Scale Communication

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Revision as of 16:35, 8 April 2014 by Paul (talk | contribs) (Testing communication)
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RS-232 Serial Communication Ports

Depending on whether the scale is wired for DTE or DCE, it may require a null modem cable or replacing and rewiring the serial connector.

RS-232 to USB Adapter

If the computer doesn't have a serial port (like the Pi) a USB/RS-232 adapter can be used. They usually map in as /dev/ttyUSB0.

The Prolific chip set has good reviews from the Linux community, but every adapter we've tested has worked fine. Check Amazon

  • Prolific PL2303HX Rev D Chipset RS-232 to USB cable Plugable Technologies

RS-232 (Null Modem) to USB Adapter

This is a little more expensive, but this is a USB/RS-232 adapter with a build in null modem. It should just plug in and work.

  • 1 Port USB to Null Modem RS232 DB9 Serial DCE Adapter Cable with FTDI, Black (ICUSB232FTN) [1]


Set up the scale. 9600 baud, 8 bit, no parity

Adam Equipment CPWplus200

See Section Section 13 of the CPW200plus User Manual for detailed instructions.

With the scale off, hold the Tare/Zero button and press the On/Off button.

Parameter Setting Rational
Auto Power Off Pr oFF Don't want the scale to turn off after a period of inactivity.
Backlight always off bL 1 Increases battery life when AC power fails.
Baudrate 9600 Default
8 Bit no parity PAr 1 Default
Transmission Mode trn 1 Default. Can set to trn 2 during trouble shooting.

Testing communication

A terminal emulation program like Minicom can be used to test the scale communication.

To talk to the scale using a terminal emulation program, configure the software so there is no flow control, either hardware or xon/xoff.

During initial testing, if trouble is encountered communicating with the scale, it may be useful to set the scale in trn 2 mode so that it continuously transmits data. It will serve as a signal generator and the data should contiuously scroll across the screen. This does not confirm that you can talk to the scale, only that the cabling is correct.

Configuring the computer's serial port

If the computer you are using (laptop or desktop) has a serial port, a USB/Serial adapter is not necessary. The null modem cable can plug into the serial port on the computer. They usually map in like /dev/ttyS0.

On the linux distributions we've tested, the serial port doesn't need configuration. However, if you have trouble talking to the scale, this is something to try.

To list the line parameters for ttyS0: stty -F /dev/ttyS0 -a


# stty -F /dev/ttyS0 -a    
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V;
flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 hupcl -cstopb cread clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel -iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke

stty can also be used to set the serial port parameters:

stty -F/dev/ttyS0  -hupcl ignbrk  -icrnl -ixon -opost  -onlcr -isig -icanon -
iexten -echo -echoe -echok  -echoctl -echoke igncr