Uno, 3G shield, temperature sensors

Projects General Guidance
1

I am planning on a project with an Arduino UNO and the 3G shield at http://www.cooking-hacks.com/index.php/documentation/tutorials/arduino-3g-gprs-gsm-gps (Note that a 2G grps sheild will not do for this project. I am specifically using the 3G shield for testing purposes for other projects)

The 3G shield requires power that can deliver a peak up to 2A. I will use a 12V 2.5A power supply with center-positive plug connected to the UNO. According to the UNO documentation this will do fine. Here is the power supply: http://robotics.org.za/index.php?route=product/product&path=55_205&product_id=214

I also want to connect one or two DF robot LM35 temperature sensors at DFRobot_LM35_Linear_Temperature_Sensor_(SKU_DFR0023)-DFRobot to the UNO.

Since I have never worked on Arduino before and have little experience with electronics I am not sure if this is okay, let alone possible. If the shield us connected to the UNO vout, where do I draw power onto a breadboard for the temperature sensors?

I am a bit worried about the amount of current that will be drawn. At 12V and current that can go "up to" 2A the regulator will fry up. But I looked at the cookinghacks forum and there are people who have used 12V power supplies in their setups so I don't know how thats possible. In fact the creators of the shield (libelium) say they usually use a12V supply in the reply in this forum post: http://www.cooking-hacks.com/forum/viewtopic.php?f=20&t=3478&sid=87f29596dd586799de4e34229bf5d75c

Very confused about how the electonics work here

Any comments would be much appreciated.

2

The short answer (without having followed through on all the links) is that when you have connected the 12V to the Arduino barrel connector the "5v" pin supplies 5V which you can use for temperature sensors and anything else that does not need a lot of current (<a few hundred mA). The "Vin" pin is in parallel and has the 12V from the barrel connector and can draw as much current as the supply can handle.

I presume the 2A requirement of the shield is NOT from the 5V - it simply would not be an Arduino shiled if it did.

3

Msquare:
The "Vin" pin is in parallel and has the 12V from the barrel connector and can draw as much current as the supply can handle.

Thanks so much for explaining that to me. My understanding of the Arduino board and how shields plug into it isn't the best and I was getting quite frustrated trying to get my head around it.

4

k290:
My understanding of the Arduino board and how shields plug into it isn't the best and I was getting quite frustrated trying to get my head around it.

The connection is quite simple. There are pin headers and pins, the connect.

The complexity is that there is no standard for how shields "work." So you need to think about what each shield is doing or look at its schematic to understand what Arduino pins it is using (and how).

5

Ah, yes its a bit difficult understanding the schematics when I've never worked with Arduino with shields before or have the actual shield in front of me.

In the below schematic I understand most of it. I've read all of the tutorials and watched the videos and it seems straight forward enough, but there's a lot in the schematic that isn't mentioned in tutorials.

I'm guessing if I plug in a 12V 2A barrel supply to the Arduino I need the V in ext. set to "Vin Pin". I'm also guessing that the V in ext. and Board Jumper boxes at the top of the schematic are telling me I choose between the two options in the boxes. Similar with flight mode and normal mode.

I'm also guessing that the pins lableled "Arduino digital I/O(2-13)" and "Arduino Analog input 0-5" correspond to the one's on the Arduino board itself. So instead of connecting sensors and things to the Arduino I connect them to the shield which then sends the signals down to the Arduino.