Maximum current draw through DIO port

[jbernardis]

What is the maximum current draw through a DIO port. Our team is planning on adding some LED's for visible signal indicators, and the LED's I have found draw 80ma. Is that too much to drive using 5 volts directly from the roborio DIO port, or would it be better to operate these off of 12 volts via a spike?

[Mark McLeod]

The 5v rail allows a max of 1a (combined so all other 5v pins are included).
https://decibel.ni.com/content/servlet/JiveServlet/download/30419-60-79765/roboRIO%20Overview.pdf

[mac]

Over the years. The few custom circuits I have inspected. Generally come to the input, output side. Not sure what max amp draw is or total draw is. Sounds like you are low enough. Thank You Mentor Mac

[FrankJ]

Page 4 of the RoboRio spec (https://decibel.ni.com/content/docs/DOC-30419) says the DIO lines can sink or source 4 mA. Unless I am missing something, happens often :), no, you cannot feed the LED directly off a DIO line.

Output high is 3.3 volts nominal.

[Mark McLeod]

I'd recommend using a Spike for LEDs or a custom circuit that only uses the DIO signal as a control.

[SousVide]

AndyMark has a DC/DC converter that will output 5V DC 10A max $18

http://www.andymark.com/product-p/am-3068.htm

[jbernardis]

It's hard to believe that a spike draws that much less than a single LED, but there is enough doubt in my mind that I think it's best to just use a spike. I can size my resistor for 12 volts instead of 5 (or 3.3).

[FrankJ]

Spike Specifications
Specification

Signal Connector:Uses a standard non-shrouded 3-wire cable.
Control Signal:High: 3V min @ 4mA Low: ground (High Max 5-12V current limited to 40 mA.)
Max Switching:20 operations per second no load, 6 operation per minute for rated life at rated load.
Operate Time:5 ms typical
Initial Release Time:2 ms typical
Mechanical Life:10 million operations
Electrical Life:100K operations at 20A, 14VDC, 1mH

The input to the spike is opto-isolated so the RoboRio output does not drive the relay directly. If I were to use a spike, I would drive it off an RoboRio relay output & use a regular spike object (or whatever you call those programing thingies) to program it.

[rich2202]

It's hard to believe that a spike draws that much less than a single LED, but there is enough doubt in my mind that I think it's best to just use a spike. I can size my resistor for 12 volts instead of 5 (or 3.3).

According to Vex, the minimium is 4mA, and is current limited to 40mA.

BTW: I think the spike can switch 5v, so you don't have to switch 12v and step it down as much.

[FrankJ]

The spike has been tested for the relay ports. I don't know if they have been tested for a DIO pin. The specs are different. The NI guys say the RoboRIO IO have been tested by teenagers & is nearly indestructible. But I am superstitious (or maybe I have more efficient teenagers. :] )

The input voltage for the spike's relay section is 12V nominal. I do not know if it will work at 5v.

[SousVide]

You also have a 5V 2A off from your VRM this year - two of them! one is for your radio, the other one we've hooked up to an LED strip.

[Mark McLeod]

You also have a 5V 2A off from your VRM this year - two of them! one is for your radio, the other one we've hooked up to an LED strip.

Radio only on the 5v/2A outputs


R32
The Wireless Bridge power must be supplied by the 5V 2A (“Radio”) output of a Cross the Road Electronics Voltage Regulator
Module (VRM) (P/N: am-2857, 217-4245) and must be the only load connected to those terminals.

[SousVide]

Radio only on the 5v/2A outputs


[/FONT]

Good thing we've got a couple of these then...

AndyMark has a DC/DC converter that will output 5V DC 10A max $18

http://www.andymark.com/product-p/am-3068.htm

[Al Skierkiewicz]

J,
When you speak of LEDs, many of us naturally think an LED string. A single LED can be switched by the DIO through a switching transistor or other driver. If your LED can operate (actually produce light) at 4 ma, you can sink that much current as quoted by Frank above.

[philso]

According to Vex, the minimium is 4mA, and is current limited to 40mA.

This does not mean one should draw anything close to 40mA from the DIO. The chip used might go into current limit mode to save itself from a potential short circuit but the chip manufacturer will never guarantee "proper operation" under these conditions, i.e. the output voltage is unknown.

[SousVide]

J,
When you speak of LEDs, many of us naturally think an LED string. A single LED can be switched by the DIO through a switching transistor or other driver. If your LED can operate (actually produce light) at 4 ma, you can sink that much current as quoted by Frank above.

We have a custom circuit that with a hall effect switch powered off from a DIO port. The circuit has a LED on it to act as an indicator when the hall effect chip has latched.

[MrRoboSteve]

Unless there's something in the 2015 rules I missed, the Pneumatics Control Module is another option for LED control.

[jbernardis]

I have a small circuit with a 2n2222a transistor and a 2k resistor that draws only 2 ma. Connecting this to the DIO port will allow switching the LED on and off and yet stay within the limitations of the DIO port.

[Mark McLeod]

I run small circuits like that off the DIO all the time.

[jbernardis]

Actually I've been doing my figuring based on 5v, but I'm pretty certain these ports operate at 3.3v. So if my transistor has a voltage drop of 0.7v, then to achieve ~2ma I need a smaller resistor than the 2k I have in mind. Based on 3.3, the voltage across the resistor would be 2.6v, so using a 1K resistor instead would limit current to ~2.6ma which is in the ballpark.

[techhelpbb]

http://dangerousprototypes.com/2011/04/25/voltage-threshold-chart/
http://www.pericom.com/assets/App-Note-Files/AN066.pdf

74HCTxxx or 74LSxxx TTL logic chips ought to be able to tolerate 3.3V inputs.

Just remember to put a voltage divider on outputs to DIO inputs to go from 5V TTL supply voltage to 3.3V.

In this way with a 74HCT240 (inverting) or 241 (non-inverting) octal buffers give you 8 buffers per chip.

These buffers are usually capable of >25mA of sink/source current.

With that one could drive the inputs of the ULN2803 that would give you 8 Darlington transistors good for 500mA up to 50V.

Not sure what you can do with that but I would advise checking the rules carefully.