Programming 328 on breadboard: confusing pin instructions?

As a novice I'm worried about getting pin connections exactly right. But some of the instructions I see online seem confusing or contradictory.

For example, the connections I'm using for programming a 328 on a breadboard are taken from

Here's a screenshot I made for easy reference:

I then turned to doing the same task with my UNO R3 itself, using the instructions here:

I haven't yet tried it. Is it correct? As shown in this screenshot I'm puzzled mainly by the apparent use of a 168 instead of a 328, surely a mistake? But also by the other two differences with the serial adapter method, namely:

  • Pin 20 (AVcc) is not connected to pin 21 (AVref).
  • Tx and Rx are not reversed

Terry, East Grinstead, UK

Hi Terry,

this looks OK as an 'exercise' to say you've had the experience, but Uno and Nano clones are so cheap on ebay that I can't see what you'd gain by DIY.

My Uno R3 clone was less than a fiver, I added a cable and a display unit for a total cost around a tenner, and the Nano was just under 3 quid.


The 168 is the little brother of the 328; older Arduinos used the 168. The pin-outs are the same (they even share the same datasheet).

Thanks @sterretje, understood.

Anyone with answers to the other two specifics please?

Terry, East Grinstead, UK

Peter: But I'd guess the total component cost of 328, veroboard and crystal etc would be a third or so of your tenner? As I said in

"I guess that now I've spent on an adapter it will be hard to find a cheaper solution."

Of course, the Nano clone approach eliminates the manual labour, so maybe I'll end up going that route anyway!

Terry, East Grinstead, UK

Follow tutorial. It is correct.
AREF should stay unconnected. It is reference for ADC and if something is set incorrectly it does not matter. It is not needed for startup.
Rx, Tx pins are equal since it is same as on-board ATmega. The output from on-board USB/serial converter is crossed on the arduino board, of course.
Just add 0.1uF decoupling capacitors on both sides, each power pin. No big deal but it's good to have these.

Thanks Budvar10, very helpful, all understood.

That design is missing a critical part - you need a 0.1uF ceramic cap between Vcc and Gnd, and between AVcc and Gnd. These should be located right next to the chip. Without these decoupling caps, depending on operating conditions, the chip may unpredictably reset or hang. It sometimes does work (parasitic capacitance in the breadboard?), however - which is why these guides that omit the decoupling caps continue to exist. But without them, your design will not be reliable, and a change in operating conditions could lead to it ceasing to work.

Thanks @DrAzzy, I’ll add both.

Terry, East Grinstead, UK