NI myRIO constant -3V on analog output

[Xenorollmops]

Hi everybody,

I was just about to test my new Project on myRIO that uses the AOs for the first time.
Unfortunatelly I observe, that the AOs om the MXP connectors only put out a constant voltage of -3V. (Checked with oscilloscope)
I can not make it change, neighter with my own FPGA project nor with the RIO IO Monitor.

The AOs on connector C however work fine.

Is there a chance, that the AOs are not fried, even though I have never used them before?

Thanks for your advice.

Best regards,
Xeno

[VA.KI]

Hello Xeno,

Have you tried LabVIEW examples?

It will be helpful if you share your project and give more details on how exactly you were going to drive the AO.

If you are afraid that the channels might be damaged then it is better to write to NI technical support and request repair.

[Xenorollmops]

Hi VA.KI,

The whole project aims towards creating a inverted UART interface for recieving SBUS protocoll, decode and translate the data to analog/digital outputs to remotecontroll a robotic snow plow.

So far I was sucessfull, except using the analog outputs on MXP A and B as stated. When I use the code provided in the attachment everything works just fine. If I however remove the correction (7) and select the AOs of Connector A or B instead of Connector C under (5) I only get constant -3V (at the MXP AOs of cause, Connector C AOs are of).
I did not try to run the outputs with another LabView example yet. Like I mentioned in the inital post, I tried to operate the MXP AOs via the Labview I/O Launcher. That works with all DIOs and AI on MXPs and with the AOs on Connector C as well.

Is there a chance, or experience that the MXP AOs might break down over time, even if never used? Afterall my myRIO is almost six years old now.

Hope this gives you additional clues. Can I provide you any additional info?

Best regards
Xeno

[Bob_Schor]

I have a myRIO that I think is older than yours (I'm guessing around 2014).  I cobbled together a tiny Test routine consisting of an AO Express VI and a Dbl "Volts" input, putting out only a single voltage, which I measured using a Voltmeter between Pins 3 (AGnd) and 4 (AO0) of MSP.  To a good first approximation (hard to hand-hold the VOM probes on the connector pins), and testing with "Volts" = 0, 5, and 10, the voltages I read were 0, 5, and 10.

Could your problem be the way you are connecting the myRIO to whatever it is driving?  You still haven't shown us your LabVIEW code, and explained what the outputs are doing, but I see the MSP C AOs going to indicators called "Left" and "Right", and mention made to "Vehicle turning".  You do realize, I'm sure, that the Analog outputs can only drive 2 mA ...

Bob Schor

[Xenorollmops]

Hi Bob,

thanks for thr reply. I hope my post made it clear that my problems only exist with Connector A and B. MSP is working perfectly.

Let me answer your questions:

---

@Bob_Schor wrote:

Could your problem be the way you are connecting the myRIO to whatever it is driving?

---

Unfrotunatlly I don´t think so. The -3V on the MXP outputs was measured with no load using a VOM as well as an oscilloscope. In my case I chose the AO(Pin2 or 4) Pins on Connector A/B and referenced it to GND (Pin 6 or 8). In my myRIO there actually is no designated AGND or DGND. They all are connected. I am feeding each of the analog signals into the input of a seperat Motor driver citcuits. The AO replaces the manual dial that used to be an potentiometer. Depending on AO voltage the rpm of the two motors differ and the vehicle turns.

---

@Bob_Schor wrote: You do realize, I'm sure, that the Analog outputs can only drive 2 mA...

Yes I do know this and it is taken care off. The imput resistance of the motordriver is very high. Additionally I connected 22k Ohms resistors between AO and driver, to avoid inrush currentspikes.

---

You still haven't shown us your LabVIEW code, and explained what the outputs are doing, but I see the MSP C AOs going to indicators called "Left" and "Right", and mention made to "Vehicle turning".

---

The analog signal are feed into the input of Motor driver citcuits. The AO replaces the manual dial, that used to be an potentiometer. Depending on AO voltage the rpm of the two motors differ and the vehicle turns.

I am very sorry if my last post did not describe the code clearly enough. I am using the code provided above. Currently I use this code with the AO on Connector C selected in the FPGA-OutputNode (5) as a workarround. I want to run the my robot with this VI but the Channel C AO 0 and 1 exchanged with the Channel A AO0 and 1. I also tried this code with MXP A and B AOs selected before with no load and load. Result is the same. 

