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Author Topic: Problems connecting servo to power adaptor  (Read 2497 times)

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Offline SixRingzTopic starter

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Problems connecting servo to power adaptor
« on: June 16, 2008, 06:04:58 PM »
Ok, I've always been more of a software guy than an electronics man. Haven't really done any electronics for a year either and tonight I'm understanding why I didn't miss it that much... >:(
My servo battery pack died this evening and I figured slaughtering a 6V adaptor and connect the whole thing to my breadboard would be piece of cake but boy was I mistaken.  :'(
Here's the setup:

Vanson Regulated 6V AD/DC 400mA
 
Servo
Power and ground connected to Vanson adapters power and ground, signal connected to PORTD on MCU (stk500 board)

STK500 board
Ground from PORTD to ground from Adaptor and Servo. Signal from PORTD to servo.


I must be missing something in the setup here, since the servo refuse to move. If I plug in a batterypack instead of the adaptor (same setup), everything is fine. I've checked voltages with multimeter and it's the same for batterypack and adaptor. Also checked with respect to both ground on adaptor side and from stk500 side to make sure ground is common. Any ideas? I'm going nuts here... :'(
Grounding things properly means burying them in the backyard...

Offline benji

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Re: Problems connecting servo to power adaptor
« Reply #1 on: June 17, 2008, 03:48:54 AM »
are u sure yer transformin 6 volts to 5 volts for the micro power using a 7805 with appropriate caps?

Quote
Ground from PORTD to ground from Adaptor and Servo.
ground from PORTD ????
what do u mean?
good ol' BeNNy

Offline SixRingzTopic starter

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Re: Problems connecting servo to power adaptor
« Reply #2 on: June 17, 2008, 04:26:25 AM »
Quote
ground from PORTD ?
what do u mean?

Sorry if I was unclear, what I meant was ground from development board is connected with ground from adaptor/servo. About using 7805 with appropriate caps, there's already voltage regulation on the stk500 board so the micro is fine. Don't have anything for mr Servo though... But I didn't use any caps with the batterypack so I thought I should be ok?
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Offline ALZ

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Re: Problems connecting servo to power adaptor
« Reply #3 on: June 17, 2008, 04:42:24 AM »
I  don't know anything about the STK500 board or the Vanson. So I am just talking off the top of my head here. It sounds like the Vanson is just not filtered well enough and is also just too weak; 400mA is not much when you start talking about running motors. Since you have regulation on the stk500 board, 6 volts is just too low to feed it.  Regulation does more than just change voltage, it also helps to kiil noise on the power rails. 

Offline Admin

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Re: Problems connecting servo to power adaptor
« Reply #4 on: June 19, 2008, 06:43:16 AM »
hmmmm I don't quite understand your setup . . .

What are your input voltages? As benji said, with a 7805 you need more like 7.2V input.

Is the same power going to the microcontroller as the servos? If so, you need some caps across ground and power because servo noise will kill your mcu.

Offline SixRingzTopic starter

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Re: Problems connecting servo to power adaptor
« Reply #5 on: June 24, 2008, 08:57:32 AM »
Here's the setup:
Code: [Select]

Wall socket -->Vanson 6V Powerwire---------------------------> Servo power input
Wall socket --> Vanson groundwire-----------------------------> Servo ground and micro ground

Wall socket --> Another adaptor (power&ground)----------> STK500 board, mcu (5V logic) -----------> Servo logic


Both adaptors are connected to the same power jack in the wall, mcu and servo share ground. Sorry for my late reply, I've been out of town for a few days.... (Please notify me if you need a picture of the setup)
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Offline Admin

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Re: Problems connecting servo to power adaptor
« Reply #6 on: June 24, 2008, 09:27:32 AM »
First, use a multimeter and look for any unusual voltages (both with the circuit on, and off). Are you sure the servos are getting a signal?

Also, how many servos are you using? What servo type? How much load?

Offline benji

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Re: Problems connecting servo to power adaptor
« Reply #7 on: June 24, 2008, 11:49:50 AM »
yea do what admin said , check if u got some weird voltages
anyways
here is some point to clearify

if you are using 2 adapters us a multimeter to check their lower voltage terminals and connect em together(ground) then connect em to the servo ground and micro ground

or just use the 6 volts adapter and in it to a 7805 to feed the micro , u simply dont need 2 adapters
good ol' BeNNy

Offline SixRingzTopic starter

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Re: Problems connecting servo to power adaptor
« Reply #8 on: June 25, 2008, 02:10:03 PM »
Well the servo have zero load, and it works fine when I use a batterypack instead of the adaptor. I measured with a multimeter and found no weird voltages, it's about the same from the pack and adaptor. Well, maybe disconnecting everything and re-connecting it again helps.... As for using a 7805 for powering the micro, I really don't see the reason to do that when the micro is mounted in a socket on a 100 dollar well developed Atmel (AVR) board built for the sole purpose of making things like powering, output/input, serial communication etc easier. I put my trust in the Atmel electronic engineers here...  8)
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Re: Problems connecting servo to power adaptor
« Reply #9 on: June 25, 2008, 02:15:03 PM »
Quote
it works fine when I use a batterypack instead of the adaptor.

This means that your adapter is unable to supply enough volts and/or current. Using a multimeter would have told you this ;)

Quote
As for using a 7805 for powering the micro, I really don't see the reason to do that when the micro is mounted in a socket on a 100 dollar well developed Atmel (AVR) board built for the sole purpose of making things like powering, output/input, serial communication etc easier. I put my trust in the Atmel electronic engineers here...

If its well developed, it should have a voltage regulator built in. Does it? :P

Remember to always:
http://www.societyofrobots.com/robot_faq.shtml#circuit_debug

 


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