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976  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Newb: can someone confirm my button circuit? on: September 23, 2008, 03:41:03 pm
I have personally created a couple of little projects that use this topology


and then

pinMode(8, INPUT);
digitalWrite(8, HIGH);

to employ the internal pullup.  It seems to work, but I have some lingering doubts about whether I am slowly burning up my Arduino pins.  If any HW guys would care to comment...?

I may have to pay a visit to the automotive store.  I read in another thread about a guy making a fountain sculpture thingy out of windshield wiper spray pumps. smiley


977  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Newb: can someone confirm my button circuit? on: September 23, 2008, 03:29:16 pm
This is very cool.  I want to play too! smiley

I have 2 questions:

1. Couldn't ChL's original switch circuit have been simplified by using the Arduino's internal pull-up resistors and the digitalWrite(pin, HIGH) trick on an INPUT pin?
2. Where can you get a solenoid water dropper?  Or solenoid toys in general?

Thanks for the post.  I would love to keep up with this project.

978  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: ON and OFF (and sleep?) on: September 23, 2008, 11:09:31 am
Wow!  I'm much obliged for the plethora of great responses.  It's a good lesson: phrase your request succinctly and you'll get a better response.  Thanks.

So to summarize helpful ideas I got:

1. Connect a relay on the power line.
2. Use AA or AA batteries.
3. Use a flip-flop
4. Latching relay to sustain power until Arduino comes up
5. The pololu proprietary solution
6. Remove all power draining stuff and just put the Arduino in a sleep state
7. 555 timer to sustain power

but my favorite, and the one I think I'll try first (I'm extrapolating here)

8. wire up an off-center motor that, when activated, knocks my little box onto its side, turning off BroHogan's mercury tilt switch. smiley  Seriously, though, thanks Bro, and thanks for the latching circuit diagram.  As a SW guy it will probably take me a day to understand how that works, but I am determined to figure it out.

Thanks, all!

979  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: ON and OFF (and sleep?) on: September 21, 2008, 10:16:29 pm
Thanks a bunch for working this through with me, Stephen.  

This is the part I'm anxious about.  Assuming my user presses the button to turn the system on, isn't there some delay time on the order of SECONDS before my sketch gets control and can force the relay control pin HIGH?  I'm worried about this interval.  What keeps the power on during that time?  Would a pullup resistor be appropriate here?


980  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: ON and OFF (and sleep?) on: September 21, 2008, 09:21:46 pm
I think I get the relay, but what does the switch connect to?  The same relay?  Is the relay controlled (somehow) by both this "power" switch and an Arduino digital pin?  Pardon my density, please. smiley

981  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: ON and OFF (and sleep?) on: September 21, 2008, 08:36:53 pm
Bump.  Let me simplify my question:

How could I wire Arduino so that it turns itself completely off (through software control)?


982  Forum 2005-2010 (read only) / Frequently-Asked Questions / ON and OFF (and sleep?) on: September 19, 2008, 09:57:58 pm
Hi all!

I'm working on a self-contained project that will be battery powered.  I want it to come "on" when the user presses a pushbutton, but then turn "off" again after, say, 10 minutes of inactivity.

This device must be very power conservative, because it won't be very feasible to swap out the 9V battery.  So what I really want is for the Arduino inside to physically turn itself OFF (and not just enter a quiescent state which appears "off" to the external world).

Being a software guy, I'm having some difficulty envisioning what kind of circuit would allow me to
   (a) switch "on" the Arduino at the push of a (momentary contact) pushbutton
   (b) switch it back "off" in response to a digitalWrite to one of the pins (after the 10 minute timer lapses)  (I don't need any advice on how to write the software.)

Any suggestions to get me started?

[As an addendum, I read somewhere in a recent post that you can put the Arduino into a sleep state.  Does anyone know how to calculate how long you'd expect a 9V battery to provide adequate power for an asleep Arduino?  If the answer to this question is favorable, I would probably opt to solve the on/off problem by simply putting the device to sleep rather than turn it completely off, since this wouldn't involve any fancy (by my standards) circuitry.]

