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

[Al Skierkiewicz]

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]

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]

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]

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]

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

[tr6scott]

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

[FrankJ]

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]

Originally Posted by tr6scott

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

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]

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

[crake]

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]

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

Thanks for the help.

[Al Skierkiewicz]

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.

[tr6scott]

Al, I don't have access to a scope.
Seeing I don't completely understand the circuitry of the sensor, or the roboRio, Let me state what I think I am to do to test.

Wire a resistor (1k, 10k) from the 3.3v+ which looks to be available on the MXP port pin 33, to the signal line of DIO6, along with the sensor output. Sensor still being powered from the 12v 2a rail of the VRM.

Did I follow that right?

[ozrien]

I tested using a QS30LV banner sensor on the roboRIO, powering it directly from the PDP, and then later with the VRM. I got the same negative results with each.

Again, the VRM is not isolated.

My banner sensor pulls the digital input rail on the RIO (from it's typical 3.3V) to 0.7V when in the "off" state [not ok]. Reading the banner sensor datasheet, I see it's "off" current is "<200uA". Reading the RIO user manual, the internal pullup in the RIO is 40Kohm. This suggests the sensor pulls about 65uA. (3.3V - 0.065mA X 40K = 0.7 V). This also matches the sensor data sheet (<200uA).

We want the voltage on the RIO digital input at least be above 2V when the sensor is "off". This is the minimum input high threshold of the RIO input. Otherwise we will always get a logic low [not ok] regardless of the beam breaking/or complete.

So... I added a 1K pullup from sensor ouput to the VRM's 5V rail. A 1K pullup to 5V along with the internal 40K pullup to 3.3V thevenizes to 4.958V with 0.975K impedence.
The roboRIO digital input rail only drops to 4.9V (really nothing at all). This follows assuming the sensor drew about 65uA in the off state.

This sounds like a simple case of checking the current leakage of your sensor against the strength of the pullup. Those sensors Scott mentioned that work have an "off" current of "<1uA" according to their data sheets.

Since the cRIO had a 10K pullup to 5V, and ~20K pulldown to ground, that thevenizes to 6.6K pullup to 3.3V. That means the roboRIO digital inputs (0 through 13) have weaker pullups, so having to add an external pullup makes sense to me, even if it is a little annoying

If that's a problem then read the datasheet of your sensors before purchasing. Or just buy some resistors.

I don't understand the poster who connected a continuity meter between sensor output and ground. Why would you do this? This is not a useful test. Also why was the system powered while doing continuity checks? Yes continuity adds current into the system. Probably was enough to makeup for the weak pull, hence the sensor started working. That's not a useful clue, especially when we have datasheets that tell us the impedances of all of our components.

[FrankJ]

So with the sensor connected, is the RobRIO reading true or false? (low volts or high volts?)