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[Alex698]

Just wondering could you use the power off of say, a laptop USB port; provided it was battery powered?

[Astronouth7303]

Originally Posted by Alex698

Just wondering could you use the power off of say, a laptop USB port; provided it was battery powered?

Only if the said LED wasn't at all connected to the switch.

Also, I think many teams would find it useful if the LED actually ment something, instead of just lighting up.

And why not just a real battery?

[EricRobodox]

ummmm, the leds will indicate certain codes the robot will run, and while it runs, we want to see what its set to.

so, getting back to topic, so wiring the led is simple as what mentioned before, pin to led to ground pin without resistor?

[jgannon]

Originally Posted by Astronouth7303

Only if the said LED wasn't at all connected to the switch.

Didn't we just establish that this isn't the case?

[EricRobodox]

well mathematically, it doesnt seem right, i just want to confirm that the statement is true, because if the math of an led is right, you dont want 5v going into it with 10mA. But if the IO automatically lowers it correctly, then ill be ok, i just wanted to make sure i was reading it correctly. i guess i am, thanks for the help. rep is on the way.

im a little pushy today, just a long rough day personally and with work(school).

thanks again

edit:
agh, wait, reread your post joey, so i dont have a confirmation if:

positive pin -- led -- gound pin

will work or if my math is correct and i need a:
positive pin -- 100-200ohm resistor -- led -- ground pin


lets just call them Circuit 1 and Circuit 2, which is the correct one?

[Al Skierkiewicz]

Eric,
The LED outputs on the OI are the 5 volt power supply through a resistor. They were designed so that you don't need to add a resistor you just connect the LED straight to the OI output. (The OI REf Guide on the IFI site explains this) The internal resistor value was chosen to provide an LED current of 10 ma. If you add external resistors you will lower the LED current even more, perhaps making them so dim you can't see them. We have used LEDs on the operator station for many years to do exactly what you are asking. We have software that helps us calibrate everything on the robot and select a variety of auto mode solutions. We do not use the LED inside a switch but rather mount them individually so that we can identify them with labels. PM me and I will give you my email if you need anything further. Time is short, good luck.

It is not legal to externally power any other devices connected directly to ports on the OI except the Chicklet. You can have a custom box, powered by external power (you supply) and connected to the dashboard that can use dashboard data to display whatever you want.
<R79> Teams are permitted to connect a portable computing device (Laptop computer, PDAs, etc.) to the RS232 Output of the dashboard port of the Operator Interface for the purpose of displaying feedback from the ROBOT while participating in competition matches. Please note that AC power will not be available at the playing field so these devices will have to run on internal batteries.
<R83> All equipment connected to the joystick ports of the Operator Interface must be powered solely through the power available through the port. External power sources of any type are not permitted on any equipment connected to the joystick ports. Portable computing devices can not be connected to joystick input ports on the Operator Interface. Powerpassive devices (e.g. joysticks that draw their power solely through the Operator Interface joystick port) are permitted. The one exception to this rule is Innovation First Incorporated USB adapters (IFI Part Number USB-CHICKLET) may be used to connect USB devices to the joystick ports of the Operator Interface. If used, this USB adapter must be powered with a 7.2V battery similar to the back-up battery. Teams can not use power from the competition port or any other source to power the USB adapter. The USB adapter must be positioned within the OPERATOR CONSOLE so that the indicator lights may be seen during inspection and operation in a match.

[Dave K.]

Originally Posted by Al Skierkiewicz

Eric,
The LED outputs on the OI are the 5 volt power supply through a resistor. They were designed so that you don't need to add a resistor you just connect the LED straight to the OI output. (The OI REf Guide on the IFI site explains this) The internal resistor value was chosen to provide an LED current of 10 ma. If you add external resistors you will lower the LED current even more, perhaps making them so dim you can't see them. We have used LEDs on the operator station for many years to do exactly what you are asking. We have software that helps us calibrate everything on the robot and select a variety of auto mode solutions. We do not use the LED inside a switch but rather mount them individually so that we can identify them with labels. PM me and I will give you my email if you need anything further. Time is short, good luck.

Al,

On Jan 29th, I communicated with IFI regarding their documentation being in error with regard to this, and to their credit the OI documentation was updated the next day.

See page 5 of the current documentation here: http://www.ifirobotics.com/docs/oi-r...de-1-30-07.pdf

In addition to their explanation here are some additional comments and observations...

The outputs are not derived off a 5V supply, the voltage varys as a function of the input voltage and appears to be a fairly consistent voltage drop of about 2.5 to 2.6V (as measured between the tether input and the open circuit LED output). Given that the tether power input could be about 12.5V, the LED outputs could see as much as 10V.

At competition, the OI power input via the competition connector would be about 9.9V at its lowest (confirmed with IFI), so the open circuit LED voltage would be on the order of 7.4V minimum.

When using the wall wart, depending upon the load that open circuit voltage will probably be around 8.4V (per IFI).

The resistor inside the OI is 470 ohms (per IFI). I calculate an effective resistance closer to 500 ohms, and IFI's new documentation puts it closer to 550 ohms.

Assuming 470 ohms, with a RED LED that has a forward voltage drop of 1.7V, a minimum of about 10-11mA would be available. When tethered, it could be as much as 16mA.

At the other end of the extreme, a BLUE LED with a forward drop of 4.5V would only have about 5-6mA available at competition.

Perhaps previous generations of OI's did power the LED's from 5V and the user manual never got edited.

The bottom line is that we do agree that when using the LED outputs to power LED's, no additional resistor is needed and I think IFI's new wording helps to clarify this.

[Al Skierkiewicz]

Dave,
This is a difference and not fuly documented since the OI manual you linked to, on page 7 "Notes:" states "[2] LED drivers provide 5V at 10mA". There are several other places in the manual where this is repeated. This is the criteria teams have used as far back as I can remember. If the LED outputs are indeed the raw input voltage, there will be times when the LEDs will extinguish due to low current. In the past we were told they were part of the 5 volt rail held up by the backup battery. I will pass this on to my software team.

Thanks,

[Dave K.]

Originally Posted by Al Skierkiewicz

Dave,
This is a difference and not fuly documented since the OI manual you linked to, on page 7 "Notes:" states "[2] LED drivers provide 5V at 10mA". There are several other places in the manual where this is repeated. This is the criteria teams have used as far back as I can remember. If the LED outputs are indeed the raw input voltage, there will be times when the LEDs will extinguish due to low current. In the past we were told they were part of the 5 volt rail held up by the backup battery. I will pass this on to my software team.

Thanks,

Hi Al,

Good catch, they clearly missed editing the note on pages 7-9, and I'll pass that along.

I originally noted the discrepency after being forced to reverse engineer the interface to design some interface electronics and was looking into a source of power other than the +5VAux pin.

As it is unregulated, it then became important to understand more about the power that is supplied via the (undocumented) competition port, so I also pressed for answers on that and got a reasonably detailed description of that as well... and that's where the information on the 9.9V supply voltage comes from. The undocumented power pin, is parallelled with the coaxial power connection.

It appears to be fine to use as intended, except for the possibility of a situation requiring a higher voltage LED such as white, or blue.