Using my Arduino board to "drive a pin low" on my external DC/DC converter.

I need some basic guidance to make sure I am not about to fry my electronics. It is about how to "bring a pin low" on an external board.

I have an Arduino project with two servos that rotate an Android phone, which is in turn driven remotely by another Android phone (See photos). I use a separate DC/DC converter to power the servos. The input to the Arduino board and to the separate DC/DC converter is a 12V battery. The project is solar powered, needs to run 24x7x365 on top of a power pole in another country and therefore needs to be very reliable and not draw much power. I am finding that occasionally one of the Hitec servos - the digital one - gets in a funk where it sits there without moving and with no load on it yet draws 700mA. If I command it to move a bit, it goes back to the idle power usage or around 8mA. But I can't afford to risk the high power usage scenario.

Fortunately, my DC/DC converter, http://www.pololu.com/catalog/product/2110, has a feature that enables the output to be turned off. This is perfect. Here is the description:

The EN pin can be driven low (under 0.3 V) to turn off the output and put the board into a low-power state that typically draws 150 ?A. The board has a 100k? pull-up resistor between EN and VIN. The EN pin can be driven high (above 2 V) to enable the board, or it can be connected to VIN or left disconnected if you want to leave the board permanently enabled.

I can see the EN pin. My question is, do I connect that pin to one of the digital outputs on the Arduino board and the ground on the input of the DC/DC converter to the ground of the Arduino board? Do I use one of the PWM digital pins or another one? I am a newbie to circuit boards and signals, so pardon my ignorance, but will there be a conflict between the 5V (I assume) output of the digital pin and the 12V input voltage of the DC/DC regulator.

I am using the Iteaduino ADK, http://imall.iteadstudio.com/development-platform/arduino/arduino-compatible-mainboard/im120411005.html, which took 4 weeks to arrive from Hong Kong, so I'd like to be sure before I fry something.

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Yes, although the pin has a pull-up to 12V, its a high resistance, 100k, so won't be a problem. Just treat as a normal digital out.

I can see the EN pin. My question is, do I connect that pin to one of the digital outputs on the Arduino board and the ground on the input of the DC/DC converter to the ground of the Arduino board?
Correct.
Do I use one of the PWM digital pins or another one?
Any of the digital pins will work (actually even the analog input pins can be used as digital input or output pins if desired) as you will be using the digitWrite(pin,HIGH or LOW) command. To use PWM commands (using analogWrite() commands) one must use on of the pins marked pwm only, but that does not apply to your need to control your external power converter board.
I am a newbie to circuit boards and signals, so pardon my ignorance, but will there be a conflict between the 5V (I assume) output of the digital pin and the 12V input voltage of the DC/DC regulator.
The note says the enable pin on the converter board is 'pulled up' with an internal resistor to the input voltage of the converter. Normally this could be a concern, but as they state the internal pull-up resistor value is 100,000 ohms that will fully protect the arduino output pin from any damage. Simply wiring from your desired arduino output pin to the enable pin and of course converter ground wired to an arduino ground is all that you will need. When you set the output pin low the converters output will be turned off and setting it to high will turn on the power converter.
Lefty

Thanks for both replies. That was reassuring and informative.

Hey! It works.

Always nice when that happens.