relay_ft245r is a Python module to control relay boards based on the FTDI FT245R chip. A popular example is the Sainsmart USB relay board.
Example code:
import relay_ft245r
import sys
import time
rb = relay_ft245r.FT245R()
dev_list = rb.list_dev()
# list of FT245R devices are returned
if len(dev_list) == 0:
print('No FT245R devices found')
sys.exit()
# Show their serial numbers
for dev in dev_list:
print(dev.serial_number)
# Pick the first one for simplicity
dev = dev_list[0]
print('Using device with serial number ' + str(dev.serial_number))
# Connect and turn on relay 2 and 4, and turn off
rb.connect(dev)
rb.switchon(2)
rb.switchon(4)
time.sleep(1.0)
rb.switchoff(2)
time.sleep(1.0)
rb.switchoff(4)There's no need to "install" relay_ft245r.py. Just put it in the same directory as the Python program that will call it.
But it does need PyUSB and, for Linux, a udev rule to be added or Windows, the libusb-win32 driver to be installed and configured.
relay_ft245r uses the PyUSB Python module to control USB devices. To add to your base Python installation, do:
sudo pip install pyusbTo control USB devices without having to be the root user, two things are required: 1) you must be part of the "plugdev" group, and 2) the FTDI device has to be part of the "plugdev" group.
Check which groups your user login belongs to:
groupsIf this list includes "plugdev", go on to the next step. Othewise, do this command except replace with your user name:
sudo addgroup <user> plugdevAdd a file called /lib/udev/rules.d/60-relay_ft245r.rules with the contents below. This example uses nano editor:
sudo nano /lib/udev/rules.d/60-relay_ft245r.rulesEnter the text below as a single line:
SUBSYSTEM=="usb", ATTR{idVendor}=="0403", ATTR{idProduct}=="6001", GROUP="plugdev", MODE="660", ENV{MODALIAS}="ignore"
Unplug All FTDI devices from USB and reattach so that this new rule is executed for each FTDI device.
On Windows, PyUSB calls into the libusb-win32 driver.
Zadig is the easiest way in Windows to install libusb-win32 and select it as the driver assigned to the FT245R board. Go to http://zadig.akeo.ie/ and download and install Zadig.
- Run the program
- Click on "Options" and then "Show All Devices"
- Back on the main dialog, select "FT245R USB FIFO" in the dropdown
- Confirm that USB ID shows 0403 and 6001
- In the pick list specify "libusb-win32"
- Click on the Replace Driver button
- Answer any popup dialogs that show up
This replaces WinUSB for libusb-win32 as the driver to control the board. The dialog should look like this before you press Replace Driver:
This error happens in Linux when the program does not have permission to access the port. (The error is a side effect and is misleading.) Fix the udev rule as documented above.
To confirm it is a user permission issue, try using sudo in front of the command to run as superuser. If it works, then it is a permissions issue with the device.
Sometimes, you need to reboot the computer; logging in and out doesn't seem to set the new user permissions.
Cannot take control of the USB device. Many possible causes:
- The device is attached to another driver (for example, if you are running a virtual machine and the device is presently connected to that virtual machine)
Correct:
rb = relay_ft245r.FT245R()Incorrect:
rb = relay_ft245r.FT245RThe second one calls out the object template instead of an object instance.
The original code for this came from https://github.com/xypron/pyrelayctl authored by Heinrich Schuchardt.
I made these changes:
-
Cleaner implementation as object oriented code (didn't need to keep passing the device handle)
-
Made it compatible with Python on Windows
-
Fixed a race condition. On Windows, PyUSB runs slow and the relays where not set reliably on some boards. Probably the bit masking is not reliable (the USB readstatus() may be happening before the previous USB write happened) so I restructured the code to only read the relay state once on connect().
This was tested on Linux Mint 18.3 (Debian) and Windows 7 Professional. It should work fine on Raspberry Pi (Debian) and Windows 10, etc.
# Copyright (c) 2016, Heinrich Schuchardt <xypron.glpk@gmx.de>
# Copyright (c) 2018, Vince Patron <vince@patronweb.com>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#
# * Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in the
# documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY
# DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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# ORIGINAL: https://github.com/xypron/pyrelayctl
#
# CHANGELOG:
# 18/06/12 vpatron
# Made compatible with Windows. Converted to object style. Excludes FT232
# boards. See https://github.com/vpatron/relay_ft245r