I must not be understanding something correctly though. If I have the regulator setup and measure it with a multimeter, I get 5.01V (perfect) but as soon as I plug in the radio receiver it quickly drops to 4.75V (not enough to power the receiver).
On the other hand though, if I have my Arduino plugged in to the USB port and use the 5V from the Arduino to try to power the receiver, I get no such voltage drop and it powers it just fine. Sadly this isn't going to cut it for me since I would like to only have to use 5V to power my entire project.
Can someone explain to me why I get that drop with the regulator and what I can do it keep 4AA batteries as close to possible at 5V?
If you look at the data sheet you'll see that the minimum input voltage for a regulated output is around 7 volts. The circuit is seemingly able to supply the 5 volts with no load but you need to up your input voltage for a loaded output. Using this type of regulator with AA cells really is a waste of power since, with 5 cells to give 7.5 volts, you will be wasting at least 30% of battery energy to keep the regulator happy.
For efficiency you might be better going with a switched mode regulator.
What would be a regulator that I could get that would keep 5V for as long as physically possible from the 4AA batteries? Or, is there a better way to keep 5V to this? I only need 3V to power my Arduino (it is a Mini) so I don't want to go too far over the 5V to power all of this.
Edit: Also, where did you read in the datasheet that it needs min 7V to keep 5V out? I am looking through other datasheets to see if I can find something that works for me but I can't seam to find where it says this information
The sentence I quoted was from the first page, right side (STANDARD APPLICATION subtitle).
You can also find the information in multiple tables (characteristic is called "Dropout Voltage").
You could use a standard 3,3V regulator if that is the version you have (3,3V Pro Mini), or a low dropout regulator, something like this: http://www.farnell.com/datasheets/78392.pdf
It has typical dropout voltage of 0,32V.
I am using a standard Mini but it works just fine with 2AA's connected to the 5V pin. The actual 5V requirement comes from the radio receiver I have. I am still trying to figure out how to get all this wired up properly but I think I will find a solution soon. Maybe putting 4AAs into the 9V pin (6-5V over the battery lifespan) then using the 5V pin to power the receiver? Maybe that would give me what I need?
I just dont want to put 4 AA's into the 5V pin on the Mini since this (as far as I understand) could kill the mini if the batteries are very fresh (giving the full 6V for the first few minutes of life)
Edit: Or maybe just 6 AAs into the 9V supply (9V fresh, 7.2V nearly empty) with the voltage regulator to power the radio receiver and an unregulated connection going to the Mini? Or would it just be best to take the "waste" and voltage regulate everything?
You can get low dropout (LDO) voltage regulators. For example LM2940CT-5.0 which has a 0.5V drop out.
Or you could look for DC-DC "Buck converter step-down module". I got some from eBay for $US 1.75 each.
A bit of testing shows that you can get 5V out of it (the one I got was adjustable) with 6V or more into it, however once the input falls below around 5.7V the output falls below 4.9V. So, much the same as the LDO voltage regulator.
What I ended up doing last night which seams to work really well was to put 6AA batteries together for ~8V and put a 5V regulator between the shift registers driving the LEDs and the batteries, then connect the 9V pin on the Mini to the batteries and then connect the 5V pin from the Mini to the radio receiver.
The thing is that just 5V isnt enough to power my Mini, the radio receiver, and the LEDs. If I run the LEDs and receiver from the same 5V, the receiver just dies off.
Maybe the best would be to have 4AA batteries connected to the LEDs with one of these http://www.pololu.com/catalog/product/2123 also connected to the batteries and the Mini and Receiver being connected to the Step-up/down chip? Would that make sense?