some issues with parallax Xbee 5V/3.3V adapter

Sarah_Lafi · 2013-04-11 10:34

Hi every one
I'm working on parallex's xbee
This is the kit that I am using..http://www.amazon.com/Parallax-XBee-Wireless-Pack-Micro-controller/dp/B00B6SF2C6
It has two xbee , 1 usb adapter and 1 5V/3.3V adapter. I'm wondering about many things regards the 5V/3.3V adapter.

First, when I tried to connect Vcc pin of the board directly to a 3.3 volt, the adaptor does not power on. But when I connect the 5 volt to Vdd, it works.
Is this normal? or my board or xbee has a problem?

And which Vss pin shall I use? I used pin#11 but the board also has another Vss pin. shall I connect both?
This is the pin out of the board that I am talking about.

Second, I noticed that the xbee tx LED which is in the board is mostly ON. although I am not connecting any wire to Dout or Din pins! I'am wondering what does the xbee transmit without connecting any thing to Din and Dout!

And the last thing is that when I tested the connectivity between the pin out of the xbee and the pin out of the board, I found that some pins are not connected ..
Is it normal?
This pictures below shows those pins that are not connected. Even the xbee usb adapter has some. Is this because of the internal circuit of the board... I will come up with the same picture for usb adapter soon ...

That is all... Waiting your help

Sarah_Lafi · 2013-04-11 10:58

In the USB XBee adaptor these pin are not connected

Mike Green · 2013-04-11 11:04

You use the Vdd pin for the +5V or +3.3V and either (or both) Vss pins for ground. The two Vss pins are connected together on the adapter board. If you have a 3.3V supply, you can connect it to Vcc, but you must leave Vdd unconnected. This bypasses the on-board regulator, but everything else should work the same.

The xBee has its own microcontroller on the module. Even if it's not connected to another microcontroller (via Din and Dout), it may try to talk to other xBees to establish a connection between them (depending on how they're configured). For example, you can set up two xBees using Digi's PC utility program to automatically establish a serial connection between them when they're first turned on. An xBee can also transmit the status of some of its I/O pins to another xBee automatically when it's turned on.

The 5V/3.3V adapter board uses both 1K series resistors and an IC (74LVC244A) to do the voltage conversion from the 3.3V logic of the xBee to the 5V logic of say a Stamp. You won't see a connection between the xBee pins and the adapter's pins because of these. The adapter's schematic gives the details. If you haven't already, look at the adapter's documentation. Parallax's webstore pages for its products generally have links to documentation, schematics, and sample code.

If you can't get the adapter to work, give Parallax's Tech Support a call.

Sarah_Lafi · 2013-04-11 11:41

Thank you for your helpful replay

Mike Green wrote: »

If you have a 3.3V supply, you can connect it to Vcc, but you must leave Vdd unconnected.

This is exactly what I did but it did not respond
Anyhow, I will use the Vdd as it worked with me. but this makes me untrust my adapter. : (

Mike Green wrote: »

This bypasses the on-board regulator, but everything else should work the same.

It bypasses only the regulator or the whole on-board circuit ?
Because the power led does not light up.

Mike Green wrote: »

The xBee has its own microcontroller on the module. Even if it's not connected to another microcontroller (via Din and Dout), it may try to talk to other xBees to establish a connection between them (depending on how they're configured). For example, you can set up two xBees using Digi's PC utility program to automatically establish a serial connection between them when they're first turned on. An xBee can also transmit the status of some of its I/O pins to another xBee automatically when it's turned on.

But why this does not happen with the xbee usb adapter? :$

Mike Green wrote: »

The 5V/3.3V adapter board uses both 1K series resistors and an IC (74LVC244A) to do the voltage conversion from the 3.3V logic of the xBee to the 5V logic of say a Stamp. You won't see a connection between the xBee pins and the adapter's pins because of these. The adapter's schematic gives the details. If you haven't already, look at the adapter's documentation. Parallax's webstore pages for its products generally have links to documentation, schematics, and sample code.

The document does not show the internal circuit of the adaptor, I mean the on-board circuit.
Could I find that on-board one?
For both this 5/3.3 V adapter and the xbee usb adapter?

