Trying to link two Arduinos over a serial link using a CP2102 module

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Hello Forum! The short story: I’m trying to connect two Arduinos over a serial link using a CP2102 USB 2.0 to TTL Module Serial Converter and having trouble. My desire is to connect the Nano USB - USB Cable - USB Female-to-Female adapter - CP2102 Module - Arduino Mega 2560 Pro Serial1 (pins 18, 19, and Ground). I think this should work, but I’ve not tried this or even used this module before. Anything obvious I’m missing?

This is the CP2102 module I’m trying to use: Amazon.com: HiLetgo CP2102 USB 2.0 to TTL Module Serial Converter Adapter Module USB to TTL Downloader with Jumper Wires : Electronics

Longer story: The reason I’m trying to do this is because I have an Arduino that is embedded in a previous project that is pretty hard to reach. But, I have access to its USB connector through a USB extension cable that I use to connect to my computer, and now I want to replace the computer with another Arduino. I don’t have easy access to get to the embedded Arduino TX/RX pins.

I tried hooking it all up and could not get the boards to communicate, so I dropped down to a testbed that is just to verify that I can get a TTL output from the module when I send it data from an Arduino over its USB connector. So my testbed is Arduino Nano USB - USB Cable - Female-to-Female USB adapter - CP2102 module. I don’t have anything connected to the TTL pins of the module. The Arduino test code is nothing more than calling Serial.begin(9600) in setup and then sending out a text string in a loop once every second. I’m powering the Arduino from its Vin pin.

When I plug in the CP2102, its power LED comes up and I get 5.0v and 3.3v out on these pins. Both the Tx and Rx pins go to 3.3v and stay there. The transmit light never blinks. I know the Arduino is sending because when disconnect the cable from the adapter and plug it into to my computer I can see the looping text string using the Arduino IDE serial monitor. If I connect the CP2102 directly into my computer and type on the Serial Monitor I do see the transmit light blink and I can see serial data with a scope on the Tx TTL pin, so I know the module works. So, for some reason, the Arduino USB output is just not getting through the CP2102 module, but my laptop can.

I rung out the USB female-to-female adapter that I need to connect the USB cord to the module and it looks good. When I look at the device detail on my computer with the CP2102 connected, I can see that it is configured for 8 data bits, no parity, one stop bit, and no handshake, which I understand is the Arduino default serial configuration.

Any help?

Thanks!

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No, I don't think so.

Your Uno is a USB peripheral. So is your CP2102 module. USB peripherals don't communicate to other USB peripherals. USB peripherals communicate with USB Hosts.

Get yourself a board that supports being the USB host end. An RPi Pico is one.

Edit: you'll also need a USB OTG (On The Go) type cable.

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Rats.

But THANK YOU so much for your help!!!

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On, and by the way, if your CP2102 module is powering up when it's plugged into your Uno, that means your Uno is one of the ones that doesn't prevent backfeeding external power to the USB 5V line. That's generally not a good thing.