Power standalone atmega328 and servo motor via 9V battery

Hello everyone, i want to power the arduino chip (standalone- not on arduino board) which is 5V btw and a servo motor which needs 6V to operate (well it operates also at 4.8V but with less torque..)

I have a 9V battery, an 7805 regulator (9V to 5V) some 10uF caps and a potensiometer.

How do i do that?

With only those components?

Your motor’s going to be running at 5V…

ok, so what else do i need?

Well before you dive into details, are you sure your 9 vdc battery can supply the current requirements for a servo? What kind of battery specifically are you working with? Small 9 volt batteries designed to power smoke alarms just don't work for servos that have motors in them.

Lefty

you mean that the 9V battery doesn't have the amperage to start the motor or that it will drain the battery quickly?

would you suggest 4 AA batteries instead?

thebigbadwolf: would you suggest 4 AA batteries instead?

Yes, that will cost you a lot less in batteries.

ok how about power? 4 AA's are more powerful than a 9V through a regulator?

Four AA batteries won't work with your 7805 because you'll need at least 7 volts input (look up your specific 7805's data sheet for specifics). I use 6 AA batteries for input. A 7805 and a 6V regulator in parallel from your 6AA batteries would probably work ok. Don't forget to decouple. http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

If you are going to more than ~8v power supply, then you could make a setup like below to supply 5v to the chip and 5.7v to the servo. If you use a 6v power source, a diode in the supply to the chip would reduce the voltage to ~5.3v.

As your servo need 6V, the obvious solution is 4 AA alkaline cells, feeding the servo directly, and feeding the atmega328p through a silicon diode.

ok got it! thanks everyone!

but, cost aside, which is more preferable, to drive the motor with 4 AA's or with a regulated 9V battery.

i've read somewhere that 4 AA have more amperage than a single 9V (regulated to 6V of course)

thebigbadwolf: but, cost aside, which is more preferable, to drive the motor with 4 AA's or with a regulated 9V battery.

i've read somewhere that 4 AA have more amperage than a single 9V (regulated to 6V of course)

You can find relevant information at http://data.energizer.com/.

so, i decided to go for the 4 AA rechargeable batteries. 4*1.2=4.8V right?

WRONG! these eneloops i bought give 5.67V, that means 1.4 each.

so the atmega328 can hold 5.5V. if i connect 5.67 will it burn? i mean for 0.17 Volts?

thebigbadwolf: so, i decided to go for the 4 AA rechargeable batteries. 4*1.2=4.8V right?

WRONG! these eneloops i bought give 5.67V, that means 1.4 each.

so the atmega328 can hold 5.5V. if i connect 5.67 will it burn? i mean for 0.17 Volts?

6V is the MAXIMUM voltage so you should be ok, but I would just toss in a series diode to drop the voltage a little more.

  1. NiMH cells can supply 1.4V when fully charged, but I think you will find that the moment you put them under load, the voltage will drop to something lower.

  2. The atmega328p is rated at 6V absolute maximum. But check the voltage rating of any other chips you are using as well.

  3. If in doubt (or if using alkaline cells instead of NiMH), you can put a silicon diode in series with the supply to lose about 0.7V, or a Schottky diode to lose about 0.3V.

afremont: 6V is the MAXIMUM voltage so you should be ok, but I would just toss in a series diode to drop the voltage a little more.

i just did and the voltage went to 3.5 or something, and i'm not in the mood to go out searching for diodes right now.

i think i'll go for it and hope that the current of the battry will drop a little ...

dc42: 1. NiMH cells can supply 1.4V when fully charged, but I think you will find that the moment you put them under load, the voltage will drop to something lower.

  1. The atmega328p is rated at 6V absolute maximum. But check the voltage rating of any other chips you are using as well.

  2. If in doubt (or if using alkaline cells instead of NiMH), you can put a silicon diode in series with the supply to lose about 0.7V, or a Schottky diode to lose about 0.3V.

yep!

thebigbadwolf:

afremont:
6V is the MAXIMUM voltage so you should be ok, but I would just toss in a series diode to drop the voltage a little more.

i just did and the voltage went to 3.5 or something, and i’m not in the mood to go out searching for diodes right now.

i think i’ll go for it and hope that the current of the battry will drop a little …

About the only way I can imagine that much voltage drop from a diode, is from putting in a Zener reverse biased. Even a Zener shouldn’t drop more than .7V forward biased, as far as I know.

Diodes are a lot cheaper than a new board.

EDIT: spelling

ouch! i guess you're right! 5.12V seems better now! :P