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.
Did you ever figure out a good solution to this?
I picked up some ferrites and some cables with ferrites included. I’ll give it a shot and see what happens.
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.
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 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 🙂
Sounds like it needs optical isolation 🙂
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. 🙂
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?