# Is there a generic way workaround R4's 8 mA current limit **URL:** \ **Category:** UNO R4 WiFi\ **Created:** [February 9, 2024, 9:39pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023 "2024-02-09T21:39:30Z")\ **Posts on this page:** 19\ **Page:** 2
**Author:** ![irakandjii](https://avatars.discourse-cdn.com/v4/letter/i/6a8cbe/32.png) [@irakandjii](https://forum.arduino.cc/u/irakandjii)\ **Post date:** [February 15, 2024, 11:45pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/21 "2024-02-15T23:45:05Z")
> [@hmeijdam](#): > > Now I am confused. I read in the datasheet it can typically source 27mA and sink 47mA. > Where did you read the 6 mA? There is also a circuit note I am still looking for that indicates to use more than 1 pin to get multiples og 6mA ![Screenshot 2024-02-15 184150](https://europe1.discourse-cdn.com/arduino/original/4X/e/c/7/ec76194e962766c8762688fe1705e5cd62ec7ca4.png) ---
**Author:** ![anon94801460](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@anon94801460](https://forum.arduino.cc/u/anon94801460)\ **Post date:** [February 15, 2024, 11:56pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/22 "2024-02-15T23:56:42Z")
> [@irakandjii](#): > > I generally use 3.3v Raspi, MEGA and 3.3 v teensy board 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. ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [February 16, 2024, 12:03am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/23 "2024-02-16T00:03:04Z")
> [@irakandjii](#): > > **Please!** No one is talking about inductive loads here. > [@irakandjii](#): > > Generally drivinig a relay A relay is an inductive load. ---
**Author:** ![irakandjii](https://avatars.discourse-cdn.com/v4/letter/i/6a8cbe/32.png) [@irakandjii](https://forum.arduino.cc/u/irakandjii)\ **Post date:** [February 16, 2024, 12:10am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/24 "2024-02-16T00:10:57Z")
Yes a relay is, I am however takling about Relay boards that accept logic signals, not directly activating a relay through a coil. ---
**Author:** ![westfw](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/westfw/32/213443_2.png) [@westfw](https://forum.arduino.cc/u/westfw)\ **Post date:** [February 16, 2024, 12:37am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/25 "2024-02-16T00:37:54Z")
> [@hmeijdam](#): > > Now I am confused. I read in the datasheet The datasheet you included was for a 74 **B** CT541, while OP is looking at 75 **H** CT541... ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [February 16, 2024, 6:57am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/26 "2024-02-16T06:57:17Z")
> [@irakandjii](#): > > I am however takling about Relay boards that accept logic signals, 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. ---
**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\ **Post date:** [February 16, 2024, 7:00am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/27 "2024-02-16T07:00:43Z")
> [@irakandjii](#): > > Thank you, I trust this will provide an additional option for future readers of the post. 74ACT240N Of course. ---
**Author:** ![irakandjii](https://avatars.discourse-cdn.com/v4/letter/i/6a8cbe/32.png) [@irakandjii](https://forum.arduino.cc/u/irakandjii)\ **Post date:** [February 19, 2024, 9:07pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/28 "2024-02-19T21:07:38Z")
> [@westfw](#): > > The datasheet you included was for a 74 **B** CT541, while OP is looking at 75 **H** CT541... 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! ---
**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\ **Post date:** [February 20, 2024, 10:44am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/29 "2024-02-20T10:44:08Z")
The 74ACT240N can source more current and has a higher Voh than the BCT541 ---
**Author:** ![westfw](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/westfw/32/213443_2.png) [@westfw](https://forum.arduino.cc/u/westfw)\ **Post date:** [February 20, 2024, 10:05pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/30 "2024-02-20T22:05:16Z")
If you go check out the BEAM robotics information ( [Solarbotics.net -- BEAM Reference Library](http://solarbotics.net/library.html), 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 (74 **A** C vs 74 **H** C, etc.) A couple of observations: 1. 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. 2. 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...) ---
**Author:** ![Wawa](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/wawa/32/1211303_2.png) [@Wawa](https://forum.arduino.cc/u/Wawa)\ **Post date:** [February 20, 2024, 11:12pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/31 "2024-02-20T23:12:43Z")
> [@irakandjii](#): > > There are many UNO shields that require 20-30 mA. Most are motor drivers or relay sets. Too many to list here. 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.. ---
**Author:** ![westfw](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/westfw/32/213443_2.png) [@westfw](https://forum.arduino.cc/u/westfw)\ **Post date:** [February 20, 2024, 11:47pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/32 "2024-02-20T23:47:58Z")
> [@Wawa](#): > > 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. 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://circuitdigest.com/microcontroller-projects/arduino-relay-driver-shield-pcb), [https://media.digikey.com/pdf/Data%20Sheets/Particle%20PDFs/Relay\_Shield\_Web.pdf](https://media.digikey.com/pdf/Data%20Sheets/Particle%20PDFs/Relay_Shield_Web.pdf)) ---
**Author:** ![irakandjii](https://avatars.discourse-cdn.com/v4/letter/i/6a8cbe/32.png) [@irakandjii](https://forum.arduino.cc/u/irakandjii)\ **Post date:** [February 21, 2024, 2:14pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/33 "2024-02-21T14:14:13Z")
> [@Wawa](#): > > 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.. **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. ---
**Author:** ![irakandjii](https://avatars.discourse-cdn.com/v4/letter/i/6a8cbe/32.png) [@irakandjii](https://forum.arduino.cc/u/irakandjii)\ **Post date:** [February 21, 2024, 2:20pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/34 "2024-02-21T14:20:00Z")
**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 ---
**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\ **Post date:** [February 21, 2024, 2:31pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/35 "2024-02-21T14:31:09Z")
> [@irakandjii](#): > > So if you have a solution please post it. What's wrong with the 74ACT240N ? ---
**Author:** ![bobcousins](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/bobcousins/32/221530_2.png) [@bobcousins](https://forum.arduino.cc/u/bobcousins)\ **Post date:** [February 21, 2024, 2:47pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/36 "2024-02-21T14:47:02Z")
> [@irakandjii](#): > > I am looking for a **generic solution** for folks that will support 20 to 30 mA or potentially more. There isn't one, at least not one that would be cheap enough for people to buy. ---
**Author:** ![UKHeliBob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ukhelibob/32/215663_2.png) [@UKHeliBob](https://forum.arduino.cc/u/UKHeliBob)\ **Post date:** [February 21, 2024, 2:54pm UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/37 "2024-02-21T14:54:09Z")
Nor would anyone new to Arduino even know that such a thing existed or was needed ---
**Author:** ![westfw](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/westfw/32/213443_2.png) [@westfw](https://forum.arduino.cc/u/westfw)\ **Post date:** [February 22, 2024, 12:51am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/38 "2024-02-22T00:51:22Z")
Generic solution: avoid the R4. ☹ ---
**Author:** ![Wawa](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/wawa/32/1211303_2.png) [@Wawa](https://forum.arduino.cc/u/Wawa)\ **Post date:** [February 22, 2024, 12:55am UTC](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023/39 "2024-02-22T00:55:28Z")
> [@irakandjii](#): > > it is very likely you go to the internet for projects, or tutorials, or just general knowledge... 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.. [Previous page](https://forum.arduino.cc/t/is-there-a-generic-way-workaround-r4s-8-ma-current-limit/1222023.md?page=1)