As it says, that's to Vin or the power jack.
I refer you to my previous comment:
So far, I have had no issues with powering up the devices with those transformers. I do appreciate your advice and input. Many users recommend them for Arduino devices. I have been on multiple sites reading everyone's input on Arduino devices. Seems like many opinions on how to do everything.
I don't know how else to tell you. I feel I've explained why you should power them with 5V to the 5V pin but it seems my explanation does not work for you. Please see reply #38. If you still don't get it then ask me a question about whatever it is you don't understand or maybe ask someone else (I'm sure others are reading this) to explain it differently, maybe my way of explaining is not right for you, that's OK, different people think in different ways.
Please don't quote that you've read this or that in countless places because that means nothing other than you've read it somewhere. This is not a competition where the highest number of citations wins. I could tell you my background and basis for my knowledge but I think that's a lousy way to express a point. That's on the same level as these idiot celebrities who say things like "I'm a super famous celebrity and I say you should cover your skin in Rancid Polecat at £150 per bottle, so go out and buy some now". What matters is the truth of what I am saying, not that it's me saying it. If I have not explained to your satisfaction then I am not the right person to help you.
Now, read my comments again and ask something or ask for someone else to give their explanation.
I thank you.
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There are many many Arduino tutorials around on the internet that are just plain wrong or at best misleading - see Instructables for an impressive list.
The classic oft repeated one is demonstrating that you can power a servo from an Arduino. And you can, just, if it's lightly loaded and power isn't provided through Vin. But you really shouldn't as it's pulling way too much current.
Same thing here. You can use the barrel jack, but it's a silly thing to do.
Like I said, I am getting a Siglent SPD3303X-E bench power supply to power the bread boards for the projects. I might get a second one to power Vin on the Arduino devices. I could use one of the 3 channels on the bench power supply for Vin set to 5V and 500mA. Eventually, the Arduino will need to be powered up and not connected to the USB cable. I have seen many use a 9V battery with the kit cable. This will require replacing batteries more often. So a transformer would be the better solution. In over 3 years of using these transformers, no issues or burn outs on the Arduino devices.
I started working on changing everything over to UART. The Mega 2560 has four serial channels to connect to the UNO devices. Only thing so far is every time I want to change the code, I have to unplug the connections. I have 4 port switches that I am going to wire with them to be able to turn them off and back on. This should help. When the TX/RX are connected, the Arduino devices won't update the changes.
https://mc.scsiraidguru.com has many complex projects with the Arduino devices and no issues or problems with the hardware.
I have been looking at a Turing Pi board and four Pi modules for it using Samsung SSD drives.
I've read through this entire thread, each post, multiple times and I still can't determine the intended functionality of all the h/w on the I2C bus.
Particularly because there seems to be lots of talk of doing things that is not in the code that has been posted.
Best I can tell the intended final functionality is that an Rpi master is attempting to talk to and control multiple slave Arduinos and then some i2c LCDs with PCF8574 based backpacks are updated.
How that is intended to happen isn't clear to me.
i.e. I can't tell if the Rpi is going to be reading data from the Arduinos and then updating the displays or if the Rpi will be attempting to command the Arduinos to update a display that the Arduino controls itself.
If it is the latter, then the Arduinos must be both slave and a master.
I'm not sure if the Arduino AVR Wire library can even handle that.
Also there can and will be all sorts of multi master issues when attempting to do that.
Not just in the multiple masters on the bus but in attempting to switch between slave and master mode.
What makes the discussion hard to process, at least for me, is that the thread is all over the map.
It starts out with questions about LCD artificacts but then is wandering around about i2c connectivity h/w design limitations / issues along with talk about multiple Arduinos, and multi master design.
The Arduino Wire library already has known issues with respect to handling certain i2c bus and timing issues, when used in a single master environment so I'm assuming moving to something more complex is almost assured to have issues.
I find the thread very scattered with lots of jumping around between topics.
My suggestion is to slow down, focus on one topic and work through that issue before jumping to next.
Also, a better and full description of how all this is intended to work is needed.
One thing I can say for sure is that as @Koepel pointed out in post #15 you should not be addressing the Wire object directly when using the LCD library API.
The LCD library handles the i2c bus, so there is no need to attempt to control it directly using the Wire library when wanting to talk to the LCD.
i.e. this:
Wire.beginTransmission(0x24); // should not be doing this
lcd20x4_24.setCursor(0, 0);
lcd20x4_24.print("0x24");
lcd20x4_24.setCursor(0, 1);
lcd20x4_24.print("0x24");
lcd20x4_24.setCursor(0, 2);
lcd20x4_24.print("0x24");
lcd20x4_24.setCursor(0, 3);
lcd20x4_24.print("0x24");
Wire.endTransmission(); // Should not be doing this
Without closely looking at the Wire library I have no idea what those unneeded Wire calls may be doing to the internal states of the Wire library or to the i2c bus.
With respect to artifacts on the LCD display,
Using the hd44780 library and hd44780_I2Cexp i/o class, I have run 8 displays on a single Arduino and don't get any artifacts.
The typical cause of artifacts (screen flicker or fading) is doing things that cause the characters at a given position to change or disappear and re-appear.
i.e. doing a clear() or printing spaces then overwriting the cleared area, or rapidly changing the characters that are written at a given position.
--- bill
I really haven't put the time into the other components just yet. I want to connect the two Arduino Mega and 7 UNOs together on a common bus to transfer data back and forth. I2C bus was having issues. I split the Mega with 3 UNOs and other Mega with 4 UNOs to use the UART Serial bus. TX0/RX0 to TX3/RX3 can do it. The issue is I have to disconnect the wires to update the code. So I will add in dip switch jumpers to turn on and off the UART bus to make it easier to upgrade the Arduino devices.
Not sure what you are really attempting to do, but it seems overly complicated.
You could jump up to something like ESP32 or ESP8266 modules and use Wifi to communicate.
MUCH faster processors with LOTs more resources as well as lower cost.
Plus you can use more modern communication interfaces like web based interfaces to fetch data and or control the device.
Or even use Rpi W zero devices.
With the zero, you can run a real OS that has multitasking along with all kinds of s/w tools and development resources available.
The cost of a Rpi W zero is less than the cost of most Arduino boards, particularly the Arduino Mega.
i.e. use known well defined and tested interfaces and APIs vs having to invent a communication method and all the needed reliable protocols to ensure its reliability.
--- bill
I have 9 Arduino devices and thought about building a cool project using all of them together along with I2C LCDs. I have many sensors I could connect to them. The idea was to use the I2C LCDs to display informaiton one arduino at a time.
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