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1876  Community / Exhibition / Gallery / Re: Simple UPS for 2 iPhones and 1 house phone on: March 29, 2013, 10:38:37 pm
Lest it come across that way, I am not trying to bash APC and their lines of of products. Rather, I believe that there is a market for UPS's that provide efficient power at a regulated 12VDC and 5VDC output to complement what is already out there.

Spot-on. APC makes fine products but they are designed to supply relatively large amounts of power for relatively short intervals. Turn that upside down and (perhaps unsurprisingly) they just aren't efficient. I'd always used APC gear, but for low power and long intervals I found that Minuteman UPS units do somewhat better, although there is still a lot of room for improvement.

Appreciate the info on Pico UPS and Dimension Eng.
1877  Using Arduino / Project Guidance / Re: Arduino based PCB - layout, crystal and planes on: March 28, 2013, 04:27:21 pm
Ground plane under the crystal can be a problem.

Additional capacitance?
1878  Using Arduino / General Electronics / Re: Ohm's Law on: March 27, 2013, 05:28:09 pm
Hey, I remember when Hertz was what it did after your took an inside pitch to the head. It was Cycles Per Second, up until the 70's. smiley-wink

Evidently there was a lot of resistance to changing from CPS to Hz. I remember a tongue-in-cheek article in QST magazine about how to convert cycles-per-second to Hertz, complete with nomographs.

My US college text books in the early 80's used V=IR, and that's what I've used ever since.'s_law

I can't find an explanation of why I for current tho.  Like many things, it was defined well before my time smiley-cool
I was told that "i" was already used for "imaginary" number in mathematics and since that comes into play in AC circuits another symbol was chosen.  The wiki thing sounds reasonable too.  Who knows? 

EEs use "j" for the square root of -1 instead of "i" to avoid confusion with current.
1879  Using Arduino / Microcontrollers / Re: DS1307 Heats up on the soldered board on: March 27, 2013, 12:05:02 pm
I thought the ATMEGA has internal pullups on the SDA/SCL i could be wrong? . like i said I dont even have the ATmega inserted on the setup and it would still over heat..

It does, and if the Wire library is being used, it will enable them. It will probably even work this way, but the pullups are technically too weak. External pullups between 2.2K and 4.7K would be best. But either way, this will not cause overheating.

Four posts in you tell us about the voltage regulator. Have you measured its output?

1880  Using Arduino / Microcontrollers / Re: DS1307 Heats up on the soldered board on: March 27, 2013, 11:35:05 am
Try placing a 100 ~200 ohms resistor between the Atmega's VCC and the DS1307.

Not sure what good that would do. You must be missing something, they shouldn't heat up. Sounds like you may have a lot of fried DS1307s at this point. If you have any unused ones yet, stop! Upload a picture of the circuit instead.
1881  Using Arduino / Microcontrollers / Re: Atmega328P-AU running on 3 C cells on: March 26, 2013, 06:03:00 pm
I'm going to implement an Atmega328P-AU, the SMD variant, in my project.  I will be loading the boot loader on it.  If I choose "Arduino Pro or Pro Mini (5V, 16Mhz) Atmega328" under BOARD when I load the boot loader, that will work for the SMD, correct?

Yes that will work. So will choosing "Uno", as Mike said the MCU is identical except for physical packaging. The actual bootloader will be different, Uno uses Optiboot. But they both work.

I've read this:

"Arduino Unos are set for the 2.7V level."

Wherever that was, it is correct. Both Uno and Pro/Pro Mini use the 2.7V BOD setting. Of course the other settings could be chosen as well (1.8V, 4.3V, or disabled).
1882  Using Arduino / Project Guidance / Re: Low Battery Indicator monitoring battery for arduino on: March 26, 2013, 05:21:49 pm
Measure Vcc without external components or dedicating a pin for the purpose:

The way I read the speed grades curve, 3.8V would be the minimum for 16MHz, but as Coding Badly points out, there is a lot of anecdotal evidence of good operation at 3.3V.
1883  Using Arduino / Programming Questions / Re: I2C question on: March 26, 2013, 03:03:45 pm
If it were me, I'd just try it and see if it works. Did you do that?
1884  Using Arduino / Project Guidance / Re: An Attiny85 I/O Network on: March 25, 2013, 08:24:48 pm
Well, how many Attiny85's can I run on a single regulator without risking overheating it? Perhaps that is also an input question as well.

