.
Which Arduino are you using? Most would be seriously under voltage with only two AA's. If this is the case you can't get 5V out if you only are supplying 3 in.
I suspect this is more of a voltage issue, but you may also have trouble drawing enough current from standard AAs. Once you have the voltage sorted out if you still have a current issue you could move to C or D cells for more current or move to NiMH rechargeable batteries. They are only 1.2V a piece, but they can generally outdo an alkaline battery in terms of current output.
I am using an Arduino Mini which, even though the docs say it needs a min of 5V, in practice it is fine with only 3. I ran it on 3V with the LED array on and it lasted a good 10 hours.
So, since the receiver seams to require 5V at all times and the arduino needs a minimum of 3, so I would need 8V in total. This is 6 AA batteries.
The thing though is that starts to get a bit heavy and I feel that I could lessen the battery amount that goes into the radio receiver. I can't find how many amps is needed to run the receiver though. Is there a way to find how many amps is needed for that and then find the lightest battery that would still provide a decent battery life to the receiver?
No, the voltages don't add. If the receiver requires 5V and the Arduino requires 3V, then the minimum voltage to run the entire thingg is 5V. But you'll need it to be regulated.
It is no a good idea to run an Arduino directly from four AA alkaline batteries. The AVR chip is rated at 5.5V max, and four AA batteries can put out 1.6V x 4 = 6.4V when fresh.
Ok, since the whole thing requires only 5V to run, then why can't I run both the LED board and the receiver from the 5V output from the Mini? If I put in ~6V (4AA) to the 9V of the Mini, the 5V output should be enough to power both...but it isn't.
This now makes some more sense. The reason the radio doesn't function off of the mini's 5V is that the regulator cannot support enough current for it to run. The simplest solution is to feed your 5V regulator from batteries that you like totaling around 6V. Linear regulators in general need to drop about 0.5-1.0 V to work well, so you should feed in a battery voltage of around or a little above 6V.
Now we have a regulated 5V supply that can drive the radio directly and the mini directly. If we put that 5V through the mini's input regulator (Vin) we would have problems, but because we already have 5V you can connect it up to the 5V pin on the mini and be good to go because you are bypassing the mini's unnecessary regulator. Do be sure your 7805 is spitting out 5V before you make this connection.
Try 4xAA (alkaline) (or 5xAA rechargeable) for this setup to start. If the life is bad you can move to larger batteries (C or D cell) or a different type of battery. Adding more batteries in series to increase the voltage will only make the regulator work harder and won't give you any additional battery life.
Actually, unless it is a low dropout regulator, linear regulators "in general" should have 2 to 3V more than the output voltage in order to regulate without dropping voltage as more current is drawn.
The 7805 in particular really requires 8V to reliably regulate to 5V. You also have to take into account any ripple on the power supply - the lowest voltage at the bottom-most portion of any ripple must be at 8V.