HOWTO Read the laser in real time

The laser measurement device is read via RS232 serial communication through the serial port on the Desktop computer located on the ground as part of the FDC laser scanner system. The laser's default mode when powered on is to be on and reading continuously. Note that only one program can read form the serial port at a time so these instructions should only be followed if a full snake scan is not currently in progress.

To read the values reported by the laser device, perform the following:

1. Make sure the laser is plugged in and is on. The plug is labeled and plugs into a power strip that sits in the top of the granite rock, towards the right. If you do not see the laser reflecting off of whatever is directly in front of it, then unplug the laser and plug it back in to reset it.

2. Open up an window on the Linux Desktop computer and type:

   minicom -o

   This should immediately start reading the laser with numbers scrolling up the screen. The values are in mm.

Troubleshooting

• If minicom refuses to make a connection, it is likely because another program has control of the serial port. Try killing the other process with the following:

  kill -9 `cat /var/lock/LCK..TTYS0`

• If you still can't get access to the serial port, reboot the Linux Desktop

• If the laser is not reading properly (too fast or too slow) try unplugging and plugging it back it.

• On rare occasions, the serial device on the computer side gets confused to the point that only a reboot will clear it to the point that communications can be established.

• If the laser reads only zeros, it probably means the distance between the read head and the surface being measured is out of range. The device has a very limited range of only about 1mm centered somewhere around 5mm. Try slipping in a piece of paper to see if you can get non-zero numbers to come up. If so, then the surface is too far away. If not, then try moving the laser further from the surface.

Contact

David Lawrence davidl@jlab.org x5567