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Author Topic: Axon current draw  (Read 1397 times)

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Offline Cristi_NeaguTopic starter

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Axon current draw
« on: April 09, 2010, 04:03:45 PM »
Didn't really knew how to name this one.... oh well...

Hi.

Can anyone make an educated guess and tell me how much current does an Axon draw during normal operation? I won't be using any servos with it, just a lot of ADC and all the processing power that i can get out of it. Plus a few digital I/O's.

Since the board has a 7805 with a TO220 case on it, i assume i doesn't draw more than 500-800mA at it's worse. Am i right?

Thanks.

Offline cyberfish

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Re: Axon current draw
« Reply #1 on: April 09, 2010, 07:44:14 PM »
Probably no more than a few mA.

Offline SmAsH

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Re: Axon current draw
« Reply #2 on: April 09, 2010, 08:14:01 PM »
I'm guessing your asking about the axon 1?
The atmega640 on the board draws extremely low amounts of current, probably under 40mA.

That's not a 7805 on there! That's an ldo regulator. It should be able to support most of your adc devices as long as their current draw isn't too high.
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Offline Admin

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Re: Axon current draw
« Reply #3 on: April 09, 2010, 10:54:06 PM »
Will you be powering sensors with the ADC bus?

Offline Cristi_NeaguTopic starter

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Re: Axon current draw
« Reply #4 on: April 09, 2010, 11:08:29 PM »
Thanks for the reply.

I'm guessing your asking about the axon 1?

That's right.

That's not a 7805 on there! That's an ldo regulator.

Didn't know that. Thanks. I was wondering how a 7805 is capable of handling 1.5A with no questions asked... Turns out it's not a 7805 ;D

If the Axon uses such a small amount of power, then i can go on with my plan. For my project i'm using a 30V power supply. so, for the Axon, i need to step down that voltage to about 8V. If i have such a small current drain, i can use a normal voltage regulator. Yes, i know i can use something more efficient, like what's on the Axon itself, but i don't feel it's necessary.

Also, on a more or less related note: in the datasheet for the Axon it says that maximum supply voltage should be 10V. Why is that? Is it because the Axon is designed with servos in mind and they can't operate at more that 7-8V? If that is so, if i don't use any servos, or i use external devices that work at higher voltages, can i feed, let's say, 15V in the Axon without problem?

Thanks again for the replies.

P.S. just saw Admin's reply. Yes, i will. I will be using potentiometers set up as voltage dividers for position encoding. I have taken that into account, and i know how much current they drain. Thanks for the reply.

Offline Admin

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Re: Axon current draw
« Reply #5 on: April 10, 2010, 12:10:29 AM »
Quote
in the datasheet for the Axon it says that maximum supply voltage should be 10V. Why is that? Is it because the Axon is designed with servos in mind and they can't operate at more that 7-8V?
Well, I never expected people to power anything greater than say 7.2V servos on the Axon, so didn't bother having it handle more.

If you go above 10V, the big blue capacitor can potentially explode, but everything else is fine until about 16V. Just replace this cap with one that has a higher rating, and it'll be fine.

Offline Cristi_NeaguTopic starter

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Re: Axon current draw
« Reply #6 on: April 10, 2010, 05:06:44 AM »
Yeah... i just saw the rating on that capacitor, now that you pointed it out. It would be an interesting idea to change that capacitor, but i don't think it's worth in my case. It would just lead to a complicated build. Besides, I'd be running 15V through that board, pretty close to 16V, too close for comfort actually.
I'll stick to my plan. I'll use a 7808 to supply the Axon. It should work nicely, i think.

Thanks.

Offline Ro-Bot-X

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Re: Axon current draw
« Reply #7 on: April 10, 2010, 05:22:34 AM »
Keep in mind that all Digital pins are connected to the input power bus, only the Analog pins are connected to the regulated 5V. This was designed like that so users can plug the servos directly and have them run from the input power bus. The servos can be powered from 4.8V up to 7.2V, usually a 6V battery is used. This is why there is a LDO voltage regulator on board instead of a regular 7805 (there are variants that support higher currents, up to 5A if I remember correctly). If you need regulated 5V on the Digital pins, you may apply a regulated 5V at the input, the on board LDO will be bypassed and you will have same voltage on all pins.
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Offline Cristi_NeaguTopic starter

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Re: Axon current draw
« Reply #8 on: April 10, 2010, 05:31:42 AM »
So, you mean that if i turn, let's say, port E5 to high, on the innermost pin on the header i'll get whatever voltage i'm feeding the Axon (8V in my case), instead of 5V? I mean, i know that on the middle pin i'll get 8V, but i didn't know that i'll be getting 8V on the digital I/O... That would complicate things a bit...

Offline Admin

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Re: Axon current draw
« Reply #9 on: April 10, 2010, 05:52:31 AM »
Quote
I'll use a 7808 to supply the Axon. It should work nicely, i think.
You can't feed the Axon 5V, as the Axon requires at least 5.3V to work :P

I think your best bet is to find another power supply.

Offline Cristi_NeaguTopic starter

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Re: Axon current draw
« Reply #10 on: April 10, 2010, 06:09:25 AM »
It's not about the power supply. I can deal with that. I was relying on the fact that a high on a digital output is 5V. Since the Axon is designed with servos in mind, i can understand why that isn't so.
All that i can do now is power the Axon at 6V, and pray. Pray on one hand that it'll be enough power, and on the other that those 6V won't fry the circuits i was planning to control with the Axon. They have a maximum input voltage of 7V. It's gonna be a helluva juggling act.

For the future, i'd really like to see 5V regulated I/O's on an Axon :P

Offline SmAsH

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Re: Axon current draw
« Reply #11 on: April 10, 2010, 06:14:31 AM »
What he meant was, the axon digital pins output 5v, the digital power bus is the battery input voltage.
The axon will work fine with a 6v input voltage so you will be fine.

Just to clear something up, the digital output pin from the microcontroller outputs 5v, the power bus may be different.
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Offline Cristi_NeaguTopic starter

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Re: Axon current draw
« Reply #12 on: April 10, 2010, 06:21:31 AM »
Aaaahhhhh....i seeeee...... thanks for clearing that up SmAsH. Well, everything is peachy keen again ;D

Anyways, you guys told me just about everything i needed about powering an Axon. I'll still be going with a cascaded design, first to 15V then to 8V. I know it's not the most efficient thing in the world, but it will work just fine for me. I'll set the final details when my Axon will arrive.

Thanks for the replies, everyone.

 


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