Depends on the regulator but in general, lots. At 5V and 8MHz, an ATtiny85 only draws 5mA. At 16MHz, 9mA. LEDs or whatever other loads are connected might actually account for the majority of the current.

If each board had a small regulator, rated for maybe 100mA, then they could maybe be used little more independently. When stacked they could be fed with 7-12V. OTOH, I don't see a lot wrong with one larger regulator feeding the whole stack, and that would cost less. Depends on what you want to do.
1885  Using Arduino / General Electronics / Re: What's in your parts kit? on: March 25, 2013, 03:57:56 pm
A couple ATtiny's.
A real-time clock.
Arduino clones are fun, Boarduinos or whatever, plus it's something to solder smiley-grin
XBees are great, like you say maybe a bit pricey. XBee ZBs (fka S2) are $17 at Mouser or direct from Digi.
I've been playing with EEPROM chips like 24FC256 lately, they're easy, fun and < $1.
1886  Using Arduino / Programming Questions / Re: Control Multiple Servos with Arduino Via Xbee on: March 25, 2013, 01:12:45 pm
Lucky catch. Would it be as simple as using an int instead?
1887  Using Arduino / Programming Questions / Re: Control Multiple Servos with Arduino Via Xbee on: March 24, 2013, 11:01:21 pm
The message variable, being of char datatype, can only hold values between -128 and 127.
1888  Using Arduino / Programming Questions / Re: Run Two Sketches Simultaneously? on: March 24, 2013, 10:50:16 pm
I am new to this, and have been searching for a solution with no resolve.

I might try some basic programming tutorials, e.g.

1.) Is there any example code out there with 2 or more sketches running at the same time?

No, because there can be only one sketch loaded into the microcontroller at a time.

2.) Is there a way to turn individual sketches on/off by pulling one of the analog inputs low?

Given that the answer to the first question is no, so is the answer to this question, BUT it's entirely possible to code a sketch to do two (or more) different things based on inputs. I might use a digital input, high and low being a binary sort of thing rather than analog, but here is a very basic framework:

#define CONTROL_PIN 8    //an input pin that controls what happens

void setup(void)
    pinMode(CONTROL_PIN, INPUT);

void loop(void)
    if (CONTROL_PIN == HIGH) {
        //do one thing
    else {
        //do something else
1889  Using Arduino / Networking, Protocols, and Devices / Re: Multiple Xbee devices on: March 24, 2013, 07:12:43 pm
If AT (transparent) mode is employed, this will require changing the DH and DL parameters each time a new receiving device needs to be designated. This includes waiting for the guard time without transmitting (default 1 second), sending the "+++" command sequence, waiting another guard time, receiving the OK, then setting the parameters. Quite an onerous process especially with 50 devices, unless they don't need to be rapidly addressed one after another.

If API mode is employed, the address of the destination device is simply included in the packet, which is sent to the transmitting XBee without guard times or command sequences. I highly recommend this library for working with API mode, it makes things much easier:
1890  Using Arduino / Microcontrollers / Re: Atmega328 at 4 MHz ? on: March 23, 2013, 08:07:01 am
Hello all.
Is it possible to run a Atmega328 at 4 MHz or even lower to save battery power?

Yes, absolutely. I've used 1MHz and I believe the internal 128kHz oscillator can also be used as a system clock, but I've read that is probably beyond the point of diminishing returns. Additional entries in the boards.txt file will be needed for alternate clock frequencies. I don't try to use a bootloader below 8MHz, and if using the internal 8MHz oscillator (either direct or divided), it may not be accurate enough for serial comm without some tuning.

Would the arduino code work like on a 16 MHz Atmega328 ?

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