roboRio limited to 8 Analog Inputs

[Jefferson]

Originally Posted by Joe Johnson

Let me stipulate...

Joe,

I don't have any experience with the items you listed outside of the NAVX, but I won't let that stop me from throwing my opinion out there.

The REVDuino looks like a good option because it does state that you can stack the MXP boards using the provided connector. You could use I2C to communicate between the roboRio and the arduino to avoid any conflict in the UART. There are enough threads here on that very topic that it shouldn't be too difficult.

The I2C breakout board is intriguing. You should be able to power it using the 5V from the VRM. Seems like a cheap and simple solution.

I really hope you can power through the MXP. The NAVX we are both using is powered with it.

Talon SRXs are really the best option to extend the analog capabilities, but I'm guessing you aren't using them if you're still looking for more analog ins.

I know that wasn't super helpful. Maybe somebody can chime in who has some experience with those devices.

[dyanoshak]

Originally Posted by Joe Johnson

* Looking at the pinouts, it looks like the REV RIOduino passes through all the MXP signals so I may be able to plug the REV RIOduino into the roboRIO then plug the navX into the REV RIOduino. I have two concerns. First, will they even physically fit together (see photo attached). Second, both want to use the UART lines -- The roboRIO TX line is no problem as I can have them both listen without a conflict. But I will have to let one or the other use the roboRIO RX line. Never a dull momemt.

Hi Joe,

The RIOduino does come with an extra connector giving you the ability to stack another MXP board on top. However, it is unlikely that the navX will clear the shield headers on the RIOduino.

One solution would be to use the REV MXP Extension Cable to mount the navX elsewhere.

Like others have stated, the RIOduino has both UART and I2C connected to the MXP. You can use I2C on the RIOduino and UART on the navX.

Be sure to check out our website for the latest documents and information about the RIOduino: www.revrobotics.com/product/rioduino

[ozrien]

Hey Joe, I understand the need for more analog.

I'm sure it's not a surprise, but I've been using Talon SRX's for my analogs when testing things, but honestly its because my sensors are close to the Talons and I'm lazy when it comes to wiring. Also 20ms was sufficient for what I was doing at the time. Also I like being able to use the self-test in the RIO web-based config to quickly-peak at sensor values (Self-test works even with no robot code, I love that).

What do you think the fastest resolution teams typically will need?
If you need faster than say a sample per 10ms, then the MXP extensions might be better, though I haven't actually used them yet.

EDIT : FYI, I saw your post about your budget. But I figured I'd chime in anyway for teams that did have SRXs.

[slibert]

Originally Posted by Joe Johnson

* Looking at the pinouts, it looks like the REV RIOduino passes through all the MXP signals so I may be able to plug the REV RIOduino into the roboRIO then plug the navX into the REV RIOduino. I have two concerns. First, will they even physically fit together (see photo attached). Second, both want to use the UART lines -- The roboRIO TX line is no problem as I can have them both listen without a conflict. But I will have to let one or the other use the roboRIO RX line. Never a dull momemt.

The navX MXP has a few dip switches on it; if the UART switch is moved to the disabled position, the navX MXP will completely stay off of the MXP TTL UART lines.

If the navX MXP UART access is disabled, you can still communicate to the navX MXP via the USB port, or you can use the I2C and SPI interfaces. The Labview navX MXP library supports any of these interfaces, however the Java/C++ navX MXP I2C/SPI libraries are not yet released.

[Dale]

An analog multiplexer might be all you need. These are available in chip form or this handy breakout board for $4.95 from Sparkfun https://www.sparkfun.com/products/9056

You just select the line you want to monitor using a digital address from your DIO and then the multiplexer acts like a really fast rotary switch to select that line which you'd feed into one of your analog inputs.

This one from Sparkfun switches in nano seconds so your ability to monitor multiple channels is likely limited by what the RoboRIO can deal with.

This particular chip/breakout board gives you 16 channels.

[Joe Johnson]

Great replies. Thanks everyone.

In the end, the coding team has come to the rescue. They have been working on a project that will need a Beaglebone Black as a coprocessor. They've already got the communication link bits worked out so really it was pretty simple to have them add some analog data to their scheme.

I hate that we have a new shiny CPU on our robots and still have to do work arounds like this but It Is What It Is.

Thanks again for all the feedback.

Dr. Joe J.