Re: Intermittent connection on field only
 

Okay then I guess we're gonna need some room in settings to try a few and see if any work out.

Be aware though, it doesn't log data as much as turn on an LED when the threshold is reached so it has only one equivalent bit of storage.

If that bit is on you went below the calibrated voltage.

If that bit is off you did not.

All the digital attachment does is calibrate the set of digital potentiometers attached to a precision reference.

(Sorry I saw only the top part of your post so I'll catch the rest next post.)

Re: Intermittent connection on field only
 

I was under the impression that someone somewhere had tried to power the D-Link AP and messed around with it long enough to characterize it's voltage and power requirements (I should think FIRST did).

The problem then is that a digital measurement will always quantize the noise. So a digital data logger always runs the risk that something happens between the samples. Most of the cheap commercial units use SD memory so they are really not much faster at catching transients than DMMs (most actually quite a bit slower).

The analog circuit doesn't have a quantized 'blind spot' as much as a response time.

I do have an FPGA based oscilloscope I made with a bunch of computer RAM but that's not nearly as small or as light. It has a mode to essentially log data into a bucket to make a digital strip recorder (for a short time beyond that it needs to dump to USB2). It's also not nearly setup as a production test piece. I did specifically design it to be driven around on the robot.

With this in mind, then I can probably rig up some small DMMs with Max/Min functionality that you could robot mount till you figure out the limits. Either that or I'm really gonna have to move my butt and try to get that FPGA oscilloscope into something I can send unsupervised.

Re: Intermittent connection on field only
 

Another possibility is I have a circuit I use in a production item I worked on that can essentially hold the lowest voltage you present to it till you reset it (within reason).

It's essentially an analog minimum detector. Sort of a minimum voltage sample and hold.

If I slap that together stand alone you could put it in the robot and drive around then measure the output with a voltage meter. It would tell you how low it went at any time it was operating.

It wouldn't tell you so much how low the D-link AP supply went before it malfunctioned but it could tell you how low that D-Link AP supply got during the match.

Actually perhaps with a few of those someone could see what the robots that kept working produced for power to the D-Link AP and what the robots that did not keep working produced for power to the D-Link AP.

I think you'd have a similar process anyway with a datalogger would you not?
This would be much cheaper and probably collectively faster to quantify the results.
I'll dig into my stuff tonight and see what's involved with making them.

Re: Intermittent connection on field only
 

This is a very long thread. I did not follow it very closely. So I apologize if I am missing the point. If the goal is to log the voltage data of the Wireless bridge during competition then why can't we do it in software? Assuming the cRIO is still up and running and only wireless bridge is losing communication, can one feed the wireless bridge's power (5V) to an analog channel and write code to log the data? Heck, even the SmartDashboard can be used for that. This year, our team has written a generic datalogger that allows us to do post mortem analysis of anything we want to log. So far, we are using it to tune PID control and evaluate data filter algorithms. But it can be used for anything.

Re: Intermittent connection on field only
 

The only reliable place you could put the data would be the cRIO itself. At the point you need it most you very probably won't have wireless access back to the driver's station (chicken and egg problem). Additionally I did go look for the way to write to the non-volatile storage on the cRIO in Java but didn't get very far, not sure you have a lot of storage to play with there.

It would require someone to tinker with the code in the cRIO and that would add another task for the cRIO to handle (which might alter the performance of the system in general).

So you'd probably need to write that software in each language you might encounter.

Not to say it can't be done, but the cRIO still suffers the same issue that you don't know just how often it can check that voltage.

What I'm proposing is able to watch the voltage *much* faster and without tinkering with the robot's software.

Though I fully admit there are circumstances in which it might not matter. For example if you're saying you measure an analog voltage used in a PID loop feedback it probably won't matter with that because that voltage changes as the consequence of mechanical movement which by comparison to a power transient is very slow.

Re: Intermittent connection on field only
 

Since we already have the datalogger (written in a C++ class), if we encounter communication issues in St Louis, we can certainly hook up an analog channel, turn on the logger and see what we get.

Re: Intermittent connection on field only
 

I'm curious, where does it store the data it collects?