Many thanks,

983  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: what is a problem?? on: September 16, 2008, 10:49:44 pm
What exactly is connected to the Arduino serial port?  Is it the GPS or the computer?  The fact that you are connecting at 4800 baud suggests the former, but then I don't see how you can Serial.print().

Or is the GPS data coming through the computer?  If so, make sure your monitor is also set to 4800 baud.  The kind of garbage you report is typical with mismatched baud rates.

I would also suggest replacing
Code:;         // Read a byte of the serial port
  if (byteGPS == -1) {           // See if the port is empty yet
  } else {


if (Serial.available())
  byteGPS =;

During that 100ms delay, up to (4800/9)/10 ~= 53 bytes may arrive and be lost!  You may also need to remove other delays in your loop, like that massive bunch of calls to Serial.print().  Parsing a GPS stream at full speed on the little Atmel processor is not a trivial task, but others are doing it.

984  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Serial protocol how-to on: September 15, 2008, 12:20:10 pm
First of all, it's good to see both Big and Grumpy in the same thread. smiley

I've been thinking about how the Arduino HardwareSerial class is pretty good for formatted text, but it would be nice to extend it for binary data.  Wouldn't it be useful to include, in addition to the print* suite of functions, something like:

void HardwareSerial::writebuf(byte *buffer, int bufsize);
void HardwareSerial::readbuf(byte *buffer, int *bufsize);

// sample usage:
byte buf[64];
Serial.writebuf(buf, sizeof(buf));

int size = sizeof(buf);
Serial.readbuf(buf, &size);

For the readbuf method, you would send the maximum size in and then the actual size would be returned.  Doesn't this seem like it would useful?  I would be happy to contribute to the implementation, along the lines of the discussion above.

985  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: How accurate can I be with Servos? on: September 11, 2008, 08:12:31 pm
Hey, quad--

I'm pretty new to motors, but I do know that if you're thinking of driving a wheeled vehicle, your scheme won't work because servos only move 180 (or sometimes 360) degrees.  See for example.  You'll want to use a DC motor, I think.

986  Forum 2005-2010 (read only) / Bar Sport / Re: Seeedstudio's 8bit oscilloscope? on: December 13, 2008, 10:17:12 am
And did you see his photo of the Duemilanove with the blinking LED 13:

987  Forum 2005-2010 (read only) / Bar Sport / Re: Seeedstudio's 8bit oscilloscope? on: December 12, 2008, 09:59:44 pm
Wow, ed, how about conducting a seminar in taking attractive electronics photos?  That's really nice.  I'm sure Seeedstudio or NKC would like to use it. smiley

988  Forum 2005-2010 (read only) / Bar Sport / Re: Seeedstudio's 8bit oscilloscope? on: November 30, 2008, 04:00:40 pm
There was a thread talking about this recently:  I'm pretty interested in this too.

989  Forum 2005-2010 (read only) / Bar Sport / Re: simple technical photo tips on: December 16, 2008, 12:10:06 am
Yes, indeed.  Thanks very much, halley.  It's nice to see all this information collected in a single place.

990  Forum 2005-2010 (read only) / Bar Sport / Re: Arduino board hierarchy on: December 06, 2008, 10:54:30 pm
@mem, I'm not sure company policy permits me to divulge the name in a public forum, but let's just say I'm a software engineer working for a chip manufacturer.  A large one.  The LARGEST one, in fact. smiley Fred and I work in the networking division.

@macegr, I appreciate your assessment.  It's a real pleasure to be in this forum with all "the good people".  Sometimes I think I spend a little too much time here -- time I could be developing Arduino projects, or working!

@Fred, please post a reply if/when you start using the forum, so that I can better assess what to do next. smiley

Cheers and thanks,

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