There is also a circuit note I am still looking for that indicates to use more than 1 pin to get multiples og 6mA
So you should have no problem adapting to modern developments in low current, low voltage I/O, and moving away from the very old, soon-to-be obsolete 5V, high I/O current board and "arduino shield" designs.
A relay is an inductive load.
Yes a relay is, I am however takling about Relay boards that accept logic signals, not directly activating a relay through a coil.
The datasheet you included was for a 74BCT541, while OP is looking at 75HCT541...
Thanks for the clarification, it is good to know these things.
Have you got a link to where you bought the relay board so we can check the current it requires. Normally these sorts of boards have a logic input to an optical isolator.
This of course is an LED so it could be a 20mA load, and if it is then yes you will need a driver, but only of the pull down sort.
74ACT240N
Of course.
Yep, my appologies.
It looks like the vendor made a substitution and I failed to catch it. I definately recieved the SN74HCT541 version and used the silkscreen code to look up the application notes once recieved them. Note to self ... double check then do it again!
The 74ACT240N can source more current and has a higher Voh than the BCT541
If you go check out the BEAM robotics information ( Solarbotics.net -- BEAM Reference Library, for example), you may find a lot of information on using and abusing 74xxx logic chip for purposes beyond the usual (motor drivers!) There's also some good summary in there for the differences between the different families of logic chips (74AC vs 74HC, etc.)
A couple of observations:
- If you are using logic chips to drive things other than ... other logic chips, you can usually get more current from them than you might expect. The 20mA (AVR) or 8mA (RA4) ratings are the max current that can be drawn WHILE MAINTAINING legal logic voltage levels. (of course, at some point you risk damaging the chip, which may or may not matter, depending on how the damage manifests itself. AVR circuits that drive LEDs direction from IO pins (without current limiting resistors!) are pretty common, and it's generally considered a feature if you can accidentally short an output pin to GND without causing catastrophic damage.
- You can increase drive capability by paralleling pins/gates. This is a bit risky with Arduino output pins, since changing them simultaneously is tricky, but you can easily double the drive strength of your 74hc541 chips just by connection two drivers in parallel.
(of course, if you're going to push the limits, it's better to do so with a $1 easily replaceable "external" chip than with the SMT processor on a $30 board...)
I have never seen a motor shield that draws more from an I/O pin than microamps, And the maximum a common relay board with opto coupler draws from an I/O pin is 2mA.
Please enlighten me.
Leo..
While it's true that most motor and relay shields have buffering and the 8mA limit shouldn't be a problem, it's also true that "microamps" and "2mA" are pretty low.
The popular ULN2803-style motor driver has an input current of about 1mA to turn on fully (an L293D, also popular, is down in 10-100uA range, though), and many opto couplers have essentially a relatively high-current LED on the driven side, set up with usual led-driving currents (5-10mA), and some are mere transistors with the usual ~1k base resistor (also in the 5-10mA range.)
(examples: DIY Arduino Relay Driver Shield PCB, https://media.digikey.com/pdf/Data%20Sheets/Particle%20PDFs/Relay_Shield_Web.pdf)
As I noted in my original post. I am looking for a generic solution for folks that will support 20 to 30 mA or potentially more.
It is NOT just relay or motor shields. They are an example.
If you are new to arduino and a learner (not me btw) it is very likely you go to the internet for projects, or tutorials, or just general knowledge. IT is VERY common to find applications within this scope that draw 20 to 30 mA or more. This far exceeds the R4's current limit. Many of learners just see UNO and and assume they are safe.
I would like this post to provide a mechanisum for such folks to avoid that pain and the cost of r4 replacement. So if you have a solution please post it.
I am starting to think there is a market for a carrier board, like the ones for the old intel Edison, nvidia's xavier, or Aruinos own pro series where pin safety is built into the carrier.
westfw thank you for your posts, this is the the kind of knowledge I would like to collect here.
I graduated P.Eng in 1978, so my current knowledge of specific IC's "friendly to the hand" is shall we say lacking. Dang I was taught by vacuum tube guys lol
What's wrong with the 74ACT240N ?
There isn't one, at least not one that would be cheap enough for people to buy.
Nor would anyone new to Arduino even know that such a thing existed or was needed
Generic solution: avoid the R4. 
Maybe you're right there. People's attitude is that "bigger is always better". If a LED has an absolute max rating of 20mA, then we should drive it with 20mA. It needs some convincing that 1-10k is fine for an indicator LED or opto LED.
I can only think of a few occasions where you actually need 20-30mA. In that case you should already have added an external transistor instead of adopting the "she'll be right mate" attitude.
Leo..