Re: Intermittent connection on field only
 

If the power transient is too fast, I expect the wireless bridge would have some sort of regulator or capacitor inside that will filter that out. Also, assuming the 12V to 5V DC-DC converter is not defective, it should filter out some amount of high frequency voltage glitches. So I would assume we are only interested in relatively sustaining drop in voltage for which a decent software datalogger should be able to pick up. I would be surprise if the DLink bridge cannot take some minor power glitches.

Re: Intermittent connection on field only
 

It stores the data as a CSV file on the cRIO. Post mortem, we FTP the file out to our laptop.

Re: Intermittent connection on field only
 

Have you had communications issues at other events and would you mind performing that test anyway?

I won't disagree about the filtering I just want to point out that Team 11 apparently already had a defective DC-DC converter powering the D-Link AP that caused us quite some headaches. That was among the points being tested (it's back a few pages in the topic).

Ultimately this possibility was already mentioned before and if you've got it working for you, I certainly won't suggest you shouldn't give it a shot. The more data and eyes the better.

If we knew the sorts of power issues that aggravate the D-Link AP's functionality we could detect and prevent them.

Re: Intermittent connection on field only
 

No, our regional event went very smoothly. There were very few field issues. Our last event was end of March. So our next chance to test it is St Louis.

Re: Intermittent connection on field only
 

I just realized that this may not entirely be applicable to the problem.

If we don't know what the minimum voltage that causes problem with the AP we do know that many teams are not having problems with their AP when they are not on the competition playing field.

We can certainly get the output voltages to the D-Link AP from a bunch of robots AP power supplies and get a feel for the deviation from AP power supply to AP power supply between robots and we can do that in the pits. If someone was willing to you could even collect AP power supply ripple data in the pits.

The voltage shouldn't really be dramatically going below that measurement.
Especially if we all agree that the power supply for the AP should be able to operate down to a battery voltage of around 5V.

Anything wrong with this idea?

Basically I could set up my little low voltage indicator board to be just below that measurement voltage (to account for some ripple).

Could even do a little statistics on the measurements from a bunch of robots and reduce the limit till statistically it would be an outlier if your AP power supply was that low. You might get a few false positives but I would think that would even out really fast. The bigger the set you work with the faster you should be able to weed out minor variations in the systems especially if you start with robots with and without AP power supply issues.

Actually come to think of it we could probably collect that data from just about all the teams that were willing to provide that even if they have their robots at home right now and are done for the season. In that case, however, probably best to poll if they had any communications issues that they ever noticed and where.

Re: Intermittent connection on field only
 

That's a reasonable assumption, but it would be good to examine the actual circuitry to make sure.

Even if it is operating as designed, it could conceivably be creating some high-frequency ripple on its output. It's not a simple linear regulator. Again, some examination is in order.

Re: Intermittent connection on field only
 

I see nothing wrong with that train of thought techhelpbb.

Regarding the D-Link's immunity to power transients I would agree that it should have appropriate filtering on the input to handle short transients. What we don't know is how it handles any kind of ripple on the power input and what the characteristics are of the regulator's output under various loads. Any noise we are getting from both the PDB and the Regulator is not characterized (publicly) as well as what effect, if any, the length of wire runs from the PDB to the regulator to the AP have. The D-Link's AC-DC power supply is presumably chosen to meet the input power requirements, but are we meeting those under all robot operating circumstances?

We know that there is an apparent failure mode of the regulator that causes the D-Link AP to behave anomalously. What I'm unsure of is what failure modes are we introducing in the D-Link over time? The environment we are subjecting the D-Link to is hardly what I assume to be the design environment of sitting on a shelf providing wireless connectivity. Are these the only factors or is the power input also causing a negative effect over time?

Are teams that are seeing communications issues using an old D-Link from previous years or have they seen issues with a new regulator and a new D-Link?

I'm really interested in performing some bench testing with the D-Link and at a minimum the regulator to help iron out some of these unknown characteristics. I have most of the measurement equipment I'd want here at home, but my one remaining issue is getting a good enough power supply to test various input power levels with differing amounts of noise, etc. I have everything I'd need to run the tests at work, but I'm unsure of my ability to do any of them (on my own time of course).

Re: Intermittent connection on field only
 

Good idea Al, I'll be doing that for certain.
I'd be careful with that expectation.

But adding a big honkin' capacitor on the power input to the radio should filter out any millisecond transients. I need to verify that the rules permit this. I'm thinking several dozens to a hundred microfarads (whatever's in the junk box)