For the testcode (I/O-Monitor), this is what I used:
https://learn-cf.ni.com/teach/riodevguide/procedure/rt_io-monitor.html

I cobbled together a tiny Test routine consisting of an AO Express VI and a Dbl "Volts" input, putting out only a single voltage, which I measured using a Voltmeter between Pins 3 (AGnd) and 4 (AO0) of MSP.

---

Please keep in mind, that I have no issues with MSP AOs, only MXP AOs. As stated before, the robot works with the current code and the selected AOs. My issue is the MXP AOs which I can not use currently because they put out -3V no matter which code or methode I try to set them with.

I hope I was ablte to answer all of your questions, or is something still unclear?

Best Regards
Xeno

[Bob_Schor]

Oops -- I was checking out the wrong set of pins!  Sorry, I'll take another look tomorrow morning (how embarrassing!).

Bob Schor

[Xenorollmops]

Hi everybody,

It's been quite a while now. Did somebody find the solution to my problem in the meantime perhaps?

I unfortunately did not.

Have a good one.

Xeno

[Bob_Schor]

My apologies.  I overlooked my earlier response (of almost a year ago), and you didn't remind me until now!  But I had a myRIO at hand, I launched the I/O Monitor (the myRIO Toolkit's version of MAX Test Panels), wired Pin C4 (AO0) to Pin C7 (AI0+), Pin C3 (Gnd) to Pin C8 (AI0-), and took the picture below.

If your myRIO is not doing this, then you might have a hardware problem. 

• Can you try the Analog I/O on Connectors A and B?  If they work, but the C Port doesn't, it sounds like your myRIO might be damaged.  Can you borrow another and test it? 
• Do you have the myRIO Software Toolkit installed? 
• Are you able to use MAX to install the myRIO Software and Firmware on the myRIO?
• What version of LabVIEW are you running, and is it the 32-bit or 64-bit version?
• What version of the myRIO Software Toolkit are you running?
• What version of Windows (and is it 32-bit or 64-bit) are you running?

Bob Schor

[Xenorollmops]

Hi Bob,

Thanks for your reply.

Just to clarefy again, Connector C works perfectly. Connector A+B do not work. I checked the output with an external oscilloscope.

But as you wished, I repeatred you test with Connector A.

Connector A test

As you can see, AO_0 does not generate any signal.

Just to be sure, I checked the function of the AI_0 with an externals voltage supply.

External stimulation with 1,5V battery

I am currently running this version of the myRIO toolkit:

MyRIO SW Toolkit

LV is 32 bit version and Windows 10 64 bit.

Max is available and the following SW is currently installed on the MyRIO:

Installed SW

Do you see a possibility that this is a software issue not a hardware defect?

Happy New Year

Xeno

[Bob_Schor]

Hello, Xeno.

     I think I have Good News for you.  I was able to replicate my findings with the C Connector (sorry I got that wrong) using the A Connector and the set of pins you used to give me the same very nice sinusoid that I showed in my previous "C" post.  Just for fun, I also connected the AI0 pin (Pin 3) to +5V (Pin 1), +3.3V (Pin 33), and AGnd (Pin 6), and got a nice clean 5V, a pretty clean 3.3V, and a very noisy 0V (but the noise was a bit or two, that is, a miniscule voltage.  But that just means my A Connector works.  How does that help you?

     It doesn't, really, but just to be sure, I took my plug-in board out of A and put it into B, and ... I got really bad readings, not unlike what you are seeing!  Oops, what did I do wrong?  I'm pretty sure this myRIO works ...

     Oh, and then I remember.  I unplugged the little board plugged into B, then looked carefully as I plugged it in, again, being sure I had it centered on the pins.  If you look carefully at the pins on the myRIO, there is enough space in the myRIO chassis to plug the 34-socket device off by one pin, so that what you think is Pin 1 on the Breakout Board is really plugged into Pin 3 of the myRIO.  When I pulled out the Breakout Board and plugged in back in, centered properly, I got a lovely reading on AI0.

     As for your software, it looks "reasonable" to me.  I'm running LabVIEW 2019 mostly, and have the LabVIEW 2019 myRIO Software Toolkit installed.  I notice you have a mix of LabVIEW 2016 and myRIO Software Tookit 2018, but I don't think that is responsible for your difficulties, I think it is "being off by one pin" (a "design flaw" when they built the myRIO -- they should have made it "impossible" to plug the Breakout Board "off by one pin".

     Do let me know if this fixes your problem, and if this makes your New Year start off very Happy.

Bob Schor