Hello,
I want to buy an arduino board (preferably an UNO) for testing out new ideas and do not want to buy a new one in case I break it by accident 
, so I am looking for a website or store that sells used arduino's.
Thank you in advance,
Jaredpi
LOL That would be rare.
Most people hold onto them unless its broken.
$30 is a cheap investment for getting into microcontrollers IMO.
Also you can get rugged clones like http://ruggedcircuits.com/html/ruggeduino.html for alittle more money.
dont think that youll find something like that if you don't want to spend a lot there are a lot of arduino cheaper compatible boards
http://shop.moderndevice.com/products/rbbb-kit
the list could continue but almost all of the cheaper versions do not have an usb to serial converter so you'll need an dedicated programmer or an usb to serial converter to program it
There are also many less expensive clones available, one that I have used and like is Adafruit's Boarduino. Many of the clones will need a separate FTDI board or cable to program them (I also use Adafruit's), which makes the initial outlay just a little more, but only one of these is needed, so that will save money when buying the second or tenth XD clone. There's very little that can be damaged with the Boarduino, other than the MCU itself. If that gets fried, it's only about five bucks to replace it.
My two favourites for lower cost...
http://www.pjrc.com/teensy/
Get a bootloaded chip
get some bits from dipmicro.com
make up your own:
atmega328
two 22 pf caps
four 100nF caps
10K resistor
16 MHz crystal
28 pin socket
piece of perfboard:
Starter Component Set 132pc w/ Proto PCB - dipmicro electronics Hey look look at that! Most of what you need.
Add 22 pf caps, 5V walwart & powerjack Power Jack 2mm 24V / 3.5A w/ Built-in Switch - dipmicro electronics
Once you get it running, can use it with Optiloader sketch to bootload your own parts.
Need a USB/Serial adapter too,
http://www.ebay.com/itm/USB-2-0-UART-TTL-6PIN-CP2102-Module-Serial-Converter-/190584335291?pt=LH_DefaultDomain_0&hash=item2c5fb62bbb
cut the RST trace and wire DTR to that pin instead.
Add some header pins, jumper to Gnd, Power, DTR (100nF cap to Reset pin), Rx, Tx.
If you are worried about breaking something on the board,
then try to get a board with fewer things that break. 
That means getting a board without surface mount chips so you can replace any
of the chips that might get "smoked".
Have a look at this board:
There is pretty much nothing on it to break except the processor
and can you can easily replace that if you use a 28 pin socket.
You will also need a USB to serial adapter to be able to download it:
--- bill
Can build up a Serial Arduino on a bare board for RS232 interface
all parts available at dipmicro.com if you can't navigate mouser's search engine
http://arduino.cc/en/Main/ArduinoBoardSerial
Different bare board also available here
http://store.nkcelectronics.com/arduino-runtime-board-rev-b.html
Setup for a resonator, see the 2nd picture.
CrossRoads:
Can build up a Serial Arduino on a bare board for RS232 interface
http://www.mouser.com/ProductDetail/Arduino/A000006/?qs=sGAEpiMZZMs0PWRNvpRp0ARF1Zt0Kmpi
all parts available at dipmicro.com if you can't navigate mouser's search engine
http://arduino.cc/en/Main/ArduinoBoardSerial
I wouldn't recommend that route as there are very fewer and fewer new computers that still have serial ports on them.
Plus, that design does not support auto reset which means you have to push the reset button each time you want
to download it.
Just my preference but for playing around, I like to use boards that can be powered by USB.
And for breadboarding, I really like the Teensy boards as you get more of everything (FLASH,RAM, pins)
than the Arduino boards for a similar and sometimes lower cost.
If Arduino shield compatibility is a must, then there are many 3rd party boards in the $15-$25 range
whith some including an on board USB to serial conversion chips.
--- bill
bperrybap:
CrossRoads:
Can build up a Serial Arduino on a bare board for RS232 interface
http://www.mouser.com/ProductDetail/Arduino/A000006/?qs=sGAEpiMZZMs0PWRNvpRp0ARF1Zt0Kmpi
all parts available at dipmicro.com if you can't navigate mouser's search engine
http://arduino.cc/en/Main/ArduinoBoardSerialI wouldn't recommend that route as there are very fewer and fewer new computers that still have serial ports on them.
Plus, that design does not support auto reset which means you have to push the reset button each time you want
to download it.
Except for a $5 USB<-->Serial converter.
Pushing Reset is not that great a hardship.
A $4 CP2102 module
http://www.ebay.com/itm/USB-2-0-TTL-UART-6PIN-CP2102-Module-Serial-Converter-/250899746996?pt=LH_DefaultDomain_0&hash=item3a6aca50b4
can be wired to the Rx/Tx lines for USB interface too.
smeezekitty:
bperrybap:
CrossRoads:
Can build up a Serial Arduino on a bare board for RS232 interface
http://www.mouser.com/ProductDetail/Arduino/A000006/?qs=sGAEpiMZZMs0PWRNvpRp0ARF1Zt0Kmpi
all parts available at dipmicro.com if you can't navigate mouser's search engine
http://arduino.cc/en/Main/ArduinoBoardSerialI wouldn't recommend that route as there are very fewer and fewer new computers that still have serial ports on them.
