OpenWrt Forum Archive

Topic: question on xbee/uart/asus wl-500gp

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Post #1
misha680
22 May 2008, 13:59

Hi,

Just a quick question, I haven't done any hardware hacking on my asus wl-500gp but am about to start. I would like
to hook up an XBee 2.5 Zigbee module, and it has VCC, GND, DOUT & DIN pins which operate at (based on my understanding of the manual found at http://www.sparkfun.com/datasheets/Wire … Manual.pdf

Supply Voltage 2.1-3.6V
Operating Current (Transmit, max output power) 40 or 35 mA at 3.3V
Operating Current (Receive) 40 or 38 mA at 3.3V

My understanding is that since the Asus WL-500G Premium UART operates at 3.3V as well, I could hook them up directly or is this incorrect?
Should I also have some resistors on the circuit to prevent anything from getting accidentally fried?

Thank you
Misha

Post #2
forum2008
22 May 2008, 14:21

From the WRT54GL. But maybe similar to the 500g Premiums:

Serial port

The WRT54GL has a 10 pin connection slot on the board called JP1 (JP2 on some v1.1 boards). This slot provides two TTL serial ports at 3.3V. Neither of the ports use hardware flow control, you need to use software flow control instead. Other routers may have similar connections. These two TTL serial ports on the WRT54GL router can be used as standard Serial Ports similiar to the serial ports you may have on your PC. In order to do this though you need a line driver chip that can raise the signal levels to RS-232 levels. You can not directly connect a serial port header to the board and expect it to work. That method will only work with devices that can connect to TTL serial ports at 3.3V. Connecting two which have 3.3V directly will work (TX - RX, RX - TX, GND - GND). Standard RS-232 devices cannot be directly connected which accounts for nearly all serial PC devices.

Once the modification is made you can have at most two serial ports to use for connecting devices etc. By default, OpenWrt uses the first serial port to access the built-in serial console on the router. You can connect to it at 115200,8,N,1 using a terminal program like Putty, SecureCRT or minicom for example. This is helpful because if you have problems communicating with your router this method will allow you easy access connecting over a serial console. By default this leaves you with one serial port left, however, there is a method to turn the console off giving you access to both ports if you really need them. It isn't recommended but it can be done.

Post #3
ligi
4 Jul 2009, 00:30

Have you done it? Im interested if the power consumption of the zigbee modules is OK for the Router. I can't find any source where is described how much current i can take out of the 3.3V line from the router ...

Post #4
misha680
5 Jul 2009, 09:22

Yes I have although have since moved away from the project.

Post #5
ligi
5 Jul 2009, 11:28

have you found any Documents which give the Information  how much current i can take from the 3.3V supply of the router?
I'm not sure yet if i can connect the ZigBee Pro modules because the tx-current is much higher (  215 mA ) than the current of the normal zigbee modules you seem to use. For my use-case i need the pro modules ( some Background here: http://ligi-tec.blogspot.com/2009/07/co … mouse.html ).
I'm just afraid that the regulator on the router gets too hot and fries my router ...

Post #6
misha680
6 Jul 2009, 04:32

Honestly I'm not really sure about any such documents I never found anything but people seemed to think my Zigbee 2.5 would be okay and I tried it and it worked. Sorry.

Thank you
Misha

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