Noise sensitivity of USB-serial converters?
November 5th, 2008 by JeffI 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.
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Tags: automotive, megasquirt
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?
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.
Sounds like it needs optical isolation
Is the converter in a metal enclosure? If so, ground it to the frame. If not, stick it in one, and then ground it to the frame
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.
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.
I picked up some ferrites and some cables with ferrites included. I’ll give it a shot and see what happens.
Did you ever figure out a good solution to this?