The Shop > Electronics & IC Programing
Scope external trigger "box" for TTL and Mains
PekkaNF:
Found some high speed optoisolators, but haven't used this type ever. It does not look that diffiicult to use, based on cursory read of the spec.
http://www.ti.com/product/6N137
www.vishay.com/docs/84732/6n137.pdf
Bit more reading on those digital isolators reveals that on the other side they seem to be easy to use. On the other hand, they must have some issues on their own like high switching frequency, probably need some more shielding than opto isolators.
Pekka
PK:
Those high speed opto's look good. You can see that they have some signal shaping and output circuitry rather than just a photo transistor. It's not hard to do this bit yourself if you have access to the base of the transistor.
Re noise on digital isolators. I used one on our load cell calibration jig. It has a 24bit ADC on it and I experimented by turning the isolator off and on. Made no difference..
PekkaNF:
Reasuring.
Re. noise. Have been reading some more and it looks like the noise of the digital isolators should not be issue (high frequency, easy to filter and low power levels).
however it looks like it needs some attention on those devices that have a DC/DC converter (too) in a "plastic" IC. I really did not know, just stumbled on this one AN-0971
http://www.analog.com/media/en/technical-documentation/application-notes/AN-0971.pdf
apparently not a show stopper or anything on general signal levels.
I remember having some layout issues with SMPSU circuits long time ago.
I read some limits also on magnetic/electric fields w/ digital isolators. Can't really relate it to yet on real life situations. I remember that HAL-sensors used on rotary encoders were big NO with big AC motors, a bit of a gaus and encoders were vomiting out whatever.
Now it looks like it is doable either way, each has it's forte and it looks like it all boils down what kind of front end I want there. One of the modern one that has digital isolators and DC/DC converter would offer low component count and size...old school is available on trough hole components and there is no need for me to learn to make PCB for itty bitty SMD:s :lol:
Pekka
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