Arduino digital IO pins numbering

Some of the pins are multi-functional.

On the UNO you have the digital pins 0-13 however the analogue input pins 0-5 can also be configured for digital IO.

On the Micro you have the digital pins 0-13 and analogue input pins 0-5, however in addition digital pins 4,6,8,9,10, & 12 can also be configured as analogue inputs.

Perhaps think of it as 20 Digital IO pins of which 6 (UNO) or 12 (Micro) can be configured as analogue inputs.

These 2 boards use a different chip, as such they have different pinouts. the UNO has a 28 pin Plastic Dual Inline Package (PDIP) which is an ATMEGA328 and the Micro has a 44 pin chip (Quad Flatpack no leads (QFN) which is the ATmega32U4

the two chips also have different internal functionality, the ATmega32U4 having quite a bit more than the 328

the Wiring based  IDE hides most of these details from you but does allow access to the common functionality through the commands like digitalWrite, digitalRead, AnalogRead etc.

ATmega328

ATmega32U4

hope this answers your question

Not that you are to be blamed in any way Dave, of course you are only trying to help and thanks for that, but to me it sounds like not being clear enough on the part of Arduino, when selling to beginners level in prototyping like i am, to say a board has 20 IOD and not 14 IOD, while they actually mean it has 12 analog instead of 6...i could have use the Uno or Pro-mini which i already have and not buy a new Micro, if i had known that actually they have 20 IOD, just like the Micro has.

This will probably be going to the other extreme but if need be you can get more info on the Atmel ATmega328 device here:

ATmega328P

The complete datasheet is around 600 pages however so expect to be skipping over a few pages until you get more familiar. However it goes into a lot more detail about  the IO port configuration options.

Peter - your explanation is at a high level and too much for me to understand, can you please try to help me if possible, by answering the following question:

i have on a robot i'm building, the following components:

1. 2 X L293D chips, which turn 4 motors and require 9 outputs (the 9th is the enable pin on all sides of both L293D, which i made common to all 4 motors).

2. 6 X servos which require 6 outputs.

3. 1 X relay which turns another type of motor, which requires 1 output.

4. 1 X bluetooth dongle, which requires RX and TX.

This is all working well on an Arduino Mega - but now i need to put it all together in a much smaller box - so anything even close to the size of a Mega won't do.

The question is: What would me the smallest Arduino board, which can handle the connections described above?

Thanks!

What sort of size are you actually hoping for ?

Are you using PWM on your L293D enable line for motor speed control as the Uno / ATmega328 only has 6 PWM outputs whereas the Leonardo / ATmega32u4 has 7 which could be crucial in your project.

You could perhaps consider just using an Atmel microcontroller on its own to get the size down.

If you don't require the 7th PWM output for the L293D then you may be interested in the Adafruit Pro Trinket

https://www.adafruit.com/product/2000

It's like a miniature version of the UNO. You lose D2 & D7 but you gain A6 & A7.

Size comparison between UNO, Pro Trinket and Trinket

https://cdn-shop.adafruit.com/970x728/2000-10.jpg

Interesting boards..actually i got a bunch of Arduino pro-mini, which might even comply to the project needs, if i will also use the analog IO. But since the pro-mini are more sensitive and tend to fry more easily, i'm trying the Arduino Micro.