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Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Ok, so after having built Steve Ward's SSTC5 (and it subsequently collecting dust), I've done up a audio modulation circuit in LTSpice, but I'm wondering about optoisolation. I'm going to connect the modulator to the SSTC using a BNC cable, but should I have 1 optoisolator (and if so which side, modulator or SSTC side?), or 2 optoisolators (and if so, where should I get the extra power from?).
This is the first scheme, 1 opto Blue is the input sinewave Red is the opto input Green is the logic output (after a pair of 74HC14's)
This is the second scheme, 2 optos Green is the input sinewave Blue is the first opto input Red is the second opto input Teal is the logic output (after a pair of 74HC14's)
In the second scheme, U2 is in the remote modulator box, U6 is in the SSTC, but where should V3 power come from, especially since V3 ground is also RF ground since BNC shield should be grounded to RF earth right? Would it be applicable to use batteries to power the input of U6?
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
Gah, don't use the SWCad in simulating any serious stuff, better use common logic and datasheet info along with test setups ;) For just the remote control box I use no couplers at all - just a screened cable. I used an opto to decouple the AVR from the beat tracker device however (just finished this night) just like using one before to rig the coil's input to PC. That's just a precaution, you can go with no optos at all. Two optos are pointless and will surely blast your system as in case you solve the power problem somehow (there are optical low-current drivers that need no high-side supply as voltage is induced on the receiver by the beam) your cable will float freely as it will remain ungrounded, eventually causing optos to break down. If you want a real full decoupling with insane CMR, better use a fiberoptic wire.
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Optoisolation on an audio modulator?
