Noise sensitivity of USB-serial converters?

I am experiencing a frustrating problem that I have seen using more than one brand of USB-serial converter.

I use a USB-serial converter as part of a Megasquirt system on my car.  When exposed to ignition system noise on the car, the USB-serial converter will lock up and stop transferring data until I disconnect and reconnect the USB connection.

Has anyone else seen this?

Just today I mocked up my serial setup on the bench and used a Van de Graaff generator to create some broadband noise to try and simulate the effect of the car’s ignition system.  Sure enough, eventually the USB-serial converter I was testing locked up.  Same exact symptoms – crash.  Without the noise source, the connection works indefinitely.

8 thoughts on “Noise sensitivity of USB-serial converters?”

  1. Is the interference getting into the cable, or the converter, specifically? Another quick and dirty fix might be to use some ferrite beads. I had to do that on some equipment that was installed in a Ford Ranger.

  2. Eric – It’s in that standard cheapo rubbery plastic stuff that all USB peripherals come in these days – the kind that are embedded in the connector.

    I’d like to keep the computer and USB stuff off the chassis ground if possible. The last thing I want is for the starter motor to decide that my RS-232 cable is the lowest impedance to ground from the engine, however unlikely that seems.

  3. fiid – that’s an idea I am working on. I’m actually thinking about building a ruggedized 50V isolated ESD protected usb-serial converter to solve the problem forever. 🙂

  4. I suspect that most of these converters don’t fully implement the RS232 spec on the serial side. RS232 is really stringent about noise protection and voltage spike protection; and the components to operate at that spec are expensive; which is why most ports are RS232 compatable, not RS232 compliant. I wonder if some chokes and caps could be placed on the serial side of the converter to increase the resilience to noise?

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