Are four wires necessary for UART use?

Other Hardware 3rd Party Boards
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Hello everyone! I'm a newbie to Arduino and I could really use some help form this amazing community.
I recently got my hands on the Arduino UNO R4, and I absolutely love it! It's a fantastic board with great capabilities. I've been experimenting with it and learning a lot.
Now, I want to take things to the next level by integrating it with the SenseCAP Watcher. For those who aren't familiar, SenseCAP Watcher is an AI assistant that can recognize models and transmit the results via UART. It's a really cool device that I think has a lot of potential.
However, I've run into a bit of a problem. As you can see form the picture, the wiring is not very aesthetically pleasing. I'm hoping to minimize the number of wires to make the integration cleaner and more streamlined.
So, here are my questions:

  1. If I only need to receive data form the Watcher, can I leave the TX wire form the Arduino unconnected?
  2. If the Arduino is powering the Watcher, can I get away with just connecting the 3.3V power line and omit the GND wire?
    Ideally, I'd like to use just two wires for this setup. Is that possible?
    I would greatly appreciate any insights, advice, or experiences you can share.
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  1. Yes, if you are certain that the Watcher does not require any input from Arduino TX.
  2. No, a shared ground connection is absolutely required.

If the Arduino is powering the Watcher, can I get away with just connecting the 3.3V

I just looked at the Watcher pages and it requires 5V power. It apparently also needs an internet connection. I suspect that the Arduino 5V output is not adequate to power the device.

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3

Thanks for the quick reply. I think I now know why I'm not getting messages, probably because there is no shared ground.

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Incidentally, I noticed that the Watcher has a 5V input pin on it, and a 3.3v pin, so I guess it doesn't have a 5V output, only a 3.3V output. I'm wondering if I connect both the Arduino and the Watcher, and they are both powered, and have DuPont wires connecting the Arduino to the Watcher, will they burn out? Is the power cable always not connectable?

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You need to fully understand the power requirements before you start making any connections. A mistake could burn out both the Arduino and the Watcher.

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Watcher is Esp32-s3 with Ai-board,camera and display. It's 3.3V MCU and it's data lines are not compatible with 5V arduino boards. You could simplify your life using some other arduino that has 3.3V MCU. Otherwise you need level converter on serial line.

Ideally you power arduino and Watcher separately and connect them only with GND and RX/TX. Watcher 5V pin can be used as output or input, 3.3V as output.

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7

The new Uno R4 board can supply more current then the Uno R3.

The 5V pin supply up to 1.2A when powered by the VIN pin or barrel jack, when powered by USB-C it can supply up to 2A.

Note: This only applies to the Uno R4.

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1.2A! What an amazing figure. Is this the maximum amount of current I can get even by connecting to the USB port of my computer?

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I wouldn't want to draw more the 500 mA from a USB port on a computer as it could damage the computer.

But if you have the board connected to a adequate power supply via the USB-C, you should be able to get at the very most 2A.

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They've done the obvious silkscreen marking on the back of the Watcher, 5V_IN, so I would assume that their 5V pin can only be used to power the Watcher, not for output.
Otherwise, I might be able to save another expensive cable and power the Arduino through the Watcher.

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Thank you for your patience, it has been very profitable for me. I would also like to know if the input voltage and current values of the plugs are what I need to focus on, if you know? I'm afraid that the high power plug I'm using will just burn my Arduino.

12

A simple phone charger will be good enough for powering the board using the USB-C connector.

If you are using VIN or the barrel jack anything between 6 to 24 volts will do.

If you worried about putting high current into your Uno R4, you can use a low current output.

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13

Yep, don't power your arduino from 5V pin. They didn't provide info about voltage regulator used on that board. Neither I found maximum current draw of Watcher.
And don't try to power anything ever without GND.
And be aware what I wrote about serial between 3.3V and 5V MCUs.

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14

The information for the voltage regulator is found here => Uno R4 WiFi, Power Supply.

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Voltage regulator of Sensecap Watcher...

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17

You need to take the Arduino specifications with a grain of salt. Many times they are wrong or misleading
For the current draw, first they say:
"the 5 V pin can provide up to 1.2 A."
Then:
"External devices with a high current draw (e.g. servo motors) should never be powered via the 5 V pin. It is mainly intended for devices drawing lower current such as sensor modules."
So what is high current, lower current, is it more than 1.2A and less than 1.2A?
Well that is quite obvious so why point out that it's intended for lower current devices like sensors.
What if I have a sensor that draws 1A, is that OK?

Personally, I would be very hesitant to go over 600mA on the 5V pin and even then I would check to see if the regulator is getting hot.

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It has a buck converter.
But I would still check to see if it is getting hot.

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That's why I made the sentiment that the Arduino can't even do a good job of powering a 5V servo.

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Do you mean Arduino?

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The Arduino is not a power supply and it was not designed to power a servo.

The 5V output is strictly a convenience, intended for a couple of low power sensors or a small display, and the manufacturer sets strict rules on the amount of current that can be drawn.

If you value your investment in the equipment, you are expected to respect those rules.

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