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10516  Community / Bar Sport / Re: Your latest purchase on: May 28, 2011, 04:27:33 pm
4.3" LCD display to go with my telemate shield.

I've owned the telemate shield for quite a while ( http://www.sparkfun.com/products/9313 ) but wasn't using it too much as all I have handy is a old CATV 9" monitor for display output. I had been looking at those small LCD displays on E-bay and finally decided one was cheap enough to go along with the Arduino/telemate combination.

While the LCD is designed to be powered from +12vdc, I've found it works fine with 8vdc I have at my Vin pin. It's drawing 213ma as shown displaying in the picture.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270720827826&ssPageName=STRK:MEWNX:IT

Here it's shown in action:




Lefty
10517  Using Arduino / General Electronics / Re: What's the best way insulate wire? on: May 28, 2011, 01:09:27 pm
Again it might be useful to know what kind of wire you are using? Uninsulated wire is pretty hard to come across by accident. Bus wire is the only example that comes to mind that is truly uninsulated.

Lefty

10518  Community / Bar Sport / Re: It's a good community ... on: May 28, 2011, 12:59:08 pm
I agree, this forum seems to be fundementally about helping others 'bootstrap' their way up the learning curve, no matter where their starting point happens to be. Ego seems to carry a minimum currency around here.

Lefty
 
10519  Using Arduino / General Electronics / Re: Correct calculation of resistor value when connecting LED? on: May 27, 2011, 02:15:58 pm
Quote
So, I know the basic formula V=R*I.

In this case I guess we have:
V = 5
R = (to be calculated)
I = ? (what should I plug in here? 0.55A?, The max source current of the Arduino?

So, two more questions arises:
- What current do I calculate with?
- Do I need to take the forward voltage drop of the LED into consideration?

First your voltage term needs to account for the forward voltage drop of your specific led. Red leds have a nominal 1.5vdc forward voltage drop, so that has to be subtracted from the source driving voltage, of 5vdc for a arduino digital output pin. So E=3.5vdc for a red led.

I is a value you select that you want to drive the led at. .02 amps is a nominal value, but useful light will be had from anywhere from 1ma to 20ma. Lets stick with .02amps

So R= E/I or 3.5/.02 or 175 ohm current limiting resistor. In reality anything from 175 to 1,000 ohms will protect the digital output pin and give you usable light. It's not important that the led is run at exactly 20ma.

Lefty

10520  Using Arduino / General Electronics / Re: using a 5v relay with arduino on: May 27, 2011, 01:04:16 am
Thanks so much for your help! I'll wire this up tomorrow morning...i'm curious....how did you know what pins go where? I couldnt tell any of that from the data sheet...
Thanks again!

From the datasheet. It's a poorly written datasheet but the diagram showing what looks like a resistor (which represents the coil) give one a hint of the wiring setup.

Lefty
10521  Using Arduino / Storage / Re: proper use of EEPROMWriteAnything ? on: May 27, 2011, 12:09:21 am
Here's another way to write/read configuration data to EE:

#include <avr/eeprom.h>

struct settings_t {
  byte b1;
  int i1;
  float f1;
  float f2;
  float f3;
} settings = {100, 40, 85, 0.2, 10};

// write to ee
eeprom_write_block((const void*)&settings, (void*)0, sizeof(settings));

// read from ee
eeprom_read_block((void*)&settings, (void*)0, sizeof(settings));


Thanks for the example. It seems simple and clean and compiles with no problems. I'll have to play with it some more later.

Lefty
10522  Using Arduino / General Electronics / Re: using a 5v relay with arduino on: May 26, 2011, 05:28:02 pm
Quote
                       3
1----------------2
                       4

it's shaped like the above thing...right now i have the arduino going into pin one and i don't know what else to do...i don't know where to power the thing or ground it or anything..the data sheet doesn't give me much as you can see...i've never used a relay before so any help would be much apreciated!


I couldn't find the spec on your link that shows 20ma coil current draw, but if it's a fact then you can drive the relay coil directly from an Arduino output pin. Your can wire it with pin 3 (of the relay) to a arduino output pin, then pin 4 would wire to a ground pin. Then a transient protection diode should be wired right at the relay with the cathode of the diode wired to pin 3 and the anode to pin 4. Pins 1 and 2 are the relay contacts that can wire to the circuit you are controlling.

Lefty
10523  Using Arduino / Microcontrollers / Re: Maximum current of a microcontroller circuit on: May 25, 2011, 10:34:42 pm
Quote
If I used one 2n2222 transistor per LED, would that cause any problems?

