I'm trying to program a Atmega168 Pro Mini 3.3V/8mhz I bought online. I followed a tutorial that walks through the steps of how to program a Pro Mini with an Arduino Uno. However, in their example they are uploading code to a Atmega328 Pro Mini though I don't think it matters.

Anyway, I followed the same steps as they did (namely hooking up Uno's ground -> ground, 3v -> Vcc, Reset -> DTR, tx->tx, rx->rx). When I attempted to upload via Arduino IDE I got the message that the programmer was not responding. I also noticed that the transfer led on the Uno was not lighting up. Did I screw up something? Also, are my hookups correct? I would think tx pin should connect to rx pin, but I just followed the instructions. Would appreciate any thoughts

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  • 1
    Did you remove the MCU from the Uno?
    – Majenko
    Commented Oct 6, 2020 at 21:30
  • yup, I took off the 328 chip
    – I Like
    Commented Oct 6, 2020 at 21:54
  • Hookup is not correct, the RX, TX lines need to be crossed!
    – Umar Sear
    Commented Oct 13, 2020 at 4:39
  • 3
    @UmarSear That's wrong. In this instance the Uno is only being used as a USB to UART adaptor, so TX->TX and RX->RX is correct. You would swap them only if you wanted the ATMega328P on the Uno to communicate with the ATMega168 on the Pro Mini.
    – Majenko
    Commented Oct 13, 2020 at 8:51

1 Answer 1


Your hookup seems to be correct. However check if there is a capacitor on the pro-mini board between DTR and reset pin, some arduino clones don't come with one. If there isn't any you can simply connect a capacitor like this: Reset pin (Arduino Uno) -> Capacitor (0.01uF for example) -> DTR (pro mini). The reason for this hookup is exmplined well here

  • 1
    They're also interfacing the 5V UNO to the 3.3V Pro Mini with no consideration for the logic level difference. Sometimes you get away with that. Anyway, rather the start another answer, I figured I'd just tack this onto yours, for integration into it or not.
    – timemage
    Commented Nov 13, 2020 at 2:36

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