[marcan]

Originally Posted by Kevin Sevcik

First, the inputs take voltages. You can see that on page 5 of the Operator Interface Reference Guide. So no need to take apart your OI when IFI tells you what's going on there.

Each port provides four analog inputs. These inputs are typically connected to joysticks and
potentiometers, providing an analog input ranging from 0 to 254 (in software) that is transmitted to the
Robot Controller.

They never mention what the requirements for wiring up anything other than potentiometers are. You can sort of guess they take raw voltages too from their description (which is what I described, using a resistor as a pull-down for pots in joysticks), but it's never really described in any sort of detail.

Originally Posted by Kevin Sevcik

Second, I don't think there's been a lot of research into this area. This is mostly due to:
A. You're limited to the 100mA you can pull from the 5V pin, and probably less.

100mA can go a long way for sensor-related electronics. Microcontrollers can use very little power if the code is done right, and sensors also really don't use that much power. Really, the only way you're going to reach that limit is if you use bad design or already-built modules, or things like LEDs.

Originally Posted by Kevin Sevcik

B. There's only so much you can do giving the RC a byte at a time using the OI.

8 analog inputs is 8 bytes, which is plenty for many control systems.

Originally Posted by Kevin Sevcik

Well. B is mostly my opinion. But I'm not really seeing what, aside from the USB chicklet, you can do with a highly custom circuit at the OI that you couldn't do with a simpler circuit and some processing or a custom circuit on the RC.

Easy example: PS2-Chicklet. Interfacing to the PS2 joystick interface is much easier than USB, and I think it could be done with less than $10 in parts. Have a microcontroller read in the digital values and output them to a digital potentiometer. If we finally decide to use gamepad control, and it turns out the digital pots work well, we're definitely not going to be using the USB-Chicklet - I already have tons of PIC microcontrollers lying around, and PS2 controllers are basically free since pretty much everyone has one lying around. No need to spend $130 on the Chicklet.

And, using the same theory with different things interfaced to the PIC, you could use pretty much anything.

Originally Posted by Kevin Sevcik

All I can come up with at the moment is some sort of up-down counter to give you very precise control over the value of the byte with a 7-segment display to tell you what you're outputting. Except that's quite likely to exceed 100mA and, again, you could do it in software on the RC and the user byte.

Software would work in that case, definitely. Even then though, that would definitely not exceed 100mA if you use low power for the LEDs or an LCD module instead (LEDs do draw relatively lots of power - one is okay, but a bunch of displays definitely exceed 100mA)

Originally Posted by Kevin Sevcik

Mostly I think the 5V, 100ma limit is just too restrictive for teams to do much fancy stuff.

It certainly could be larger (say 500mA), but 100mA is still enough to get some play out of things. Also, as far as what I plan to connect goes, the limit probably stretches to 120mA, which according to the IFI docs would limit voltage to 4.5V (still fine for my circuit). Remember, there are tons of things out there that run on little bitty AAA batteries, and those things don't really store that much energy. It just takes some low-power design. I'm really considering using a certain device which draws around 50mA worst-case (and it's a pretty advanced device). You'll hear more about it if it works out.