This program provides a bridge between two serial devices connected by USB to serial cables. These are used, for example, in Lakeshore temperature controllers.
The intent is to run the program on a small computer such as a raspberry pi or a beagle bone. As a man in the middle, the bridge can act as a translator, converting one serial protocol into another, or tying different serial devices together.
This version is set up specifically for talking to a Lakeshore 336 temperature controller.
Clone the github repository onto your raspberry pi:
cd ~ git clone https://github.com/scattering/serial_bridge.git
Add a pointer to the ls336 program to /etc/rc.local:
sudo nano /etc/rc.local
Just before the exit 0 line, add the following:
python /home/pi/serial_bridge/ls336.py
Copy the rules file to /etc/udev/rules.d:
sudo cp serial_bridge/10-ftdi.rules /etc/udev/rules.d sudo chmod 644 /etc/udev/rules.d/10-ftdi.rules
When you restart the raspberry pi, it will automatically start the bridge communication, even if there is no keyboard or screen attached.
If you do not have a network connection, copy the current version of the repository onto a usb drive:
https://github.com/scattering/serial_bridge/archive/master.zip
and expand it on the raspberry pi. This will create a directory such as /home/pi/Desktop/serial_bridge-master on your pi. Either adjust all the commands above to use this new directory in place of serial_bridge, or move the directory to /home/pi and rename it to serial_bridge.
The Rasbian operating system already contains drivers for the common cp210x usb to serial connector, so no drivers need to be installed.
When a USB serial device is plugged in, it creates a /dev/ttyUSB* device, where * is some small integer. Unplug the device and plug it back in, and the number may be different. Plug two devices in in a different order, and the they may have different numbers. This makes it difficult to work consistently on a headless box with no user interface.
The solution to this problem is to set up a udev rule to create a serial device named for the device which is plugged in. In order to do so, you first need to plug in your devices and run the following:
usb-devices | grep "^[PS]\|^$"
This will produce output such as the following:
P: Vendor=1d6b ProdID=0002 Rev=03.12 S: Manufacturer=Linux 3.12.22+ dwc_otg_hcd S: Product=DWC OTG Controller S: SerialNumber=bcm2708_usb P: Vendor=0424 ProdID=9514 Rev=02.00 P: Vendor=0424 ProdID=ec00 Rev=02.00 P: Vendor=067b ProdID=2303 Rev=03.00 S: Manufacturer=Prolific Technology Inc. S: Product=USB-Serial Controller P: Vendor=1fb9 ProdID=0301 Rev=01.00 S: Manufacturer=Silicon Labs S: Product=Model 336 Temperature Controller S: SerialNumber=336AB50
In our case, we were looking for the Model 336 Temperature Controller and the USB-Serial Controller. Using these values we can create a rules file /etc/udev/rules.d/10-ftdi.rules:
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="1fb9", ATTRS{idProduct}=="0301", NAME="ttyLakeshore336"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="067b", ATTRS{idProduct}=="2303", NAME="ttyOutputRS232"
Set the proper permissions on the file:
sudo chmod 644 /etc/udev/rules.d/10-ftdi.rules
Next time the LS 336 is plugged in, a new /dev/ttyLakeshore336 link will be created.
If you have multiple devices of the same type that can be connected at the same time, you will want to distinguish them by serial number. For this particular Lakeshore 336, you would change the symlink to string ATTRS{serial}=="336AB50" to the rule.
Changes to the configuration should be pushed back to the repository. The following command shows details of what has been changed:
git diff
The following command commits the changes to the repository:
git commit -a -m "description of change" git push
Please use a meaningful description so that your future self remembers why the change was done.