Hi, I have looked at the schematic for the Xbee Explorer regulated board and see a diode on Din. Can anyone tell me what it is for? It appears to be backwards.
Odd.
Product description says board has 3.3 to 5V level shifters but I see none.
If that diode was a Zener, maybe it protects the Din pin from voltages higher than 3.3V. Schematic doesn’t show a Zener symbol.
I’m thinking they are using the Diode to drop the signal voltage down to an acceptable level. If it is a normal diode then 1.7V drop is pretty average and you are right there at 3.3V…pretty simple way of conditioning the input signal.
I am going to assume that is what is going on. I am designing a circuit that I want to interchange the Basic FTDI breakout and the xBee breakout…I am assuming based on the pinout that I sould be able to do that without issue.
I thought normal silicon diodes forward drop is more like 0.7V rather than 1.7V.
someone must have the answer…
Hi guys,
I too am having problems with this seemingly misplaced diode.
I have been successfully communicating between 2 XBee Pro modules with the use of the Explorer Serial (one end connected directly to the PC, the other to a 5V Arduino Mega via RS232<->TTL conversion).
Recently, I have purchased an XBee Explorer Regulated to cut out the need for the RS232 conversion and reduce the size.
When I use this new configuration, the Arduino is able to receive data but not transmit.
To test the system, I transmitted 0xFF constantly from the Arduino to the Explorer Regulated to see what voltage appears at DIN. I would expect ~3.3V but got more like 0V.
My next step was to look at the schematic which is when I made a similar discovery to Mike2545. I would have thought a simple resistor would be more suitable to drop the voltage down from 5V to 3.3V.
Could somebody please help?
After consulting my supervisor, he pointed out that this diode configuration would work if there is an internal pull up resistor in the XBee on the DIN line; and of course there is. This configuration means that any voltage can be applied to DIN to switch between XBee’s Vcc (3.3V) and ground.
However, by default, the DIN pull up resistor is disabled so you must enable it via an Explorer USB or something similar then save it to non-volatile memory.
Hope this helps.
Yeah I’m having the same problems with DIN.
Had everything working just fine with out the board then bought the board and could no longer transmit. pretty lame …
If you want better level shifting for the XBee, have a look at [AdaFruit’s XBee adapters. They work very well.](XBee Adapter kit [v1.1] : ID 126 : Adafruit Industries, Unique & fun DIY electronics and kits)