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Author Topic: Using regulated power in $50 robot, need some help  (Read 1692 times)

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Offline kiritTopic starter

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Using regulated power in $50 robot, need some help
« on: December 02, 2008, 04:25:26 PM »
Hi, I bought a kit from sparkfun http://www.sparkfun.com/commerce/product_info.php?products_id=114 and i wanted to put everything on a breadboard, before going to the proto board(pc board). My confidence in soldering is not very good yet. So anyways, my question is this. If i have 4.8v of regulated power, can i skip the 5v power regulator and big capacitor and just power the MC pin 7 from the power bus, the 2 servos from the power bus too? Thanks in advance.
« Last Edit: December 02, 2008, 04:26:19 PM by kirit »

Offline airman00

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Re: Using regulated power in $50 robot, need some help
« Reply #1 on: December 02, 2008, 05:31:41 PM »
short answer : no you can't

soldering is easy and practice makes perfect
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Offline ArcMan

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Re: Using regulated power in $50 robot, need some help
« Reply #2 on: December 02, 2008, 06:02:07 PM »
Take a look at your MC data sheet.  It will tell you what the acceptable voltage supply is.  If 4.8V falls within the spec'ed voltage range, then your OK.
However, powering your servos from the same regulated supply as your MC can cause problems, as airman implies.  You at least need some filtering between the servo supply and the MC supply (which capacitors give you to some extent).
« Last Edit: December 02, 2008, 06:06:54 PM by ArcMan »

Offline pomprocker

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Re: Using regulated power in $50 robot, need some help
« Reply #3 on: December 02, 2008, 06:54:48 PM »
Thats not a very good kit. The one that curiousinventor.com sells, there are pins coming off the unregulated power. So you can get regulated and unregulated power. You can also attach a heat sink and a breadboard pot to get anywhere up to the max 37vdc that the regulator can handle depending on your power supply input.

Offline kiritTopic starter

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Re: Using regulated power in $50 robot, need some help
« Reply #4 on: December 02, 2008, 07:05:53 PM »
Well according to the atmega8 data sheet, it requires between 4.5-5.5v and the servo needs between 4.8v-6.0v (hitec hs-311). Is there a non-complicated reason why it wouldnt work? Sorry for the noob question, Im still quite early in my EE education. ;)

Offline airman00

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Re: Using regulated power in $50 robot, need some help
« Reply #5 on: December 02, 2008, 07:27:09 PM »
4.8V battery does not stay at 4.8V the whole time , it will vary - when the battery is about to die it will not have 4.8V , it will have less. Therefore that battery directly is not giving a constant set voltage - the voltage will vary over time.

A 5V regulator gives a constant 5V as long as the voltage is over 6V ( or in most cases 7 V). A microcontroller needs a constant voltage to be able to do "stuff" like do analog readings etc. A varying voltage makes a different Voltage reference for the microcontroller,  which means the microcontroller will not be able to get good readings since the thing it is comparing all the readings to is constantly changing ( since the battery is constantly getting power sucked out of it by the circuit)
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Offline kiritTopic starter

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Re: Using regulated power in $50 robot, need some help
« Reply #6 on: December 02, 2008, 08:24:02 PM »
airman00, Im not initially planning on using 4.8v battery power. Im using 4.8v of wall power. Basically im looking at setting this thing up on my breadboard and programming the servos to 0 and then hacking them. After I get this plus some basic programming done to test things out, I was going to solder things up and get the 6v nimh battery as the tut suggests. But for now I was just going to get a wall-wart power supply hook it to this power regulator kit from sparkfun, and put it on my breadboard. Like I said above, Im a noob in these things, but shouldnt this give a steady 4.8v of power to both the servos and the MC since its getting a constant supply of power from the wall plug?

Offline airman00

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Re: Using regulated power in $50 robot, need some help
« Reply #7 on: December 02, 2008, 08:25:15 PM »
you need to give the servos the same voltage when modifying as the voltage you use when actually using the servos
Check out the Roboduino, Arduino-compatible board!


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Offline kiritTopic starter

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Re: Using regulated power in $50 robot, need some help
« Reply #8 on: December 02, 2008, 08:43:05 PM »
you need to give the servos the same voltage when modifying as the voltage you use when actually using the servos
That I did  not know. Frack! Guess Im going to have to go the battery route, for this to work. Thanks for the heads up.

Offline Admin

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Re: Using regulated power in $50 robot, need some help
« Reply #9 on: December 04, 2008, 10:04:31 PM »
Its a general rule of thumb to calibrate sensors/electronics under as realistic a scenario as possible ;D

 


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