View Full Version : 5v DC motor query

09-12-2009, 08:11 PM

I'm trying to drive my dc motor (a toy helicopter's plastic fan attached to it) through PIN 12 (PWM, but digital by default) from my Sanguino (VCC = +5v and PIN HIGH = +5v). One problem that I've noticed is that sometimes the motor grinds to a halt and doesn't restart if I manually stop the fan by obstructing it with a pen. This is true even if I connect the dc motor directly to the VCC & GND of my Sanguino. I gently need to nudge the fan to restart the rotation. Any reasons for this? (I've made sure that the dc motor shaft is tightly fitting into the fan's receptacle).

Another observation is that compared to the motor running directly from VCC & GND, if I run it through a PIN, the rotation is noticeably less vigorous. Am I missing something?


09-12-2009, 08:26 PM
An AVR cannot drive an motor :) its that simple. You need intermediate circuitry for starters. From what i think there is not enough juice ( current ) to drive the motor, avr can source max 40mA.

Give some details about the motor also you need a H-Bridge etc which has about 1 - 2 V voltage drop. what are you trying to make ? .

09-12-2009, 10:38 PM
Thanks! I knew I was missing something basic.

Unfortunately I only know the i/p voltage of this motor - I salvaged it from a toy. I am newbie as such to some of these concepts - my experiments till date were limited to LED's.

Is there a good tutorial to help me thru for dc motors(on this site or external)?

I am just trying my hand on basics currently - don't have anything big in mind yet. Its been just a week that I got this Sanguino. What I do have in mind for this project is to connect the motor, a 16x2 LCD and a piezobuzzer in one circuit with some assortment of LED's. I plan to give digital as well as analog o/p's to these components with the LCD displaying some runtime status messages. Next I plan to desolder some old rc toys, a tv remote control, an old mobile phone to source some exciting components and probably build something more useful.


10-19-2009, 11:42 PM
if your motor was salvaged from an old R/C car than it must be of rating around 5-6V.
Most of the electronic components use 5v for operation.so:
use seperate power supply for motor driver and microcontroller
"This is true even if I connect the dc motor directly to the VCC & GND of my Sanguino. I gently need to nudge the fan to restart the rotation"
Torque is the main problem. what kind of power supply are you using? because most probably your motor is not getting the required starting current. Try a different motor instead...
Then try a light motor driver like spdt relay driven by transistor or a power transistor.
I don't think an H bidge is needed in your case as you are using only one motor... and are rotating it in one direction only.
if you just want to go for an IC that can amplify the current being used by motor than go for ULN2003(vcc=5v).
for h bridge i recommend first relay based( for small scale) or go for L293D.
if you just want to drive motor in one dierction than go for ULN or else use NPN power transistor as switch TIP122
if you want to rotate your motor in both directions go for L293d.if motor still halts than buy new one.

06-09-2010, 04:03 PM
Also see if the motor you have is a Brushless DC motor. These have a predilection for not starting up after stopping midway. I've heard that a lot of "flying" toys use BLDC motors; I could be wrong of course.

06-09-2010, 10:26 PM
I don't think its BLDC.