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Want to start by saying I'm a mechanical/aerospace engineer, and I'm fairly out of my depth here. My current project is on a load-testing rig. Ultimately, it will use a Honeywell HG1120 IMU to give the location/orientation of a test article. I have so many questions that it's hard to know where to begin, but I'll start with a couple basic ones:

1) The table below shows the connector pin description (as a side note, the document doesn't give a pin schematic, would it be safe to assume 1 is in the upper left, increasing in number to the right?). I have read that I need to connect voltages to both pins 11 and 12 for power, but seeing no VSS, do I need to decouple these with any grounds (frankly, I'm not even sure what that wiring should look like).

2) What does the PWR_RTN (Power Return) pin refer to? Do both of these pins need to be wired, and to what?

3) Given the choice between SPI and RS-422, which would be more "user-friendly" to implement on a PC with LabView?

Any help at this point is appreciated, but the simpler terms the better (at least giving me a direction to learn in).

enter image description here

Edit: image of the unit's connector. I have a breakout board that I can use to wire to a plug for a PC. That's another thing I need to figure out. enter image description here

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  • \$\begingroup\$ Do you have a table for "device configuration" settings? You may need to program this to activate the interfaces, they may not all be active by default. \$\endgroup\$ – Mattman944 May 29 at 22:41
  • \$\begingroup\$ Yeah, they show the combination for the 4 DIO pins that set what communication protocol it uses. It also has CAN2A/B available, but that didn't seem to be as helpful in my initial research. \$\endgroup\$ – dboston May 30 at 0:18
  • \$\begingroup\$ This idea is not really going to work very well. You might get orientation, you will not get location. Unless your goals are fairly crude and brief you probably need to chose a more appropriate position sensing technology instead. \$\endgroup\$ – Chris Stratton May 30 at 1:04
  • \$\begingroup\$ Yes, heed Chris' warning before you invest too much time and money. Accelerometers in this price range are usually not accurate enough to be the primary position sensor. They are often used as supplements to GPS to fill in outage gaps. But, you haven't explained your application in detail, and even if you did, I am hardly qualified to make a final judgement, get an expert in the field. \$\endgroup\$ – Mattman944 May 30 at 2:13
  • \$\begingroup\$ I appreciate the feedback. Frankly, I'm fairly new to this project. I got handed this particular IMU and, since I'm doing integration and interfacing for the rest of the sensors (which are analog and make sense to me), was told to figure out how to make it work. The primary goal is really orientation, to reference whether our test article is straight or tilted. I don't know what drove the decision for this unit, but I believe robustness was a large factor. If someone can suggest an alternative that is easier to use, similarly robust and accurate, and not too costly, I'd love to hear it. \$\endgroup\$ – dboston May 30 at 12:21
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1) Post a picture of the connector. I would assume that the unit contains decoupling.

2) Connect the minus of your power to PWR_RTN (power return). For higher reliability, they have provided 2 power (VDD) and 2 power return. Don't share the power return with your other grounds if possible, make the unit be the single point ground if you can.

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  • \$\begingroup\$ However, can the 2 VDD and 2 power return come from the same power source? I'd guess this defeats the purpose of having two pins. \$\endgroup\$ – dboston May 30 at 0:32
  • \$\begingroup\$ Yes, same power source. Two for redundancy. At the current specified, it is doubtful that both are required. BTW, I worked for Honeywell for 30+ years. I have some knowledge of their high-end Ring-Laser Gyros, really nothing on this one, other than some similarities to the RLG. \$\endgroup\$ – Mattman944 May 30 at 1:13
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I think RS-422 is more user friendly to implement on a PC. Not sure about LabView though. You will need a USB-to-RS422 adapter module/cable and Virtual COM port drivers, and some terminal software (so you can enter commands in to fiddle with things before you get LabView to take the place of your human hands).

You did not link the datasheet, but if the IMU responds to ASCII, then interpreting commands with human eyes and sending commands with human fingers through terminal software just got easier.

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  • \$\begingroup\$ The installation sheet is unfortunately only available on request rather than just a link, or I would have put it up. Do you happen to know a good tutorial on setting this kind of thing up with terminal software? Most IMU (videos) I've found are people showing off a fairly simple setup without any real instruction. \$\endgroup\$ – dboston May 30 at 0:14
  • \$\begingroup\$ Its super simple. install drivers, plug in cable, open up terminal software, select COM port, done. well, also set up the baud rate and a few other settings that are device dependent. its like installing your webcam. \$\endgroup\$ – DKNguyen May 30 at 1:43
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1) The table below shows the connector pin description (as a side note, the document doesn't give a pin schematic, would it be safe to assume 1 is in the upper left, increasing in number to the right?). I have read that I need to connect voltages to both pins 11 and 12 for power, but seeing no VSS, do I need to decouple these with any grounds (frankly, I'm not even sure what that wiring should look like).

The only thing that the documentation indicates is the connector type, these are not keyed connectors apparently, usually you can tell by the key. Not indicating the pin number in the documentation is a really stupid decision or omission on honeywells part. I'd contact them directly and tell them that their documentation stinks, and you need to know what pin 1 is. This is what it says about connectors:

Recommended mating connectors are SAMTECH part numbers FLE-112-01-G-DV or CLP-112-02-F-D or equivalent.

Usually you can tell if the connector is keyed or it may be marked on the connector, but sometimes people don't follow the pin numbering on the connectors so best to ask the manufacturer. Another thing that could be a good indication is to use a Digital Multi Meter (DMM) and use the continuity mode on the ground pin to find the no connect pins (Pins 19-21 and 23)

2) What does the PWR_RTN (Power Return) pin refer to? Do both of these pins need to be wired, and to what?

PWR_RTN is most likely the power return for pins 11 and 12 to the negative portion of the power supply for Vdd. DGND is for the ground of the digital interface (probably mostly for spi)

3) Given the choice between SPI and RS-422, which would be more "user-friendly" to implement on a PC with LabView?

RS-422 will proabably be the easiest way to interface as Labview is compatible and there are plenty of RS-422 cards available and USB to RS-422 (pci cards are better because they have better polling and response times than USB). SPI will most likely require some kind of software to write and a learning curve on interfacing.

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