I often transfer my projects from the UNO and breadboard to Veroboard, mounting the 328 on a 28-pin IC socket for easy subsequent editing. Is there any other Arduino board with more than the UNO's 20 I/O pins that I could use in the same way, with my small stock of 328 chips? Or is 20 the limit of the chip itself?
(I'm exploring the I2C approach to pin extension in a parallel thread.)
23 is the Limit of the 28 pin DIP chip.
But normally only 20 are free for IO.
Check the ATMega328 data sheet for the full details.
Thanks, interesting, but unless that extra 3 are accessible on the UNO I'm still looking for an alternative board.
Are you looking for an alternative board or an alternative processor ?
If you are prepared to program your Veroboard mounted projects in situ rather than by plugging in a chip previously programmed in an Arduino board then chips with more pins are available, albeit not in DIP packages
Using an ATmega2560 chip, for instance would give you plenty of pins
|Digital I/O Pins|54 (of which 15 provide PWM output)|
|Analog Input Pins|16|
They are not accessible on the UNO because they are not normally accessible on the 28 pin chips you have. Two pins are used for CLK and one for the RESET.
You could use the Pololu A star 328PB boards. These have pins A6 & A7 capable as an output. They also have extra pins as well, capable of being another I2C bus and serial port.
Are the 328PB chips DIL packages so that they can be programmed in the board then moved to the Veroboard mounted project which is what I think @Terrypin wants to do ?
No they a quad flat pack but the form factor is nano size with another 5 pins on the bottom edge.
Board, and the 2560 is not only expensive but also OTT for my present needs.
Programming in situ is a sound option. I did buy an adapter a year or so ago with that in mind. But making the Vero and the extra programming seemed hard work and I've since got into the current work flow habit.
I also invested in pluggable 328s and still have four left.
But in that parallel thread
https://forum.arduino.cc/t/overcoming-insufficient-number-of-uno-pins/1087795/15
the voltage ladder suggestion by dougP could be my salvation. I have yet to go looking but there may well be a simple library around that helps code it.
Thanks, looks a nice board and reasonable value, but I need one with pluggable 28 pin 328.
Ah - UKHeliBob beat me to it.
I have resisted the temptation to merge the topics despite them being flagged as duplicates, but using I2C interface to the LCD and a resistor ladder on an analogue input will certainly reduce the number of pins needed
Do you need extra I/O?
What is the application?
Have you considered port expander ICs?
Thanks.. Tom.. 
Covered in earlier posts.
And in another thread.
Why open another thread about I/O problems?
Sorry.. Tom..
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