That should work just fine.

Lefty

10524  Using Arduino / General Electronics / Re: LM317 Help on: May 25, 2011, 02:58:47 pm
@Grumpy_Mike

Thanks! smiley-grin

I hope I'm not too annoying with all these questions smiley-razz, maybe something like this? http://www.nteinc.com/specs/2900to2999/pdf/nte2987.pdf

Could you also tell me what exactly am I look for? N-Channel MOSFETS?

Mouser shows that at $7 a pop: http://www.mouser.com/ProductDetail/NTE/NTE2987/?qs=sGAEpiMZZMutXGli8Ay4kFfMPLZ9xW8yKOlRS6m%252bwN0%3D

Sparkfun sells a logic level N-channel power mosfet for a buck: http://www.sparkfun.com/products/10213

Lefty
10525  Using Arduino / Installation & Troubleshooting / Re: Switching between boards on: May 25, 2011, 10:56:35 am
The Uno and the Duemilanove use different USB PC software drivers. Review the installation instructions and be sure you have installed the FTDI drivers that the Duemilanove requires.

Lefty
10526  Using Arduino / Programming Questions / Re: Watchdog Timer help please! on: May 25, 2011, 03:05:32 am
Quote
Anyone know if I can load a bootloader right with the arduino software over USB?

Any 328 based board can run the newest Uno 328 bootloader code. Once loaded you will then have to select the uno board from then on, even if it's a physical 2009 board or some clone board, etc, as long as it has a 16mhz clock source.

 As far as how to burn a bootloader and what you need, that has to be one of the most frequently posted topic these days, a search will show the several methods.

Lefty

10527  Using Arduino / Programming Questions / Re: Watchdog Timer help please! on: May 25, 2011, 02:36:52 am
Quote
Some posts suggest that if you use the watchdog timer on a stock bootloader, it will definitely loop your board. Others say that it MIGHT loop your board... Still others post tutorials on how to do it without any mention at all as to whether its safe to use or not. So which is it?


There is some history to the problem. The arduino bootloader from a few 'boards' ago would not handle watchdog timer resets correctly, where if WDT timed out it would cause a reset which would activate the bootloader code, which didn't handle the WDT correctly (it didn't disable the WDT) so it would just time out once again (after it's programmed timeout period) and restart the bootloader once again, etc. So that must be what 'loop the board' means, although I hadn't heard it called that. More like stuck in a WDT timeout loop.

Anyway, adafruit was the first to release a 3rd party bootloader code that correctly handles WDT interrupts so it doesn't get trapped in the bootloader. And I know that the newest UNO board has an updated bootloader that also handles WDT correctly. I can't say about other arduino boards, as I've made it a practice to use the adafruit bootloader for all my 328 based boards.

Lefty
10528  Using Arduino / Programming Questions / Re: analogReference(INTERNAL) error on: May 25, 2011, 02:07:37 am
Quote
I have tried it with 'INTERNAL1v1' and 'INTERNAL2v56'  and get the same error.


You were on the right track, however as they say, C is case sensitive, so try it with a big V.

Quote
INTERNAL1V1: a built-in 1.1V reference (Arduino Mega only)
INTERNAL2V56: a built-in 2.56V reference (Arduino Mega only)

Lefty
10529  Community / Bar Sport / Re: Your latest purchase on: May 24, 2011, 09:20:57 pm
Yes I think I got it from them.

And yes, I wanted to have a fallback in case I did something I shouldn't to the fuses. Like disable serial programming.

Nice programmer. Here is my version using a ladyada usbtiny and using a windows avrdude GUI:

 





Lefty
10530  Using Arduino / Installation & Troubleshooting / Re: External power supply usage? on: May 24, 2011, 08:46:18 pm
Alright, I'm using an UNO. The reset thing just has to do with the fact that I'm keeping time without an RTC. If there's a power failure setting the time again is no big deal, but I'd rather not have to set the time every single time i hook up my laptop.

There is no problem with having external power and USB power on at the same time. The boards that have an auto-voltage selector circuit will always utilize external power if it's avalible, that is it has priority over usb power. However having your arduino board reset or not is more a function of the PC software you are using and if it activates the DTR signal or not. Most arduino boards these days have the auto-reset on DTR function so if it's important that your running sketch is not reset then you might consider disabling that function and only enabling it when needing to upload a new sketch.

Lefty
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