Hey guys, this forum has been quite helpful for me so I thought I'd utilize your gargantuan intellects for my benefit once more. I'm working on a project that will be using an ATmega, some servos, and possibly a piezo or small speaker. I'm not privy to current and voltage and whatnot so I need help. I know that current is like pressure and other basic theory but I'm not too sure how to apply it. Here's my setup: ATmega, 3 small servos, one med. servo, and one buzzer/speaker. I'll have another just like it, but with one less small servo. I want this to be powered using one wall wart, but I'm not sure how to calculate what I'll need, and I'm not familiar with the hardware solutions that are available.
the med. servo will turn ~100 degrees and back every 8 hours. The small servos will turn ~90 degrees and back when activated by an rfid tag on a cat. I will write the code to make sure that the big servo waits until the small servos are done with any movement before it moves.
I'm not asking for a specific answer, and I haven't picked out my servos yet so I don't have the operating volts or amps. I'm looking for information that I can apply universally so I don't have to ask anything like this again.
By the way, I've never really done anything like this before so assume I'm almost totally ignorant with your explanations.
tercelkisor:
I haven't picked out my servos yet so I don't have the operating volts or amps. I'm looking for information that I can apply universally so I don't have to ask anything like this again.
Problem with servos is that the datasheets don't seem to give the current. A rule of thumb is 1Amp, it seems, but you won't ever really know unless you measure it. Most servos are 4.8 to 6V, that's usually the easy part; the current is the unknown.
So you need to add up the currents that might be needed at the same time- you're minimising that by coding the motions for different times-, and get a supply that gives that current (say 2 or 3 Amps for arguments sake) at 6V probably.
I suppose pressure was a bad choice of word. I guess I meant that current was like current in a river or something, but thanks for the correction. So can the ATmega handle that many amps? Am I right in assuming that the voltage pretty much remains constant? The amps are decreased as components are used, correct? I guess I'm scared of having 3 amps going to the atmega while the servos aren't in use. Is that a legitimate fear? Thanks for the reply.
No... current is drawn by the user, not imposed by the supply.
So if you have a supply capable of 3Amps and one component consumes 1/2Amp and the other 2A, if the 2A one is off, the 1/2A one still only takes its 1/2. Then if they both are on, and take a total of 2.5, the left over capacity of .5A is just available for a third component but doesn't force itself on anything.
Oh! thanks! I thought it was much more complex than that. So to sum up. 6v (All the ones i've looked at are in the 6v range and there will be a 5v voltage regulator for the atmega and a 3.3v regulator for my rfid readers. the small speaker or piezo is negligible because they will be use when the small servos are used) anyway, 6v , and the total amount of amps I need for the max load that will be run? Should I go a little higher in amperage for wiggle room or is that not an issue?
I suppose pressure was a bad choice of word. I guess I meant that current was like current in a river or something, but thanks for the correction. So can the ATmega handle that many amps? Am I right in assuming that the voltage pretty much remains constant? The amps are decreased as components are used, correct? I guess I'm scared of having 3 amps going to the atmega while the servos aren't in use. Is that a legitimate fear? Thanks for the reply.