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Electronics => Electronics => Topic started by: Mastermime on May 08, 2012, 03:57:09 PM

Title: Do I need resistors? And a question about Xbees
Post by: Mastermime on May 08, 2012, 03:57:09 PM

Hello everyone,


I am using two 12v High power LEDs that draw approximately 1 amp.  I am using the Axon II and am connecting these LEDs to the 'Unregulated' section.  I will need resistors because it is unregulated, right?

Main Question: First off, I am novice when it comes to Xbees so bear with me.  I recently purchased an Xbee Pro XSC Development Kit (http://parts.digikey.com/1/parts/1628310-kit-starter-xbee-pro-900mhz-xbp09-xc009-dk.html (http://parts.digikey.com/1/parts/1628310-kit-starter-xbee-pro-900mhz-xbp09-xc009-dk.html))

I am not sure where I make the connections from my development board to my Axon II.  There is a picture below of the transmitter (not sure if that helps).  It's really difficult to find documentation on the board.  I'm pretty sure this is the datasheet of the development board though. http://ftp1.digi.com/support/documentation/xbibudev_schematic.pdf (http://ftp1.digi.com/support/documentation/xbibudev_schematic.pdf)

Title: Re: Do I need resistors? And a question about Xbees
Post by: mstacho on May 09, 2012, 07:19:28 AM

1) Yes, you need a resistor.  You choose the resistor value so that you draw 1A.  For instance, if my LED drops 0.7V and my supply is 12V, then I have 11.3V.  I want 1A, so I choose an 11.3 Ohm resistor (Granted, 11.3 is hard to find :-P So either make it in series/parrellel or use a slightly larger one that does exist)

2) XBEE is UART, if I'm not mistaken.  RX -> TX, TX->RX, make sure you tie the GNDs together and keep the voltage the same.  IF you want to use USART (the S stands for Synchronous), then you get to use the clock stuff and CTS/RTS.

MIKE

Title: Re: Do I need resistors? And a question about Xbees
Post by: Soeren on May 09, 2012, 11:49:38 AM

Hi,

Quote from: Mastermime on May 08, 2012, 03:57:09 PM

I am using two 12v High power LEDs that draw approximately 1 amp.  I am using the Axon II and am connecting these LEDs to the 'Unregulated' section.  I will need resistors because it is unregulated, right?

You will not need resistors because the voltage is unregulated, you'll need them to limit current.
Perhaps the LEDs comes with current limiting already, but using an approximate value may be detrimental to the lifespan of the LED(s), better post either a datasheet or a link to info about them.

Title: Re: Do I need resistors? And a question about Xbees
Post by: jkerns on May 09, 2012, 02:06:29 PM

Quote from: Mastermime on May 08, 2012, 03:57:09 PM

Hello everyone,


I am using two 12v High power LEDs that draw approximately 1 amp.  I am using the Axon II and am connecting these LEDs to the 'Unregulated' section.  I will need resistors because it is unregulated, right?

You will need a resistor and I believe you will need some kind of interface (transistor) between your LED and the Axon. If I am reading things right, the Axon I/O pins will only sink about 20ma - not enough to drive your 1 amp LED.