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151  Using Arduino / General Electronics / Re: Resistors and application usage... on: August 08, 2012, 11:34:29 am
I can explain the LED part.

as in your example, LED is rated 2.6v forward voltage and 28ma.
If you apply 5V, that means the 2.4v must go somewhere (2.4+2.6=5).  That's where the resistor comes in.
To calculate the resistor value, you know the voltage (2.4) and the current (28ma), so R= 2.4/0.028 = 84.71 ohms.  
152  Using Arduino / General Electronics / Re: Problem with relay wiring on: August 07, 2012, 11:36:30 am
I initially got a 5v relay board also and it just takes too much current to activate the relays. So I switched to 12v relay board.
If you are stuck with the 5v relay, instead of getting a 7v power supply, you can get a dc-dc buck converter for like $1 shipped (I got 2 for $1) and it can step down 12 to 5 v very efficiently (without getting hot) compared to using the linear regulator. Search ebay for LM2596.
153  Using Arduino / General Electronics / Re: Time for a new iron on: August 01, 2012, 02:52:59 pm
That is a Hakko 936 clone from China.

That model is a retired product  It's not for sale any more...

This is it's replacement Hakko 926 clone from China, perhaps you meant this:

Sorry, that's the one I meant. I'll probably pick one up next week.

It seems to be have good reviews.

I got that one from sparkfun and been using it for a couple months and it works very well.
154  Using Arduino / General Electronics / Re: Where can I purchase a 120ac in isolated transformer? on: July 30, 2012, 03:15:13 pm
The learning objective is just that, "learning." The final outcome of this project
is to have a functioning benchtop variable AC to DC transformer from 1volts to maybe 24volts. I know I can purchase one on Amazon for a relatively low price, but I want to build one to learn the theory and the functionality.

no objections to the learning part. just merely suggesting that there might be more beneficial areas to spend your resource on (perhaps build a switching power supply?). as it is like learning vacuum tubes circuit. its a bit outdated.
155  Using Arduino / General Electronics / Re: Where can I purchase a 120ac in isolated transformer? on: July 30, 2012, 01:34:06 pm
what exactly is your learning objective?

I did a benchtop power supply project like 30 years ago and I can't imagine that will have the same learning value nowadays.
156  Using Arduino / General Electronics / Re: Will this ethernet module work for Arduino UNO? on: July 26, 2012, 06:07:43 pm
Well, I'm thinking about just getting the official arduino ethernet shield... Though the price is quite wack ($50, with shipping)

I highly recommend this

if they have one on auction, you can usually get it for almost half that price.  they ship via their amazon store so you get it in a week.
157  Using Arduino / General Electronics / Re: Will this ethernet module work for Arduino UNO? on: July 26, 2012, 11:53:10 am
you can get w5100 based ethernet modules (with micro SD) now for $10-$12. IMHO, not worth saving $5 to go though all the trouble and headache to make the $5 module to work.
158  Using Arduino / General Electronics / Re: Arduino Uno Referance Design Query on: July 26, 2012, 11:49:33 am
This is just a personal belief:  I believe subtle errors like this one are present in the reference design to throw off clone makers who just take the files and produce them verbatim.  Maybe it was just a mistake, maybe it was intentional.

that's why there is a  fineprint saying "subject to change without notice".
there is a similar situation with the ethernet shield, the eagle file  left in a resistor that makes auto reset to not work.
I would not go as far as calling them "clone" makers. after all, this is supposed to be "open source".  cloning implies copying without authorization.  True there are some projects out there that pretend to be open source by doing things like leaving key component values out, extra component added or removed, etc. arduino's case is certainly not as the above post is implying, as you can email Massimo directly can he will tell you exactly what the correct circuit should be.
159  Using Arduino / Networking, Protocols, and Devices / Re: HTTP Server running with Ethernet library =] on: June 08, 2012, 02:06:56 pm
ajax support would be nice. useful for updating the value for a few fields without refreshing the entire page.
can you elaborate on iphone compatibility? is it for things like supporting the apple-touch-icon used by safari browser client? jquery?