Plus, that design does not support auto reset which means you have to push the reset button each time you want
to download it.Except for a $5 USB<-->Serial converter.
You can get USB to RS232 serial converters on Ebay for a bit under $2 shipped,
but that still won't get you auto reset working using that Arduino RS232 Serial board design.
You would still need to add a transistor, 2 resistors, a diode and a cap to that board
to properly level shift the DTR signal from RS232 to TLL level to drive the RESET signal on the AVR.
Thats quite a few parts to stick on the back of the Arduino board.
Now when you are building the board you could leave off all the RS232 level shifting parts
(T1, T2, D2, D3, C8, R3, R4,R5,R6,R8)
and then use a cheap cp2102 USB to TTL serial converter (which is TTL based, for about $3 shipped off ebay) and wire it
in using a pigtail connector, and then either hook up the RTS line directly to the AVR reset line or hook up a .1uf cap
from DTR on the cp2102 to the reset line on the AVR.
But all that requires quite a bit of in depth knowledge which may be beyond that
of a someone just starting out.
So, IMHO, is not worth it for someone just getting started,
especially when you can buy kits or ready made solutions
that include all the needed components for about the same overall cost.
jaredpi, I think the biggest thing to take into consideration is that you don't have to get
an official "UNO" board to run all sketches and libraries that run on the mega328.
The older boards and the 3rd party boards which come in many different form factors
will work just fine.
Just decide which form factor you want and jump right in.
If you are worried about accidentally burning up your AVR chip, then get a board
that uses a socket for the AVR chip.
--- bill
Most USB to serial converters output TTL since regular serial ports will operate at that level and shift voltage up is somewhat difficult.
As long as you use it with only a USB adapter, you could skip the level converters.
Here is my take on starting with a bare Arduino RS232 PCB.
Its pretty hard to beat the total cost of the some of the kits and prebuilt boards
unless you happen to have quite a bit of parts laying around in your personal parts stash.
But my assumption is that someone worried about breaking their UNO board doesn't have a stash of
parts laying around.
So if you start adding up the total parts cost, for something like the Mouser PCB at $6.72 then add in
a pre-programmed AVR for about $5.00 then start adding in the connectors for a few bucks, and then the crystal
a few caps and resistors, the reset button, and the RS232 connector for a $1 or so. Then add in shipping and
you really start to push up near or over the $20 mark to assemble
the Mouser PCB.
Then you may have to toss in a USB to RS232 adapter and you are looking at
at least low 20s before you have a working board - and one without Auto reset.
(ok you could cheat and wire a cap from DTR to the RESET line if you know the USB to serial adapter
is at TTL levels)
But for starting a bit under $20 (shipped) you can get assembled UNO clones. Here are some examples:
http://www.ebay.com/itm/ARDUINO-UNO-ATMEGA328-ATmega8U2-Serial-USB-Cable-/130624219183?pt=BI_Electrical_Equipment_Tools&hash=item1e69cf682f
One that includes a free proto shield:
http://www.ebay.com/itm/ARDUINO-UNO-ATMEGA328P-ATmega8U2-Serial-FREE-Proto-Shield-PCB-/130619906155?pt=LH_DefaultDomain_0&hash=item1e698d986b
A freeduino kit:
http://store.nkcelectronics.com/freeduino-arduino-diecimila-compatible-board-complete-kit.html
A seeduino assembled board:
http://store.nkcelectronics.com/seeeduino-fully-assembled--arduino-compatible.html
--- bill
Yeah, but where's the fun satisfaction in that?
Or the timely delivery:
"Estimated between Wed. Jan. 25 and Tue. Feb. 7"
Who wants to wait a month for parts?
dipmicro.com can get you all the parts needed in about 2 days, buy a PCB & a bootloader uC from mouser or nkcelectronics, be assembling in under a week and back here asking how to download sketches & run Optiloader to make more bootloaded uS....
I respect the concern regarding damaging a new Arduino as I myself fried my first one ( a smd UNO) when I shorted the 12v vin to the 5v supply.
I have since resurrected it with what I'm calling my "phoenix shield" which has a 28 pin dip socket and all the pins wired out as standard with the 5v supply and usb interface to program it coming up through the old board. I had to grind off the old chip with a dremel but the shield works a treat.
In the end, after buying all the individual components, I could have just bought a complete new one for roughly the same price but it was a good learning experience and well worth the effort and now I have something I can experiment with and not worry that I'm going to make it worse than it already is.
So don't fear buying a new one. Just get one with a standard dip socket and not the smd version and you'll be right.
So don't fear buying a new one. Just get one with a standard dip socket and not the smd version and you'll be right.
Unfortunately the USB<->Serial chip seems to be the most fragile.
smeezekitty:
So don't fear buying a new one. Just get one with a standard dip socket and not the smd version and you'll be right.
Unfortunately the USB<->Serial chip seems to be the most fragile.
I guess I was lucky with my misfortune then
Still you could modify a board to work around that too...