Re: Maximum current draw through DIO port
 

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.

Re: Maximum current draw through DIO port
 

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

Re: Maximum current draw through DIO port
 

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.

Re: Maximum current draw through DIO port
 

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

Re: Maximum current draw through DIO port
 

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.

Re: Maximum current draw through DIO port
 

http://dangerousprototypes.com/2011/...reshold-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.