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Trimble event marker input  


John Hamilton
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I have a device which has a trimble event marker input and a 1 pps output that connects to a receiver via a lemo port. I bought it when I purchased a new 4700 in the late 90's. Never used it. 

The event marker input is a bnc connector. I want to rig up a normally open momentary action switch to apply a voltage to the event marker input. Has anyone done something like this? Any ideas on how to do it? 

According to the receiver manual...

The event is triggered when the source pulse voltage transitions
between 1.0 V DC and 2.0 V DC in less than 100 nsec. Trimble
recommends that you use TTL level inputs. You can configure the
receiver to recognize either a positive (rising) or negative (falling)
voltage as the leading edge of a pulse. The accuracy of the associated
time tag recorded for an event is determined by the GPS accuracy
(typically less than 1 µsec.).
The 5700 receiver records each event in the current data file.

4 Replies
Bill93
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A switch will probably bounce too much and give multiple signals, i.e. several within 10 msec.  You are going to need something to prevent that without slowing down the transition time (as a capacitor and resistor would tend to do). This link explains the problem.

TTL runs on 5 volt supply (CMOS may also work) and your circuit needs to makes a single transition in each direction.

Maybe look up   switch debounce   or    one-shot monostable multivibrator    to find a circuit that appeals to you.  There are zillions of circuits out there, but I'm haven't kept current to know what to recommend today.

Or wait for Jim Frame to come to our rescue.

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John Hamilton
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Thanks, Bill...but way over my head. My father was a PhD EE but he is no longer around. I do know a EE professor at VT, I will see what he says. 

Back when I bought the device they were being used (maybe still are) to record the instant of shutter activation on a photogrammetric camera (i.e. timetag the image)

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Shelby H. Griggs PLS
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@john-hamilton the aerial cameras are definitely one usage for events and they photo centers are still recorded the same way. The camera sends a pulse, the GNSS receiver records that and the events are interpolated between the regular epochs.

I have bought receivers with the event input ports since 2001 in case the regular on board receiver crapped out in the airplane and we needed a quick backup plan. Leica supplied the cables as an option and it was pretty much plug and play with the Leica receivers into the camera system, but primarily we use a dedicated receiver with each sensor so haven't got a lot of experience with the survey receivers.

I do know that timing is everything, including length of cable runs, delays in the camera, etc. all are critical at acquisition speeds in an airplane. I also know that from time to time we have fought spurious events, usually a bad cable, etc. and there is some features in the receiver whereby a time guard can be added to NOT record a 2nd event within the defined time frame, helps a ton from signals getting on the cable. You can also set both positive and negative edge of the pulse and if you want to add a constant time correction, those are all menu options within the Leica receivers.

All that isn't likely much help, but then again maybe it gives you some ideas...

SHG

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John Hamilton
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My timing requirements are not nearly as stringent as for photogrammetry. I want this to mark time for astro observations. I found an old pocket shortwave receiver that still works and receives WWV. I believe there are issues using phone numbers to call WWV, since everything went digital I imagine there can be delays due to the use of packets rather than continuous transmission. I do have an app on my phone that tries to synchronize, and comparing it to the radio it seems to be pretty accurate. Unfortunately I am not very knowledgeable about electronics, but the reason for that is a long story about my college years.... 

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