This is a short tutorial* to show you how to interface the Bluetooth module with the Arduino Mega Sensor Shield. Here we are going to use Serial Channel 2 of the Arduino Mega to commuicate with the Bluetooth. First of all, wire up the circuit as shown below.

*A more detail tutorial for how to use the Bluetooth module can be found here.

Power up the Arduino via USB, and you can see the Red LED on the Bluetooth module is blinking, which means the Bluetooth link is not established. Download this test code to the Mega. The code randomly generates numbers from 18 - 22 to simulate two temperature readings every 3 seconds. Once download complete, close the Arduino IDE, and now the Bluetooth can be tested in puTTY and our Serial Temp Monitor. 

Test in PUTTY

Open puTTY and enter the COM number the Bluetooth link. As can be seen below, mine is at COM4.

Then connect the Bluetooth to puTTY with Baudrate = 9600

If the connection is established successfully, then you can see the LED on the Bluetooth module stays on. And in puTTY, you will receive strings like below.

Test in Serial Temp Monitor

Download the executable SerialTempMonitor, and open it. Please make sure that the Bluetooth link is disconnected from puTTY, and the LED on the Bluetooth module is blinking.

Click on "Connect", after one moment, the temperature reading should appear.

If all working, congratulations, you are now ready to build a wireless temperature monitor. Finally, put all the components together, and load this code to your Mega, it should all work. The Serial Temp Monitor is an opened source C# program, developed by Hobbyist.

SerialTempMonitor Source Code Download

In this tutorial, you will learn how to interface the SD Card Module to the Arduino Mega via a Sensor Shield. Firstly, let's take a close look at the SD card connector on the Mega Sensor Shield.

The 6-pin SD Card connector is actually a SPI bus, and their pin designation is described in the table above.

Of course, the Mega Sensor Shield isn't essential to interfacing the SD Card module to the Arduino Mega, however, it absolutely makes life easier and adds reliability to your device.

There is one important reason why the Arduino Mega is chosen instead of the Arduino Uno (or any Arduino with the ATmega 328 microcontroller). There is only 2 KB of SRAM in the ATmega 328. SD card buffer requires 512 Byts, that's one quarter of the available memory. By putting a few Serial.print functions in the code, it's pretty easy to run out of SRAM in the ATmega 328 before you know it. As SRAM runs out, heap and stack clashes, and your program's behaviour can become strange and inconsistent. As confusing as it can get, it's hard to tell whether it's the 'bug' in the code or short of SRAM, a situation no one wants to go into. On the other hand, the Arduino Mega has 8 KB of SRAM, that's sufficient to most embedded programming, and plenty of room can be left for future improvement / extension.

Download this SD card library into the Arduino/libraries folder.

Once it's wired up, download this sketch to the Arduino Mega, make sure you have the correct board and serial com selected. Open the Serial Monitor, and set the Baudrate to 9600, if the SD card is working correctly, you should see something like this.

If it fails to initialize, try the things below:

1. Shut down Serial monitor, unplug the USB cable, wait for about 10 seconds (wait for the capacitors to discharge) , and plug it back again. Start Serial monitor, and push the reset button.