I imagine this would barely fit on an UNO and a mega would be required right?
160  Using Arduino / General Electronics / Re: Arduino Uno or Mega. on: June 08, 2012, 12:13:24 pm
if you are not going to use the SD card on the shield, you will have maybe 10k left of program space just using the ethernet shield. If you are going to use the SD card as well, use the mega.

if you use that lcd keypad, you will need to disconnect pin 10, which will just keep the backlight on.
since you are already looking on ebay, you can get the ethernet shield for $13 or less there and mega for around $30.
161  Using Arduino / General Electronics / Re: The inexpensiveness of foreign component dealers relative to US dealers. on: June 07, 2012, 11:16:40 am
I highly doubt tayda sells fake or defective parts.

from reading this thread, its amazing to read the reasons people come up with to justify the exorbitantly higher price they pay for the same parts. These people are a salesman's dream come true.  As for higher prices from U.S. sellers, I can see how a store with an actual store front has higher overhead, etc. needs a higher markup in order to make a profit, (and I don't mind buying from them from time to time) but for someone operating an online business out of a new york apt? well maybe the rent there is high...
162  Using Arduino / General Electronics / Re: Where to buy electronics components and parts on: June 06, 2012, 08:12:41 pm
This is what my tracking looks like. One week to deliver. Granted I am in SF bay area, delivery is faster than domestic UPS that takes 10 business days to deliver coast to coast. It takes longer if the package goes through Los Angeles, which may explain why your delivery time is a little longer (I see you are in SoCal). But from what I see in tracking info, it spends the most time at Los Angeles customs facility.

163  Using Arduino / General Electronics / Re: Where to buy electronics components and parts on: June 06, 2012, 05:09:49 pm is my first choice. digikey is my second choice for quickly getting that one or two missing part that I need. Digikey minimum shipping is around $2.50, which is really nice. most other U.S. electronics parts stores charge double or more than that even if you just buy 1 small part.

I ordered from tayda several times and the package usually arrives in a week. On all my previous orders, the package comes from Massachusetts. This last order was shipped from Colorado. The company is based in Thailand.

my last order from tayda, placed 5/31. status shipped on 6/1. received the package today 6/6.
shipping charge is $2.60.

if you are not in a hurry, you can get parts really cheap, and I mean really cheap on ebay auctions. (buy it now is a different story). I just got 2 step down buck converters for $1 shipped with tracking (they normally go $3.90 buy it now each). If you stick with Top Rated Ebay sellers and sellers with >99% rating, you will get your package in 10 business days or less. I'd say over half the stuff I get from ebay Chinese sellers in about 7 business days, and more than half that time the package is stuck at U.S. customs (you can tell from the tracking info. Los Angeles customs takes a long time, while San Francisco customs seems faster, around 2 , 3 days max.

I'd say shop around and stick with what works best for you. What works for others may not work for you.
164  Using Arduino / Programming Questions / Re: Testing code without upload it? on: June 05, 2012, 11:08:35 am
I can see from HugoPT point of view that once you have used a simulator, you can't see how you survived without one.  Its more than just about the number of times you flash the memory.
165  Using Arduino / Programming Questions / Re: Changing eeprom datas without uploading the software ? on: June 01, 2012, 02:54:42 pm
How does one run that command? in Windows?
Just open the DOS/Command Prompt box and type that in at the arduino folder directory?

that's pretty much it. you may need to specify full path name to the program and to the conf file.
you can turn on verbose upload on arduino IDE to see the exact command arduino makes, and you can do the same in a dos prompt.

like if I upload the blink sketch, this is what arduino does

E:\arduino-1.0\hardware/tools/avr/bin/avrdude -CE:\arduino-1.0\hardware/tools/avr/etc/avrdude.conf -v -v -v -v -patmega328p -carduino -P\\.\COM1 -b115200 -D -Uflash:w:C:\TEMP\build2046637769768951399.tmp\Blink.cpp.hex:i

or modify as needed, say to write eeprom. you will need -cstk500v1 instead of -carduino.
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