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16  Using Arduino / General Electronics / When NOT to have a common ground? on: May 21, 2011, 09:09:55 am
Are there cases when one wouldn't want a common ground in a project?

My current project:
- 1 stepper motor driven by Gecko - 20V power supply
- 1 TIP120 - controlling fan powered by 20V power supply
- 2 7805 regulators driving 2 servos

I have a common ground between the Arduino + the 20V power supply.

Are there any issues (for example when sinking current) when you wouldn't want a common ground?
17  Using Arduino / Motors, Mechanics, and Power / Re: Mixed voltage power supply solutions? (driving stepper + servos) on: May 18, 2011, 11:44:31 am
Thanks for the reply. FWIW - I just did a test running the 7805 w/ 20 V input (using all the filtering caps as specified here: I hooked up an LED to the 5 V output (along with the servo) and while the servo motor runs the LED dims. I expected the caps to prevent that sort of brownout - so I'm not sure running the Arduino off the 7805 would work.

The 7805 gets pretty hot too. Will put on a heatsink, etc. but may have to try another chip as you suggest (though 7805 chips in hand vs mail order delays, etc.)
18  Using Arduino / Motors, Mechanics, and Power / Mixed voltage power supply solutions? (driving stepper + servos) on: May 18, 2011, 09:44:49 am
Hi - I tend to develop projects using a 5/12/variable bench PS that can deliver 3 amps (with a wall wart for the arduino). All good but when it comes time to deploy the project I need to come up with mixed voltage/current sources and that is where I get stuck for a good solution.

In a current project I am driving a big stepper with a 20v PS, and also need to drive 2 servos and a 24 v fan. I am going to control the fan off the 20 V PS using a TIP120 transistor and am resigned to using a wall wart for the arduino.

The problem is the servos - each one draws @ .25 A with a peaks @ 1 A. I have tried using one 7805 V reg off the 20 V PS to power both but the 7805 gets very hot and (I assume) goes into thermal shutdown:  combined current draw peaks > 1.5 A.

 I am going to try using one 7805 for each servo to see if that works. Short of getting a 3rd PS for just the servos, is there a better way? I don't like running the 7805s so hot and wasting all that power.

Long winded... sorry! ;-)
19  Topics / E-Textiles and Craft / Re: Flexible displays? on: March 12, 2011, 08:05:53 pm
also, check out this link:

that video is hilarious!
20  Using Arduino / Motors, Mechanics, and Power / Servos: backlash + noise? on: February 26, 2011, 03:49:22 am
Noobie servo questions:

I haven't worked with servos before and I'm wondering what sort of backlash one can expect with them. I also haven't priced/sourced them yet - so are cheap ones likely to suffer from more backlash or is servo gearing overall generally tight?

Also noise - when I have seen servo projects, they tended to have pretty loud gearing/motor noise (say compared to non-servo gearhead DC motors) Is that  just a characteristic of all servos or just low(er) end?

21  Using Arduino / Motors, Mechanics, and Power / Re: New User here - Need major help selecting a high powered stepper shield on: February 25, 2011, 07:40:18 pm
Don't know of any shields etc. but as someone above said, a couple of Geckos would work just fine.

To do it on the cheap you can just stack a couple of H-Bridges and control the steppers through code.

Or use a chip like this:
22  Using Arduino / Motors, Mechanics, and Power / Driving a 1.4V 3.8A Vexta? on: February 01, 2011, 11:27:07 am
Hi - I have a 1.4V 3.8A Vexta  unipolar (4 wire) stepper pulled from some recycled hardware.

It's a nice motor I am wondering how (and if it is worth bothering) to drive it. I usually use H-Bridges (L293 or SN754410NE) but those won't handle that current. Apart from buying a dedicated driver ($$) for this motor is there a cheap way I can drive this?

As an aside - can someone explain what the deal is with low voltage/high current steppers? I've used high voltage/high current motors before but this one seems like an oddball.

23  Forum 2005-2010 (read only) / Troubleshooting / Re: Programming Question on: June 26, 2008, 06:45:51 pm
someone else will chime in with a better idea... but I would approach that through an array and use cos() or sin(). With the array, you get the next value for the lead LED of your curve and push it's current value to the next position in the array- doing that in a repeat loop so all the values get shifted
24  Forum 2005-2010 (read only) / Troubleshooting / Re: Incorrect baud rate on Arduino BT on: May 02, 2008, 12:45:51 am
You set the baud rate on the Arduino when you call Serial.begin(baudRate). This is usually done during the setup() function. Just load a sketch with the baud rate you want.
25  Forum 2005-2010 (read only) / Troubleshooting / Re: Matrix lib won't compile (v0010) on: November 03, 2007, 09:39:59 am
awesome - thanks! (I think Wiring handles libs differently as I don't recall needing to use the #includes)

this forum/community/project/*wildcard is so great!


26  Forum 2005-2010 (read only) / Troubleshooting / Matrix lib won't compile (v0010) on: November 02, 2007, 09:13:43 pm

I tried to use the Matrix example in v 0010 and get the error: "Matrix" type not defined - this is on OSX 10.4.10 using arduino NG. Also tried the Sprite example from the same lib and got the same error.

I've used this lib before with the Wiring board and the code looks exactly the same.

Also tried it with v 009 and got the same error. Is this something with my setup or?


27  Forum 2005-2010 (read only) / Bugs & Suggestions / Search/Find/Replace should include all tabs on: September 19, 2009, 02:15:28 pm
(this may have already been noted)

Currently search/find/replace only address the current tab. For small projects this isn't a problem but for larger projects (or those of us who hate scrolling...) multi-tab projects are a convenience in keeping things organized.

If it is not too complicated to implement full search would be a nice addition.
28  Forum 2005-2010 (read only) / Bugs & Suggestions / Re: floating serial monitor window: suspend output on: September 17, 2009, 04:03:47 pm
Hmm... spoke too soon - thought I could just switch out a file from the app bundle. Guess I have to build a binary- don't know how to do that  smiley-sad
29  Forum 2005-2010 (read only) / Bugs & Suggestions / Re: floating serial monitor window: suspend output on: September 17, 2009, 03:58:58 pm
Thanks for your efforts - I thought it must have been mentioned before. I'll give your revised version a try.

30  Forum 2005-2010 (read only) / Bugs & Suggestions / floating serial monitor window: suspend output on: September 17, 2009, 01:10:21 pm
Hi - I like the floating serial monitor window but some functionality is lost compared to the old split pane approach (maybe this has already been noted?).

If I have a sketch that outputs to the monitor on loop() some values I want to examine can be quickly scrolled out of the window. With the split pane I could just click the serial output button to turn it off and the lower pane would retain the output values. With the current floating window, this won't work - clicking the serial monitor button only opens the window - so there is no way to suspend output.

Having either the monitor button toggle output but not close the window, or a new button within the floating window to suspend output would restore the earlier functionality.

Like the new command key feature to comment code!


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