There is a design flaw with the XBee Explorer Regulated (WRL-09132). There is a diode in series with the UART data input pin, causing a 0.6 Volt potential drop (like all diodes…). Well, if you hook up a standard 3.3 Volt logic to this input, it may barely work (although, its still bad engineering practice and will destroy your noise margin on your logic input). But many 3.3 Volt devices, such as my San Jose FV-M8 GPS have a 2. 8 Volt logic level output. As such, the 0.6 Volt diode drop lowers the logic level right into the “forbidden region” and the XBee just sends out garbage.
Desoldering the diode and replacing it with a wire fixes everything, and the TX/RX LEDs still work.
Anyway, point is, you can’t just put diodes in series with logic inputs without causing all sorts of noise and compatibility problems.
This diode issue has been discussed of the SoR forum as there have been some micros that don’t pull the line low enough.
I have not had a problem with the diode using a PIC16F873 at 5V to drive the XBee serial input through the Explorer board at 57.6kb. This diode will prevent the destruction of the XBee Din if one tries to drive it with a 5V signal and I feel it was a good idea for SFE to put the diode on the board. It is much easier to bypass the diode than cutting a trace to add the diode. SFE does publish the schematic and it is the user’s job to examine the schematic and determine the usability of the board.
Granted, a note on the schematic about bypassing the diode for 3.3V systems would have been nice.
Just a thought here guys. I think the explorer is mainly pointed at users that have micros running @ 5V and need to protect the xbee… if you already have 3.3V logic you could use the BOB and some xbee headers!
The only backdraw it’s the larger amount of pins you’ll have on your pcb or protoboard but it’s a lot cheaper and gives you access to all the xbee’s pins.
This part is well overdue for a re-design as it can not provide enough current for the XBee 900 Pro/XSC devices.
I pointed this out of SFE and they said they were aware of the issue, yet months later the product page still hasn’t been updated with a warning and no revisions to the design have been made.
gussy:
This part is well overdue for a re-design as it can not provide enough current for the XBee 900 Pro/XSC devices.
I pointed this out of SFE and they said they were aware of the issue, yet months later the product page still hasn’t been updated with a warning and no revisions to the design have been made.
Too much effort SparkFun?
PM the moderator? Maybe he has a good email address for SFE