Photoeye's not working-Difference between RoboRIO and Digital Side Card?

tr6scott · January 25, 2015, 11:01am

We have been using the Banner DS18VN6LP photoeyes for a few years now, and absolutely love them, the packaging, the polarized light, the multiple mounting options.

http://www.bannerengineering.com/en-US/support/partref/17406#wiring

The DSC and roboRio have pull up resistors, so when nothing is wired, all inputs read TRUE, high value. When you want to get a signal, you need to short the signal pin of the PWM to ground.

On the DSC, these sensors worked find when powered from the 12v PDP, and were NPN so would short the signal to the negative of the battery.

Yesterday we stripped two bots of controls and were testing the sensors pulled off to put back into stock for this year on the roboRio.

We were powering them from the VRM 12V 2A connectors, and all of these Banner sensors tested bad, they would not read changing states on the roboRIO.

We also had some Allen-Bradely units similar to the logomotion line following sensors, but in a different tubular packaging that worked fine.

I fine it really odd that all of the banner sensors tested bad, so I do not have faith in the test.

So now I am thinking maybe the VRM has some circuitry that may isolated the ground being shorted by the sensor?

I did not think to test sensors when powered from a PDP channel.

Any hardware guys can explain what is going on, or what power source I should be used to power the sensors so the RoboRIO can sense the ground state?

Jared · January 25, 2015, 11:36am

I’ll bet that the 12 volt supply on the VRM is isolated for some reason.

We’ve always powered our yellow banner sensors straight from the PDB with no regulator, and we’ve never had any issues. You may want to try this.

ozrien · January 25, 2015, 12:29pm

The VRM is not isolated. If you measure the voltage difference between the VRM ground and the Rio ground you should find it to be very close to zero .

Measure the light sensors input voltage to confirm its powered properly. Then measure the signal voltage to see why the readings from the Rio don’t match your expectations. That might reveal what’s going on.

Lightfoot26 · January 25, 2015, 12:57pm

You are not alone! We were testing our banners on the new control system and experienced the exact same thing! The similar Allen-Bradley sensors that came in the KOP in 2012 worked fine! I did find (and this is a weird observation that may or may not have anything to do with the problem) when I probed for continuity across the signal line at the roboRIO while it was plugged in, and the negative terminal the sensor was plugged into at the PDP, the sensor began functioning properly both on the meter and in code. Weird I know, but it was something I noticed.

tr6scott · January 25, 2015, 1:37pm

Omar,

Is the power supply leg to the roboRio isolated ground?
Seeing there is another team having issues with Banner sensors, I am going to and wire the sensor power from the same source as the roboRio power and test on Tuesday.

I could also drop one of these sensors off to you for testing Monday on my way home from work.

Scott.

Al_Skierkiewicz · January 25, 2015, 3:43pm

Seth,
Can you tell us which meter you were using and I am guessing you were in continuity mode and not resistance mode? It is possible that there is a component in series with the negative lead on one or more of the control components. Your meter might have reduced the impedance sufficiently to allow the sensor to turn on. Depending on the component and the series impedance, it is possible that the sensors are not receiving sufficient power supply to operate. As I remember, the Banner sensors require a specific power supply voltage.

Alan_Anderson · January 25, 2015, 5:06pm

We plan to use Banner sensors this year. I had expected to use the VRM’s 12 volt supply to power them. Testing them on our robot-in-progress is now high on my to-do list for our next work session on Tuesday.

Lightfoot26 · January 25, 2015, 5:19pm

Al, I guessed that some circuitry internal to the meter was affecting my results but I couldn’t quite put my finger on it. I was in continuity mode and I believe it was on one of our Extech MN35’s (I am away from the shop and can’t confirm this, but I am fairly confident that’s the meter we used). It was very odd, but the sensor functioned perfectly with the meter in place and operated as Scott described in the original post when the meter wasn’t being used. If it helps, the working Allen-Bradley sensors are the 42EF-D1MNAK-A2 and the Banners we tested were the QS30LV.

Al_Skierkiewicz · January 26, 2015, 8:52am

Seth,
That meter, as most modern meters, apply a current to the probes when in the “diode” mode and then measure the voltage drop directly. In a normal diode or transistor junction, the meter would read 0.7v. The specs say that the current in this meter is limited to 1 ma when in the diode mode.
I have to ask, was the “ON” indicator on the sensor illuminated and the output was not sensed by the roboRio? The RoboRio has a 40k pullup resistor to 3.3 volts which may not be enough to pas current through the Banner sensor.

tr6scott · January 26, 2015, 8:51pm

Did some more extensive testing tonight during our meeting.

