A weird problem arose this week. I needed to develop a data logger that would operate on a piece of rotating machinery, and had a 4 slot cDAQ at hand.
I purchased an Intel compute stick and installed LV on it, developed the application, set it up to run a remote panel over wifi. All good... until I came to run the PC off a USB power bank.. well, it runs OK, stable OS and all BUT the cDAQ repeatedly and continuously connects/reconnects to the USB port (other USB peripherals are fine). Tried three different power banks, right up to 3.6A output. Same result.
Use a mains USB adapter, and it's fine.
End result, the workaround was to connect a 5V regulator to the cDAQ 12V power supply (battery sourced) and run the PC off that.
I'd be interested to know what the issue is: Why would the issue occur only with a USB power bank, only affect the USB port connectivity, and only when a cDAQ is connected (although perhaps other powered USB devices could have strange behavior)
Which cDAQ are you using? It would also be very helpful if you could attach a picture of your setup. It sounds like you are using something similar to a cDAQ 9134, which cannot be powered via the USB slot.
Also, this link has relevent information on powering a cDAQ device in general.
It is indeed a 9134, but it is powered from an independent supply. As far as I can tell, powering the PC from any other 5v supply except a usb powerbank allows normal operation. The usb powerbank is a convienient portable power source, being readily available, battery managed, and standardised in terms of charging etc.
I'll get some pictures up.
The testing I needed to do has been completed, so there is no pressing need for a solution now. But an interesting problem..
To externally power a cDAQ device we would suggest the use of batteries. This White Paper explains how to select a battery that may work best for your application and the connectivity section at the bottom of the page details how to connect the batteries to a cDAQ.
Would it be possible to use batteries instead of a USB power bank for your project?
here are some diagrams. Sometimes used instead of the battery to power the cDAQ was an Anker Powercore powerbank- this is a Qualcomm equipped powerbank that can output 12V 1.5A by a simple voltage level handshake on the USB data lines- for which I used a microcontroller to do. This powers the cDAQ fine. (why ?- high capacity, fully battery managed and protected, standardised charging from any USB source).
Regardless of which power source used with the cDAQ, the results are the same.
Thank you for attaching those diagrams. They definitely helped to clarify your setups. I have continued to research and discussed this with other colleagues at NI. At this point it seems that:
1. The issue might be because you have two floating power sources, which is described in this link. Since there are two separate voltage sources it could be that there is a ground loop being created. The first setup you have would be grounded by the wall connection, and the second setup only has one battery and therefore would not have this ground loop interference.
2. This is not as likely, but even if a device such as the Intel Compute Stick is not receiving the proper power it may exhibit some, but not all of its functionality. This means that the OS could be functioning properly even if the device is not sending the proper signals to the cDAQ. Again, this is not likely based on the specs that you provided.
I am thinking it is more likely 2) as the wall adapter is ungrounded, and I have tried grounding the powerbank to the cdaq.
..and thinking about it, the processor etc in the PC will be running of lower voltage rails - 3.3V and lower, therefore glitches caused by power supply interaction on the 5V may not effect the processor, but could disrupt the peripherals
The next thing I will try will be to cut the +5V line in the USB cable, so there is no way for any power supply interaction.
and scope it too
Decoupling capacitors are also yet to be tried
Those are some great next steps! Let me know what conclusions/questions you have upon completing those tests.