Question 39254 in Ubuntu Question posted in
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Ubuntu server, 8 relay usb board need to turn on more than one at ounce

I bought a china usb 8 relay switch board. It shows up in ubuntu server as a serial device. I figured out the commands to get it to work.

*Set Baud Rate of relay board

stty -F /dev/ttyUSB0 9600 -parity cs8 -cstopb

To start relay controller:

echo -e -n "x50" > /dev/ttyUSB0

To activate relay for commands:

echo -e -n "x51" > /dev/ttyUSB0

To turn on relay

echo -e -n "x(number)" > /dev/ttyUSB0*

But my issue is if I turn on relay 1 (/x01) and then turn on relay 2 (/x02) relay 1 turns off. I’m trying to automate and will need it to turn on more than one relay at a time. I went thru with testers and started mapping each number, Like 03 turns on relay 01 and 02. But there has to be an easier way. Any help would be grateful.

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2

Answers


  1. 0

    It is a bitwise control.

    For example to turn on only port 0 (the first), you send xFE.

    (echo "obase=16" ; echo $((255 ^ 1)))|bc| sed -e 's/^/\x/'
0xFE

    Essentially take 255 and subtract these values for each port you wish to start:
    |Port|Number|
    |–| —|
    |0|1|
    |1|2|
    |2|4|
    |3|8|
    |4|16|
    |5|32|
    |6|64|
    |7|128|

    To turn relay 1, 4, 5, and 7 you need to send:

    255 (all 8 bits stop)  - 2 (bit 1 start) - 16 (bit 4 start) - 128 (bit 7 start) = 109.

    In hex 109 is 6D, so send x6D to the device.

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  2. 0

    A more visual example:

        #!/bin/bash 
    varfolder=/dev/shm
    
    for i in $(find -L /sys/bus/usb/devices/ -maxdepth 2 -name "ttyUSB*"); do
            usb=$(egrep -i "2303" $i/../modalias >/dev/null && echo "${i##*/}")
    check=$(grep PRODUCT= /sys/bus/usb-serial/devices/$usb/../uevent)
    if [ "$check" == "PRODUCT=67b/2303/300" ]; then
    releport=/dev/$usb
    fi
       done
    
    ## this word "modif" depends on the linux interface language
    modf_time=$(stat /sys/bus/usb-serial/devices/$usb | grep  modif)
    init_time=$(<$varfolder/init_usb_relay)
    
    if [ "$modf_time" != "$init_time" ] ; then 
    echo -e -n "x50" > $releport
    echo -e -n "x51" > $releport
    echo $modf_time > "$varfolder/init_usb_relay"
    fi
    
    # 87654321
    # turn off 6 and 5 relay
    relstatusbin=11001111
    relstatus16=$(echo "ibase=2;obase=10000;$relstatusbin"|bc)
    echo -e -n "x$relstatus16" > $releport

    Known issues:

    • If the USB wire does not carry enough electricity to hold the relay coil then the relay will not energize. In this case, additional power is required. Or simultaneously turn off a smaller number of relays.
    • Contacts can stick.
    • Contacts may burn.
    • If the device stopped accepting commands, then in order not to reboot Linux, you need to remove the device rm -f /dev/ttyUSB0
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