Questions about arduino UNO and my project

Hi folks,

I´m a newbie with arduino and eletronics, but I must say that after I entered this new "world" or arduino, i realize I could bring toghether some of my wanna do projects. I´ve recently aquired an Arduino UNO, in order to develop a aquarium monitor system, like many did in other sites and this forum.

I´m having issues now with the capabilities of arduino, and if it will be able to deal with my sensors. My question really at this point is related to the capacity of arduino and it´s pins.

My project involves:

1) LCD Module with 4 switches keypad. 2) RTC Module 3) Ethernet and SD Shield, to access information on web and store sensor parameters on SD. 4) 1 Temperature Sensor Probe 5) 1 PH Probe 6) 2 relay modules, to access hardware (pumps and so) 7) dimmable control for leds, moonphase and so.

Can an arduino UNO support all this connections at once? Or will I run out of pins and need to do a multiplex?

Any help will be great


You might have a pin conflict with 1) and 3). I'd suggest wandering over to, looking up your shields, and verifying that they won't conflict.

Most RTC modules use analog pins 4 and 5.

You're quite vague on 7).

Overall it looks like you're going to run short on pins. You might consider an Arduino Mega (or clone) which are now available at prices around $30 via eBay.

Hi Chagrin,

Thanks for the responses.
The Item 7 in more detais:

2 LED drives that will be dimmable by arduino and will simulate sunrise and sunset. Problably will have to use the PWM ports right?


Hi Folks,

I think I figure out a way to wire all the stuff I´m planning for my controller but I would love to get your insights. After doing a small research, I´ve come up with the following sensors /shields and attributes:

Arduino Uno REV3
Temperature Sensor - 1-wire - (DS18B20)
RTC Shield
CO2 Monitoring - Carbon Monoxide Sensor - MQ-7
LCD Shield + Keypad
Ethernet Shield + SD
Piezo Vibration Sensor - For “knocks” on glass
LED Lighting Controls

Well, in order to wire all these, I´ve come up with the following schema, wich has to use one of the Analog A/D as a digital port, in order to free one of the PWM ports for the leds:

Temperature Sensor - D2
RTC - A4,A5
CO2 - A0
LCD - D9,D8,D7,D6,D5 and A3 as Digital 17
Ethernet - D10,D11,D12,D13
KeyPAD - A1
Piezo - A2
SD - D4
LED - D3

In this way, all ports are taken, but I don´t need a multiplex or anything to build up the project. I´ve decided not to manage PH, since the probes are a problem. If I decide so, I would use a multiplex on an analog port.

Do you guys see a problem in this design?

Also, I know it´s possible to use more than one sensor on the 1-wire schema, but hot to do it? Is there a way to plug two sensors on the same Analog Port, been one Input and the other Output?

Attached you can find the ports taken by this project.


An additional 1-wire sensor is just attached as the first one, in parallel. You address them by their serial number (you have the possibility to "ask" on the bus for everyone listening on it).

Thanks Pylon.