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I have a set of serial scales. They communicate at 2400 E 7 2. I have used these scales on many other devices so I know they work. They put out a constant stream of data. The O/S is 64 bit Windows 8.1 and I am using a HL-340 serial to USB cable. The drivers came from here http://www.cesareriva.com/release/wp-content/uploads/2011/02/ch341_hl-340_windows_drivers.zip

The drivers installed without a problem and under the device manager I see USB-SERIAL CH340 (COM10) Selecting the properties it says the device is working. I have set the port settings for the correct speed and parity.

I would like to verify that the scales are connected so I am using PuTTY. I have set the speed and parity and the PuTTY log confirms that COM10 has been opened. But I am not getting any data appearing. I would have expected some data, any suggestions?

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  • There is no real connection to be established when using serial connections, you basically just check whether you can send/receive data.
    – phk
    Nov 5, 2015 at 12:21
  • They put out a constant stream of data -- is this data ASCII or could also be binary data? putty might not show non-ASCII data.
    – wurtel
    Nov 5, 2015 at 15:11
  • @phk there is still a physical and protocol connection
    – CarbonMan
    Nov 5, 2015 at 23:03
  • @wurtel it is a stream of ASCII characters with <STX> and other control codes included
    – CarbonMan
    Nov 5, 2015 at 23:05

1 Answer 1

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Couple things to check.

  1. Have you used that USB-Serial-Adapter on other computers with no problems. Some of those adapters the drivers/chip-set can be weird and not allow some types of devices to work correctly. Try the same adapter on another computer maybe a different OS if you can. See if you can find a computer with a real serial port, and check the scales there.
  2. Have you checked the Com port settings in device manager? The adapter probably installed at a default settings of 9600/n/8/1, where you need 2400/E/7/2 (2400 baud rate, even parity, 7 data bits, 2 stop bits) The adapter in device manager should read 2400/E/7/2 as well. Device Manager---Ports(Com & LPT)--Properties of your Com Port---Port Settings tab

  3. What brand of scales are these? Have you talked to the manufacturer to make sure those com port settings are indeed correct?

  4. Some serial scales when viewing from a terminal window, require a command entered for them to return the weight. Not knowing what scales you have, it's hard to know.
  5. After you check/change the settings in device manager for the com port, on the "Port Settings" tab, go to "Advanced" and turn the "Receive Buffer" and "Transmit Buffer" down to the low setting. USB-Serial-Adapters internals are much faster with data than a normal serial port, and I've seen on occasion where turning those values down can help alleviate problems.
  6. Try This Driver as it looks like the adapter is based on the Prolific chipset, which a lot of USB-Serial-Adapters use. I have had problems when the right driver was not installed. It would install and look fine, but would get consistent output to the serial device. I would uninstall the old driver first, reboot, then try this one.

I would lean more towards #1 or #2 being the problem. Have use a lot of different brands of USB-Serial-Adapters and some just don't work for certain things.

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  • 1. The scales definitely work on other devices so it is probably the cable. 2. The device manager settings are correct. 3. The settings for the scales are correct 4. No command is required. 5. I don't believe it is to do with buffer overruns 6. I'll have a look at those drivers
    – CarbonMan
    Nov 5, 2015 at 23:57
  • You could try 2400 E/7/1, 2 stop bits is a bit exotic and ignoring the second stop bit might work, if the driver doesn't handle 2 stop bits.
    – wurtel
    Nov 6, 2015 at 8:01
  • @wurtel I agree, I thought the 2 stop bits was a bit odd, but going from OP's saying those settings worked on other scales I didn't bring it up.
    – N. Greene
    Nov 6, 2015 at 15:13

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