The Working AB Part number was
42CA-P2MNB-A2

Another non-functioning Banner sensor was QS30LV

We also found the following Banner Switches to also work.
T18SN6FF50

T30SN6FF400

I tested with the sensors connected to the both the 12v 2a power rail, and also wired direct to the same power leads as the roboRIO without any impact on working state.

Both non-working Banner part numbers status lights work as expected, and I tested multiple sensors of each type, Power indicator works, and sensor tripped worked, just would not fire the roborio input.

crake · January 26, 2015, 10:04pm

Questions:

What are the properties of the Banner sensor? What clues does the sensor datasheet give you?
What is the pull up/down configuration of the roboRIO for that particular DIO line? Hint, pg 15 of the user manual - or look above
What does this circuit look like when “on”? “off”?
Will this work?
If not, how can you change the circuit to make this work?

Extra bonus

Why did hooking up a multimeter make this work?

tr6scott · January 27, 2015, 6:14am

I guess it is no longer accepted to ask “Any hardware guys can explain what is going on, or what power source I should be used to power the sensors so the RoboRIO can sense the ground state?”

If you are not going to explain what is happening, could you at least give some links on where I could go to find the answer?

I’m just trying to figure out if I have spend another $600 on sensors that work with the roboRIO, so we have a functioning bot is the near future.

From your post, you obviously believe there is some way to make these sensors work with the roborio, yet I am no closer to finding that answer.

tr6scott · January 27, 2015, 6:27am

Looks like the roborio has 40kOhms to 3.3v pull ups, while the DSC has 10kOhms to 5v pull up.

tr6scott · January 27, 2015, 6:37am

Sensor Cut Sheets, DS18 non-working, T18 working.

FrankJ · January 27, 2015, 8:17am

We have not got this far yet so I really have not tested anything. But. The RoboRIO is actually 3.3V (5V compatable) (If I understand what the NI guys said.)& the side car was 5V? Assuming you are not seeing the 0V state, maybe the Banner is not pulling the pin low enough?

Looking at the RoboRIO specification Low state is 0.0 V to 0.8 V. On state for the DS18 is <1.8 volts. So it working looks iffy. On state for the T18 is <1V The RoboRIO spec is on the NI web site.

Although looking at the NI 9403 (CRio DIO module) it has the same 0.8V max for V low Maybe it is more forgiving?

Alan_Anderson · January 27, 2015, 8:20am

The suspicious difference I see is the “ON-state saturation voltage”.
DS18: < 1.6V @ 100 mA
T18: < 1V at 10 mA dc, < 1.5V at 100 mA dc

Perhaps the roboRIO input’s logic 0 threshhold is too low for the DS18 to satisfy without assistance. When I get to the workshop on Wednesday I plan to do some experimentation.

tr6scott · January 27, 2015, 9:06am

Thanks Guys, the delivery on the AB ones are 2/16 from the factory…

crake · January 27, 2015, 9:17am

Forgive me, I was channeling my physics professor there for a moment. He never told me the answer directly (team 900, am I right?)

There are a couple of differences between myRIO and cRIO.

myRIO DIO (for the most part - there are exceptions with DIO14 and DIO15 which are 2.2k to 3.3V) have 40k pull up to 3.3V

cRIO DIO with side car has a 10k pull up to 5V AND a weak >20k pull DOWN (internal to an ASIC on the NI 9403 module).

This means that the roboRIO has a far weaker pull up than the cRIO w/side car.

From the datasheets it isn’t entirely clear to me how they have NPN circuit configured, but I suspect that if you had a strong pull up your sensor will start working. I agree that the differences in saturation voltages is a strong candidate as to why some sensors work with roboRIO as-configured while others don’t.

Anyway, try placing a nice strong pull-up on DIO to 3.3V (say, 1k).

tr6scott · January 27, 2015, 9:25am

For the record, I was testing with DIO6 on the base interface, aka NOT MXP connector.

Thanks for the help.

Al_Skierkiewicz · January 27, 2015, 9:31am

Chris,
I would suggest the same thing, although I think I would start with 10k to limit current. However, I am still trying to analyze why a meter, testing continuity, between two common points should make this work. The lights on the sensor indicate that switching is taking place. I would expect that the output of the Banner sensor is a photo transistor that includes a series resistor for over current protection. However, simply connecting a meter seems to indicate that the power common wiring is not as low impedance as one would expect. I would suggest someone with a scope actually check the operation of the sensor and report your findings.