Frequently Asked Questions
Bluetooth connections
Robot often disconnects from XRPCode
The most frequent cause of Bluetooth disconnects is low batteries. This can cause the Bluetooth connection to be unreliable or completely unavailable. Make sure that your batteries are fully charged, ideally having 2 sets of rechargable batteries so that one can always be recharging.
Windows development computers
The Windows operating system, in particular, often has a 10 to 15 second reconnection time. This happens while waiting for an initial connection, or reconnecting after pressing the STOP button. This delay can often be avoided by letting the program exit, that is run to the end of the file. If, instead, a running program is interripted using the Stop button in XRPCode, then the connection has to be reestablished and it might take up to 15 seconds.
Infinite loops
A common way to write user control (or teleoperated) programs is to have an infinite loop where the game controller buttons and joystick values are read and the motors are set accordingly. The problem with this style of program is that the only way to stop this program is with the Stop button or resetting the robot, and in either case, restarting will have the long delay. You can eliminate that long delay by making sure that you program exits when it’s finished.
This can easily be done by changing the unconditional loop to one that can be stopped so that the program exits and the connection is maintained. This can be done by using a button to trigger program termination. A convenient button to use is the User button on the XRP control board, although one coule also use a gamepad button as a trigger to stop the program.
Below are examples of having an infinite loop, and a loop that terminates with the User button.
The following program uses a differential_drive (differential_drive) object and a Gamepad object (gp) and shows how an infinite loop might be used for a teleoperated driving program. Notice that the program doesn’t ever exit from the loop and so the only way to end the program is to use the stop button or reset the robot:
while True:
differential_drive.set_effort(gp.get_value(Y1), gp.get_value(Y2))
The next program uses a loop that can be ended by using the user button on the XRP control board. Upon pressing the button the loop ends, and the the program stops without requiring a lengthly reset:
while not (board.is_button_pressed()):
differential_drive.set_effort(gp.get_value(Y1), gp.get_value(Y2))
XRP not appearing in the Bluetooth pairing window
If the name is not showing up in the Bluetooth pairing dialog box, then the XRP may need to be reset. You can press the reset on the XRP, or turn the switch off and back on. When using the switch, make sure the XRP is not connected via a USB cable, as that cable provides power and the XRP will not turn off fully by the switch. If this does not start the XRP showing its pairing address, then see the Wrong Firmware section.
Refresh page
There are times when the browser gets confused about the bluetooth connection. XRPCode will now pop up a dialog to letting you know to refresh the page when it sees these conditions. But, if you get to the point of the XRP spinner is going for more than 20 seconds then refreshing the page and resetting the XRP is a good course of action.
Can’t connect
If the XRP bluetooth address is showing up, but it never finishes pairing after hitting the Pair button, then try refreshing the web page and resetting the XRP.
Multiple XPRCode pages open
XRPCode is designed to only have one window open at a time. If you have more than one XRPCode open, close all them and then re-open one and try again.
Wrong firmware or libraries
For bluetooth to work it must have both the correct version of MicroPython and the correct version of the XRPLib libraries. Always let XRPCode update your MicroPython and XRPLib to the latest.
XRPCode won’t connect even with a cable
Assuming you have checked that you are using a USB data cable and not just a USB power cable. Then check to see if a disk drive shows up when you connect the XRP to the computer with the USB cable. The drive name may be something like:
PICODISK
RPI-RP2
RP2350
If you see one of those drives when plugging in the XRP you need to manually put MicroPython back onto your XRP. Follow this link on how to do that: