Arduino Ethernet, how many digital pins can be used?

Projects General Guidance
1

Hi all,

I'd like to use an Arduino Ethernet as a datalogger for some sensors I have in my home (temperature, humidity, ...). The coding part (server side and client/Arduino side) is tested and works. :slight_smile: But now I'm wondering how many sensors the little Arduino Ethernet can use.

On the website I learned there are 14 Digital I/O Pins: 10 to 13 used for SPI, 4 used for SD card and 2 W5100 interrupt. So is it correct to assume I can use 8 digital pins (14 - 6 = 8 )? If so, where are those pins? I see pins with nr 2, 3, 5, 6, 7, 8 and 9 on the board. Which one am I missing? :slight_smile:

The reason I'm asking is that I'd love to add an LCD to my project, but typically the LCD will use like 6 pins so that leaves only two pins for my sensors. Is there a way to limit the number of pins used by an LCD? Or is there a way to increase to number of digital pins on the Arduino?

Thanks for all your thoughts!!

Jan

2

You could use an LCD with a IĀ²C chip, only needs 2 pins. Thet are bit more expensive though.

3

The analog pins can be used as digital pins, too.

Which one am I missing? :slight_smile:

Maybe 0 and 1? You counted pin 2, but you said that's used by the ethernet shield.

4

Thanks for the reply. If you check the official photo of the Arduino Ethernet (see http://arduino.cc/en/Main/ArduinoBoardEthernet) pins 0 and 1 are labeled with TX and RX (if I can read it correctly). Do they have a special meaning, or can I just use them like pin 3 or 7 or ...

Thanks,
J

5

Do they have a special meaning, or can I just use them like pin 3 or 7 or ...

Yes, and yes, if you don't need the special meaning.

Of course, uploading sketches makes use of the special meaning of pins 0 and 1...

6

Thanks for the quick reply!

I'm sorry for asking a bit more explanation (newbie here :slight_smile: ) ... You are saying I can use pins 0 and 1, but they are also used when uploading sketches (I'll be using the USB 2 Serial Adapter). So when uploading sketches I need to disconnect whatever may be connected to pins 0 and 1?

Thanks again!

7

So when uploading sketches I need to disconnect whatever may be connected to pins 0 and 1?

Yes, and then in the sketch, you can't use Serial.xxx().