Very thankful
Sarah

Chris Savage · 2013-04-11 11:50

I just wanted to confirm (as the designer of the board) that what Mike said is accurate. You only need one VSS (Ground) pin as they're internally connected together. And you can either apply 5V to the VDD pin or 3.3V to the VCC pin (but do not connect both). If you look at the schematic as Mike suggested, the resistors on the buffer outputs are to prevent a programming mistake from driving against an output and damaging the adapter or the microcontroller connected to it. If you could post a picture of your connections we could more easily see if everything looks good.

Chris Savage · 2013-04-11 11:53

Sarah_Lafi wrote: »

In the USB XBee adaptor these pin are not connected

Not sure what you mean here. The schematic diagram shows the connections for all pins and three of the ones you show as not connected do in fact connect to the USB and XBee Module.

Mike Green · 2013-04-11 11:54

"power led does not light up" ... This shouldn't happen. You might call or e-mail Parallax Tech Support directly

"why this does not happen ... adapter?" ... I don't know. It's really a function of the configuration stored in the xBee module and has nothing to do with the adapter.

Both the 5V/3.3V adapter webstore page and the USB adapter webstore page have links to their respective documentation and the schematic. Look under the heading "Downloads & Resources" on the right about 2/3 of the way down the webpage.

Chris Savage · 2013-04-11 11:55

Sarah_Lafi wrote: »

And the last thing is that when I tested the connectivity between the pin out of the xbee and the pin out of the board, I found that some pins are not connected ..
Is it normal?
This pictures below shows those pins that are not connected. Even the xbee usb adapter has some. Is this because of the internal circuit of the board... I will come up with the same picture for usb adapter soon ...

How are you determining that these pins are not connected? I have a feeling you're using a continuity meter, and if that is the case it won't work because the I/O lines are buffered. Please let us know how you're testing these pins.

Sarah_Lafi · 2013-04-12 09:40

Chris Savage wrote: »

How are you determining that these pins are not connected? I have a feeling you're using a continuity meter, and if that is the case it won't work because the I/O lines are buffered. Please let us know how you're testing these pins.

Yean I tested it using a continuity meter...

Sarah_Lafi · 2013-04-12 10:12

I would like to thank you very much sir. Mike Green and sir. Chris Savage for providing me with these helpful information and links especially the schematic link.It was very helpful. I got the idea after I saw the diagram. I came to know that 3.3\5 volt adapter internal connection is OK.
Now, the only problem with that 3.3\5 volt adapter is the Vcc pin but no problem since I can use Vdd pin.

But about my USB adapter I still think that the four pins: RSV, DTR, Vss and IO5 should be connected when they are tested using a continuity meter. Because when I refer to the xbee usb adapter I found that they are not buffered. Isn't it?

Mike Green · 2013-04-12 10:45

I'm not sure what you're calling RSV. Is it RSSI? Both RSSI and IO5 (Associate) are connected to LEDs on the adapter. DTR is connected to the FT232RL USB interface chip. There's only one Vss pin and it's connected as ground throughout the adapter, xBee module, and USB interface. Remember that a multimeter measures resistance by connecting a battery to a circuit and measuring the current that flows. Depending on the polarity of the battery, the current that flows can vary if you connect it to diodes, transistors, or ICs. A continuity meter only works with wires and low value resistances.

Sarah_Lafi · 2013-04-12 12:05

I mean these pins ...

They have a direct link. For example if I connect one terminal to the DTR of the board and other terminal to the DTR of the XBee they should be connected.. No resistor or any device are connected in between.

Mike Green · 2013-04-12 12:29

I would agree that you should be able to measure continuity between J1 and J3 at the two Vss pins, between DTR and /DTR, and between Reserved and RSV. You want to do this with the xBee removed and without power applied to the adapter. I'm very surprised that you can't measure continuity between the two Vss pins. There may be a bad solder connection on the adapter in which case you should contact Parallax Tech Support directly to get the adapter replaced.

dgately · 2013-04-12 14:58

Did you look at the follwing web page?

http://learn.parallax.com/kickstart/32440

Sarah_Lafi · 2013-04-14 04:01

Yeah I did

dgately · 2013-04-14 07:52

Sarah_Lafi wrote: »

Yeah I did

Sorry, I thought that the page would help, but it looks like you have tried the same connections...

some issues with parallax Xbee 5V/3.3V adapter

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