Adafruit Motor Shield External Power Supply

[kruzan]

edit: resized images

[adafruit_support_bill]

Very nice soldering! I don't see any obvious problems there.

as it is now, if i have 9.6v battery pack disconnected, and the 9v battery disconnected, the arduino is trying to power everything from usb.

What do you mean by "power everything"? Is the green LED lit? Do the motors move or make noise?

[kruzan]

Very nice soldering! I don't see any obvious problems there.

Thanks

What do you mean by "power everything"? Is the green LED lit? Do the motors move or make noise?

the green led goes bright and dim as the sketch runs (dim when a motor powered). right now just using the following sketch:

Code: Select all

#include <AFMotor.h>
AF_DCMotor motor(1, MOTOR12_64KHZ); // create motor #2, 64KHz pwm
AF_DCMotor motor2(2, MOTOR12_64KHZ); // create motor #2, 64KHz pwm

void setup() {
//  Serial.begin(9600);           // set up Serial library at 9600 bps
//  Serial.println("Motor test!");
  
  motor.setSpeed(255);     // set the speed to 200/255
  motor2.setSpeed(255);     // set the speed to 200/255
}

void loop() {
  //Serial.print("tick");
  
  motor.run(FORWARD);      // turn it on going forward
  motor2.run(FORWARD);      // turn it on going forward
  delay(1000);

  //Serial.print("tack");
  motor.run(RELEASE);      // stopped
  motor2.run(RELEASE);      // stopped
  delay(1000);

  //Serial.print("tock");
  motor.run(BACKWARD);     // the other way
  motor2.run(BACKWARD);     // the other way
  delay(1000);
  
  //Serial.print("tack");
  motor.run(RELEASE);      // stopped
  motor2.run(RELEASE);      // stopped
  delay(1000);
}

the shield works, it operates as expected with usb, external 9v, external 9.6v all connected.
i have a double pole swith that turns both external supplies off at once, without usb connected it shuts down, but when usb is connected and i turn the switch off, the led gets dimmer, but stays on.

[adafruit_support_bill]

Hmmm. What do you measure across the EXT_PWR terminals when the switch is off?

[kruzan]

with just the arduino plugged in via usb
ext gnd to left side of power jumper floats from 3.4v to 3.7v
ext gnd to right side of power jumper is steady 4.2v
across the ext power terminals is floating 3.5v to 3.8v
infinite ohms between power jumper pins

voltage across jumper pins floats .462v to .675v
still connected to jumper pins unplug usb goes to -1.52 volts and steadily drops
when plug in usb jumps to 2.7v then as soon as led comes on goes back to floating .462v to .675v

[kruzan]

maybe its the same issue where some can not boot a pc if usb and external power connected to the arduino?

[kruzan]

ok so i start over i have every wire removed from arduino and shield, and i took shield off.
using hooks on the jumper pins positive on left pin negative on right pin (with the reset button and ext_pwr block to your left)
no voltage reading to speak of, 0 millivolts
place shield on arduino (that is not powered at all) and reads 1.3volts dc that slowly drops.
i plug in usb and voltage goes to -3volts. the led on the motor shield is not lit. the arduino power led is lit.
press reset on motor shield
led on motorshield lights up voltage drops from -3 volts to floating around -.4 to -.6 volts
remove usb voltage goes to 1.5volts then slowly drops
remove shield from arduino and voltage drops to 0 millivolts

[adafruit_support_bill]

These measurements are on the EXT_PWR terminals with nothing at all connected to the terminals?
I can understand floating values when things are not connected, but there shouldn't be enough current to light the LED.

[kruzan]

across the ext power terminals is floating 3.5v to 3.8v

with only usb cord plugged in to arduino

[adafruit_support_bill]

That's curious. Floating voltages on unconnected terminals is not unusual, but there is not usually enough there to light the LED. I have another shield back at my lab which I can check later this afternoon, but If everything else works fine I don't think it is anything to worry about.

[kruzan]

That's curious. Floating voltages on unconnected terminals is not unusual, but there is not usually enough there to light the LED. I have another shield back at my lab which I can check later this afternoon, but If everything else works fine I don't think it is anything to worry about.

well then back to my origional question, how can i set it up so the shield is only powered when EXT_PWR is connected

i have arduino uno smd plugged in via usb to a laptop
i have external power going to arduino that is switched (9 volt battery)
i have external power going to EXT_PWR on motorshield that is switched. (9.6 volt battery pack)

when i power everything up arduino/motorshield does what the code says running the motors
when i disconnect external power (leave usb connected) green led on motorshield does not turn off, it cycles bright and dim (dim when running motor)

[adafruit_support_bill]

Is there enough current to actually run the motors? Or does the LED just get dimmer?
Can you post a diagram showing how your batteries and switches are wired?

The logic circuits on the shield will be powered as long as the Arduino has power. Disconnecting EXT_PWR just means that the H-bridges have no high-current source to control.

[kruzan]

Is there enough current to actually run the motors? Or does the LED just get dimmer?

there is not enought current to actually turn the motor, but i can hear motor hum trying to work

Can you post a diagram showing how your batteries and switches are wired?

see attached

The logic circuits on the shield will be powered as long as the Arduino has power. Disconnecting EXT_PWR just means that the H-bridges have no high-current source to control.

[adafruit_support_bill]

What I suspect you are seeing is a little VCC leaking through the H-bridge. I'll try to reproduce that later this afternoon.

The only way to completely eliminate it would be to cut all power (VCC and EXT_PWR) to the shield. You would need to cut the 5v trace and run it through your switch to do that.

[kruzan]

Ok, sounds good. Thanks for your help!