USB to TTL communicates, but won't upload

Using Arduino Project Guidance
1

I'm working on communicating with Arduinos via their RX and TX pins for two reasons: 1) Future plans to work with standalone ATmega 328, 2) Need to test the serial pins on an older Arduino, which I suspect I damaged previously

After fighting an unsuccessful battle with this HiLetgo CP2102 Module, I switched to this DSD TECH USB to TTL Serial Adapter.

I've tested on a Nano and an Uno. (EDIT BASED ON HAMMY'S RESPONSE: Separate tests. Mac to Nano, then Mac to Uno.) Both successfully send/receive data in serial monitor, but when I try to upload a new sketch it summons the demon known as avrdude:

avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00

I've done loads of reset attempts, reconnects, reboots.

Thanks in advance. Please let me know if I've left out any pertinent details.

2

to be programmed over UART the MCU must contain bootloader, otherwise only ISCP

3

Your circuit doesn't have the necessary reset-via-DTR that is present on the Uno and Mega. You can not serial upload using the bootloader, unless the reset pin is toggled at the right time by that circuit.

4

I might be reading the post wrong but …

Communicating from Arduino to Arduino is done direct without a rs232/TTL convertor .
If these pins are wired together , then you’ll need to disconnect before you can upload any sketch

5

My understanding is that the OP has connected a serial to USB adapter to the Uno RX/TX pins, and wonders why it's not possible to upload a sketch that way.

6

Yes, correct. Edited the post for clarity.

1 Like
7

Please, please don't edit previous posts. It creates confusing threads.

If the RX/TX pins are connected to some external circuit, the on board USB/serial converter can't access the pins properly, and so that won't upload either...

"clarity" would be a diagram...

8

Just this...

IMG_2642
IMG_26421411×855 94.4 KB

9

As Aarg says, DTR required.

DTR
DTR1560×2080 305 KB

10

The power of pictures and diagrams!

11

Fascinating! Here I go researching DTR. Any guidance to send me on my way?

This adapter module has RTS and CTS pins. Those aren't of use in this case, are they?

IMG_8020
IMG_80201920×2560 521 KB

12

They are of use, but not relevant for this application. By the way, soldering connections is a good way to make them work. :wink:

13

Look at the reset circuit on the Uno and Mega, the schematics are freely available on this site.

14

Remember, ALL the USB communication is by messages. There is NO electrical connection to the DTR. It is triggered by a particular message that tells the Arduino USB interface chip to toggle the DTR.

15

Your adapter has a DTR solder hole inside the case.

You may be able to use RTS instead. Connect it through a 0.1 microfarad capacitor to the Reset pin of the Arduino UNO. When you switch to a stand-alone ATmega328P, put a 10k pull-up on the Reset pin.

16

One can also program via usbasp .........

https://www.youtube.com/watch?v=q_K4hp-3EjQ

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