BOE Shield questions

Buck Rogers

Hello!
A while ago I bought from Microcenter the BOE Shield from Parallax. That's http://www.parallax.com/product/35000 and since when running the servo examples from the Basic Stamp family, I'm now aware that the servos need an external power supply.

When using that gizmo how would I arrange for an external power supply to be available for both the board (Arduino, a Netduino (Dot Net programming languages and same form factor) or the Propellor ASC+ at http://www.parallax.com/product/32214 )?

Looking at the different things available to power the bots I see several excellent boards. But, ah, where I do go from there?


Incidentally I've obtained two new servos, one is the RS Micro Servo and the other traveled with a kit of assorted components of theirs.


I grok that this shield follows the entire board that Parallax makes for the BASIC Stamp, except for the presence of the processor and some assorted support gadgetry.

Now looking at the one in that above sentence, http://www.parallax.com/product/28850 there, I see that there's a presence for external power to be applied to the servos. Would that jumper for VDD or VIN to be the answer to the above question on power for the BOE Shield? Or do I have something else missing?

Franklin

All those micros have a 2.1mm power jack and if you power from that the shield should have that available on the vin pin for use with the servos.

Buck Rogers

Franklin wrote: »

All those micros have a 2.1mm power jack and if you power from that the shield should have that available on the vin pin for use with the servos.

Hello!
I quite agree. However when I wrote those some what of a ramble sentences, I was thinking along the lines of what happens during the debug phase of the code that the target will be running.

During that phase the target is typically wearing a USB cable, although one Arduino shape is more along the lines of the occupant of an empty Altoids tin, and the user needs to use a serial device similar to the Prop clip.

Incidentally the setup won't be in the position of doing what the complete BoeBot on an Arduino will be doing, the board will be supporting a servo who'll be managing a contraption. And that if I manage to figure out how to write the programming for it, and what board I select.

GordonMcComb

The BOE Shield has a power switch where moving it to position "2" applies the external power at the jack, or the external power through the onboard 1A regulator, to the servo headers. Your Arduino can be powered by the USB cable still connected, if there. As you discovered, while the USB 2.0 ports on most PCs can handle one (unloaded) servo, there could be problems running two servos. This is why it's always wise to test servo-based projects where the servos derive their power separately from the USB cable.

Where the servo headers derive their power depend on the setting of the jumpers, as you noted. In the Vin position, the servo headers get the full voltage at the power jack -- that's okay if it's 7.2V or lower, but most servos cannot tolerate higher voltages. Be sure to check the specs of the servos before using this setting at supply greater than 7.2V. Parallax's new High Speed Servos are an example of motors that can run at up to 8V.

In the 5V setting, the servos connect to the BOE Shield's on-board regulator. That regulator can power 2 standard servos, but could have difficulty with larger digital servos under load.

Note that the Arduino and BOE Shield are both powered by Vin. The Arduino gets its power directly, and it is regulated through the Arduino's own regulator. That regulated juice is available at the 5V pin ON the Arduino board -- this pin is also exposed on the BOE Shield. The 5V taps above the breadboard area are powered by the BOE Shield's regulator. (It also has a 3.3V regulator, separate from the one on the Arduino.) This power is available if the switch is in position "1" or "2."