so , just bought some pre-bootloaded ATmega328(p/pu) to which I need to upload sketches on a breadboard using uno TX and RX pin as FTDI

Here is what I am to do.

  1. I connected Uno GND and Reset .

  2. Arduino Tx to Standalone Atmega Tx

  3. Arduino Rx to Standalone Atmegaa Rx

  4. Connected Crystal , capacitor to standalone pin 9, 10 (XTAL) then grounded it with 2 coupling capacitor.

  5. Standalone vcc to arduino 5v Standalone GND to Uno GND

Is it possible to do what I need to or i need to buy some USB to TTL devices from the Amazon again?

Thanks for your precious time...

2 Answers 2


That sounds about right.

The only problem is that normally, when a serial connection is created, the Arduino's reset pin is briefly pulled LOW. You would have to do that manually on the ATMega on your breadboard. I can be a bit tricky to get the timing right.

There is no easy way to get this signal to your breadboard ATMega, while keeping the reset pin on the UNO's ATMega LOW.

Removing the ATMega from the UNO board would work.

  • I have got to get the right time to reset after uploading the code so, i am doing it manually without FTDI which saved some of my bucks :) Commented Feb 20, 2021 at 5:43
  • @SubhaJeetSikdar I changed the firmware on the ATMega8u2 on my UNO to also toggle one of the header pins next to it, when it tries to reset the ATMega328P. That way I could upload to custom ATMage328P based board over serial :-)
    – Gerben
    Commented Feb 20, 2021 at 13:59
  • Can you please send me a video or article link about how you changed the firmware of the programmer ic ATmega8u2, well , mine one seems to be ATmega16u2 Commented Feb 20, 2021 at 18:32
  • I programmed it via DFU. The firmware can be found at github.com/arduino/ArduinoCore-avr/tree/master/firmwares/…. Change Arduino-usbserial.c to also change one of the ISP pins where it currently change the reset-out pin. It's been way to long, so I don't have the files anymore. Proceed at own risk.
    – Gerben
    Commented Feb 21, 2021 at 18:47

https://youtu.be/EoHD0m3uUhA. Ig this should do it. There are many more tutorials on YouTube to achieve this.

  • What if I don't want to remove the factory installed atmega on arduino. Actually I dont want to remove factory installed at mega, is there any other way to do this without removing previously installed atmega Commented Oct 28, 2020 at 5:41
  • If u don't remove the pre installed at mega then it will try uploading the code to both of them which will be a big problem for you . Then you have only one other option to use a FTDI module
    – xbox gamer
    Commented Oct 28, 2020 at 6:08
  • What if i connect the ground and reset of the arduino before uploading sketches on breadboard ATmega? Commented Oct 28, 2020 at 6:46
  • Sorry I am not able to understand what u are asking
    – xbox gamer
    Commented Oct 28, 2020 at 7:32
  • images.app.goo.gl/g2gEeuHJ9dKAd6hY6 Commented Oct 28, 2020 at 10:03

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