| ??? 11/13/07 01:38 Modified: 11/13/07 02:32 Read: times |
#146913 - No, no, no,.... Responding to: ???'s previous message |
Farshad said:
USB-serial converters are very sensitive to EMI. It's very easy to lock them up mostly because of sensitive nature of some USB interface chips (and a lack of WD circuit in them perhaps). It seems the amount of EMI that can pass through the OPTO is enough to lock it up. NO! They aren't more sensitive than any other chips. And, no, it doesn't have to do with watchdogs etc. Stop thinking that a chip is the cause of EMI problems. It's YOU, and how YOU handle these chips. You can suppress EMI by suited measures to any level you want, by shielding, grounding and filtering. And don't think, that an opto is a shield against EMI. That's also wrong! You can only prevent low frequency current loops and the related hum. But an usual opto has so much input to output capacitance, that it behaves like a short circuit for ESD and high frequency EMI. More, optos and their wiring can (due to their isolating nature) show dangerous impedance resonances, making the equipement becoming extremely sensitive to EMI for certain resonance frequencies. So, stop thinking about an opto as an EMI shield, that's entirely wrong! Kai |
