roboRio limited to 8 Analog Inputs

[topgun]

Looking at the roboRio I see only 4 Analog inputs on the controller itself and 4 available on the expansion port. This seems rather limiting. It's not like some of the sensors give us a choice on how to interface to the controller.

How can we get around this limit?

[AdamHeard]

Originally Posted by topgun

Looking at the roboRio I see only 4 Analog inputs on the controller itself and 4 available on the expansion port. This seems rather limiting. It's not like some of the sensors give us a choice on how to interface to the controller.

How can we get around this limit?

Using an external microcontroller (like an arduino) to read inputs, then pass values over i2c is doable.

[Jon Stratis]

What are you doing that requires 8 analog inputs? There may be other ways to accomplish the same goal without going to the complexity of an additional microcontroller.

[ozrien]

Talon SRX also has a single analog input. That might be another way to get the analog voltage into the RIO (over CAN bus). You don't need to use the sensor for closed-looping, you can just use CAN bus to get more analog inputs that way.

The analog in is 3.3V max but with the analog encoder breakout, you can wire a 5V signal (the breakout scales it to 3.3V).

Default update rate is 100ms, but that can be overridden depending on language. Also if you "select" the sensor programmatically, you can get it at 20ms per update.

[Monochron]

Originally Posted by ozrien

You don't need to use the sensor for closed-looping, you can just use CAN bus to get more analog inputs that way.

Huh, I hadn't realized that. You can just send the analog values back to the Rio to use?

[ozrien]

Talon SRX always sends the analog value even if its not selected. See software referenc manual for details. But you can always call the getanalog* functions.

[crake]

There are several ways to extend the IO capabilities of roboRIO. The use of I2C and SPI (both options on the MXP connector as well) and communication protocols such as CAN give a lot of flexibility. It is an excellent opportunity for the development of "value-add" accessories for the control system.

[Joe Johnson]

Originally Posted by crake

There are several ways to extend the IO capabilities of roboRIO. The use of I2C and SPI (both options on the MXP connector as well) and communication protocols such as CAN give a lot of flexibility. It is an excellent opportunity for the development of "value-add" accessories for the control system.

Let me stipulate that I am finding this problem late and that I should have discovered it sooner. I assumed the new shiny FIRST controller would come with enough IO to support using all the great new sensors that are becoming available to FIRST teams.

Philosophically, we are planning to have a pot provide analog position for pretty much every motor we're using (except for the ones that drive the wheels, which use quad encoders, of course). Given this philosophy, it is really easy to use more than 8 Analog input channels.

Does anyone have a solid solution to this 8 ADC limitation?

I am trying to decide if I should use an Arduino and if so, then which one?

Is it legal to use a Leonardo powered off the roboRIO's USB? If so, does the roboRIO have drivers that recognize he Leonardo's USB Serial Port? I know others have suggested using I2C to communicate with the roboRIO, but it seems to me that it would be simpler if the roboRIO code can get to Leonardo's USB Serial Port.

Another option is the REV RIOduino. Has anyone had luck using this? We are using navX MXP card which may block this solution.

IF NOT ARDUINO, THEN WHAT?

I was thinking of this I2C Breakout Board from Adafruit? Thoughts?

My team needs a solid, reliable easily implemented solution without a lot of fuss and muss. I am sure that this is not a unique problem. If you have figured this out, please share.

Joe J.

P.S. I don't want to hijack this thread but if we go with the Adafruit ADC option, what about powering it? Can I take power from the MXP or do I need to go through a fused line from the PDP as R30, R37 & R42 (collectively) imply?

* 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.

[juchong]

What are you wiring up that requires more than 8 analog inputs? Maybe use encoders instead of potentiometers?

[Tom Line]

If your appendages are using one manipulator or less, you could shift some of the analog pots to absolute encoders to lighten the load.

[adciv]

Originally Posted by Joe Johnson

My team needs a solid, reliable easily implemented solution without a lot of fuss and muss. I am sure that this is not a unique problem. If you have figured this out, please share.

How many ADC Total do you need?

The easiest solution I can think of would be to add a 2nd RIO to the robot and transfer the data over Ethernet to your primary. It's costly, but meets your requirements. Short of that, the adafruit device looks interesting (I'm now investigating this for us for next year).

[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.

[Joe Johnson]

Originally Posted by juchong

What are you wiring up that requires more than 8 analog inputs? Maybe use encoders instead of potentiometers?

Suppose you have a lift? It would be nice to know where it is, yes?

Maybe you want to know where a tote is as try to align to it for a pick up or a drop off? Switches are nice, but analog values seem better don't they?

How about a chassis something akin to this one? Sure would be nice to know which way your wheels are pointing, yes?

Maybe you have something for picking up cans? Sensors to help position things or to discover the can location add up.

How about a gyro or two together with a 3 axis accelerometer?

Getting over 8 analog inputs seems pretty easy.

As to encoders, they are great but they have the problem of not knowing where they are when you wake up. I'm not saying that FIRST did a lousy job preventing brown outs with the new control system but I am saying that I wouldn't bet my season on the robot never going dark momentarily during a match.

Callin' 'em as I see 'em.

Dr. Joe J.

[Alan Anderson]

Originally Posted by Joe Johnson

As to encoders, they are great but they have the problem of not knowing where they are when you wake up.

Absolute rotary encoders don't have this problem. Models with many different types of digital output are available: parallel Grey code, I²C, SPI, synchronous serial, etc. A quick look at the Digi-Key catalog suggests that something appropriate for an arm or swerve steering sensor costs about $25 (which is admittedly more expensive than a good potentiometer).

But you need to bring your toolbox up to date. The Talon SRX motor speed controller has sensor inputs built in, and that's a simple way to add more analog inputs exactly where they are needed.

[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