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protecting coils from back emf
Looks like serious overkill to me. All you need is a decent diode like a 1N4004 across the relay coil to snub the back emf. Dump the resistor and don't spend a lot of bucks on a transient suppression diode. I'm assuming that the relay is not as big as a house...
protector ethernet cali
There is a strong possibility that the lightning is not hitting the cable, but is causing a difference in the ground potentials between the two end systems sufficient to damage the equipment. Its a well-known effect.
And, I second the idea of fiber optics. Not very...
generator attenuators
Actually, to cut your signal down by half, a 3 dB attenuator is the right size. They are common for oscilloscopes, with bnc connectors on both ends. Try an instrumentation supply or EBAY.:D
Re: Ground loop concerns?
Yes, worry for sure.
Common grounds can help if distances are short, but the notion that there is something out there called "equi-potential ground" is an academic fantasy.
A really good solution is to use a simple optical isolator chip at the receiving end...
how to remove the 50hz noise from oscilloscope
If you are measuring with a scope, make sure to use the ground lead on the scope probe. Not some other ground arrangement, the ground clip that comes with the probe itself. Connect that to a board ground as close as possible to the signal you are...
The solutions proposed using voltage dividers neglect that you may actually want to put some load on the resulting voltage. If you draw any current, the voltage divider will be incorrect. You may consider a series current limiting divider and a 12 volt Zener diode.
Re: Simple Question
Since the other two connections are good, you seem to be doing it correctly. I would make sure the non-functioning line was done right, no insulation stuck in the connection or something like that. But, if no error is found, you most likely have a defective part. Good...
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