TLC5940 Servo motor control problem

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm using the TLC5940 to build a PWM expander to control 8 servo motors. I've been using the library:
http://www.arduino.cc/playground/Learning/TLC5940

I uploaded the following example provided with the library:

/*
This sketch sweeps a servo on channel 0.

To connect a servo:

  1. Put a 2k-5k pull-up resistor (R0 below; I've tried with 3.3k) between the
    servo control output pin and +5v.
  2. Connect that same pin to the servo's control line like so

servo data pin
| _____
OUTn ----+----[_____]---+5v
R0

Steve Pomeroy <steve ~AT~ staticfree.info>, 2009-01-20 */

#include "Tlc5940.h"
#include "tlc_servos.h"

#define SERVO_CHANNEL 0
#define DELAY_TIME 15

void setup()
{
tlc_initServos(); // Note: this will drop the PWM freqency down to 50Hz.
}

void loop()
{
for (int angle = 0; angle < 180; angle++) {
tlc_setServo(SERVO_CHANNEL, angle);
Tlc.update();
delay(DELAY_TIME);
}
for (int angle = 180; angle >= 0; angle--) {
tlc_setServo(SERVO_CHANNEL, angle);
Tlc.update();
delay(DELAY_TIME);
}
}

For some reason, my servo motor isn't doing anything. I have the schematic wired just as shown on the library's site in the Arduino playground. The servo I'm using is the large servo from Sparkfun (which they do not provide a datasheet for >:( ):

Help please!! This has been driving me crazy for the last week! Thanks in advance!

2

One basic mistake often made is trying to power the servo from the arduino board. You need a seperate power source for the servo. Does your servo work with the basic "sweep" servo demo sketch?

3

Yes. And the power going to the servo was provided by the Arduino. I didn't think the TLC5940 used that much power.