Lynxmotion Smart Servo RS-232 Control

I am trying to control the Lynxmotion smart servo with an RS-232 signal. The setup is a USB to RS-232 adapter connected to a RS-232 to TTL converter using a Max3232 chip which is connected to the smart servo. I have powered the servo and Max3232 separately and have a common ground between all the devices however no signal gets through to the servo. Why might this be? The eventual goal is to control the servo with a PLC that has an RS232 port.

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Hi @Silverwolf_7,

Welcome to the RobotShop community!

Sounds like an interesting idea!

It may be best if you can make a drawing (or clear picture(s) with annotations) of your setup. Sometimes images are just better to show off these things.

In the meantime, here’s an idea of what I think you explained looks like. Let me know if I got that right:

Well, the typical things to check would be:

  • Any of the equipment for communication may be faulty (the drivers for the USB<>RS232 adapter, the adapter itself and the RS232<>UART (TTL) adapter)
  • Any connection between two components for wires connected to the wrong place (inverted, flat out wrong pins, etc.), broken or intermittent physical connection (especially with stuff like pre-made jumper cables).

At the very least you should verify the TX/RX lines on the LSS side (easy since it has two ports) to ensure that the lines have the right voltage level when at rest (using a multimeter). If you have an oscilloscope or logic analyzer I’d recommend testing the signal lines (TX and RX) at the various points of connection between the adapters to figure out if any of the data makes it through. Does the LSS ever change its LED color at all during communication?

Also, if the signal does make it from the USB<>RS232 all the way to the LSS bus, is it possible the baud rate is mismatched? The current LSS are shipped with a default baud rate of 115200 but this can be change to many other baud rates. Also of note, does all of the adapters in the “pipe” support / are set (if settings are possible) / compatible with whatever baud rate you are using? This shouldn’t normally be an issue but might still be worth checking quickly.

I await your reply to further help out with this.



Your drawing is correct. I have found that the issue lies with the cables and logic conversion. I will update with a complete solution when the new cable arrives. Thanks.

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Great! Glad to know to have identified the issue.

Yes! Please let us know what you fixed to resolve this. I’m sure this can be helpful to other community members who may face similar issues in the future!