| Electronics > Projects, Designs, and Technical Stuff |
| "Trigger box" for advanced/complex scope triggering? |
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| donmr:
As many have said, building a general purpose trigger box would be hard and you should just get a better scope. BUT - I have often found it helpful to build custom logic into a circuit to aid in debugging and this could certainly include detecting events that one would like to trigger a scope from. For example a register whose value is compared to an address bus could output a signal when that address is accessed. |
| bd139:
Hewlett Packard 1620A trigger box :-+ (I saw one of those being used with a digital scope in about 1995 still) |
| meretrix:
--- Quote from: bd139 on December 04, 2018, 10:07:13 pm ---Hewlett Packard 1620A trigger box :-+ (I saw one of those being used with a digital scope in about 1995 still) --- End quote --- Oh neat! I'd never heard of this, but it looks awesome. ::Searches for manual PDF:: |
| meretrix:
--- Quote from: donmr on December 04, 2018, 09:50:48 pm ---As many have said, building a general purpose trigger box would be hard and you should just get a better scope. BUT - I have often found it helpful to build custom logic into a circuit to aid in debugging and this could certainly include detecting events that one would like to trigger a scope from. --- End quote --- That's what I had to do for this thing at work, an experiment to see if the relay contacts in a piece of equipment would arc under worst-case conditions. I had two 277V AC sources, one a programmable supply and the other a variac running off wall current. The two supplies were out of phase with each other: the output of the variac "drifted" along with the wall current frequency (so there wasn't even a reliable phase relationship between the two). And the programmable supply, while its output frequency could be changed in 0.01Hz increments, had no means of simply synchronizing to the mains input frequency. I needed to switch between the two supplies (using a relay) when the two AC sources were 180° out of phase, and at the peak of their waveforms (so there was approximately 800V potential between them: I was trying to cause a failure). So what I really wanted was this trigger: TRIGGER = (PHASE(CH1, CH2)==180) & (CH1 >= 390V) & (CH2 <= -390V)) Which, it seemed to me, I should be able to generate using my oscilloscope's measure/math functions. In the end, I built a little detector board out of two transformers, some diodes, voltage dividers and a quad op amp, and a little Microchip 8-bit MCU with ADC to generate the trigger. It worked perfectly, but... yeah, I guess I wished I had a really low-latency "general purpose" piece of equipment that I could just program to do this. Oh, and even with all this effort, I still wasn't able to make the relay fail... :-\ |
| rhb:
I'm a little surprised a LeCroy wouldn't do what you wanted, but likely it's an option. However, rather than try to capture this on a scope, it seems to me more appropriate to deliberately create worst case conditions, abuse a relay for a large number of cycles and then examine the contacts. Also for this case a spectrum analyzer would tell you if it were arcing. |
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